Lipids of aquatic sediments and sedimenting particulates

Pro9. Lipid Res. Vol. 21, pp. 271-308, 1982

0163-7827/82/040271

Printed in Great Britain. All rights reserved

38519.00,/0

Copyright © 1982 Pergamon Press Ltd

LIPIDS OF AQUATIC SEDIMENTS A N D SEDIMENTING PARTICULATES P. A. CRANWELL

Freshwater Bioloqical Association, Windermere Laboratory, Ambleside, Cumbria, LA22 OLP, U.K. CONTENTS I. INTRODUCTION

II. DEPOSITIONAL SEDIMENTARY ENVIRONMENTS A. Lacustrine B. Estuarine/deltaic C. Intertidal D. Continental shelf E. Deep sea

271 272 272 272 273 273 273

III. SOURCES AND FATE OF ORGANIC MATTER IN AQUATIC ENVIRONMENTS A. Sources B. Factors affecting lipid preservation C. Methods for following initial stages of lipid diagenesis

273 273 274 275

IV. CHEMICAL STATE OF SEDIMENTARY LIPID COMPONENTS

275

V. FEATURES OF LIPID COMPOSITION REFLECTING THE ORIGIN OF SEDIMENTARY ORGANIC MATTER A. Homologous series B. Carbon number range C. Carbon preference index D. Modality of the carbon number distribution E. Pseudohomologous series F. Stereochemistry G. Isotopic composition

275 276 276 276 276 276 277 277

VI. LIPID COMPONENTSOF AQUATIC SEDIMENTS A. Hydrocarbons I. n-Alkanes 2. n-Alkenes 3. Branched-chain and cyclic hydrocarbons 4. Aromatic hydrocarbons B. Alkyl esters and triacylglycerols C. Ketones D. Alcohols 1. n-Alkan-l-ols 2. Branched-chain and cyclic alcohols 3. Miscellaneous alcohols E. Carboxylic acids 1. n-Alkanoic acids 2. Branched-chain and cyclic monocarboxylic acids 3. Alkenoic acids 4. c~,o)-Dicarboxylic acids 5. Hydroxy acids F. Steroids G. Hopane derivatives H. Carotenoids

277 277 277 280 281 285 288 289 291 291 292 293 293 293 293 298 298 299 299 303 303

VII. SUMMARY

305

REFERENCES

306

1. I N T R O D U C T I O N T h r o u g h o u t t h e e a r t h ' s h i s t o r y , o r g a n i c d e b r i s h a s b e e n d e p o s i t e d in a q u a t i c s e d i m e n t s w h i c h m a y b e s u b d i v i d e d , a c c o r d i n g t o age, i n t o R e c e n t s e d i m e n t s , t h o s e l a i d d o w n in t h e Q u a t e r n a r y p e r i o d ( 0 - 1 0 6 yr), T e r t i a r y s e d i m e n t s ( 1 0 6 - 7 0 × 10 6 yr) a n d A n c i e n t sedim e n t s , t h o s e o f p r e - T e r t i a r y age. T h e s e d i m e n t c o l u m n o f t h e e x i s t i n g o c e a n s g o e s b a c k J.P,L.R. 21/4 a

271

272

P.A. ('runwell

to the Jurassic period (140 190 x 10~' yr ago), while those lakes formed during the last glaciation contain organic sediments only of the Holocene epoch ( < c , 104 vr old), thus emphasizing the wide variation in age of organic matter in aquatic enxironments. The organic debris incorporated into sediments is that portion of the total carbon lixed during photosynthesis which escapes immediate recycling. Living organisms producc a wide range of secondary metabolites, or biolipids; the structures and composition of the lipids of aquatic organisms have received much attention from natural produc! organic chemists and have been reviewed elsewhere in this journal. The solvent-soluble compounds extracted from aquatic sediments, termed geolipids, retlect the original organic source materials and the subsequent diagenetic processes to which this material has been subjected. Information relating to the origin and history of geolipids is present m the form ol their molecular structures, relativc abundances and isotopic composition. ('ompared with the biolipid precursor, structures of geolipids in sediments may,' be (I) unaltered, (2t partly altered, rearranged or degraded, (3) extensively altered, e.g. after thermal treatment, or (4) completely degraded to ( ' 0 2 or methane. The most stable compounds, tho,,,e unaltered or partly altered but retaining a structural similarity with the biosvnthesized precursor, have been used as "biological markers" of sediment input derived from the respective source organisms, or as indicators of environmental conditions under v\,hich sedimentation o c c u r r e d ) ~ The aims of organic geochemical analysis of aquatic sediments ma~ be su.nmarizcd as: (1) recognition of lipid patterns characteristic of different environments, (2) recognition of intermediates in the conversion of biolipids present in source organisms into the geolipids of ancient sediments, (3) correlation of geolipids with the depositional history ot the sediment profile, and (4) recognition of ubiquitous or specific biolipids not previously characterized b~ natural product chemists. This review is restricted in scope to naturally-occurring specilic lipid components m freshwater and marine Recent and Tertiary sediments, and to the physical, chemical and biological processes causing early diagenesis of the original lipids in a variety of aquatic environments. It updates similar reviews on lake e and marine ~2 scdimenls but excludes anthropogenic inputs from naturally-occurring and manufactured sources and natural input from thermally-mature geological sources (oil seeps). Publications which have appeared mainly since mid-1977 are reviewed. Details of analytical methods ma~ be obtained from the primary sources. II.

I)EI'()SITIONAL

SEDIMENTAR~

ENVIRONM[

NTF,

A. Lacustrine Sedimentary deposits forming in shallow, productive lakes, in which autochthonous input is dominant, are believed to be modern analogues of deposits which have produced certain oil shales, 17 while sediments of unproductive lakes, in which organic input is mainly of terrestrial origin, may be modern equivalents of deposition which formed certain coals. 2'~ Small lakes situated in glacially-formed valleys receive a more homogeneous allochthonous organic sediment input, derived from soils eroded from the drainage basin, than does the coastal marine environment which receives sediment by potamic transport from a large land area and in which tidal movements cause resuspension and mixing. Lakes thus constitute a simpler ecosystem. The low sulphate levels in many freshwaters result in markedly different bacterial populations decomposing the organic matter, compared with the marine environment. B. Estuarine/Deltaic These deposits are modern equivalents of palaeoenvironments which have generated non-marine petroleums, due to the expected high contribution of land-derived organic

Lipids of aquatic sediments and sedimenting particulates

273

matter. The change in salinity in estuaries causes flocculation of dissolved material of freshwater origin while the change in surface charge characteristics of clay minerals causes differential coagulation of minerals such as illite and montmorillonite. Rapid deposition in estuaries results in a change from aerobic to anaerobic conditions in the pore waters. Other aspects of estuarine chemistry have been reviewed.Z C. Intertidal Climate is a major factor influencing the vegetation of the intertidal zone. In tropical coastal regions, mangrove swamps constitute a major depositional environment which has been studied. 69'99'136 In the intertidal zone of subtropical regions, algal mat formations occur. The layered structure, containing recognizable populations of microorganisms, facilitates correlation of lipids with the source organisms, t°~ The sediments which accumulate are the modern equivalent of stromatolitic ancient sediments. Salt marsh is a characteristic temperate zone intertidal environment in which lipid diagenesis has been studied. 2 D. Continental Shelf A wide variety of environments exist close to the continents so that, in contrast to the high redox potentials found in pelagic sediments, many near-shore sediments in basins with restricted circulation, such as the Black Sea, are anoxic. Other rapidly-accumulating organic-rich sediments show a thin upper oxidized layer. The proximity to the continents usually implies the presence of terrestrial organic input; however, sediments rich in autochthonous matter occur in areas of high productivity adjacent to arid continents; the sediments of Walvis Bay are of this type. z6 E. Deep Sea Carbon isotope studies on the small proportion of organic matter in these sediments indicate an origin from marine biomass, the biolipids of which undergo extensive breakdown during sedimentation through the long water column. 133 II. S O U R C E S

AND

FATE OF ORGANIC

MATTER

IN A Q U A T I C

ENVIRONMENTS

A. Sources Organic matter deposited in aquatic environments includes both autochthonous and allochthonous components, the former consisting of material generated within the basin of deposition whereas the latter consists of material reaching the depositional environment by potamic or aeolian transport. Autochthonous input is, in part, of direct biological origin, derived from the intact biolipids of organisms in the overlying water, and, in part, of indirect biological origin, consisting of microbial and chemical transformation products generated within the water column and sediment. Allochthonous input is derived from a variety of sources, including direct biological input from terrestrial organisms (e.g. leaves) and indirect biological input, consisting of organic matter from terrestrial biota which has been degraded by soil microorganisms prior to transport into the aquatic environment. Other sources are weathering and erosion of ancient sediments and anthropogenic inputs arising from combustion, naturally-occurring sources (oils and coals) and also synthetic products. Input of lipids to contemporary sediments can be assessed by analysis of lipid components in organisms contributing directly to the sediments. In specific sediments, input derived from mangroves, 36 spring moss, 79 algae and zooplankton, 96.1°5 a sulphatereducing bacterium 13 and other marine bacteria 99 has been identified. Such studies are valuable for assignment of the sources of lipid constituents in older sediments.

274

Cran~cll

P.A.

Sediment profiles contain a historical record of source organisms in the h~rm ~,t' m~vphological residues such as pollen spores, providing evidence of changes in lerre,',lrial vegetation, diatom frustules and other algal remains, s~s-' reflecting changes in trophic status, and animal microfossils, reflecting changes ill oxicitx or tempe]aturc. >~' l)o~ncore changes in lipid distributions and in the abundance of specilic biologic~fl marker> can be correlated with the morphological record. ~s in the change in algal inpul in the Black Sea, is or with direct observations on phytoplankton abundance, using specilic carotenoids.S~"l d-2 B. I"actm'.~ 'tlli'c/iml Lipid l'resertatio~t

Only' a small proportion of the biolipids added to or genert~ted within the aquan,. environment becomes incorporated into the sediment. Some chemical and biological factors affecting the fate of biolipids within the aquatic environment are depicted in Fig. 1. The earliest diagenetic reactions are brought about within the water column b~ microorganisms which consume and degrade the primary photosynthetic products and synthesize their own biolipids and cellular debris. The dissolved oxygen contcni of lhc water, a m~00r factor determining the extent of preservation of organic matter and the nature of the microbial population, is itself related to the level of organic productivit5 and also to the topography of the depositional basin, which influences water circulalitm and, therefore, nutrient supply. 4-2 An oxic water column and sediment:x~ater interfacc result in poor preservation of organic matter, both quantitativel3 and at the molecular level in the lipids. 4-~ Anoxicity within the water column preservcs the more labile biolipids by decreasing predation and bacterial degradation, so that a greater proportion ot organic input reaches the sediment. The temperature, salinity and pH of the water also affect bacterial activity and species composition. Within the sediment, lhe redox conditions and pH are important factors in detcrmi[1ing the further transformations of lipids. Sediment depth profiles beneath oxic ~z~tc~> show a change from oxic to intermediate and reducing zones with increasing depth, \khilc the profile beneath anoxic overlying water is completel 5 anoxic. As bactcti~ arc concentrated at the sediment.~ater interface of both oxic and anoxic scdimenls, rapid remoxal

UPTAKE OF COz BY ALGAE I

TERRIGENOUS INPUT OF NATURAL PRODUCTS AND POLLUTANTS, • 9- NITRATES AND PHOSPHATES INPUT OF NATURAL PRODUCTS

1 /.p.~!~4

ARISING

REDOXPOTENTIAL

_

-~--

-:--2:7

-

DEPOSITION 0 . 0 | - I c m /

~.:..~.~.~:~_

~

COLUMN

_- _ _ ~ _

.

~

k

~'~-'~'P!

t ~

.~ ,.-:c..-='--~,.:~,. & ~ :

: :2-:-- 2~-?:7]__ -77-: -- ~ I-~ ]21-7

_

RATE OF

IN WATER

_

_

-

-

;

__ -

Z,~= ~

?2 . -_ - :

~q.~,X~;~..,~.~_.

~ ~, ~ ~r - ' :,~ ' '_' - - '~~ ' ' :~¢ ~ ~' ~ ' ' ,; " .

~

~

~

AERATION

BY

,:

ACT/V/T~=_,,,,~ OF ;~ ING !

AEROBIC

LAYER BACTERIAL~..!:

COMPLEX ORGANIC PROCESSES

-:--'..~'~!.',?~'~,.~J-~-;.,:-,'-,~.CC-:::!:'r,

FI~;. I. Diagram showing interdependent chemical and biological factors inltucncmg tt~c f;m_'~,1 biolipids deposited in Recent sediments. Reproduced. with permission, from S~ic~ t'r~,u~'c,, Ovlbrd. 63, 523 11976).

Lipids of aquatic sediments and sedimenting particulates

275

of organic matter from this active zone will enhance the degree of lipid preservation. In anoxic environments, the slower decomposition rate, absence of benthic macroorganisms and high sedimentation and accumulation rates result in good preservation.

C. Methods for Followin9 Initial Staqes of Lipid Dia,qenesis The origin and fate of organic compounds within the water column overlying the sediment can be analysed by deploying sediment traps at varying depths and determining the fluxes of the major lipid classes in the particulates, which consist of recognizable fragments of source organisms. 133 Selective mineralization of organic matter of marine planktonic origin compared with terrestrial detritus has been demonstrated using sediment traps.l oz A simplified laboratory study of the marine food web, in which the lipid content of copepod fecal pellets was compared with that of their food (phytoplankton), has been used to determine the fate of copepod wax esters. 45 Incorporation into fecal pellets of lipids of autochthonous origin appears to be a major mechanism by which these labile compounds reach the sea floor.~28 The fate of bacterial lipids in sediment consumed by a deposit feeder, Arenicola marina, has also been studied.~3 The short-term fate of organic compounds in Recent sediments can be followed by incubation of l'~C- or 3H-labeled "marker" compounds, either in the laboratory or in situ, under environmental conditions. Techniques for introduction of the label with minimum disturbance have been developed. 66 In addition to earlier studies, 2 the fate of labeled 5ct-cholestan-3fl-ol in algal mats has recently been reported. 44 One alternative approach is to incubate an enhanced amount of a sedimentary constituent under aerobic or anaerobic conditions, with isolation of the products; 93 another method is to follow changes in abundance of major constituents in the original sediment profile. 56 IV. C H E M I C A L

STATE O F S E D I M E N T A R Y

LIPID

COMPONENTS

Extraction procedures involving saponification, transesterification or demineralization were formerly used in the isolation of sedimentary lipids, but the recognition that considerable amounts of fatty acids in sediments could only be recovered by saponification has led to the use of extraction procedures in which chemically-distinct forms of the major lipid classes can be separately analysed. 33'64'76'84 Carboxylic acids, for example, may exist in sediments in a free state and also esterified to long-chain alcohols: such forms may be isolated by direct solvent extraction. Carboxylic acids may also occur as salts and complexes with the metal ions of clay minerals or esterified to hydroxyl groups which are part of the kerogen or humic polymeric insoluble organic matter: such acids may be isolated by solvent extraction after hydrolysis. Lipids such as aliphatic hydrocarbons, lacking polar functional groups, are also released by hydrolysis, although the binding mechanism is uncertain, but may result from trapping in macromolecular cage structures formed by hydrogen bonding of peripheral groups] 2 Various terminologies are used to describe the lipids released from sediments by hydrolysis, including 'bound', 'post-hydrolysis' and 'non-solvent extractable'. An alternative fractionation technique consists of separating the sediment according to particle size, followed by lipid analysis on each fraction. ~2° The coarser particulates consisted of higher plant debris, recognized by microscopy, and gave n-alkane and alkanoic acid distribution patterns differing from those of the silt and clay fractions. A method for fractionation of sediments according to density has also been described, using microscopic analysis of the three fractions to determine their composition. 65 However, the corresponding lipids have not been studied. V. E E A T U R E S O F L I P I D C O M P O S I T I O N R E F L E C T I N G THE O R I G I N OF S E D I M E N T A R Y O R G A N I C MATTER

Several parameters useful for relating compounds occurring in sediments with possible sources of organic input are outlined below.

276

P. A, Cranwell

A. ttomologous Series Homologous series of compounds, resulting from biosynthesis b~ the process of carbon chain elongation with acetate units, occur in many organisms and often survixc in sediments. Series of dominant members differing bx t~o carbon atoms are produced which can be characterized by two further parameters, the carbon number range and the carbon preference index (CPII, as outlined below.

B. Carbon Ntmdwr Ra,rle An organism synthesizes lipid series, each having a characteristic carbon number range, a feature which is often preserved in aquatic environments, except those in which extensive bacterial alteration has occurred. During the initial stages of diagenesis, shortlx after the death of the organism, the relative abundance of shorter-chain homologues max be decreased, especially in terrestrial detritus.~°~ This process continues in surficial sediments of lakes in which higher-plant detritus is d o m i n a n t ) ~ however, the distribution of longer-chain alkane homologues, fl)r example, survives at least 10,000 years in the sediment. ~'~ Algae and other aquatic microorganisms synthesize shorter-chain homologous series than those in the wax coatings of higher phmts. Due to the direct input to the sediment of lipids from aquatic organisms, often under scasonall\ anoxic condition~, preservation is better than in terrestrial detritus which may be subjected to extensive aerobic degradation at the soil surface. The predomimmce of the n-C~ alkane, t\)r example, in l 1,000 year-old sediment of Greifensee. Switzerland, provides a qualitative record of primary productivity in this lake. even though anaerobic degradation has been shown to occur quite rapidly. 5" ('. ('arhon Prq/i, rem'e lmlev

Many species sho~. considerable carbon preference in their biosynthesized straightchain compounds, particularly alkanes, carboxylic acids and alcohols. Bacteria. however. do not show a prominent carbon preference in their lipid composition, so thai the ('Pl can be used to distinguish between inputs from different sources. Extractable J>alkanes in sediments often show a high CPI. characteristic of higher phmts, ~hile bound alkanes in the same sediment show a low CP1 suggesting a bacterial origin, consistent with the presence in other bound lipid classes of biological markers of a predominant bacterial input. 33,3'~

D. Modalitv O[the CarBon Ntulther Distribution1 Since aquatic organisms possess signilicantly lower carbon number ranges than terrestrial detritus of higher-phmt origin, the modality of the carbon number distributions within homologous series occurring in sediments provides a further useful source indicator. Unimodal distributions may be indicative of a single type of source material. whereas distributions having several modes suggest mixed sources. Within a bimodal distribution of wax esters from lacustrine sediments, marked differences in CP1 within each mode have been observed; 3~' esters in the range C38 Cso showed a strong evencarbon predominance, characteristic of higher phmts, while the ('24 C3s straight-chain esters showed a lower even carbon dominance. However, the source of the latter esters is not yet known. E. P,wudohomolo:/ou,~ Serie,~

Pseudohomologous series, s u c h as acyclic isoprenoid alkanes or polycyclic isoprenoid alkanes with side chains differing in length, such as hopanes, also occur. Multibranched non-isoprenoid C20 and C2s alkanes and related alkenes from unidentilied source organisms have been found in marine sediments, s The stereochemistry of acyclic and polyc'~c-

Lipids of aquatic sedimentsand sedimentingparticulates

277

lic isoprenoid compounds provides an additional parameter for source identification, as discussed below.

F. Stereochemistry Stereochemical data is valuable for source identification since biosynthetic pathways in living organisms are almost always stereospecific, forming a single stereoisomer which may possess several chiral centers. Degradative pathways such as the a-oxidation pathway of fatty acid degradation in plants result in one ~-hydroxyacid enantiomer accumulating so that information about source organisms and about transformation processes may be obtained. Stereoisomers may undergo epimerization to give a thermodynamically more stable configuration during diagenesis and maturation in ancient sediments, thus enabling the recognition of fossil lipid input to recent sediments. Pristane isolated from a recent lacustrine sediment was shown to be derived from both a biological and a pollutant source. 1°4 Stereochemical analysis of extended hopane derivatives in recent sediments and decayed algae has shown that one of the C22 diastereoisomers of 17~(H)-homohopane, previously attributed to mature geological sources, also has a previously unrecognized biological origin, lo4

G, Isotopic' Composition The isotopic composition of sedimentary organic matter provides an approximate means of distinguishing between terrestrial and aquatic input. T M Formation of biological material via photosynthesis results in a difference in 13C content between organisms utilizing atmospheric carbon dioxide and those using dissolved bicarbonate as carbon source. Temperature influences the degree of fractionation between the two reservoirs. In higher plants, two distinct synthetic pathways operate, producing differing 13C/12C ratios. Variation in isotopic composition between the extractable lipids of sediments and residual organic matter also o c c u r s . 54"93 6 1 3 C values for the total organic matter thus provide an average for all sources of input to the sedimentary environment. Preferential remineralization of autochthonous relative to allochthonous particulate matter has been detected by ,~13C measurements.~02

VI. LIPID COMPONENTS OF AQUATIC SEDIMENTS

A. Hydrocarbons 1. n-Alkanes Recent studies on lacustrine sediments, summarized in Table 1, show that the parameters characterizing homologous series (Section V.A-D) correlate with trophic status and with the relative sediment input from allochthonous and autochthonous biota. Sediments deposited when the lakes were oligotrophic show a unimodai distribution, maximizing at C2~, C29 or C31, with an overall CPI value exceeding 4. Lake Huron surficial sediments showing lower CPI values have been polluted by petroleum products. 8v In eutrophic lakes, bimodal distributions, in which the abundance of C Iv may exceed that of higher homologues, are observed; CPI values lie in the range 2-4. Lakes having an intermediate trophic level show a bimodal distribution in which the abundance of C~v has a corresponding intermediate value. The C,7 alkane has been widely attributed to algal input but may only provide a qualitative record of such input in early post-glacial sediments because anaerobic degradation occurs, s6 Alkane distributions maximizing in the C2~-C31 range and showing high CPI values have been attributed to higher plant sources in which these alkanes occur in the surface waxes. 123 Several alkane distributions, often those in surface sediments, show a weak maximum at C23 in addition to the

278

P. A. Cranwell TABLE 1. n-Alkanes in Lacustrine Sediments

Source Lake Haruna, Japan Laguna Lejia, Chile Pyramid Lake. USA Lake Huron. USA

Lake Michigan. USA

Greifensee, Switzerhmd Colin Scott Lake, Ontario Cam Loch, Scotland Crose Mere. England Crose Mere, England Loch Clair. Scotland Rostherne Mere, England

Upton Broad, England

Sample type and number Depth prolile I I I)

1-rophic state

Lipid species

(a) Oligotrophic (hi Mesotrophic

Extractable

Surface sediment ll ) Algal mat Foam & detritus Depth prolile 1141

(al Oligotrophic

Extractable Extractable Extra~_'table "It>tat

Depth protilc (21i Surface (10)

{b) Mesotrophic Oligotrophic Oligotrophic

lolal lo[al

Particulates in Water Column protilc (31 Faunal debris in particulates 13) l)cpth profile (l(I) Surlhce Surface sediment Depth profile (6! Stlrface + one lower section Sediments (2) age < 500 years Sediments (2/ age < 400 years Sediment. max age 200 3r 5 size fractions Depth prolile {3)

totai [ohll (a) Oligotrophic !b) Mesotrophic (el Eutrophic Eutrophic Oligotrophic !at Mcsotrophic (bt Oligotrophic Eutrophic Eutrophic Oligotrophic Eutrophic

(a~ Mesotrophic Ih) Eutrophic

I xmLctable

Extractable Iotal Total Extractable Bound Extractable Bound [!xlructable

l:.xtractable Bound Extractable Bound

*Most abundant homologue in bold type. +CPI wdues calculated for less than overall carbon number rangc. chain lengths discussed above {Table 1). There is evidence to suggest a higher plant origin s<1°3 a n d also that selective decay of ('2s relative to ( ' , - (':1 alkancs occurs in sediment profiles. In L a g u n a Lejia, however. C2,~ was d o m i n a n t in the sediment and also in the overlying algal mat. t I s C o m p l e x a l k a n e distributions, showing u n u s u a l m o d a l i t y patterns and lo\,~ ( ' P l values, were observed in sediment trap particulates from 3 depths in the \~ater c o l u m n of Lake Michigan. 88 Sediment trap particuhttes from freshwater bodies appear to bc less studied than those from the m a r i n e e n v i r o n m e n t (see below): data from a d d i t i o n a l sites is needed to elucidate the processes modifying lipid d i s t r i b u t i o n s d u r i n g sedimentation. V a r i a t i o n s in extraction procedure appear to have a small effect on the d i s t r i b u t i o n pattern, as total alkanes o b t a i n e d by s a p o n i f i c a t i o n - e x t r a c t i o n resemble extractable alkanes from similar e n v i r o n m e n t s . In oligotrophic and mesotrophic sediments examined by Cranwell (Ref. 36 and u n p u b l i s h e d data), the b o u n d alkanes form a very' small proportion of the total and would not significantly affect the overall distribution. B o u n d alkanes do, however, differ c o n s i d e r a b l y from extractable alkanes in CPI value and chain-length distribution, s3'3~' The low C P I wtlue in b o u n d alkanes from sediments u n p o l l u t e d b,~ p e t r o l e u m products was a t t r i b u t e d to bacterial activity.

Lipids of aquatic sediments and sedimenting particulates

279

TABLE 1 (continued). Carbon range (a) (b)

Abundance #g/g Notes

Modality

Maxima*

CPI

31 17 or 23, 31 23, 29 23, 29 29 23, 29 17 or 18, 23, 29 17, 29 17, 25, 27 or 29

5.2 7.1 4.1-5.6 1.6 1.4

14-35

1 2 2 2 1 2 2 or 3 1 or 2 2 or 3

16-38

2 or 3

17, 25, 29

2.2-3.5

6 80 2O 2 6 Saline lake 7 13 5-45 1-27 Transects of basins. Petroleum pollution, Saginaw bay 36-127

17-35

2 or 3

18, 22 or 25, 31

0.7 1.2

60-840

17-33 17 33 17 33 17-33 15-31

1 2 2 2 1

31 17, 29 17, 29 17, 29 27

3.9-5.7t 4.7 7.7t 3.8 + 1.5 averaget 4.7-6.5t

17-33 16-35 15-28

l l 2

27 or 29 27 or 31 17, 23

2.7, 6.1 5.3-7.5 2.6, 3.0

16-31

2

17, 27 or 29

16-33 17-35 15-33 16-33

3 1 1 or 2 1

17, 23, 31 31 17 or 18, 31 27 or 29

4.4 2.2 5.5, 7.7 1.0, 1.7 2.5-4.0

16-33 16-31 15 33

2 3 2

19, 29 17, 22, 29 17, 27

5.3 0.9 1.2 4.9

16 35

1

29

1.1

17-35 17-35 15-33 14-33 15 33 17-33 17 33

Average 4.4 Average 5,1 1.8-3.3

Ref. No 64

(a) Postglacial mud (b) Lacustrine chalk (ct Sapropel Sapropel

113 90 91

88

56

25 5-15 15-29 13-21 28 12 110-210 4 10 CPI decreases and rel abundance of C ~7 increases as particle size decreased 34~38 2-6 70 Surface 50

31 32 33 36 120

37

n - A l k a n e s i s o l a t e d f r o m five p a r t i c l e size f r a c t i o n s o f a l a c u s t r i n e s e d i m e n t s h o w e d differences in d i s t r i b u t i o n a n d C P I c o n s i s t e n t w i t h t h e p r e d o m i n a n c e o f h i g h e r p l a n t d e b r i s in t h e c o a r s e r fractions, c o n f i r m e d by m i c r o s c o p i c e x a m i n a t i o n , a n d an i n c r e a s e in g e o l i p i d o r b a c t e r i a l lipid i n p u t in t h e finer fractions. 121 T h e fatty a c i d d i s t r i b u t i o n s of t h e finer s e d i m e n t f r a c t i o n s also i n d i c a t e d a b a c t e r i a l origin. In an o x i c i n t e r t i d a l m a r i n e s e d i m e n t f r o m an a r e a free f r o m t e r r e s t r i a l runoff, e x t r a c t a b l e n - a l k a n e s r a n g e d f r o m C ~ 5 - C 3 3 m a x i m i z i n g at C17, C29 a n d C 3 t , w i t h a n o v e r a l l C P I v a l u e o f a p p r o x i m a t e l y 2.6. T M T h e sea grass, Zostera muelleri, w h i c h o c c u r r e d s p a r s e l y at the s a m p l i n g site, was a m i n o r c o n t r i b u t o r of t h e s e d i m e n t a r y a l k a n e s , as also w e r e d i a t o m s , c u l t u r e s f r o m the s e d i m e n t s h o w i n g C I 4 C31 a l k a n e s w i t h no o d d - c h a i n p r e d o m i n a n c e ; h o w e v e r , the s o u r c e o f the p r e d o m i n a n t o d d - c h a i n a l k a n e s c o u l d n o t be identified. F r a c t i o n a t i o n o f an e s t u a r i n e s e d i m e n t to give sand, silt a n d clay size f r a c t i o n s s h o w e d t h a t C 1 5 - C 4 o a l k a n e s w e r e present, m a x i m i z i n g at C17 o r C l s a n d C29 o r C31. 2° As in t h e l a c u s t r i n e s e d i m e n t , 12~ the r a t i o of h i g h e r p l a n t to t o t a l a l k a n e s was g r e a t e s t in the s a n d size f r a c t i o n . O t h e r i n t e r t i d a l e n v i r o n m e n t s o n w h i c h g e o c h e m i c a l studies h a v e c o n t i n u e d a r e algal m a t s a n d a s s o c i a t e d a l g a l - l a m i n a t e d s e d i m e n t s f r o m a n u m b e r of localities. ~°° W i d e

280

P.A. ('ran~ell

ranges of extractable n-alkanes are often observed, maximizing at "('1 r, compatible with the most abundant microorganisms. In profiles of mats from Abu Dhahi. there was little or no contribution front homologues > ( ' 2 o e ~ ho~.ever, in lo~er levels in algal mal profiles from Laguna Guerrero, ('2. and ('2~ alkanes became dominant due either to an increased higher-plant contribution in the past or better resistance to microbial degradation relative to , C l , . t''~ Land-locked marine basins show a predominance of terrestriall\-derived n-alkancs in the sediments, thus Puget Sound contained a uniform geographic distribution of ,-alkancs (C~a ( ' : s t with a CP1, over the range ('20 (',~. of 3 -~- 0.6. s R i v e r inwash is the main transport mechanism for terrestrial delrilus, as reflected in the higher CPI2,, :., (4.6) for stations located off the mouths of the largest rivers. The annual accumulation of individual hydrocarbons in sedimentary particulate matter of D a b o b Bay, Puget Sound. has been compared with that of the corresponding compounds in 210pb_dated bottom sedunents. - Rapid decreases in the net accumulation of hydrocarbons ~cre observed between the sediment traps and the sediment. In lhe latter, the ('e5.2- _,,.~ ,-alkanes characteristic of terrestrial phml ~vaxcs. become predominant b3 4 6 c m m the sediment. At this depth, the ('Plzo :a is 4.5 compared with an average of 2.5 in the sediment traps. Preferential diagenetic alteration of the bulk organic matter collected in sediment traps is also evident from comparison of (' N ratio and ~$1,~(. values with those for the underlying sediment, which tire characteristic of terrestrial organic thriller. Two distinct shelf cnxironments in the Gulf of Mexico were recognized from hydrocarbon distributions. Sediments near the Florida coast contained ,-alkanes in which ('~was dominant while sediments closer to the Mississippi River contained larger amounts oflipids, t h e , - a l k a n c s of which were dominated bx odd homologues characteristic of terrestrial sources. 5a Particulate lnatter in the water co]unln contained ('~,, ('~e n - a l k a n e s s h o t ~ . i n g a ( ' P l value i n t h c r a n g e 0 . S 1.3, d c p e n d i n g o n depth and season, and dominant alkanes either in the ('1<~ ('22 or ('2~ ('_~o range: a bimodal distribution was often observed. -1 The low ( ' P l x.alues and dominance of e v c n chain homologues in particulate matter contrasts v~ith the distributions in sediments from this region. 5~ again suggesting rapid diagenesis of autochthonous organic matter. Sediment lrtip particulates collected at a deep sea location sho~.cd a rapid turnover of bulk organic matter in the upper portion of the water column. Alknnes of planktonic origin (#l('l- and ('l<,)t~cre dominant {it till depths, ~ i l h smaller anlounts of ('_,~ ('~l alkancs, indicating hmg r;.inge transport of continentally-derived material. 1~-* Anal\.ses of alkanes in sediments from the deeper oceanic areas, mainl\ performed on cores obtained bx the Deep Sea Drilling Project (DSDP). have been reviewed recenth:, x22 Sedimcnts of the Tcrtiar\ period (Pliocene age)exhibited ;I-'
1()~

"~ n - A l k e n e s

A homologous series of ,-alkenes was reported in surficial sediment and older lacustrine chalk deposits of Greifensee. s<' Constituents having an odd number of carbon atoms predominated in the younger sediment, and were attributed to higher-plant input because similar olefins were detected in the leaves of reeds, ss Extractable (7~ C ~ alkenes showing an even carbon number predominance were reported in sediment from

Lipids of aquatic sedimentsand sedimentingparticulates

281

the oligotropic Loch Clair. 36 A similar distribution has been reported in a peat profile 1°3 and in peat-forming plant species, indicating allochthonous input as the source of alkenes in Loch Clair, the drainage basin of which contains peat. The location and stereochemistry of the double bond in the alkenes was not defined in the above studies; however, both the mobility of the alkenes during separation from alkanes by argentation thin layer chromatography and the gas chromatographic retention indices suggest that the constituents in Loch Clair sediments are alk-l-enes, consistent with the presence of homogous alk-l-enes with prevalent even homologues in leaf waxes.Z16 Polyenes have rarely been reported in aquatic sediments; however, nC21:6(1) was detected in a surficial intertidal sediment and also in diatom cultures obtained from the sediment. ~2~'~3~ A direct input from photosynthetic diatoms, dinoflagellates and other algae known to contain this alkene was postulated. In Black Sea sediments rich in coccolith tests, C37(2) and C3a n-alkadienes having ~ol 5 and tJ922 unsaturation and corresponding trienes with additional unsaturation at ~o29 were detected, together with the analogous methyl and ethyl ketones. 78 These ketones and alkenes are markers of input from the marine alga Emiliania huxleyi,~26"~ 27 the coccolith tests of which were identified in the sediment. CH 3CH2(CH=CHCH 2 )6CH3

CH3(CH2)13 CH "-" CH (CH2) 5 C H :

(1)

CH (CH2)12 CH2CH 3

(2)

(3)

(4)

(5)

(6)

3. Branched-Chain and Cyclic Hydrocarbons A commonly reported feature occurring in gas chromatograms of total hydrocarbons obtained from polluted recent freshwater and marine sediments is the presence of an unresolved complex mixture (UCM) in the range C17-C33, 2°.132 whereas sediments remote from anthropogenic activities do not contain elevated hydrocarbon levels or a UCM. Natural input of UCM hydrocarbons, derived from erosion of sedimentary rocks, has been postulated to explain UCMs in the range C15-C25 in early post-glacial sediments of Greifensee. 56 The presence of pristane and phytane, in approximately equal amounts, provided further evidence of a geological input to these sediments. Fractionation of sediment according to particle size has shown the UCM to be mainly associated with the clay fractions. 2°.~2° As complex hydrocarbon mixtures formed by geological processes over long time periods cannot be directly related to source input, the UCM in sediments will not be discussed further.

282

P.A. ('ranwell

Sources of monomethyl-branched and acyclic isoprenoid hydrocarbons have been summarized. 2'22 The main acyclic isoprenoids, pristane (3: R~-~-CH3) and phytane i3: R~CH2CH~), widely distributed in recent and ancient sediments, are derived from tile phytol side chain of chlorophyll a via oxidative and reductive pathways, respectively: tile pristane:phytane ratio provides an index for assessment of palaeoenvironmental conditions of sedimentation. <~ As few primary biological sources of phytanc arc kno,an, its presence in modern sediments is usually attributed to fossil fuel input, whereas pristanc is a major hydrocarbon of zoophmkton. Recent studies of sedimenting particulates showed pristane present only in the deepest sediment trap in Lake Michigan, possibly indicative of a zoophmkton fecal pellet input. 88 Remineralization of pristane derived from plankton, shortly after deposition, was postulated from sediment trap data for Dabob Bav.~<'2 Pristaine remaining in Dabob Bay sediments originated from another source in which it was protected from remineralization by incorporation into a rnatrix of resistanl material. Barrick e t al. s also noted a rapid decrease in pristane concentrations near the sea sediment interface. In the deep oceans, signiticant depletion of pristane, ('~- and ('~,~ alkanes, relative to other alkanes in sedimenting particles, occurred in the uppermost sediment trap. ~~-~ Marine sediments varying in age from Holocenc to Cretaceous. in which high concentrations of methane occur or from environments where methanogens have been recognized, contain tile acyclic isoprenoids, 2,6,10,15,19-pentamethyleicosanc, squManc (4) and lycopane (5).23 The first two of these isoprenoids have recently been recognized m lipids of methanogenic bacteria, consequently this suite of isoprenoids may bc regarded as biological markers of methanogenic bacteria in marine sediments. 2,6,10,14,1S-Pentamethyleicosane was isolated from Tertiary sediment deposited in a lagoonal saline environment: 13~ this isoprenoid occurs in a thermoacidophilic bacterium. Unsaturated olefins related to pristane and phytane, intermediates in the diagenesis of phytol. '.3 have been reported in marine sediments deposited in tile last 100years, 5 m D S D P sediments, ~s in surficial sediments from Greifensee (3 G ( ' peaks155 and in algal mltts,~°~ the various layers of which contained phyt-l-erie, phyt-2-cne. 3 additional ph~tene isomers and a phytadiene. In a sediment from Upton Broad, a shallow productive lake, ~ GC MS analysis of bound hydrocarbons showed six constituents (A-F: Fig. 2)eluting between nCls and n('l, , alkanes, each showing a molecular ion M ~ at m,z 278. Compounds B and E were assigned the neophytadiene (6) and 1,3(4)-phytadiene structures b\ comparison \~ilh

~oo I

D

I

J

C RIC

22

I 17

[ 2O

i

400

600

800

1000

SCAN

FIG. 2. Reconstructed ion c h r o m a t o g r a m of hydrocarbons in the range ('~ (722 from G ( ' MS analysis of bound hydrocarbons from U p t o n Broad (55 65 cm) sediment. Selected members of ~-alkane series are numbered: peaks B, E and F are phytadienes (see text!.

283

Lipids of aquatic sediments and sedimenting particulates

published mass spectra. 1°3'~24 The gas chromatographic retention indices of isomeric phytadienes 6'7 suggest that E has the t r a n s configuration and that compound F may be 2,4-phytadiene. Compounds A, C and D all show a base peak in their mass spectra at m/z 123 and were not identified. A more recent surficial sediment sample contained an additional constituent eluting between peaks C and D and showing a mass spectrum almost identical with that of peak E. The GC retention index and mass spectrum suggest that this additional component is cis-l,3(4j-phytadiene. C17-C2o Alkanes containing a single methyl group on carbon atoms 4, 6, 7 or 8 occur in blue-green algae. The presence of these alkanes in lacustrine 2 and marine 112 sediments and also in algal mats ~°° has been reviewed. In a recent lacustrine sediment from Crose Mere, a small lake in which blue-green algae comprised 10'~;, of the annual phytoplankton ~o7 the combined abundance of 7- and 8-methyl heptadecanes was 1) ''j of the amount of n-alkanes. In surficial sediments from two eutrophic lakes, Upton Broad and • and 1.50.... Priest Pot, the abundances of methyl heptadecanes relative to n-alkanes (30°/,~ / respectively) are consistent with the relative abundance of identifiable blue-green algal cells in these sediments, s~ respective figures being 40'~,, of total cells in Upton Broad, but only a few colonies in Priest Pot. Tricyclic diterpenoid hydrocarbons, derived from functionalized diterpenes having the abietane (7), pimarane (8) or kaurane (9) skeletons, which occur in the resins of higher plants, have been found in marine sediments. 11~ Aromatized derivatives are widespread (see Section VI A.4). A suite of C19 and C2o tricyclic diterpenoids containing 0-2 double bonds has been detected in Puget Sound, 4 among which fichtelite (10), sandaracopimaradiene (11), and isopimaradiene (12) were identified; unidentified compounds were postulated to be epimers of these structures. A lack of correlation between these diterpenoids and plant wax n-alkanes in the sediments indicated a need for further investigation of the sources and geochemical pathways of the diterpenoids. A series of extended tricyclic diterpanes CnH2n_ 4, with n ranging from 20-25, was detected in an algal mat and underlying sediment from Laguna Lejia; ~~3 an unidentified CzoH32 cyclic hydrocarbon had been previously reported in algal mats.~°° Two tetracyclic hydrocarbons with structures (13) and (14) occur widely in recent marine and deltic sediments, Eocene and recent freshwater sediments. 3° Formation of structure (13) from lupanone, a compound having a pentacyclic triterpene skeleton widely distributed in higher plants, has been demonstrated in the laboratory. 3° Sediments from a wide variety of environments contain branched-chain or cyclic hydrocarbons, both saturated and unsaturated, which have 20 or 25 carbon atoms, suggest-

(7)

(8)

(9)

(11)

(12)

./.._

(10)

284

P. A. ('ranwell

( 13 )

(14)

ing an isoprenoid derivation, but are of unknown structure. A branched-chain acyclic alkane C20H42, which elutes between nC~: and pristane on non-polar silicone GC phases, has been obtained from Gulf of Mexico shelf sediments, 54 recent lacustrine sediments (Ref. 33 and unpublished data) and sediment from Puget Sound, a land-locked marine environment, s It has been suggested s that this compound is indigenous to the marine environment but this is probably incorrect in view of its occurrence in freshwater sediments. 33'1'~1 The structure has recently been elucidated. T M Two monoenes, which were converted into the C20H42 alkane on hydrogenation, occurred in Puget Sound sediment. 5 An analogous compound, giving a mass spectrum (Fig. 3) showing the same characteristic fragment ions as the above two isomers, was a major alkene in freshwater sediments from Cam Loch, Loch Clair and Upton Broad (Cranwell, unpublished observations). Four acyclic C25 hydrocarbons, containing 3 or 4 double bonds, were present in sediment of Puget Sound and were suggested to be pseudohomologues of the above ('2o compounds, consisting of pairs of geometric isomers about one of the double bonds. 5 These authors noted that previously reported C2s olefins obtained from sediments ~ contained at least one ring, based on hydrogenation studies. A bicyclic ('2s diene has been found in sediment from Rhode Ishmd Sound s and Puget Sound. "~ In sediment from the latter site, up to 5 C30 polyenes were also present, two of which were structurally homologous with the C2s bicyclodiene, while a third C30 polyene, also present in sediment trap samples, 1°2 showed similarities with the major acyclic C20 and ('25 multibranched hydrocarbons discussed above. The structures and sources of the acyclic highl~ branched C20, C2s and C30 compounds are not known, but structural similarities with 69 100

83 50

126 111

196

140

,11

I I

M/E

100

210

r

]

150

I L

, m

200

i

250

280 m 300

FI(;. 3. Electron impact mass spectrum of C2o monoene of unknown structure, prcscnl in free alkenes isolated from Upton Broad (55 65 cm} sediment.

Lipids of aquatic sedimentsand sedimentingparticulates

285

hydrolysis products obtained from antibiotics of some soil and marine Actinomycetes were noted. 4 Other cyclic non-aromatic hydrocarbons present in sediments are those derived from the sterol nucleus, pentacyclic triterpanes having the hopane nucleus, and tetraterpenoids derived from carotenoids. These will be discussed below, together with functionalized derivatives. 4. Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons present in the aquatic environment may be pollutants, originating from combustion of fossil fuels, other pyrolytic processes and spillage of petroleum products, or may be derived from naturally occurring biogenic precursors. 92 Pollutant input to recent aquatic sediments can be recognized from the decrease in abundance with increasing depth in the sediment and from the relative abundance of the parent aromatic hydrocarbon and its alkylated homologues. Petroleum sources are deficient in the parent compound but show distributions maximizing at the C3 or C4 alkyl homologue while fossil fuel combustion typically produces a distribution which is dominated by the parent compound. 132 Natural mechanisms such as differential water solubility of higher alkyl homologues relative to the unsubstituted parent may modify these homologue distribution patterns. Aromatic hydrocarbons derived from pollutant sources will not be considered further. Naturally-occurring polycyclic aromatic hydrocarbons are generated in several depositional environments by early diagenetic processes. With the notable exception of perylene (15), 135 the aromatic hydrocarbons derived from biogenic precursors are usually incompletely aromatized or contain alkyl substituents, the location and structure of which reflect the precursor compound. Sediment profiles from a number of lakes 64'117'134 and a continental shelf marine site ~35 show an increase in perylene concentration with increasing depth, reaching a maximum within the top metre, suggesting in situ generation in a reducing environment from an as yet unknown precursor. Lower down the sediment profile, variations in perylene content may be associated with changes in source material, as in Greifensee where climatic change altered the relative allochthonous and authochthonous input.134 The marine site is believed to have negligible terrigenous input, 134 thus questioning earlier hypotheses that perylene was formed from a terrestrial precursor. Perylene was the most abundant aromatic hydrocarbon in five sediment sections from DSDP sites in the Japan Trench 18 and in an earlier Cretaceous sediment. 19 Among the sedimentary aromatic hydrocarbons derived from biogenic precursors, a series of phenanthrene derivatives (Formulae 16-20), formed by dehydrogenation of abietic acid, a major component of pine resin, were detected in two lakes having forested catchments. 117 It was concluded, from the depth profile of retene (20), that formation from abietic acid was a fast reaction. Retene and pimanthrene (21) were also reported in sediment from Lake Washington, around which coniferous forest predominated until recently, but were absent in sediments of three Swiss lakes the drainage basins of which contained few conifers. 134 Retene and simonellite (19) have also been detected in sediments of Pleistocene to Miocene age from the Japan Trench; 18 the abundance of the former remained constant, while that of the latter decreased with increasing depth. Tetracyclic and pentacyclic hydrocarbons, varying in the extent of aromatization, occur widely in Recent 38'74'117'134 and older 3'18 sediments. These hydrocarbons are believed to originate from the 3-oxygenated pentacyclic triterpenes which occur widely in higher plants. Two pathways (Fig. 4) have been postulated, one in which ring A was lost, followed by successive aromatization of rings B, C and D, to give the tetracyclic series, and a pathway in which aromatization began in ring A, giving pentacyclic derivatives.74,114,117 Loss of ring A occurs during photolysis of the 3-keto derivative (Fig. 5); 30 microorganisms may initiate formation of excited ketones in sediments. Ring-A cleaved intermediates laave also been isolated from sediments. 3°,38

P.A. Cran~ell

286

(15)

(16)

(18)

(17)

(19)

(20)

(21)

In A m a z o n River and C a r i a c o T r e n c h sediments, tetracyclic c o m p o u n d s with the p r o p o s e d structures 23, 24, 26 a n d 27 were r e p o r t e d 7"~ while, in s e d i m e n t s from L a k e Washington'3"~ a n d u n p o l l u t e d lakes. 38'~1~ c o n s t i t u e n t s with p r o p o s e d structures 22, 23. 25 27 were present. Structures 23 and 26 were c o n f i r m e d by synthesis. ~l"~t~-~ The tetrah y d r o c h r y s e n e derivatives 25 a n d 26 have also been found in Recent Baltic Sea sediments. 1 ~'~ Little v a r i a t i o n in c o n c e n t r a t i o n of the tetracyclic derivatives (22 27) o c c u r r e d

Pathway

I

HO

Ct - A M Y R I N

Pathway {

i

------ll--

II ;

;

~

HO

a

- AMYRIN

FI(;. 4. Retlction p~Lth~',a_~sfor formation of tetra- and pentacyclic aromatic h>drocarbons from R-am,,.rin.i i v

Lipids of aquatic sediments and sedimenting particulates

o:oo%oo

287

C

% C--

\ FIG. 5. Proposed m e c h a n i s m leading to loss of ring A of pentacyclic triterpenes.

(22)

(23)

(25)

(24)

(26)

(28a,

g =

(27)

(29a,

... ) H ""

(28b, R= O)

Ho~,,. R =

.-) H -'"

(29b, R =

O)

R1

/'/,,

Rj

R

(30)

(31a)

R, = n , R2

=

Me

( 3 1 b } R I = Me, R 2 = H J.P,L.R,

21/4--c

(32a)

R~ = H, R2

..-"

=

Me

( 3 2 b ) R1 = Me, R2 = H

288

P.A. ('ranwell

within the top metre of lacustrine profiles. ~1: Sediments from Greilkmsec contained only compounds 25 and 26 which showed greatest abundance in deltaic sediments of the inflowing rivers, suggesting ;.lll association of the precursor colTlpounds with coarsegrained material. J'~'* The presence of this suite of tetracyclic compounds i22 27) in lacustrine sediments ~s has been correlated with thai of the presumed precursors, fl- {28at and ~-amyrin (29a) and lupeol (30). the related ketones and acidic tetracyclic compounds which are proposed intermediates in the loss of ring A from the pentacyclic precursors. Sediment of the Cretaceous period contained, in addition to t~vo of the above octahydrochrysenes, pentacyclic compounds with one to four aromatic rings representing successive stages in dehydrogenation of the nucleus. -~ Tetra- and octahydropicenc derivatives 31 and 32, respectively, have been tentatively identified in recent lacustrine.* ~-.J~4 river and marine"* sediments and also m Pleistocene and earlier sediments from the Japan Trench. L B. ,41k vl Eslers and 7)'iac.vlqlvcerols Alkyl esters are widely distributed in nature, 73 particularly m leaf waxes of higher plants and in marine organisms. Variations in the chain length, degree of unsaturation and extent of branching of esters occurring in various source organisms provide a potential means of distinguishing sedimentary input from these different sources. In an oligotrophic lake, alkyl esters in the range C38-Cs0, showing a high even homologue predominance characteristic of higher plant waxes, were reported. 39 Surficial sediments from two eutrophic lakes, Upton Broad and Crose Mere, contain a suite of C24 C36 esters in which either the alkyl or acyl moiety is iso- or anteiso-branched, in addition to saturated esters within the same range and smaller amounts o f m o n o - and dienoic C2~ ('.~s esters.:~ As corresponding n- and branched-chain ('2,, C.~, esters from the two sites sho~ed a similar molecular composition and because iso- and anteiso branching is characteristic of microbial lipids, it was suggested that the branched-chain esters originate from the microbial populations associated with decomposition of organic matter in productive lakes. However. these esters do not appear to have been detected in discrete organisms. A similar suite of esters may occur in an intertidal sediment, based on the composition of saponification products.~2~ Wax esters in an algal mat, the underlying sediments and m dry foam accumulating on the shore of a high altitude lake consisted of ( : s (',~2 saturated and minor quantities of ('2a and ('2~ monoenoic alkyl esters attributed to microbial sources. ~~-~ The molecular composition of co-during esters differing only in alkyl-acyl pairing may provide a means of distinguishing input to sediments, based on reports from different environments, j°'~'39'1 ~3 There are, however, few reports of compositional data on the wax esters in organisms from which the feasibility of this approach can be assessed.

Reports of alkyl esters in the marine environment are summarized bv Simoncit. ~~: Alkyl esters attributed to zooplankton have been detected in oceanic slicks and surficial marine sediments. 1°~ Recently C~2 (',~,, esters were identified in diatomaceous sediment from Walvis Bay. 1° The presence of isoprenoid esters and the chain length distributions of the alkyl and acvl moieties indicated a zooplankton origin: ho~ever, the absence of unsaturation was atypical of zooplankton and may result from diagcnesis. Alkvl esters could not be detected in 2000-year-old sediment from the same site. suggesting thal their survival in sediments is relatively short. Alkyl esters isolated from sediment trap particulates collected at several depths in the deep ocean contained ('2~, C,,,, homologues, a m o n g which C3,,:~ and C~x:l. derived from zooplankton, were dominant at all depths I ~-~ but were degraded more rapidly than saturated esters. Triglycerides have been isolated from a marine diatomaceous ooze a p p r o x i m a t e b 1700 years old: TM they ranged from C,,s C51 and were thought to be present in protective structures such ;.is diatom spores. Surviwfl of lipid species such as triglycerides is notable in view of the lipolytic activity in sediments. Triacylglycerols in sedimentary p a r t i c u l a t e s ranged from C4s C63, with Cs~.s3,ss.sv compounds predominating. ~3~ Differences in

Lipids of aquatic sediments and sedimenting particulates

289

composition of the acyl moiety occurred with depth, triacylglycerols in the uppermost trap contained mainly C~8:o, C18:~ and C~6:o fatty acids while in the lower trap in the mesopelagic zone C22:6 and C2o:5 were more abundant than saturated or monoenoic acyl substituents. The variation in composition may be attributed to differences in biological communities within the water column, or to release of compounds below the uppermost trap.

C. Ketones A homologous series of alkan-2-ones occurs in the readily extractable lipids from lacustrine 36 and intertidal marine 119 Recent sediments and also from sediments of Tertiary age.18 The distribution resembles that of n-alkanes in the same sediment but the correspondence is usually not close enough to substantiate a precursor product relationship involving ketone formation by microbiological oxidation of alkanes. Formation of alkan-2-ones from terrestrially-derived n-alkanes, prior to the organic matter reaching the lake, was postulated to explain the lack of an additional maximum at C~v in free ketones from the sediments of a productive lake, corresponding with a dominant free alkane derived from phytoplankton. 36 The alkan-2-ones present in bound lipids from an unproductive lake showed a lower odd-carbon predominance and relatively higher abundance of shorter-chain homologues than did extractable ketones in the same sediment. 36 The isoprenoid 6,10,14-trimethylpentadecan-2-one occurs in recent and older marine,18'112 lacustrine24 and intertidal *2s sediments; the stereochemistry is compatible with an origin from phytol. 24 Unsaturated straight-chain methyl and ethyl ketones have been identified in marine sediments varying in age from Recent to Miocene. ls'Ts'*zv The Cs7 and C38 alken-2-ones and C38 and C39 alken-3-ones were identical with compounds isolated from a marine coccolithophore Emiliania huxleyi; ~25 double bond positions in ketones isolated from a Black Sea coccolith-rich sediment were determined. 78 The structures were heptaconta- 15,22-dien-2-one (33), octaconta- 16, 23-dien-3-one (34) and octaconta-9,16,23-trien-3one (35). The abundance of these compounds in marine sediments may be attributed to a resistance to biological degradation, since the copepod Cahmus helgolandicus assimilated only a small proportion of these ketones when feeding on E. huxleyi.

CH3(CH2)I3 CH = CH (CH2) 5 CH = C H (CH2)12COCH 3

CH 3 (CH 2) ~3CH = CH(CH2)sCH = C H (CH2)12 COCH2CH 3

(33)

(34)

CH 3 (CH2)I3CH= CH (CH2)~CH "~ CH(CH2)sCH -- CH (CH2JsCOCH2CHB

(35)

HO

(36a,

R=

H%)

(36b,

R= O )

(37)

290

p.A. (*ran~sell

M i d - c h a i n ketones have been isolated from a n u m b e r of sediments, including d i a t o m a ceous s e d i m e n t from Walvis Bay, in which a suite of s t r a i g h t - c h a i n ketones in the range C ~ C43 occurred. ~° T h e ('3~ a n d ('4o alkan-1O-oncs were d o r n i n a n l , but their origin is u n k n o w n . M i d - c h a i n ketones occur in higher plants but usually show a d o m i n a n c e of the o d d - c a r b o n h o m o l o g u e s and a c h a i n - l e n g t h d i s l r i b u t i o n c l o s e l \ follo\~ing that o1 the n-alkanes. T r i t e r p e n o i d ketoncs of higher plant origin have been detected in e x t r a c t a b l e iipids from Recent lacustrine, 3a deltaic 3° and T e r t i a r y m a r i n e sediments. TM T h e most xkictclx o c c u r r i n g c o n s t i t u e n t s are t a r a x e r - 1 4 - e n - 3 - o n e (36b), o l e a n - 1 2 - e n - 3 - o n e (28b), urs-12-en3-one (29b), a n d f r i e d e l a n - 3 - o n e (37). T h e presence, in sediments, of p a r t i a l l y - a r o m a t i z e d h y d r o c a r b o n s derived from these p r e c u r s o r s was n o t e d above.

36b 100

37

RIG

29b I

,!

I 4

r

2400

i

i

I

I

I

2600

2800

3000

SCAN

2800

3000

SCAN

A3 100

RIC

B2

2400

2600

FIG. 6. Partial reconstructed ion chromatograms of free (upper) and bound (lower) ketones isolated from Loch Clair (10-20 cm) sediment. Numbers denote structures assigned to respective constituents. Key to other constituents: A1, A2~ A3 = C2~, C28 and C29 stera-3,5-dien-7-ones, B1, B2 = C28 and C29 3-keto-steranes.

Lipidsof aquatic sedimentsand sedimentingparticulates

291

Marked differences were observed in the composition of free and bound cyclic ketones isolated from sediment of Loch Clair, as shown by the partial reconstructed ion chromatogram (R.I.C.) traces (Fig. 6) for compounds eluting between nC28 and nC33 alkan-2ones. Higher plant-derived triterpenoid ketones occurred only in the free lipids. Bound ketones consisted of two hopanoid ketones and two series of steroidal ketones. One series, identified by mass fragmentography of the m/z 231 ion, consisted of C28 and C29 3-keto-5~-steranes. The second series showed a base peak at m/z 174 and molecular ions consistent with C27, C28 and C29 steroid dienones. Comparison of the mass spectra with those of authentic standards eliminated the 1,4-dien-3-one and 4,6-dien-3-one structures and supported the 3,5-dien-7-one structure. The corresponding dienol was suggested as a microbially-formed intermediate in the formation of steratrienes. 5~ In each series, the C29 component was dominant, consistent with the relative abundance of free or bound sterols in the sediment. 36 The hopanones were tentatively identified, by comparison with published mass spectra, as a trisnorhopan-21-one (38) and isoadiantone (39).

~

0

(39)

(38)

~

O

H (40)

D. Alcohols 1. n-AIkan-I-ols

Until recently, few studies of primary alkanols occurring in sediments had been reported; these were summarized by Simoneit. ~2 Homologous series within the range Ct4-C34 have been detected in a number of recent lacustrine 3~,36.~° and intertidal marine sediments, ~29 also in D S D P core samples from the Japan Trench, ~8 marine particulates ~33 and algal mats. 28 With the exception of the sedimenting particulate matter, in which C~6 and C~8 predominated, distribution patterns maximized in the C22 C28 region, characteristic of higher-plant input. ~23 In the bimodal distribution found in extractable (free and esterified) alkanols from an intertidal sediment, the C22 C28 alcohols were attributed to input from the sea grass, Zostera muelleri, 67 while the lower homologues were attributed in part to wax esters of unknown origin. ~29 The distribution patterns of free, esterified and bound n-alkanols from surficial sediment of an oligotrophic lake and from an eutrophic lake are shown in Fig. 7 (upper and lower, respectively). The chain length patterns indicate a major contribution from higher plant sources to the free alkanols at both sites; however, esterified alkanols in the latter sediment were attributed to authochthonous sources, 33 while those in the former are derived from higher plants. 39 Little information is available about sources of bound n-alkanols; however, there is some evidence that decomposer organisms give rise to distributions of bound alkanols maximizing at C22 .36

292

P.A. ('ranwell

30"

14

69

10.

40 [ 2o ._,_l_], ,[., .

g I.

3

i

I i

30"

III

=

f

i

79

20.

f4o]1[

20 [,I

' I.d,, o i l ,. I,

2O

,o .hi ..... 12

i

i

18

24

•. 30

12

I!.a.i.~_l 18 Carbon

.

24

,

3~0

12

18

i

I

24

30

Number

FIG. 7. Percentage composition of free (left), esterified (centre) and bound (right! n-alkanols isolated from Loch Clair (>10 cm (upper) and Crose Mere 12 25 cm (lower) sediments. Figure at top right of each histogram gives percentage contribution to total n-alkanols in the sediment.

Rapid diagenesis of the lower free alkanols ( < ( ' 2 0 ) o c c u r s during lhe deca 3 of higherplant material leading to peat formation: ~°3 a similar change was noted in the distribution of total n-alkanols in a prolile from an intertidal sediment, in which a maximum at C~o at the surface changed to a dominance of ('ee in deeper sections. '''~ Monoenoic n-alcohols in the range ('22 ('2~ ~ere detected m sediments from the Japan Trench ~8 but the site of the double bond was not determined.

2. Branched-Chain aml ('yclic Alcohols Branched-chain and cyclic alcohols other than phytol and stcrols, respectively, have been little studied. However, iso- and ante/so-branched alkanols ha~e been identified in a D S D P sediment core 1" and in Recent lacustrine sediments) 4 Free, esterilied and boup, d branched/cyclic (B/C) alcohols isolated from a sediment differ in composition, thus oddcarbon Cts C2~ iso- and a n t e i s o - a l k a n o l s were minor constituents of the free B/C alkanols isolated from both a productive and an unproductive lake, but were dominant in the bound alkanols) 4 These components were attributed to input of microbial lipids. Iso-C14 and Ct6 alkanols occurred in low relative abundance in free B/C alcohols isolated from an oligotrophic lake but were abundant in the corresponding lipid component of the productive Crose Mere and are probably derived by hydrolysis of wax esters which have recently been isolated from this sediment profile. 3~ The isoprenoid alcohol phytol (40) occurs widely in sedimems and dihydrophytol sometimes co-occurs with it. In an intertidal sediment receiving input of chlorophyll-a, degradation proceeded, with increasing depth, via non-chlorin phylyl esters, followed by incorporation of phytol into a bound form which was hydrolysed at greater depth in the profile with release of free phytol. ~ Phytol was the major alcohol in estuarinc and coastal sediments studied by wm Vleet and Quinn '2~ and was accompanied by about 10% dihydrophytol which had exclusive RRR stereochemistry, indicative of formation by a microbially-mediated reduction of phytol. In contrast to the studies of Johns et al., 6~ surficial sediments contained mainly bound phytol, and there was no discernible increase in the proportion of free phytol with increasing depth. The stereochemistry of free and bound dihydrophytol isolated from a lacustrine sediment also showed a dominance ot the RRR isomer, again indicative of microbially-mediated double bond reduction. 2"t Pentacyclic triterpenoids bearing a hydroxyl group at C-3, which occur widely in higher plants, have been isolated from marine '~° and Recent freshwater ~s sediments. In

Lipids of aquatic sediments and sedimentingparticulates

293

the latter, the main constituents of the free B/C alcohols were the 3fl-hydroxy derivatives 28a, 29a, 30 and 36a. Sterols and hopanols are reviewed in Sections F and G, respectively (below).

3. Miscellaneous Alcohols From the sediment of the Black Sea, a series of alkan-l,15-diols and related alkan-15one-l-ols having 30-32 carbon atoms have been isolated. 8° The source of these compounds is unknown as they have not been identified in organisms. However, it was suggested that they may be derived either from the abundant coccolithophores in this sediment or from mycolic acids, present as bacterial cell wall components. A series of alkan-2-ols having exclusive 2S stereochemistry, detected in the bound lipids of lacustrine sediments, 34 was attributed to the complex lipids of bacterial cell walls.

E. Carboxylie Acids 1. n-Alkanoic Acids Saturated fatty acids occur ubiquitously in organic sediments of all ages and have been examined extensively,z'l~/ Recent studies have focussed on compositional differences between extractable and bound forms within a given sediment and on changes in composition with depth, attributable to early diagenesis of the more-labile constituents in contemporary sediments (Table 2). Extraction procedures involving saponification of the total extractable lipids give an acidic fraction which may contain acids derived from solvent-soluble esters. Prior separation of free fatty acids from modern sediments of both productive and unproductive lakes affords a chain length distribution pattern different from that of esterified extractable or bound acids (Fig. 8); the proportions of the chemically distinct forms also differ. Other research groups have distinguished fatty acids bound to humic materials from those bound to the residual sediment, lz5 The widespread distribution of n-alkanoic acids in organisms enables their use as indicators of sedimentary source materials only in the most general terms, so that constituents with chain lengths greater than 20 have been attributed to input derived predominantly from higher plants while those in the C Iz-Cls range have been attributed to aquatic source organisms. 112 These correlations are supported by other lipid components in the respective sediments and by analysis of suitable source material. Early diagenesis of homologues below C2o occurs in the uppermost sediment horizons (Table 2) and diagenesis must also occur in terrestrial detritus before deposition in the aquatic environment, since C~6 and Ct8 acids are very abundant in terrestrial biota, as wax esters and glycerides.6° Differences in composition of bound and free acids, in sediments from many environments and sediments varying in age from contemporary to Miocene (Table 2), have been attributed to input from different source organisms, but these differences also reflect, in part, the greater stability of the bound form with respect to diagenesis.

2. Branched-Chain and Cyclic Monocarboxylic Acids The presence of iso- and anteiso-branched acids ranging from C9 to C19 in freshwater 2 and marine 112 sediments has been reviewed. These acids are characteristic of bacteria and presumably are residues of the microbial populations decomposing organic matter. The higher abundance ratio of branched:straight-chain C15 + CIv acids in bound compared to free lipids 64 and the higher abundance of iso- and anteiso-acids in the bound than in the free branched/cyclic saturated acids 33 have been considered to indicate that bound fatty acids are predominantly of microbial origin. A bacterial contribution of branched-chain and unsaturated acids to a marine sediment has been demonstrated by analysis of lipids from bacterial cultures obtained from the sediment. 99 10-Methyl C16

294

I'. A. ('ranwell

TABLE 2. n-Alkanoic Acids in Sediments Source

Sample type and number

Lipid species

Carbon range

(a) Lacustrine sediments Lake Haruna, Japan

Depth prolile 1131

[Inbound Bound

14 32 1.4 ~2

Lake Stoma, Japan

Depth prolile (20)

Extractable

12 34

Lake Suigetsu, Japan

Depth profile (271

Extractable

12 ~4

Rostherne Mere. England

Sediment particle size fractions 15)

Extractable

12 2s

Laguna Lejia, Chile Crose Mere, England Loch Clair, Scotland

Surficial sediment

Free

12 32

Sediment

Free Bound Free

t0 30 10 24 14 t2

Bound

12 30

Sediments age < 60~rr 12) Sediment age > 400.~r Depth profile ( 141

Free Bound Free Bound Total

12 10 t2 IO 12

Surlicial sediment

Total

t4 24

Depth prolile {3)

Total

I4

Sediment trap depth profile (41

Extractable

14 26

Surface

Free

12 20

Profile (3)

Free

9 29

Surface

Extractable

I4 IS

Upton Broad, England

Pyramid k.. USA

Lake Huron, USA

(bl Settling particulates Lake Michigan, USA

Atlantic ocean

T ~ o sections

30 20 32 30 30

.22

(c) Algal mats L. Lejia, Chile L a g u n a Ouerrero. USA Abu Dhabi

Lipids of aquatic sediments and sedimenting particulates

295

TABLE 2 (continued).

Modality

Maxima

CPI value

Abundance

Notes

2 2

16, 24 16, 22 (weak)

5.3 _ 0.6 5.5 _+ 0.7

4000-16,900 ppm org. matter

14, 24

3 7

--

2

16, 24 or 26 or 28

--

--

I or 2

16 and/or 24

5 9.5

80-750#g/g (total fatty acids)

2

16, 24

4.0

7/~g/g

C14-C~8 more abundant in bound form. U n b o u n d : bound ca 1.0 Good preservation of components above C20 in core. Decrease in abundance of shorter-chain acids in top 20 cms. Acids above Czo more abundant below 15 cm. Proportion of C~2 C2s decreases with particle size down to 4~b fraction, correlating with decrease in higher plant fragments, but increases in clay fraction (possible geolipid input) Under algal mat (see below)

2

2 1 2

16, 26 16 16 (weak), 24

7.7 13.7 4.5-4.8

725 ppm org C 430 ppm org C 2190-4760 ppm org C

2

16, 22 or 24

7.8-9.2

800-1380 ppm org C

1 or 2 2 2 2 1 or 2

16, 26 12, 16 16, 26 16, 26 16 and 24 or 30

6.4-6.6 7.8-8.3 9.7 9.7 --

1620-2710 p p m org C 2200-2330 p p m 630 ppm org C 1330 p p m org C 23 7 4 0 p p m

l

16

--

13-127 ~g/g

16

1

16

2

16, 24 (weak)

6.9

1

16

1.1-3.9

I

16

--

170 lag/g

64

84 85

83

120

113 33

Distribution of these and esterified acids given in Fig. 8. Stability of bound acids greater than free Free/bound = 2.6-3,3 See Fig. 8. C o m p o n e n t s above C20 more a b u n d a n t in free lipids Changes in abundance and distribution at onset of reduction in lake volume

36

37

90

91

Faunal debris separated from sediment at each depth. Little difference in FA composition. Composition reflected planktonic source. Flux decreased with increasing depth.

1

Ref. no.

88

133

113 101 28

296

P. A, ('ranwell TABLE 2 (continued). Sample type and number

Source

Lipid species

Carbon range

(d) Estuarine and intertidal marine sediments Corner Inlet, Australia

Surface

Extractable

1_ _8

Profile (7)

Total

12 28

Low Isles. Australia Buzzards Bay, USA

Mangrove swamp

rl'otal

9 24

Depth profile (4)

Extractable Bound

14 22 14 22

Narragansett Bay, USA

Depth profile (4)

Extractable Bound

12 20 12 20

(e) Marine sediments Continental Shelf

3 sites

Total

12 36

{f) Ancient sediments Japan Trench

Various depths (5)

Frec Bound

12 32 14 30

Bay of Biscay,

Various depths (3)

Extractable

8 32

30-

73

5

22

., .,.i,1,1..,.].1.1.,J.,,

20-

10-

g

,

i

60-

39

'I +ll,lll I: ..,,I.,. 60

20

40-

20-

I 12

h

18

I

. . . . .

24

,.I,,I.,.,.,.,,.

28

.

30

33

10

16

Carbon

2'2

2'8

10

•

16

22

.

.

2'8

Number

FiG. 8. Percentage composition of free (left), esterified (centre) and bound (right) n-alkanoic acids isolated from Loch Clair 0-10 cm (upper) and Upton Broad 0-6 cm (lower) sediments. Figure at top right of each histogram gives percentage contribution to total n-alkanoic acids in the sediment.

297

Lipids of aquatic sediments and sedimenting particulates TABLE 2 (continued).

Modality

Maxima

2

16, 24 (weak)

CPI value

Abundance

35/~g/g

Notes

Acids >C2o attributed to

Ref. no.

130

Zostera.

5 93 ppm

t or 2

16 and 24 or 26

1

16

--

1 1

16 16

---

33-59 #g/g 27-42 ug/g

1 1

16 16

---

14-34 #g/g 23-42 #g/g

2

16, 24

4.9-6.6

6-36 pg/g

2 2

16, 26 16, 24 (weak)

---

176 ng/g 18 ng/g

2

16. 24

--

Micro-organisms are main source of acids
69

99 Bound is 65-69yo total acids. Constant ratio suggests no significant production or protection of bound relative to u n b o u n d with increasing depth. U n b o u n d acids decrease faster than b o u n d with increasing depth

48

125

llO

Free > bound fatty acids in 3 of 5 sections Acids above C20 attributed to higher plant sources.

18

and C18 acids and cyclopropanoid acids were also found both in the sediment and in total anaerobic heterotrophs cultured from it. Among the acyclic isoprenoid acids derived from phytol, the stereochemistry of phytanic acid isolated from lacustrine and lagoonal sediments, an algal mat and the underlying intertidal zone sediment showed, in each case, a preference for one isomer, consistent with microbial processes of formation from phytol. 24 A wide variation between sites in the ratio of SRR to RRR isomers was attributed to different microbial populations; a constant isomer ratio was observed for extractable and bound phytanic acid from the same site. Diterpenoid acids, which occur in conifer rosin and are, therefore, good markers of terrigeneous input to sediments, have been reported in marine sediments varying widely in age and location; 11a dehydroabietic acid (41) was predominant. Triterpenoid acids having the hopane skeleton are reviewed in Section VI.G.

(41)

298

P.A. Cranaell

3. Alkenoic Acids The positional isomer composition of monoenoic acids isolated from a lacustrine sediment has been reported. 84 Compounds in the range C~ s ('e6 were detected and had double bonds at carbon atoms 7. 9 . . . etc. up to the {,)5 position, in the homologues above Clg, the ~,~9 isomer was predominant, consistent with either a bacterial or a higher plant origin. In the extractable lipids, C16 was the dominant chain length while ('~ 8 was dominant in bound lipids. The relative abundance of 18:1~,)7, considered as an indicator of bacterial input, was higher in the extractable than in the bound lipids. Unsaturated acids having an odd carbon number, in particular the Cls and C ~ ~,~6 and ¢¢)8 isomers. were not attributed to a specific source by Matsuda and Koyama. 84 Analysis of lipids of a marine sediment and lipids of bacteria cultured from the sediment indicate that these pairs of isomers are also valid markers for bacteria. ~ In a marine diatomaceous sediment, monoenoic straight and branched-chain acids below C20 contained double bonds at the A:, k '~ and A 1~ position and were attributed to algal and microbial sources, x~ Above C2o the straight chain acids were unsaturated at the A ~~ and /515 positions, and were thought to be derived from yeasts. Branched chain monoenoic acids, including i~l, A7-15:1 and iso A9-17:1, occur in aerobic heterotrophs cultured from an intertidal sediment 99 and also in Desulphovihrio sp., bacteria omnipresent in marine sediments, t3 In addition to the above cis-monoenoic acids, zrans unsaturated acids occur as minol components of lacustrine ICranwell, unpublished data), river, estuarine and coastal marine sediments. ~ 1 2 s These acids, mainly consisting of 16: 1~,)7, I S :1 ¢,)7 and 18:1~,~9. were attributed to direct bacterial input. Analysis of unsaturated fatt; acids from a marine bacterial isolate showed trans monoenoic straight-chain, iso-branched IC~, ( ~ 1 and anteiso-C~v acids. 5~ Polyunsaturated acids occur mainly in contemporary anoxic sediments and probably result from direct deposition of the source organisms. 1"~° Sediment from a mangroxc swamp 9'~ and another intertidal site T M contained many components characteristic of planktonic organisms, including 16:2c94 and 16:2~,)7 indicative of diatoms, and 20:4~o6 and 20:5o)3 which occur widely in eukaryotic algae a~' and were also detected in a freshwater productive lake. ~~ Analysis of sediment trap particulates from the deep sea shows a rapid breakdo~.n of polyenoic acids derived from planktonic sources, onlx trace quantities being present in the lowest traps. ~~-~ Decomposition of unsaturated acMs x~a., faster in sediment of an oligotrophic lake than in a productive lake: polyenoic acids decayed more rapidly than monoenoic acids. ~°

4. :<~,J-Dicarhoxylic 4cids Sediments from freshwater 31"~''* and marine ~''~'~31 Recent environments and also older marine sediments 18 contain a homologous series of saturated dicarboxylic acids. In the sediment profile studied by lshiwatari et al., ~4 both free and bound fractions showed a bimodal distribution maximising at C~, and C22 or C24, differing only m the higher abundance of ('~6 in the bound fraction. The similarity between the distribution of mono- and c<~,)-dicarboxylic acids was interpreted as evidence of the latter resulting from microbial oxidation of the former. In sediments associated with mangrove swamps, direct input of ~.,o)-di-acids derived from cutin and suberin has been postulated. ~'8 In another intertidal environment, a good correlation was observed between the distribution of ~.a,)-di-acids in the sediment and that in the sea-grass Z. muelleri: the chain length maximum occurred at (2~,, considerably higher than most other sediments for which data are available. A parallel chain-length distribution of ~.,~,)-di- and ~,MLvdrox_~ monocarboxylic acids v,.as found m some sediments suggesting that microbial oxidation of the latter, derived from higher plant cuticular lipids, occurred. 31 In Pleistocene sediment from the Japan Trench. TM flee C lo ('~, diacids were present, excluding a ('~, contaminant, while the bound component contained C~o ('2~ acids having ~. much lower cxencarbon tgreference than distributions in recent sediments.

Lipids of aquatic sediments and sedimenting particulates

299

5. Hydroxy Acids

2-Hydroxy aliphatic acids within the range C12-C2s occur in lacustrine, 35 intertidal T M and marine 9 recent sediments and also in ancient sediments. 3'~ s Because 2-hydroxy acids occur widely in nature, source correlations are difficult but are facilitated when the stereochemistry of the separate free and bound components is studied. Free and bound 2-hydroxy acids above C2o, isolated from a lacustrine sediment, showed predominantly R stereochemistry consistent with a higher-plant source, in which they are by-products of the ~-oxidation of fatty acids. 35 The shorter chain constituents may have been derived from both higher-plant and microbial sources. 2-Hydroxy carboxylic acids were found in extractable lipids from Cretaceous marine sediment 3 but only in the bound lipids isolated from the Japan Trench Is and Walvis Ridge. '4 3-Hydroxy carboxylic acids also occur in lacustrine 2v'35 and marine 9'1 s sediments and in algal mats, 27 showing a higher abundance in the bound lipids than the 2-hydroxy isomers. The C l o - C l s straight chain and iso and anteiso branched chain constituents predominating in the bound lipids have been attributed to microbial activity within the sediment; the acids have the R stereochemistry characteristic of cell wall constituents in gram-negative bacteria.' 2,35 (~)-Hydroxy acids occur in the cuticular waxes of plants or in a bound form in the polymers cutin (C,6, CIs) and suberin (range C,6 C2,). In lacustrine sediments studied by Cardoso et al., 27 only bound m-hydroxy acids were present, while in an algal mat these acids were absent. The distribution in an intertidal sediment closely resembled that in the sea-grass Z. muelleri, the main species at the sampling site. 13' The distribution patterns of bound u3-hydroxy acids isolated from the Japan Trench i s resembled those of the bound 2,u3-dicarboxylic acids, showing maxima at C,6 and C22.

F. Steroids

The parent compounds of a wide range of sedimentary constituents having the tetracyclic steroid skeleton are the sterols which are characteristically distributed in living matter and relatively stable in sediments, thus facilitating recognition of the origins of sedimentary organic matter. Earlier reviews of sterols in lacustrine 2 and marine 112 sediments have appeared. A major difficulty in determining the relative sediment input derived from higher plant and algal sources arises from the close similarity of their major sterols, which may differ only in stereochemistry at C-24. Recently the gas chromatographic resolution of 24R and 24S steranes and stanols, derived from naturally occurring sterols by hydrogenolysis and hydrogenation, respectively, s6 and the separation of the parent sterols' ,9 have been reported. Earlier studies showed that stanols in recent sediments were derived in part from various living organisms and, in certain environments, from stenol hydrogenation (see Ref. 2). Under oxidative conditions, as in surficial sediment from an oligotrophic lake, preferential degradation of the stenols resulted in concentration of the stanols, even when no conversion of stenols to stanols took place. 94 Under anoxic conditions, reduction of stenols to stanols occurred at a rate controlled by the redox potential and proportion of autochthonous organic matter in the sediment. 95 Marine sediments contain a complex mixture of stenols, each co-occurring with its nuclear saturated analogue. Sediment input derived from a wide variety of organisms can be recognized from morphological residues of the latter and can be correlated with sterol content. A Black Sea sediment rich in dinoflagellate cysts contained dinosterol (42), a compound only previously reported in dinoflagellates, as the major sterol. 15 Major constituents in a diatomaceous sediment from Walvis Bay '3s were an unidentified C27 A 5'22 sterol, 23,24-dimethylcholesta-5,22E-dien-3/3-ol, which has been found in a coral and, more recently, in diatoms '29 and gorgosterol (43) which occurs in the Anthozoan group of coelenterates, a group of organisms not reported in Walvis Bay. However, the saturated analogue occurs in jellyfish which have been found at this site. The sterol compo-

300

P.A. ('ranwell

(42)

(43)

(44)

sition of an intertidal sediment was correlated with the sterols in diatoms cultured from the sediment and with those of another source material, the sea-grass, Z . mtwlh_,ri. 12,~ The abundance of 24-methylcholesta-5,22E-dien-3fl-ol in the culture and sediment indicated a significant diatom input to the latter, while the presence of dinosterol was attributed to input of dinoflagellate lipids. Sediment input from marine fauna was postulated to account for a proportion of the 5~x-stanols, C26 sterol derivatives and cholesterol. Neogene sediments from the Japan Trench contain a complex mixture of sterols, of which 69 have been characterized. 21 Many constituents are those occurring in more recent marine sediments (see above references) and were assigned to similar sources. However, 24(E and Z)-ethylidene- and 24(E and Z)-propylidenecholest-5-en-3fl-ols, compounds considered to be specific to marine biota, were found, ~8 as also was a novel sterol, 27-nor-24-methyl-5ce-cholestan-3fl-ol, (44) possibly derived from a sponge. 21 Sediments of the intertidal zone, associated with the presence of blue-green algal mats, contain A s and A 5'22 stenols, together with the corresponding 5~-stanols and k2e-ste nols. 2s'¢'2 An increase in the stanol:stenol ratio in the uppermost section of a profile was substantially greater for ('2~ sterols than for C2~ or C29 sterols. ¢'2 This feature was attributed to biological selectivity, either in the production or alteration of sterols. Oligotrophic lakes usuany contain a fairly simple suite of sterols consisting of C2~, ('2s and C29 components having A ~ and A s'22 unsaturation, together with the analogous compounds saturated at C-5, in which C29 components predominate, 31'-s" indicative of higher-plant input/'3 Surficial sediments of two small productive lakes, Upton Broad and Priest Pot, contained a wider variety of sterols resulting from a range of source organisms, so that the proportions of C27, C28 and C2,~ sterols can no longer be used to detine ecological systems, as proposed by Huang and Meinschein/'3 The gas c h r o m a t o g r a m of free sterols (as trimethylsilylethers) obtained from Priest Pot is shown in Fig. 9 and the free sterol composition of both sediments is given in Table 3. The distribution of sterols according to structural type is shown in Table 4. In the surface sediment of Upton Broad, algal residues consisted mainly of green and blue-green species, with some diatoms, s~ Recent records of plankton show that green algae have been abundant but that benthic blue-green algae are also major primar_~ producers. Diatoms are abundant in Priest Pot during the spring phytoplankton maxim u m while small species of green algae are dominant during the summer but algal

Lipids of aquatic sediments and sedimenting particulates

301

H R)

K~

D

P T

M

O

H

C

N L

i

125

FE

l

i

l

100

75

50

TIME(rain)

0

I

I

25

FIG. 9. Gas chromatogram of free sterols isolated from sediment of Priest Pot (0-5 cm). Identities of constituents A-V given in Table 3. (Conditions: 50 m x 0.2 mm i.d. SE-30 column at 245 °, using H 2 carrier gas at 1.6 kPa inlet pressure.) The strong peak eluting after 30 min is 5~-cholestane, an internal standard.

remains in the surface sediments consist mainly of colonies of another green alga, Scenedesmus, and planktonic diatoms. In Upton Broad, A5'22 sterols, the major structural type, consisted mainly of cholesta5,22E-dien-3fl-ol; 24-methylcholesta-5,22E-dien-3fl-ol and 23,24-dimethylcholesta-5,22Edien-3fl-ol, all of which have been identified in diatoms (see Ref. 129). In Priest Pot, A5'22 TABLE 3. Identification and Composition of Free Sterols in Sediments from Priest Pot (0-5 cm) and Upton Broad (0-6 cm) ~o Composition 3 GC peak ~

RRT 2

A B C D

0.880 0.910 1.000 1.030

E

1.110

F G H I J K L

1.140 1.268 1.284 1.293 1.308 1.325 1.375

M

1.410

N O P Q

1.440 1.470 1.616 1.625

R

1.667

S T U V

1.740 1.760 1.840 2.070

Identification Cholesta-5,22E-dien-3fl-ol 5ct-Cholest-22E-en-3fl-ol Cholest-5-en-3fl-ol 5ct-Cholestan-3fl-ol 24-Methylcholesta-5,22E-dien-3fl-ol 5ct-Cholest-7-en-3fl-ol 24-Methyl-5ct-cholest-22E-en-3fl-ol 24-Methylcholesta-5,24(28)-dien-3fl-ol C28 monoene 24-Methylcholest-5-en-3fl-ol 24-Methyl-5ct-cholest-24(28)-en-3fl-ol 24-Methyl-5ct-cholestan-3fl-ol 23,24-Dimethylcholesta-5,22E-dien-3fl-ol 23,24-Dimethyl-5ct-cholest-22E-en-3fl-ol 24-Ethylcholesta-5,22E-dien-3fl-ol 24-Ethyl-5ct-cholest-22E-en-3fl-ol 24-Methyl-5~-cholest-7-en-3fl-ol 24-Ethyl-5~-cholesta-7,22E-dien-3fl-ol 24-Ethylcholest-5-en-3fl-ol 24-Ethyl-5ct-cholestan-3fl-ol 24-Ethylcholesta-5,24(28)Z-dien-3fl-ol 24-Ethyl-5ct-cholesta-7,24(28)Z-dien-3fl-ol 4~,23,24-Trimethyl-5~t-cholest-22E-en-3fl-ol 24-Ethyl-5ct-cholest-7-en-3fl-ol -

-

Upton Broad

Priest Pot

13.0 1.4 5.0 3.7 3.5 2.6 1.5 0.5 2.0 1.0 tr 1.5 13.7 0.2 2.6 tr 5.6 12.7 12.7 4.0 0.4 1.0 -10.4

tr tr 3.0 9.0 1.7 -1.4 1.0 3.0 2.4 3.0 4.6 2.8 tr 6.6 2.3 4.3 9.0 11.0 13.4 -3.0 6.6 5.6 4.0

-

-

1GC peaks refer to Fig. 9. 2With respect to Cholest-5-en-3fl-ol trimethylsilyl ether. 3tr = trace. Composition of peaks E, M, R estimated from size of molecular ion in mass spectra.

302

P. A. ( ' r a n w e l l "FAm~i 4. D i s t r i b u t i o n of Sterols, as "i, of Total Sterols, A c c o r d i n g to Structural Type Percentage t [ IlSat tlra[ioi1 sites £~.,22 A ez A~ None A A -'22

Upioll

Broad

Q.N 3.1 IS.7 9.2 18.6 12,7

Pricst Pot 1 l.l 10.3 16.4 27.0 9.9 9.0

sterols are rather less abundant and differ in composition, lacking cholesta-5,22Edien-3fl-ol and containing 24-ethylcholest-5,22E-dien-3fl-ol which may be of higher plant origin. A 7- and AT'22-sterols have seldom been reported in sediments, but 24-methyl and 24-ethyl-5~-cholest-7-en-3/#ol and 24-ethyl-5a-cholesta-7,22E-dien-3fl-ol, the main constituents of this group, occur in several species of green algae, 98"1°s and also, in very small amounts, in blue-green algae and in protozoa, s8 The abundance of intact green algal cells in both sediments suggests an algal origin of the sedimentary A T- and Av'22-sterols. The higher ratio of 5ct:A s sterols in Priest Pot may be attributed to a more extensive degradation under oxidative conditions of accumulating organic material, giving a more rapid removal of stenols relative to stanols. 96 The preservation of chlorophyll pigments in Upton Broad, reflected in the green colouration of the uppermost 15 cm of the sediment profile, suggests that anoxic conditions prevail at the sediment surface at this site so that reduction of z~S-stenols to stanols occurs. 53 The distributions of extractable n-alkanes, n-alkanoic acids and wax esters (Cranwell, unpublished data) indicate a higher terrestrial input to Priest Pot than to Upton Broad sediments; the higher combined abundance of C29 sterols (A s + 5~) in the former may also be attributed to terrestrial detritus, in which higher stanol/stenol ratios are observed than in the source organisms, due to preferential decomposition of stenols. 93 Differences in composition between extractable and bound sterols have been reported in marine 7s'~' and in lacustrine 33'~ sediments. Dinosterol (42i was domimmt in frec sterols of a Black Sea sediment core while 24-methylcholesta-5,22E-dien-3fl-ol was dominant in the corresponding bound sterols. Surface sediments from three stations m Walvis Bay showed similar distributions of free and bound sterols, but at two other sites different distributions were obtained. ~7 In the absence of terrestrial runoff, bound sterols in Walvis Bay sediments were attributed to marine organisms, and their high abundance was attributed to enhanced stability due to association with siliceous, carbonate or chitinous exoskeletons. The presence of esterified sterols has been recognized in extractable lipids from Buzzards Bay, 7~ Lake Mendota 61 and Loch Clair. 39 The main difference in composition of free and esterified sterols in Loch Clair was the lower 5~-stanol:A 5stenol ratio of the esterified components, attributed to their greater resistance to microbial attack, compared ,~'ith the free sterols. Bound sterols also show lower stanol: stenol ratios than free sterols in the same sediment. 36''~3 Sterol ethers containing C8 or C~ either moieties linked to C2~, ('28 and (-'2~ sterols have been detected in a diatomaceous recent marine sediment ~° while, in ancient diatomacous sediments, similar compounds having C 9 - C ~ alkyl groups were detected: ts their source is not known. Diagenesis of sterols in recent marine sediments gives mixtures of sterenes in which the A 2 isomers usually predominate with some steradienes and trienes. 4~'51 Saturated steroid ketones (stanones), postulated intermediates in formation of sterenes, have also been found in marine sediment from Walvis Bay. sz Unsaturated and saturated steroidal ketones have been found in a lacustrine sediment (see Section VI.C). Studies on the diagenetic fate of 5~-cholestan-3fl-ol, by radiolabeled incubation in algal mats, have

Lipidsof aquatic sedimentsand sedimentingparticulates ~

303

.... R

(45a) R = ~CH (CH3)2 R = --CH(CH3)(CH2)2(CHOH)3CH2OH

(45b)

--C(CH3)--- C H 2

(4~C)

R =

(45d)

R=--C(CH3)2OH

(45~) R= --CH(CH3)(CH2)3OH

shown the formation of 5~-cholestan-3-one with some radioactivity incorporated into non-solvent extractable residues. 44 G. Hopane Derivatives

Over 100 derivatives of the hopane (45a) skeleton have been recognized in sedimentary organic matter from a wide variety of environments. Hopane derivatives occur in a few higher plant species but microorganisms are the main source of extended (> C3o) hopanoids which are believed to have a function in procaryotes equivalent to that of sterols in eukaryotes. 9~ The main feature in distributions of hopane derivatives in sediments is the presence of extended hopanoids ranging up to C36, in which one to five carbon atoms form an n-alkyl group attached to C-22. The presumed precursor, bacteriohopane tetrol (45b), was isolated from Acetobacter xylinum 49 and has since been isolated from surficJal lacustrine sediments together with the unaltered bacterial constituents, diploptene (45c) and diplopterol (45d), and products derived from the tetrol, l°a The latter products consisted of the C32 primary alcohol (45e) and the 17~H isomer, the isomeric 17fill and 17~H C31-C33 carboxylic acids and the C27, C29-C32 alkane derivatives. For compounds having more than 30 carbon atoms, two diastereoisomers at C-22 may occur; however, in many Recent sediments, only one C-22 epimer, having the R-configuration, is present. This configuration was recently confirmed in the case of the 17fill, 21flH-C32 acid by NMR. ~8 In recent sediments, the hopanoid alkanes are mainly the 17fill, 21fill-isomers, also as single C-22 diastereoisomers. In more mature sediments, these compounds are convered into the thermodynamically more stable 17~H, 21fill isomers present as C-22 diastereoisomeric pairs. 2° A more detailed bibliography of hopane derivatives in sediments has been given by Ourisson et al. 97 H. Carotenoids

Carotenoids occur widely in all photosynthetic and in some non-photosynthetic organisms. Although some individual carotenoids are widely distributed, others are specific to a type of organism and may be used as biological markers in recent sediments. Earlier examples of this approach were reviewed by Watts et al., 14° who studied three types of environment, two eutrophic lacustrine sediments, two algal mats, and a marine continental shelf anoxic environment. With the exception of the marine sediment, all samples contained glycosidic carotenoids of myxoxanthophyll (46) type, characteristic of bluegreen algae and consistent with the abundant phytoplankton in the lakes and the compoSition of the algal mats, respectively. These and other algal mats 122 also contained spirilloxanthin (47), rhodopin (48) and 3,4-dehydrorhodopin, characteristic of purple

J.P,L.R21/4 . o

304

P.A. ('ranwell ORhamnose

AcO /

(46)

OMe

~

~

~

~"

~

~

~

~

(4"/) OH

(48)

OMe

o

(49)

0

HO

OAc

(50) jOH

(51)

(52)

~

OM~

Lipids of aquatic sedimentsand sedimenting particulates

305

O

HO~

O

H

(54)

ORhamnose

ORhamnose

OH

(55)

photosynthetic bacteria. Marine sediment from the Cariaco Trench contained spheroidenone (49), suggesting input from non-sulphur purple photosynthetic bacteria, but lacked the carotenoids, peridinin (50), diadinoxanthin (51) and fucoxanthin (52), associated with Dinophyceae, Chrysophyceae and Bacillariophyceae, respectively, the anticipated major phytoplankton input.~4° The relative instability of fucoxanthin during sedimentation has recently been noted during analysis of sediment trap particulates, t°6 Ester hydrolysis, dehydration and epoxide opening were postulated processes giving rise to the observed products; structurally similar carotenoids, e.g. peridinin (50), should undergo analogous transformations. Diagenesis of carotenoids within a marine sediment profile showed that double bond reduction occurred over differing time scales, depending on the carotenoid ;139 stability increased in the order canthaxanthin (53), zeaxanthin (54), fl-carotene. In recent sediments, carotenoid stratigraphy can be used to determine changes in the composition of phytoplankton in lakes undergoing eutrophication. 14z Correlation with phytoplankton records was used to relate changing concentrations of oscillaxanthin (55) in the sediment profile with changes in the population of the blue-green algae Oscillatoria, the source of this carotenoid. 59 VII. SUMMARY Contemporary sediments from a variety of aquatic environments contain lipids characteristic of source organisms. Diagenetic processes are evident in these sediments, either from the presence of transformation products, such as sterenes derived from sterols, and partially-aromatized hydrocarbons derived from pentacyclic triterpenes, or from changes in relative abundance of homologous series of biolipids. Selective mineralization of the shorter-chain homologues, presumably because these are more-viable substrates for microorganisms, occurs in recent sediments and may have been overlooked in using lipid distributions for the interpretation of input sources in older sediments. Chemical specia-

306

P . A . (nnBvell

lion of sedimentary lipids into free, esterified and bound components has revealed differences in composition and in relative stability to diagenesis, pre-Quaternary sediments also contain free and bound lipids in ahich shorter chain constituents arc more abundant in the bound component, as in Recent sediments. Further studies are needed Io determine the sources a n d o r structures of certain sedimentam constituents and to t}blain additional detail about changes in lipid composition of sedimcntine particulates x~ithin both oxic and anoxic regions of the water colunm. Ackmm'h'd$lement~ I thank the Director of the Frcsh,aalcr Biological Association l\~r pcrmi~,sion t t , ' a n t e thb, review. T h a n k s arc also due 1o Mr T. [. Furnass for dra\\ing lilt Iigurcs and to Miss t. M. E\t]ns for t5 ping the manuscript.

(Received 5 April 1982)

REFERENt

ES

1. ASlt)N, S. R. II1 Chenlieal O{e{mo~lraphv. Vol. 7 {2nd Editionk pp. 361 44{L AGtdemic l'rcss, L o m h m . 197b. 2. BARNI!S, M. A. and BARNtS. W. C. Ill Lakes: (']lemislrv. (;eolool, PIn~i¢~. pp. 127 152. Springer. New York, 1978. 3. BARNES, P. J.. BRASSEtL, S. C., COMtl, P.. EC/LINrON, G.. M c E v m ' , J., MAXWH i. J. R., WARI)ROPLR. A. M. K. and VOLKr~AN. J. K. In Initial Reports qfthe Deep Sea Drillino Project. Vol. XLVIII, pp. 965 976. U.S. Govt. Printing Office, Washington. 1979. 4. BARRI{'K, R. C. and HH}C, ES, J. I. Geoehim. eosmochim. Acta 4fi, 381 392 {19811. 5. BARRWK, R. C., HEDGES, J. I. and PETERSON, M. L. Geochim. cosmoehim. A~ta 44, 1349 1362 (19801. 6. BLUMER, M., ROBERTSON, J. C.. GORDON, J. E. and SASS, J. J. Biochem. 8, 4067 4074 {1969}. 7. BLUMER, M. and THOMAS, D. W. Scieme 147, 1148 1149 (1965). 8. BOEHm, P. D. and QU1NN, J. G. Estuar. Coastal Mar. Sci. 6, 471 494 (1978). 9. BooN, J. J., DE LANGE, F., SCHUYL, P. J. W., DE LEEUW, J. W. and SCHEYCK, P. A. In Advam'e.n iJl Or~tatm Geochemistry 1975, pp. 255 272, E N A D I M S A , Madrid, 1977. 10. BOON. J. J. and I)~ Lllu\\'. J. W. Mar. Chem. 7, 117 132 (1979i. I I. BOON, ,l. J. I)I! LEEr \~,..l.W. and BURLIN{iAMI!, A. L. Geoehim. eomm)cllim. Iota 42, (}31 644 { 197,";}. 12. BOON, J. J., Dl L l l t \ v . J . W . , HOIK.(7,. J. v.d. and VOSJAN, J. H. J. Butt, 129. 1183 II91 11977L 13. BOON, J. J., LIEFKENS, W., RIJPSTRA, W. i. C., BAAS, M. and DE LEEUW, J. W. In Enciromnental Biogeochemistry and Geomicrohioloyy, Vol. 1, pp. 355-372. Ann Arbor Science, Ann Arbor, 1978. 14. BOON J. J., MEER, F. W. v. d., SCHUVL, P. J. W., Dr LEEUW, J. W. and SCHEN(:K, P. A. In Initial Report.s q/

the Deep Sea Drillim! Project Suppl. Vol. XXXVIII-XLI, pp. 627 637, U.S. Govt. Printing Office. Washington, 1978. 15. BOON, J. J. RIJPSTRA. W. 1. (.2, I)t LAXGI, I-'., I}I [,IIIJkV. J. W.. Y()SHIt)KA, M. and Sttl\llZl , x Xillllr( (Lomhm}277, 125 127 119791. 16. BOON, J. J.. RIJPSTRA. W. 1. ('.. Ill L i l t \\. J. W. and BtRl IN{IAMI. A. L. (~eochim. co',tllo(]litH, trill 44. 131 134(19801. 17. BRAI)LI'~. W. tt. Geol. Soe. Am. Bull. 77, 1333 1337 11966L 18. BRASSEI,t, S. C,. ('OMIq, P. A., EGLINrON, G,, ISAA('S{)N. P. J.. M c E v o s . J.. M,\X\v]2I L. J. R.. 1H{}XlSON, 1 D. TIBI{t,TrS, P. J. (2 and Vt)EKMAN, ,1. K. In hlitial Reports O[ the Deep Sea Drillinq Project, Vol. LVI, I,VII, pp. 1367 139(t. U.S. Ciovt. Printing Office, W a s h i n g t o n 1980. 19. BRASSEII, S. ('.. COMI]. P. A.. E{.iI,INION, G.. M c E \ o h , J., MAX\VIII. J. R., Q I l r k l , J. M. [. and Vt)LKMAN,J. K. In hlilial Reporl,s o['the Deep Sea Drillimt Project. Vol. L, pp. 647 664, I !.S. ( i o \ i. Printing Office, Washington, 1980. 20. BRASSEI,L, S. C. and EGI.IN ION. G. ]n Analvti(al ]eehmqm,s i, Enciromnental (llemi~trl. pp, I 22. PcrA~m o n Press, Oxford, 1980. 21. BRASSELt, S. (2 and EGI,INTON, G. Nature (Lomlonl 290, 579 582 l1981L 22. BRASSELL, S. C., EGLINTON, G., MAXWELL, J. R. and PHILP, R. P. In Aquatic polhaatlls. ]ran."ili~rmati~ol aml Biological Effects, pp. 69 86, P e r g a m o n Press, Oxford, 1978. 23. BRASSILL, S. (2. WAl~,l)R()l'l(R. A. M K.. THOMSON. I, I).. MAXVVlI.E.J.R. ;111,,I I-(H INI(}N (i. \'(lll~tt' (London) 290, 693 696119811. 24. BROOKS, P. W., MAX\VII.I., J. R. and PAInN('I, R. L. Geochim. cosmochim, h t a 42, 1175 I ISO I I97SI 25. BROWN. R. A. and SIARNFS, P. K. 3,1ar. Pollut. Bull. 9. 162 165 119781. 26. CAI.VfRl. S. E. In ('henlieal Oceanooraphy, Vol. 6 {2nd Edi/ionk pp. IS7 280. Academic F'rcss. I~ondola, 1976. 27. CARI)OSO, J. N., EGLINF{)N, O. and HI)LLOWAY, P. ,]. [11 Adl'ances in Or~lani~ (;t,oc]lelHialrl. 197.:,. [;]Z 273- 287, E N A D I M S A . Madrid 1977. 28. CARI)(}SO, J. N., WAITS, C. D., MAXWtCLI. J. R., GOOI)FELI.{)W, R., e(il INll}N, G. Lllld G{)I t'BI{ , S. ('II{uH. Geol. 23,273 291 {1978}. 29. COOPER, B. S. and MURCHISON, D. G. In Organic Geochemistry, pp. 699 726. Longman. L o n d o n , 1969. 30. COR~ET, B., ALBRECHT, P, and OURISSON, G. J. Am. chem. Soc. 102, 1171 1173 (19801. 31. CRANWEtA,, P. A. Chem. Geol. 20, 205 221 (19771. 32. CRANWI!LI.. P. A. In Interactions between Sediments and Freshwater 1976. pp. 133 14{t. ,lunk and Pudoc. The Hague, 1977.

Lipids of aquatic sediments and sedimenting particulates

307

33. CRANWELL,P. A. Geochim cosmochim. Acta 42, 1523-1532 (1978). 34. CRANWELL,P. A. Chem. Geol. 30, 15 26 (1980). 35. CRANWELL,P. A. Geochim. cosmochim. Acta 45, 547-552 (1981). 36. CRANWELL,P. A. Org. Geochem. 3, 79-89 (1981). 37. CRANWEEE,P. A. In Advances in Oroanic Geochemistry 1981, in press. 38. CRANWELL,P. A. In Studies in Palaeolimnology and Palaeoecoloyy, University of Leicester Press, in press. 39. 40. 41. 42.

CRANWELL,P. A. and VOLKMAN,J. K. Chem. Geol. 32, 29 43 (1981). DASTILLUNG,M. Ph.D. Thesis, Strasbourg University, 1976. DASTILLUNG,M. and ALBRECHT, P. Nature (London) 269, 678-9 (1977). DEGENS, E. T. and MOPPER, K. In Chemical Oceanography Vol. 6 (2nd Edition), pp. 59-113, Academic Press, London, 1976. 43. DIDYK, B. M., SIMONEIT,B. R. T., BRASSELL,S. C. and EGLINTON,G. Nature (London) 272, 216 222 (1978). 44. EDMUNOS,K. L. H., BRASSELL,S. C. and EGLINTON, G. In Advances in Organic Geochemistry 1979, pp. 427-434, Pergamon Press, Oxford, 1980. 45. EGLINTON, G., HAJIBRAHIM,S. K., MAXWELL,J. R. QUIRKE, J. M. E., SHAW, G. J., VOLKMAN, J. K. and WARDROPER, A. M. K. Phil. Trans. R. Soc., Ser. A 293, 69 91 (1979). 46. ERWIN, J. A. In Lipids and Biomembranes of Eukaryotic Microorqanisms, pp. 42 143, Academic Press, New York, 1973. 47. FARRINGTON, J. W., FREW, N. M., GS('HWEND, P. M. and TRIPP, B. W. Estuar. Coastal Mar. Sci. 5, 793-808 (1977). 48. FARRINGTON,J. W., HENRICHS, S. M. and ANDERSON,R. Geochim. cosmochim. Acta 41,289 296 (1977). 49. F/JRSTER, H. J., BIEMANN,K., HAIGH, W. G., TATTRIE, N. H. and COLVIN, J. R. Biochem. J. 135, 133-143 (1973). 50. FRE¥, D. G. Mitt. int. Verein. theor, anqew. Limnol. 20, 95-123 (1974). 51. GAGOSIAN,R. B. and FARRINGTON, J. W. Geochim. cosmochim. Aeta 42, 1091 1101 (1978). 52. GAGDSIAN,R. B. and SMITH, S. O. Nature (London) 277, 287 289 (1979). 53. GASKELL,S. J. and EGUNTON, G. Nature (London) 254, 209 211 (1975). 54. GEARING,P., GEARING,J. N., LYTLE,T. F. and LYTLE,J. S. Geochim. cosmochim. Acta 40, 1005 1017 (1976). 55. GIGER, W. and SCHAFFNER,C. In Adt,ances in Or,qanic Geochenlistry 1975, pp. 375-390, ENADIMSA, Madrid, 1977. 56. GIGER, W., SCHAFFNER,C., and WAKEHAM,S. G. Geoehim. cosmochim. Acta 44, 119-129 (1980). 57. GILLAN, F. T., JOHNS, R. B., VERHEVEN,T. V., VOLKMAN,J. K. and BAVOR,H. J. Appl. Ent'iron. Mierobiol. 41,849-856 (1981). 58. GOODWIN, T. W. In Lipids and Biomemhranes of Eukaryotic Microorqanisms, pp. 1-40, Academic Press, New York, 1973. 59. GRIFFITHS, M. Limnol. Oceanoyr. 23, 777 784 (1978). 60. GUNSTONE, F. D. An Introduction to the Chemistry and Biochemistry of Fatty Acids and their Glycerides, Chapman and Hall, 1967. 61. HASSETT,J. P. and LEE, G. F. Water Res. I1,983-989 (1977). 62. HUANG, W.-Y. and MEINSCHEIN,W. G. Geochim. cosmochim. Acta 42, 1391-1396 (1978). 63. HUANG, W.-Y. and MEINSCHEIN,W. G. Geochim. cosmochim. Acta 43, 739-745 (1979). 64. ISHIWATARI,R., OGURA, K. and HORIE, S. Chem. Geol. 29, 261-280 (1980). 65. ISHIWATARI,R., TAKAMATSU,N. and ISHmASHI,T. Jap. J. Limnol. 38, 94-99 (1977). 66. JAVOR,B., BRASSELL,S. C. and EGUNTON, G. Oceanologica Acta, 2, 19-22 (1979). 67. JOHNS, R. B., GILLAN, F. T. and VOLKMAN,J. K. Geochim. cosmochim. Aeta 44, 183 188 (1980). 68. JOHNS, R. B. and ONDER, O. M. Geochim. cosmochim. Acta 39, 129-136 (1975). 69. JOHNS, R. l., VOEKMAN,J. K. and GILLAN, F. Z. APEA Journal 18, 157 160 (1978). 70. KAWAMURA,K., [SHIWATAR1,R. and YAMAZAKI,M. Chem. Geol. 28, 31-39 (1980). 71. KENNICUTT, M. C. and JEFFREY, L. M. Mar. Chem. I0, 389-407 (1981). 72. KHAN, S. U. and SCHNITZER, M. GeochinL cosmochinL Acta 36, 745 754 (1972). 73. KOLATTUKUDY,P. E. (Ed.) Chemistry and Biochemistry of Natural Waxes, Elsevier, Amsterdam, 1976. 74. LAELAMME,R. E. and HITES, R. A. Geochim. cosmochim. Aeta 43, 1687-1691 (1979). 75. LEE, C., FARRINGTON, J. W. and GAGOSIAN, R. B. Geochim. cosmochim. Acta 43, 35-46 (1979). 76. LEE, C., GAGOSIAN, R. B. and FARRINGTON,J. W. Geochim. cosmochim. Acta 41,985 992 (1977). 77. LEE, C., GAGOSIAN, R. B. and FARRINGTON,J. W. Orq. Geochem. 2, 103 ll3 (1980). 78. DE LEEUW, J. W. MEER, F. W. v. d., RIJPSTRA, W. I. C. and SCHENCK, P. A. In Advances in Or.qanic Geochemistry 1979, pp. 211 217, Pergamon Press, Oxford, 1980. 79. DE LEEUW,J. W., RIJPSTRA,W. I. C., BOON,J. J., DE LANGE, F. and SCHENCK,P. m. In Interactions between Sediments and Freshwater 1976, pp. 141 147. Junk and Pudoc, The Hague, 1977. 80. DE LEEUW, J. W., RIJPSTRA, W. I. C. and SCHENCK, P. A. Geochim. cosmochim. Acta 45, 2281-2285 (1981). 81. LIVINGSTONE,D. Ph.D. Thesis, Leicester University, 1979. 82. LIVINGSTONE,D. and CAMBRAY,R. S. Nature (London) 276, 259-261 (1978). 83. MATSUDA,H. Geochim. cosmochim. Acta 42, 1027-1034 (1978). 84. MATSUDA,H. and KOYAMA,T. Geochim. cosmochim. Acta 41,341-345 (1977). 85. MATSUDA,H. and KOYAMA,T. Geochim. cosmochim. Acta 41,777-783 (1977). 86. MAXWELL,J. R., MACKENZIE,A. S. and VOLKMAN,J. K. Nature (London) 286, 694-697 (1980). 87. MEYERS,P. A., BOURBONNIERE,R. A. and TAKEUCHI,N. Geochim. cosmochim. Acta 44, 1215-1221 (1980). 88. MEYERS,P. A., EDWARDS, S. J. and EADIE, B. J. Gt. Lakes Res. 6, 331-337 (1980). 89. MEYERS,P. A., LEENHEER,M. J., ERSTFELD, K. M. and BOURBONNIERE,R. A. Nature (London) 287, 534-536 (1980). 90. MEYERS,P. A., MARING, M. B. and BOURBONNIERE, R. A. In Advances in Oryanic Geochemistry 1979, pp. 365-374, Pergamon Press, Oxford, 1980. 91. MEVERS,P. A. and TAKEUCHI, N. Or(4. Geochem. I, 127 138 (1979).

~,()8

P.A. ( ' r a m \ e l l

92. NH:v, J. M. Pol~cyclic 4romati~ llvdrocarhons m the 4quatic t'aciromnent, Applied Science, lxmdon, 19>). 93. NISHIIMt'RA, M. (;coc/Iim. ~o.~moc]lilH. d~la 41, 1817 1823 (19771. 94. NISHIMt RA, M. Nature (l,omlcm) 270, 711 712 11977). 95. NISlIIMUR,\, M. Geochim. cosmochim, t ~ l a 42, 349 357 119781. 96. NISHIMURA, M. and Ko'~ AMA, T. Geochim. to.~moc/lim. I('hl 41, 379 385 (19771 97. Ot RISSON. O.. AI.BRI(III, P, and R{)ItMIR. M. PItrc Ippl. ('hem. 51,709 729 (19791. 98. PNrrlRSON, G. W. Lipids 6, 120 127(1971). 99. PIRR'~. (_]. J.. VIIIKM\N, ,[. K.. ,J()IlNS. R. B. and BAXl)R, tt. ,I. (;eochim. cownocJlinl. I~ta 43, 17t5 1725 11979). 100. PHILP, R. P. In Biogteochemistrv olAncieat and Modern Enrir,nments, pp. 173 185. Australian Academy ol Science, Canberra, 1980. 101. PHIt, P, R. P.. BROWN, S.. ('AI,VIN, M., BRASSEIA,, S. and EGI,INTON, O. In Enriromnental Biooeochemistry and Geomicrohiolo,qy, Vol. I, pp. 255 270, Ann Arbor Science, Ann Arbor. 1978. 102. PRAHL, F. G., BICNNIiTT, J. T. and CARPINTER. R. Geochim. cosmochim. Acta 44, 1967 1976 11980f 103. QtUUK, M. M, Ph.D. Thesis. Bristol University, 1978. 104. QUIRK, M. M.. PAIIIN(I. R. k., MAXWEll.. J. R. and W i n : A t i l t , R. 1:. In 4nalvtical Te;lmiqucs in Em'iromnental ('hemislrv. pp. 23 31, Pergamon Press, Oxford. It)SO 105. Rill), W. E Geochim. co~nlochim, h t a 41, 1231 1245 (19771. 106. Rrt{Pl;rA, D. ,I. and (bx<;~)sl,xN, R. B. Nature (l, omhml 295, 51 54 11982). 107. R~','NOlDS,('. S. Br. ph~¢)t, d. 8, 153 16211973L 108, ROtIMIR, M., DASlII I t'N(i, M. and ()t~mss(~N G. Naturwi,,wnschalh'n 67, 456 458 (1980). 109. SAR(;ENr. J. R.,GAI'rEN, R. R. and MclNroSH, R. Mar. Chem. 5, 573 584 (19771. 10. SHIC/ARAKI, Y. and ISmWArARI, R. Jap. Y. Limnol. 42, 72 81 11981). 11. SIMONlilI, B. R. W. (;eo~him. cosmochinl. ,lcta 41, 463 476 (1977). 12. SIMONIII, B. R. T. In ('heroical Oceallc,:lral~hl. Vo[. 7 (2nd EditionL pp. 233 :;11, Academic Press, l.ondon, 1978. 13. SIbI()Nlll. B. t . T., iIAI.PI{RN. H. 1. and DII)'~ K, B. M. In Bioocochenlistry o/ tncicnt aad Alo&'ra Enrironments, pp. 201 209, Australian Academ 3 of Science, Canberra, 1980. 14. SI",'CKI:Rlil 115, ('.. GRI Ini:r, A. ('H., AI r~rl~ t11, P. and Ot rlsso-;, G..I. ('hem. Re~. (M) 374~, 3777 {1977L 15. SI'5('KIRtl I1. ('., GP, IINt R. A. ('ti., AIAW,I( H1, P. :.lnd OtrlsS()N, (]. J. ('/l('m. I{~'x. (M) 3N01 3828 {1977i. 16. SIRANSKS, g.. STRIClBI., M. and Kt mIKa. V. ('olh'~t. ('=ech, Chem. (','mmnm. 35. 882 8'-)1 (1970L 17. TaN. Y. g. and t h l l . M. (;eochinl. cosnlo~him. .,Iota 45, 2267 2279(1981), 18. TAYIX)R, J., WARI)ROP|R. A. M. K. and MAXWELl, J. R. "li'trahedron Left. 21, 655 656 1198(11. 19. THOMI'SON, R. H., PArTI!RSON, G., TIIOMPSON, M. J. and SIOVt~R, H. T. Lipids 16, 694 699 (19gl I. 12(I. TltOMI,Sl)N. S. and E~,,I Ix t~x, G. (;t,ochim. ~osnloc'Jliln. Acta 42, 199 207 (19781 121. TttOMI'SON, S, and E(,I INION. G. Estuar. (oastal Ahtr. Sci. 8, 75 86 (19791. 122. TIIIBI rTs, P. J. ('., iVl,xx\kllI. ,1, R. and (}ill l'lll('. ~. 111 Em'ir~mmvntaI Bi¢*gleochvnli:,lrl aml Gc~mticrot~iolofty, Vol. I. pp, 271 284. Ann Arbor Scicncc. Ann Arbor, 1978. 123. TI'I.I.OCH, A. P. In Chemistry and Biochemistry of Natural 14')txes, pp. 235 287, Elsexier. Amsterdam, 1976. 124. URI~A('tl, G. and S1m~K, W..I. 4or. Food Chem. 23. 20 24 11975). 125. '~A~ VI td-.r. E. S. and Q~ lxy. J. G. Geochim. cosmochim. A~ta 43, 289 303 11979), 126. VOLKMAN, J. K.. EGLINrON. G.. CORNfiR, E. D. S. and FO,RSlaER{;, T. E. V. Phvtochemistrv 19, 2619 2622

(1980). 127. VOLKM.,XN, J. K., ['(il IN Ill\, (J.. (_'ORNI R. [{. 11. S. and SaR(n x~, J. R. In Adcamc~ in Or~lani~ Ge,tlu'mi~tr~ 1979. pp. 219 227. Pergamon Press. Oxli~rd, 1980. 128. V()I K,',I,\N, ,1. K.. ]*ARRIN(iH)N..1. W., (}.'~(;()SlAN, R. B alld WAKIIIAM. S, ( i -h/tamc; in (h3fa~li¢ (;c,,chemi~lrl' 1981. in press 129. VOL:-,M.,\N, J. K., (Jill ,\"-:. |:. T.. ,IoltNS. R. B. and t:xn IXlO'-,, (5. (;cochinl. co,~mo~llim, t t ' / a 48, ISI7 182S 119811. 130. VOIKMAX, J. K. and JoHNs, R. B. 3,'aturc (Loadonl 267, 693 694 (19771. 131. Vol KMAN, J. K., ,]OIINS. R. a., GILl AN, F. T., Pt{RR',, G. J. and BA','~)R, H. J. (ivochinl. cosmo~him, h t a 44. 1133 I143 119801. 132. WAKIttAM. S. G, and I",\ItI~,IN~iI(~N,.I.W. In ('ontaminalll5 amJ Sediments. Vol. I pp. 3 32. Ann Arbor Science, Ann Arbor, 198(I. 133. WAKEHAM, S. G., FARRINt;TON, J. W,, GAGOSIAN, R. B., LEE. ('., DE BAAR, H., N~GRH.Lk (i. E.. TRIPP. B. W., SMITH, S. O. and FREW, N. M. Nature (London) 286, 798 800 (19801. 134. WAKIItAM. S. G., S(HAII.NIR. ('. and GR;I R. W. Geochim. co,~lnochim..*l~ta 44, 415 429 119811L 135, WAKIIIAM. S. O., S(HAFFNIR. ('., (}IGI{R, W.. BOON, .1. J. and DI [,tl!I w, J. W. (,eochim. ~,,~mochim. t(la 43, 1141 1144(19791. 136. WANNIGAMA, g . P.. V()l KMAN, ,1. K., (}Ill AN, ]:. T., NI('H()I S. P, I). and JoHNs, R. B. t'h~tochen~istrt 2(L 659 666 (19811. 137. WAI'H:S, D. W.. HAt (i. P. and Wlcl:lli. D. H. Geochim. cosmochim. Acta 38, 381 387 (1974), 138. WARDROPt!R, A. M. K., MAXWlCLI_ ,I. R. and MORRIS, R. J. Steroids 32, 203 22I (19781. 139. WAllS, ('. D. and MAX\\I{IL, J. R. Geochim cosmochim, d o r a 4 1 , 4 9 3 497 (19771. 140. WATTS, C. D., MAXWeLl, J. R. and KJOSt{N, H. In Advances in Organic Geochemistry 1975, pp. 391 413, E N A D I M S A , Madrid, 1977. 141. YoN. D. A., MAXWI!LI,J. R. and R'CBACK, G. Tetrahedron Lett. 23,2143 2140 (19821. 142. ZCkLI(;. H. Limnol. Oceam~ltr. 26, 970 976 (19811,