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Provenance, concentrations and nature of sedimentary organic nitrogen in the gulf of Maine
Marine Chemistry, 25 (1988) 291-304 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
291
Provenance, Concentrations and Nature of Sedimentary Organic Nitrogen in the Gulf of Maine
LAWRENCE M. MAYER
Ira C. Darling Center, University of Maine, Walpole, ME 04573 (U.S.A.) STEPHEN A. MACKO
Departments of Earth Sciences and Chemistry, Memorial University, St. Johns, Newfoundland, A1B 3X5 (Canada) LEON CAMMEN
Bigelow Laboratory/or Ocean Sciences, West Boothbay Harbor, ME 04575 (U.S.A.) {Received February 29, 1988; revision accepted June 13, 1988)
ABSTRACT Mayer, L.M., Macko, S.A. and Cammen, L., 1988. Provenance, concentrations and nature of sedimentary organic nitrogen in the Gulf of Maine. Mar. Chem., 25: 291-304. Factors controlling the provenance, concentrations, and nature of sedimentary organic matter (SOM), particularly the nitrogenous fraction, were examined for sites throughout the Gulf of Maine and two of its estuaries. Stable nitrogen isotope data corroborate previously reported Br: C ratios in indicating that macroalgae are important contributors to organic nitrogen pools in estuarine sediments. Significant contributions of terrigenous organic carbon in both the estuaries and the deep basins of the open Gulf are not accompanied by significant contributions of terrigenous organic nitrogen. Variations in concentrations of organic carbon, nitrogen, chlorophyll, and enzymatically hydrolyzable protein throughout the Gulf and its estuaries can be explained largely by variations in the delivery rate of organic matter to the benthos and the specific surface area of minerals in the sediments. Chlorophyll and protein concentrations represent relatively fresh organic matter and exhibit greater sensitivity to organic delivery variations than do total organic carbon or nitrogen. A strong, linear relationship between organic carbon and surface area is consistent with monolayer adsorption of SOM on mineral surfaces, which appears to inhibit degradation of the SOM. Amino acid compositions are remarkably constant throughout the Gulf, with large differences seen only with elevated tyrosine in estuaries and elevated basic amino acids and methionine in the open Gulf. Leucine and glutamic acid correlate with chlorophyll concentrations in open Gulf sites. Enzymatically hydrolyzable protein comprises small to major fractions of total hydrolyzable amino acids. Amino acid-nitrogen : total nitrogen correlates inversely with total nitrogen.
0304-4203/88/$03.50
© 1988 Elsevier Science Publishers B.V.
292 INTRODUCTION Estuarine and continental shelf sediments act as major sinks of sedimentary organic matter (SOM) in the global carbon cycle (Berner, 1982 ). This importance stems from their relatively shallow depths, high primary productivity, and high sedimentation rates. Notwithstanding this importance, few comprehensive studies of basin-wide distributions of concentrations, provenance, and quality of SOM in shelf areas have been reported. This paper provides such a study for the Gulf of Maine, including two of its associated estuaries. Provenance studies in coastal areas have concentrated on systems receiving primarily phytoplankton, seagrass, and terrigenous inputs. High-latitude coastal regions, however, may receive significant inputs from macroalgae (Mann, 1982 ). Macroalgal organic matter has been shown to provide a signiiicant trophic resource in sediments (reviewed in Reichardt, 1987), but its significance in contributing to bulk SOM has not been assessed. The Gulf o1: Maine provides a region in which to examine the potential importance of such inputs. The concentration of SOM is dependent on a number of factors related to rates of organic matter delivery to sediments and organic matter survival once deposited. In this study we focus on the roles of organic delivery rates and grain size variations. This paper provides special focus on the nitrogenous components of SOM. This fraction plays a critical role in the trophodynamics of sediment ecosystems (Tenore, 1983), as well as forming a significant fraction of SOM. We have concentrated on the proteinaceous materials in SOM, measured both as total acid-hydrolyzable amino acids and as enzymatically hydrolyzable proteins. Amino acid spectra have been used in a variety of studies to examine the provenance and transformations of organic nitrogen in sediments (Degens and Mopper, 1976). METHODS AND MATERIALS Areas sampled (Fig. 1 ) included the open Gulf of Maine and two of its estuaries - the Sheepscot and Damariscotta. Most of the open Gulf of Maine samples were obtained on cruises in the summers of 1979, 1980 (for isotope measurements ) and 1982 (for other chemical analyses ); other areas were sampled at times between 1978 a n d 1987. A variety of sampling devices was employed, including Shipek grabs, box corers, and gravity corers, and push-core sampling in intertidal areas. Samples were immediately frozen and thawed only for analysis. Only the top 1-2 cm was sampled for this study. Samples of the macroalgae Fucus vesiculosis and Ascophyllum nodosum were collected by hand from the rocky intertidal zone in the Damariscotta estuary, freeze-dried, ground in a Wiley mill, and frozen.
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Fig. 1. Map of the Gulf of Maine showing locations of sampling stations. Subsets of this sampling array were used for various analyses reported here. Open circles in the open Gulf refer to samples in Fig. 3. Small and large rectangles show location and enlargement of Sheepscot/Damariscotta estuaries. Total carbon and nitrogen analysis was performed after vapor phase acidification of samples to remove carbonate minerals. Analysis was carried out on either a Hewlett-Packard 185B or a Carlo Erba 1106 Elemental Analyzer. Precision on these analyses is typically better than 3% (1 s.d.). Bromine analysis was carried out by X-ray fluorescence as reported in Mayer et al. (1981). Amino acid analyses were performed by standard 6 N HC1 hydrolysis at 100 ° C under N2 for 24 h, followed by pH adjustment to ~ 3, and isocratic separation into individual amino acids using cation exchange HPLC with post-column derivatization with ortho-phthalaldehyde (OPA) and fluorescence detection (St. John Associates, Adelphi, MD). Precision is better than 10% (1 s.d. ). Protein analyses were by the modified Coomassie Blue method of Mayer et al. ( 1986 ),
294 and represent larger polypeptides amenable to protease hydrolysis. Phytopigment measurements were carried out fluorometrically after acetone extraction of the sediment and hexane separation of chlorophyll (modified from Whitney and Darley, 1979). Stable carbon and nitrogen isotopes ratios were determined on cryogenically purified gases following a 900 ° C combustion conducted under vacuum in quartz tubing for 1 h. Analyses of the gases (CO2 or N2) were conducted on either a Nuclide 6-60 RMS or a VG Micromass 602E and are reported in standard delta notation relative to PDB for gI3C and atmospheric nitrogen for g*~N. Typical precision on these analyses is ~ 0.1%o (1 s.d. ). Sediment specific surface areas (SFA) were measured by nitrogen adsorption, using a one-point B E T method on a Quantachrome Monosorb. Samples were pretreated with boiling hydrogen peroxide and sodium pyrophosphate to remove most of the organic matter; the measured surface area thus represents primarily the mineral surface area. Outgassing at a temperature of 350 ° C for 15-20 rain was found to be necessary to completely remove adsorbed water and achieve accurate readings. The nitrogen adsorption method yields different surface areas, particularly for coarser-grained sediments, than the cetyl pyridinium bromide (CPB) method reported in our earlier papers (Mayer et al., 1981; 1985). The relationship between the two measurements, from an intercalibration of 37 samples, is given by the equation (units of m 2 g- ~) SFAnitrogen-- 1.13 (SFAcpB) - 8 . 1
r2--0.91.
RESULTS AND DISCUSSION Sources of organic matter
Mayer et al. (1981) presented evidence, using a combination of g1~C and Br: C ratios, that the Sheepscot and Damariscotta estuaries receive both marine and terrigenous organic inputs. They also suggested that relatively high Br: C ratios indicated significant macroalgal inputs to the SOM pool, because macroalgae typically found in these estuaries show enriched Br concentrations relative to phytoplankton. The g*SN ratios on the same estuarine samples as those in Mayer et al. (1981) substantiate this suggestion (Fig. 2). A plot of gleN and Br: C values for samples along the Damariscotta estuary (Fig. 2b) shows parallel variation between these two parameters; the correlation between the two variables has r2= 0.79. The gISN ratios show positive deviations from the normal values of about 6-7%0, which are indicative ofplanktonicalty derived organic matter (Fig. 3), at the same sites where Br:C ratios show elevated values from the normal planktonic values of 6-8 mg Br g- 1 C (Mayer et al., 1981 ). These anomalously high g*SN values are indicative of the dominant macroalgae in this estuary ~ Fucus vesiculosis and AscophyUum nodosum which gave values of 8.1 and 7.9%0, respectively. The ~3C values of both these Damariscotta sediment samples and the macroalgae are similar to those of planktonic carbon. Together, the Br: C and nitrogen isotope data indicate
295
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Fig. 2. Longitudinal transects going upstream from the estuary mouth, of (a,b) 515N ( solid circles ) and Br: C (open squares); and (c,d) 513C (solid circles) in sediments of the Sheepscot and Damariscotta estuaries.
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296 that macroalgae may be locally dominant contributors to the organic nitrogen pool, and perhaps the organic carbon pool as well, within this estuary. The plots of ~13C and $1~N values in the Sheepscot estuary (Fig. 2a,c) are discordant with one another, in the sense that the ~ 13C ratios show a transition from an essentially pure, terrigenous organic source at the head of the estuary to a mixture of about 2/3 terrigenous and 1/3 marine algal source at its mouth, while the ~15N ratios change from primarily terrigenous values at the head to primarily marine values at the mouth. This discordance is due to the mixing of a high C: N terrigenous endmember with a relatively low C : N contribution from the marine endmember - - presumably some mixture of planktonic and macroalgal organic matter. Samples from the open Gulf of Maine show primarily a planktonic origin in both their ~I~N and ~13C values, consistent with the overwhelming dominance of planktonic production relative to macroalgal or terrigenous input. In this fashion the Gulf of Maine is typical of most shelf ecosystems. However, a plot of the $13C values vs. water depth of the sample (Fig. 3a) shows a highly significant trend (r 2= 0.44, p > 0.99 ) of increasingly terrigenous character of the SOM with increasing depth. The simplest explanation for this trend is that the basins, particularly Wilkinson Basin in the western Gulf, serve as partially effective traps for terrigenous material escaping the estuaries. This trapping role for the basins has been hypothesized for trace metals escaping the estuaries of the Gulf of Maine (Lyons and Gaudette, 1979). This trap is also analogous to the occurrence of relatively terrigenous-rich organic matter in the silty mid-shelf sediment found on the otherwise sandy Washington continental shelf (Hedges and Mann, 1979; Prahl and Carpenter, 1984 ). A similar plot of $~5N values with depth (Fig. 3b) does not show a similar trend toward isotopically lighter values associated with terrigenous nitrogen, but rather they become isotopically heavier with depth. This trend may indicate input of macroalgal detritus to the deeper parts of the Gulf, consistent with frequent observations of large rafts of floating macroalgal debris in the open Gulf. The lack of terrigenous influence on ~15N values is also consistent with the reduced isotopic visibility of terrigenous nitrogen in SOM at the mouth of the Sheepscot estuary. An important conclusion to be drawn from these inconsistencies between carbon and nitrogen isotopic compositions in both the estuarine and deeper parts of the Gulf is that discussion of the provenance of organic matter is an over-generalized approach. It is quite possible for the organic carbon and the organic nitrogen in any one sample to have different origins. Concentrations A variety of factors have been shown to influence the concentrations of organic matter in sediments. These factors include grain size, rate of organic
297 delivery to the sediments, sedimentation rate, and perhaps the redox state of the overlying water column (Trask, 1939; Miiller and Suess, 1979; Premuzic et al., 1982). The influence of two of these factors - - grain size and the rate of delivery of organic matter - - can be tested with the data from this study. Grain size control can be assessed by the relationship between organic matter concentration and the measured specific surface area. The rate of organic matter delivery to, the benthos has been shown to be related to two variables - - positively to primary production and inversely to the depth of the overlying water column (Hargrave, 1973; Suess, 1980). Primary productivity probably decreases with distance from shore - - and hence increasing depth - - in the Gulf of Maine; evidence for this trend is the decreasing level of phytoplankton biomass off.. shore determined from direct measurements (O'Reilly and Busch, 1984) and satellite photos of this region (Yentsch et al., 1986). Hence greater depths of the water column represent areas of both decreased primary production and decreased efficiency of delivery of this production to the benthos; in the discussion that follows depth can be used as a single parameter which is inversely related to organic delivery to the sediments. The redox state of the water column is not an important variable in the Gulf of Maine, where the water column is well-oxygenated. The influence of sedimentation rates on organic matter accumulation cannot be addressed in this study as very few data are available for the Gulf. The variations throughout the Gulf may not be important, however, because the influence of sedimentation rate in the equation relating organic matter accumulation, productivity, and sedimentation rate (Miiller and Suess, 1979) shows a reduced influence of this latter parameter relative to productivity. The concentrations of total carbon, total nitrogen, chlorophyll and proteinnitrogen all exhibit a decrease with depth in the Gulf of Maine (Fig. 4). Grain size, expressed as sediment specific surface area, is also an important correlate for total carbon and nitrogen, though not for protein or chlorophyll (Fig. 5). Multiple linear regression analyses of these data indicate that 60, 74, 41 and 49% of the carbon, nitrogen, chlorophyll, and protein-nitrogen total variances can be explained by the combination of depth and grain size. The influence of depth on protein and chlorophyll concentrations is much stronger than on total carbon or nitrogen concentrations. These two types of measurements are indicative of the labile fraction of sedimentary organic matter most likely to exhibit a response to the influence of the rain rate of freshly produced organic matter. This depth control on the amount of labile organic matter is reflected in decreasing bacterial and macrofaunal populations with depth (Mayer et al., 1986; Watling and Cammen, unpublished data). Total carbon and nitrogen concentrations show an abrupt decrease for samples collected deeper than 70 m (Fig. 4a,b). O'Reilly and Busch (1984) found phytoplankton biomass to decrease markedly at sites seaward of this depth.
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For these deeper sediment samples, grain size alone accounts for essentially all of the explained variation in total carbon and nitrogen, with no depth influence evident. This fact can be seen in Fig. 5a,b, which separates data from samples taken above and below 70 m. For the samples from sites deeper than 70 m, the regression of carbon and nitrogen on surface area haveslopes of 0.51 mg-OC g - i sediment and 0.07 mgN g - 1 sediment. These slopes are consistent with a roughly monolayer coverage of organic matter on mineral grains (Weiler and Mills, 1965; Tanoue and Handa, 1979; Mayer et al, 1985). These data fit tightly to the regression line, and attempts to relate the residuals from the regression line to water depth were unsuccessful. This tight fit to the grain size regression suggests that the concentrations are n o t a s responsive to organic delivery variations as protein and chlorophyll levels.The re~uced sensitivityto organic input variations implies that carbon and nitrogen concentrations are 'buffered' by some grainsize-related factor. The S O M in these offshore stations is dominated by refractory material, as indicated by very slowly decreasing concentrations downcore (Mayer, unpublished data). This buffering at approximately a monolayer coverage of grain surfaces supports the suggestion of Suess and Mfiller (1980) that adsorbed organic matter is difficultto metabolize.
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Fig. 5. Organic carbon (a), total nitrogen (b), protein-nitrogen (c, protein×0.167), and chlorophyll (d), vs. sediment specific surface area for all samples in Gulf of Maine and estuaries. Data for organic carbon and nitrogen are separated into those samples from sites < 70 m (open squares ) and > 70 m (closed diamonds ) for purposes of illustration. The multiple linear regression cited in text pools both depth intervals.
Amino acids and proteins Amino acids occur in sediments in a variety of forms, ranging from minor contributions by free monomers to a dominance of polymeric forms such as fresh proteins and humified peptide material. This compound class represents the largest pool of nitrogenous material identified to date, although sedimentary amino acids often do not comprise the major fraction of sedimentary organic nitrogen. Strong acid hydrolysis, as used in this study, should liberate most if not all bound amino acids. Our protein technique, however, should measure only those larger polypeptides amenable to enzymatic hydrolysis; this measure should therefore represent a relatively labile component of the total amino acids. Total hydrolyzable amino acids contributed from 12 to 81% of the total nitrogen in these samples. These contributions may be higher by a factor of 10-20% if as much as all of the aspartic and glutamic acids were present as
300
asparagine and glutamine. These two latter amino acids lose amide nitrogen on acid hydrolysis and are analyzed as aspartic or glutamic acids. A significant fraction of asparagine and glutamine in soils has been found (Sowden, 1970). There was no strong surface area or depth control found on the amino acidnitrogen:total-nitrogen ratio. Instead, a significant inverse correlation was found with the total nitrogen concentration (Fig. 6). This decreasing fraction of nitrogen in identifiable amino acids with increasing total nitrogen may reflect either a real shift toward another form of nitrogen or an increasing humification of amino acids (with perhaps lower availability to acid hydrolysis) in samples with higher total nitrogen. This finding is consistent with that of Bordovskiy (1965), who noted an increasing humification of carbon and a lower acid hydrolyzability of the organic carbon with increasing carbon content in samples from the Bering Sea. The protein nitrogen constitutes a small fraction of the total nitrogen in these surficial sediments, ranging from 3 to 14%. This ratio shows a strong depth dependence (Fig. 7), indicating that the nutritional quality of organic matter decreases strongly with depth. Protein nitrogen forms a larger fraction 1.0-
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of the amino acid nitrogen, ranging from 10 to 24% at all but one site. An intertidal sediment, with high organic loading, had a ratio of 133%, i.e., there was apparently more protein than acid-hydrolyzable amino acids. The 33% discrepancy between the two measurements is probably due to a combination of factors such as incomplete estimation of amino acid nitrogen due to decomposition of some amino acids during acid hydrolysis and ignoring nitrogen contributions from asparagine and glutamine. It is also possible that we overestimate protein nitrogen through use of an inappropriate standard (see Mayer et al., 1986). The amino acid spectra of 30 samples from throughout the open Gulf and its estuaries showed a remarkable consistency (Fig. 8). The coefficient of variations (as per cent of means) of all of the major amino acids - those constituting > 5% of total residues - were < 11%, which is roughly the analytical variability. The overall spectra are similar to those found in a number of studies from North Atlantic sites (e.g., Degens and Mopper, 1976; Rosenfeld, 1979; Sargent et al., 1983; Henrichs and Farrington, 1987). There were, however, some significant trends among the estuarine and open Gulf sites. Basic amino acids were enriched in deeper Gulf of Maine sites relative to the estuaries, while the aromatic amino acids showed the reverse trend (Fig. 9). Histidine followed the basics trend, but is not included in this plot because other amino-containing material, such as amino sugars, co-elute with the histidine peak in our isocratic separation. Tyrosine dominated the aromatic trend, with concentrations averaging 3.8% of total residues in the estuaries and 0.61% in the open Gulf. This difference was also reflected in a decreased concentration of tyrosine in samples from the mouths of the estuaries relative to upstream sites. As this decrease occurred in both estuaries, it reflects some aspect of the estuarine environment, rather than an influence by 3O IJJ
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Fig. 9. Basic amino acids (lysineplus arginine) vs. aromatic amino acids (tyrosine plus phenylalanine) for shallow ( < 70 m) and deep ( > 70 m) sites. terrigenous organic matter. There was also a higher proportion of methionine in the open Gulf relative to the estuarine samples. Among samples from the open Gulf, there were positive correlations between the chlorophyll concentrations and the fractions of leucine and glutamic acid. These correlations reflect the fact that these two amino acids are commonly enriched in plankton relative to sedimentary organic matter (Henrichs and Farrington, 1987). CONCLUSIONS Organic nitrogen derives from a mixture of terrigenous, macroalgal and planktonic sources. Macroalgal nitrogen is an important constituent of the nitrogen pool in estuaries and may comprise a small but detectable fraction of nitrogen in the deeper basins. Macroalgal transport into the deeper basins ol" the Gulf is consistent with the trapping of terrigenous macrophytic carbon in these sites. In both estuarine sites and deep basins there are apparently differing origins for the carbon and nitrogen components of the organic matter. Organic matter concentrations throughout the Gulf can be explained largely by variations in organic delivery rates, represented by water column depth, and grain size. The grain size dependence is consistent with a monolayer adsorption of organic matter which appears to inhibit the organic loss rate. Measures of total organic matter show greater control by grain size while measures of the labile component of organic matter, e.g., enzymatically hydrolyzable protein, are more dependent on the organic delivery rate. Acid-hydrolyzable amino acids and enzymatically hydrolyzable protein constitute generally minor fractions of total nitrogen, and protein is usually a minor fraction of amino acids. The total amino acid fraction is inversely related to the total nitrogen, which may reflect increasing humification of nitro-
303 gen in o r g a n i c a l l y e n r i c h e d s e d i m e n t s . T h e a m i n o acid s p e c t r a are r e m a r k a b l y h o m o g e n e o u s t h r o u g h o u t t h e Gulf; e x c e p t i o n s are h i g h e r a r o m a t i c a m i n o acids in t h e e s t u a r i e s a n d e n r i c h e d b a s i c a m i n o acids a n d m e t h i o n i n e in t h e o p e n Gulf. T h e i n f l u e n c e of r e c e n t l y d e p o s i t e d p l a n k t o n i c m a t e r i a l is e x p r e s s e d in a m i n o acid s p e c t r a b y e n r i c h m e n t of leucine a n d g l u t a m i c acid. ACKNOWLEDGMENTS T h i s w o r k w a s s u p p o r t e d b y g r a n t s f r o m t h e N S F ( I S P 8011448 a n d O C E 8700358), P e t r o l e u m R e s e a r c h F u n d , N O A A - S e a G r a n t ( R / L R F - 4 5 ) , a n d N S E R C . W e also t h a n k L. Schick, J. W a u g h , a n d E. L a n g t o n for t e c h n i c a l a s s i s t a n c e , D. S c h n i t k e r for s a m p l i n g a s s i s t a n c e , a n d P. J u m a r s for c o m m e n t s on the m a n u s c r i p t . T h i s is c o n t r i b u t i o n no. 204 f r o m t h e D a r l i n g M a r i n e Center.
REFERENCES Berner, R.A., 1982. Burial of organic carbon and pyrite sulfur in the modern ocean: its geochemical and environmental significance. Am. J. Sci., 282:451-473. Bordovskiy, O.K., 1965. Accumulation of organic matter in bottom sediments. Mar. Geol., 3: 33-82. Degens, E.T. and Mopper, K., 1976. Factors controlling the distribution and early diagenesis of organic matter in marine sediments. In: J.P. Riley and R. Chester (Editors), Chemical Oceanography. Academic Press, London, pp. 59-113. Hargrave, B.T., 1973. Coupling carbon flow through some pelagic and benthic communities. ,J. Fish. Res. Board Can., 30: 1317-1326. Hedges, J.I. and Mann, D.C., 1979. The lignin geochemistry of marine sediments from the southern Washington coast. Geochim. Cosmochim. Acta, 43: 1809-1818. Henrichs, S.M. and Farrington, J.W., 1987. Early diagenesis of amino acids and organic matter in two coastal marine sediments. Geochim. Cosmochim. Acta, 51: 1-15. Lyons, W.B. and Gaudette, H.E., 1979. Sediment geochemistry of Jeffreys Basin, Gulf of Maine: inferred transport of trace metals. Oceanol. Acta, 2: 477-481. Mann, K., 1982. Ecology of Coastal Waters. University of California Press, Berkeley, CA, 322 pp. Mayer, L.M., Macko, S.A., Mook, W.H. and Murray, S., 1981. The distribution of bromine in coastal sediments and its use as a source indicator for organic matter. Org. Geochem., 3: 37-42. Mayer, L.M., Rahaim, P.T., Guerin, W., Macko, S.A., Watling, L. and Anderson, F.E., 1985. Biological and granulometric controls on sedimentary organic matter of an intertidal mudflat. Estuarine Coastal Shelf Sci., 20: 491-503. Mayer, L.M., Schick, L.L. and Setchell, F., 1986. Measurement of protein in nearshore marine sediments. Mar. Ecol., Prog. Ser., 30: 159-165. Milller, P.J. and Suess, E., 1979. Productivity, sedimentation rate, and sedimentary organic matter in the oceans I. Organic carbon preservation. Deep-Sea Res., 26A: 1347-1362. O'Reilly, J.E. and Busch, D.A., 1984. Phytoplankton primary production on the northwestern Atlantic shelf. Rapp. P.-V. Reun. Int. Explor. Mer, 183: 255-268. Prahl, F.G. and Carpenter, R., 1984. Hydrocarbons in Washington coastal sediments. Est. Coastal Shelf Sci., 18: 703-720.
304 Premuzic, E.T., Benkovitz, C.M., Gaffaey, J,S.and Walsh, J.J., 1982. The nature and distribution of organic matter in the surface sediments of world ¢~eans and seas. Org. Geochem., 4: 63-77. Reichardt, W.T., 1987. Burial of Antarctic macroatgal debris in bioturbated deep-sea sediments. Deep-Sea Res., 34: 1761-1770. Rosenfeld, J.K., 1979. Amino acid diagenesis and adsorption in nearshore anoxic sediments. Limnol. Oceanogr., 24: 1014-1021. Sargent, J.R., Hopkins, C.C.E., Seiring, J.V. and Youngson, A., 1983. Partial characterization of organic material in surface sediments from Balsf~orden, northern Norway, in relation to its origin and nutritional value for sediment-ingesting animals. Mar. Biol., 76: 87-94. Sowden, F.J., 1970. Action of proteolytic enzymes on soft organic matter. Can. J. Soil Sci., 50: 233-241. Suess, E., 1980. Particulate organic carbon flux in the oceans - surface productivity and oxygen utilization. Nature, 288: 260-263. Suess, E. and Mtiller, P.J., 1980. Productivity, sedimentation rate and sedimentary organic matter in the oceans II. - Elemental fractionation. In: Biogeochimie de la Mati~re Organique h l'lnterface Eau-Sediment Matin. Colloq. Int. CNRS, pp. 17-26. Tanoue, E. and Handa, N., 1979. Differential sorption of organic matter by various sized sediment particles in Recent sediment from the Bering Sea. J. Oceanogr. Soc. Jpn., 35: 199-208. Tenore, K.R., 1983. Organic nitrogen and caloric content of detritus III. Effect on growth ot deposit-feeding polychaete, Capitella captitata. Est. Coastal Shelf Sci., 17: 733-742. Trask, P.D., 1939. Organic content of recent marine sediments. In: P.D. Trask (Editor }. Recent Marine Sediments. Am. Assoc. Petrol. Geol., pp. 428-453. Weiler, R.R. and Mills, A.A., 1965. Surface properties and pore structure of marine sediments. Deep-Sea Res., 12: 511-529. Whitney, D.E. and Darley, W.M., 1979. A method for the determination of chlorophyll-a in samples containing degradation products. Limnol. Oceanogr., 24: 183-186. Yentsch, C.M., HoUigan, P.M:, Balch, W.M. and Tvirbutas, A., 1986. Tidal stirring vs. stratification: Microalgal dynamics with:special reference to cyst-forming, toxin-producing dinoflageUates. In: J. Bowman, C.M. Yentsch and W.T. Peterson (Editors), Tidal Stirring and Plankton Dynamics, Springer-Verlag, Berlin, pp. 224-252.
291
Provenance, Concentrations and Nature of Sedimentary Organic Nitrogen in the Gulf of Maine
LAWRENCE M. MAYER
Ira C. Darling Center, University of Maine, Walpole, ME 04573 (U.S.A.) STEPHEN A. MACKO
Departments of Earth Sciences and Chemistry, Memorial University, St. Johns, Newfoundland, A1B 3X5 (Canada) LEON CAMMEN
Bigelow Laboratory/or Ocean Sciences, West Boothbay Harbor, ME 04575 (U.S.A.) {Received February 29, 1988; revision accepted June 13, 1988)
ABSTRACT Mayer, L.M., Macko, S.A. and Cammen, L., 1988. Provenance, concentrations and nature of sedimentary organic nitrogen in the Gulf of Maine. Mar. Chem., 25: 291-304. Factors controlling the provenance, concentrations, and nature of sedimentary organic matter (SOM), particularly the nitrogenous fraction, were examined for sites throughout the Gulf of Maine and two of its estuaries. Stable nitrogen isotope data corroborate previously reported Br: C ratios in indicating that macroalgae are important contributors to organic nitrogen pools in estuarine sediments. Significant contributions of terrigenous organic carbon in both the estuaries and the deep basins of the open Gulf are not accompanied by significant contributions of terrigenous organic nitrogen. Variations in concentrations of organic carbon, nitrogen, chlorophyll, and enzymatically hydrolyzable protein throughout the Gulf and its estuaries can be explained largely by variations in the delivery rate of organic matter to the benthos and the specific surface area of minerals in the sediments. Chlorophyll and protein concentrations represent relatively fresh organic matter and exhibit greater sensitivity to organic delivery variations than do total organic carbon or nitrogen. A strong, linear relationship between organic carbon and surface area is consistent with monolayer adsorption of SOM on mineral surfaces, which appears to inhibit degradation of the SOM. Amino acid compositions are remarkably constant throughout the Gulf, with large differences seen only with elevated tyrosine in estuaries and elevated basic amino acids and methionine in the open Gulf. Leucine and glutamic acid correlate with chlorophyll concentrations in open Gulf sites. Enzymatically hydrolyzable protein comprises small to major fractions of total hydrolyzable amino acids. Amino acid-nitrogen : total nitrogen correlates inversely with total nitrogen.
0304-4203/88/$03.50
© 1988 Elsevier Science Publishers B.V.
292 INTRODUCTION Estuarine and continental shelf sediments act as major sinks of sedimentary organic matter (SOM) in the global carbon cycle (Berner, 1982 ). This importance stems from their relatively shallow depths, high primary productivity, and high sedimentation rates. Notwithstanding this importance, few comprehensive studies of basin-wide distributions of concentrations, provenance, and quality of SOM in shelf areas have been reported. This paper provides such a study for the Gulf of Maine, including two of its associated estuaries. Provenance studies in coastal areas have concentrated on systems receiving primarily phytoplankton, seagrass, and terrigenous inputs. High-latitude coastal regions, however, may receive significant inputs from macroalgae (Mann, 1982 ). Macroalgal organic matter has been shown to provide a signiiicant trophic resource in sediments (reviewed in Reichardt, 1987), but its significance in contributing to bulk SOM has not been assessed. The Gulf o1: Maine provides a region in which to examine the potential importance of such inputs. The concentration of SOM is dependent on a number of factors related to rates of organic matter delivery to sediments and organic matter survival once deposited. In this study we focus on the roles of organic delivery rates and grain size variations. This paper provides special focus on the nitrogenous components of SOM. This fraction plays a critical role in the trophodynamics of sediment ecosystems (Tenore, 1983), as well as forming a significant fraction of SOM. We have concentrated on the proteinaceous materials in SOM, measured both as total acid-hydrolyzable amino acids and as enzymatically hydrolyzable proteins. Amino acid spectra have been used in a variety of studies to examine the provenance and transformations of organic nitrogen in sediments (Degens and Mopper, 1976). METHODS AND MATERIALS Areas sampled (Fig. 1 ) included the open Gulf of Maine and two of its estuaries - the Sheepscot and Damariscotta. Most of the open Gulf of Maine samples were obtained on cruises in the summers of 1979, 1980 (for isotope measurements ) and 1982 (for other chemical analyses ); other areas were sampled at times between 1978 a n d 1987. A variety of sampling devices was employed, including Shipek grabs, box corers, and gravity corers, and push-core sampling in intertidal areas. Samples were immediately frozen and thawed only for analysis. Only the top 1-2 cm was sampled for this study. Samples of the macroalgae Fucus vesiculosis and Ascophyllum nodosum were collected by hand from the rocky intertidal zone in the Damariscotta estuary, freeze-dried, ground in a Wiley mill, and frozen.
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Fig. 1. Map of the Gulf of Maine showing locations of sampling stations. Subsets of this sampling array were used for various analyses reported here. Open circles in the open Gulf refer to samples in Fig. 3. Small and large rectangles show location and enlargement of Sheepscot/Damariscotta estuaries. Total carbon and nitrogen analysis was performed after vapor phase acidification of samples to remove carbonate minerals. Analysis was carried out on either a Hewlett-Packard 185B or a Carlo Erba 1106 Elemental Analyzer. Precision on these analyses is typically better than 3% (1 s.d.). Bromine analysis was carried out by X-ray fluorescence as reported in Mayer et al. (1981). Amino acid analyses were performed by standard 6 N HC1 hydrolysis at 100 ° C under N2 for 24 h, followed by pH adjustment to ~ 3, and isocratic separation into individual amino acids using cation exchange HPLC with post-column derivatization with ortho-phthalaldehyde (OPA) and fluorescence detection (St. John Associates, Adelphi, MD). Precision is better than 10% (1 s.d. ). Protein analyses were by the modified Coomassie Blue method of Mayer et al. ( 1986 ),
294 and represent larger polypeptides amenable to protease hydrolysis. Phytopigment measurements were carried out fluorometrically after acetone extraction of the sediment and hexane separation of chlorophyll (modified from Whitney and Darley, 1979). Stable carbon and nitrogen isotopes ratios were determined on cryogenically purified gases following a 900 ° C combustion conducted under vacuum in quartz tubing for 1 h. Analyses of the gases (CO2 or N2) were conducted on either a Nuclide 6-60 RMS or a VG Micromass 602E and are reported in standard delta notation relative to PDB for gI3C and atmospheric nitrogen for g*~N. Typical precision on these analyses is ~ 0.1%o (1 s.d. ). Sediment specific surface areas (SFA) were measured by nitrogen adsorption, using a one-point B E T method on a Quantachrome Monosorb. Samples were pretreated with boiling hydrogen peroxide and sodium pyrophosphate to remove most of the organic matter; the measured surface area thus represents primarily the mineral surface area. Outgassing at a temperature of 350 ° C for 15-20 rain was found to be necessary to completely remove adsorbed water and achieve accurate readings. The nitrogen adsorption method yields different surface areas, particularly for coarser-grained sediments, than the cetyl pyridinium bromide (CPB) method reported in our earlier papers (Mayer et al., 1981; 1985). The relationship between the two measurements, from an intercalibration of 37 samples, is given by the equation (units of m 2 g- ~) SFAnitrogen-- 1.13 (SFAcpB) - 8 . 1
r2--0.91.
RESULTS AND DISCUSSION Sources of organic matter
Mayer et al. (1981) presented evidence, using a combination of g1~C and Br: C ratios, that the Sheepscot and Damariscotta estuaries receive both marine and terrigenous organic inputs. They also suggested that relatively high Br: C ratios indicated significant macroalgal inputs to the SOM pool, because macroalgae typically found in these estuaries show enriched Br concentrations relative to phytoplankton. The g*SN ratios on the same estuarine samples as those in Mayer et al. (1981) substantiate this suggestion (Fig. 2). A plot of gleN and Br: C values for samples along the Damariscotta estuary (Fig. 2b) shows parallel variation between these two parameters; the correlation between the two variables has r2= 0.79. The gISN ratios show positive deviations from the normal values of about 6-7%0, which are indicative ofplanktonicalty derived organic matter (Fig. 3), at the same sites where Br:C ratios show elevated values from the normal planktonic values of 6-8 mg Br g- 1 C (Mayer et al., 1981 ). These anomalously high g*SN values are indicative of the dominant macroalgae in this estuary ~ Fucus vesiculosis and AscophyUum nodosum which gave values of 8.1 and 7.9%0, respectively. The ~3C values of both these Damariscotta sediment samples and the macroalgae are similar to those of planktonic carbon. Together, the Br: C and nitrogen isotope data indicate
295
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296 that macroalgae may be locally dominant contributors to the organic nitrogen pool, and perhaps the organic carbon pool as well, within this estuary. The plots of ~13C and $1~N values in the Sheepscot estuary (Fig. 2a,c) are discordant with one another, in the sense that the ~ 13C ratios show a transition from an essentially pure, terrigenous organic source at the head of the estuary to a mixture of about 2/3 terrigenous and 1/3 marine algal source at its mouth, while the ~15N ratios change from primarily terrigenous values at the head to primarily marine values at the mouth. This discordance is due to the mixing of a high C: N terrigenous endmember with a relatively low C : N contribution from the marine endmember - - presumably some mixture of planktonic and macroalgal organic matter. Samples from the open Gulf of Maine show primarily a planktonic origin in both their ~I~N and ~13C values, consistent with the overwhelming dominance of planktonic production relative to macroalgal or terrigenous input. In this fashion the Gulf of Maine is typical of most shelf ecosystems. However, a plot of the $13C values vs. water depth of the sample (Fig. 3a) shows a highly significant trend (r 2= 0.44, p > 0.99 ) of increasingly terrigenous character of the SOM with increasing depth. The simplest explanation for this trend is that the basins, particularly Wilkinson Basin in the western Gulf, serve as partially effective traps for terrigenous material escaping the estuaries. This trapping role for the basins has been hypothesized for trace metals escaping the estuaries of the Gulf of Maine (Lyons and Gaudette, 1979). This trap is also analogous to the occurrence of relatively terrigenous-rich organic matter in the silty mid-shelf sediment found on the otherwise sandy Washington continental shelf (Hedges and Mann, 1979; Prahl and Carpenter, 1984 ). A similar plot of $~5N values with depth (Fig. 3b) does not show a similar trend toward isotopically lighter values associated with terrigenous nitrogen, but rather they become isotopically heavier with depth. This trend may indicate input of macroalgal detritus to the deeper parts of the Gulf, consistent with frequent observations of large rafts of floating macroalgal debris in the open Gulf. The lack of terrigenous influence on ~15N values is also consistent with the reduced isotopic visibility of terrigenous nitrogen in SOM at the mouth of the Sheepscot estuary. An important conclusion to be drawn from these inconsistencies between carbon and nitrogen isotopic compositions in both the estuarine and deeper parts of the Gulf is that discussion of the provenance of organic matter is an over-generalized approach. It is quite possible for the organic carbon and the organic nitrogen in any one sample to have different origins. Concentrations A variety of factors have been shown to influence the concentrations of organic matter in sediments. These factors include grain size, rate of organic
297 delivery to the sediments, sedimentation rate, and perhaps the redox state of the overlying water column (Trask, 1939; Miiller and Suess, 1979; Premuzic et al., 1982). The influence of two of these factors - - grain size and the rate of delivery of organic matter - - can be tested with the data from this study. Grain size control can be assessed by the relationship between organic matter concentration and the measured specific surface area. The rate of organic matter delivery to, the benthos has been shown to be related to two variables - - positively to primary production and inversely to the depth of the overlying water column (Hargrave, 1973; Suess, 1980). Primary productivity probably decreases with distance from shore - - and hence increasing depth - - in the Gulf of Maine; evidence for this trend is the decreasing level of phytoplankton biomass off.. shore determined from direct measurements (O'Reilly and Busch, 1984) and satellite photos of this region (Yentsch et al., 1986). Hence greater depths of the water column represent areas of both decreased primary production and decreased efficiency of delivery of this production to the benthos; in the discussion that follows depth can be used as a single parameter which is inversely related to organic delivery to the sediments. The redox state of the water column is not an important variable in the Gulf of Maine, where the water column is well-oxygenated. The influence of sedimentation rates on organic matter accumulation cannot be addressed in this study as very few data are available for the Gulf. The variations throughout the Gulf may not be important, however, because the influence of sedimentation rate in the equation relating organic matter accumulation, productivity, and sedimentation rate (Miiller and Suess, 1979) shows a reduced influence of this latter parameter relative to productivity. The concentrations of total carbon, total nitrogen, chlorophyll and proteinnitrogen all exhibit a decrease with depth in the Gulf of Maine (Fig. 4). Grain size, expressed as sediment specific surface area, is also an important correlate for total carbon and nitrogen, though not for protein or chlorophyll (Fig. 5). Multiple linear regression analyses of these data indicate that 60, 74, 41 and 49% of the carbon, nitrogen, chlorophyll, and protein-nitrogen total variances can be explained by the combination of depth and grain size. The influence of depth on protein and chlorophyll concentrations is much stronger than on total carbon or nitrogen concentrations. These two types of measurements are indicative of the labile fraction of sedimentary organic matter most likely to exhibit a response to the influence of the rain rate of freshly produced organic matter. This depth control on the amount of labile organic matter is reflected in decreasing bacterial and macrofaunal populations with depth (Mayer et al., 1986; Watling and Cammen, unpublished data). Total carbon and nitrogen concentrations show an abrupt decrease for samples collected deeper than 70 m (Fig. 4a,b). O'Reilly and Busch (1984) found phytoplankton biomass to decrease markedly at sites seaward of this depth.
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For these deeper sediment samples, grain size alone accounts for essentially all of the explained variation in total carbon and nitrogen, with no depth influence evident. This fact can be seen in Fig. 5a,b, which separates data from samples taken above and below 70 m. For the samples from sites deeper than 70 m, the regression of carbon and nitrogen on surface area haveslopes of 0.51 mg-OC g - i sediment and 0.07 mgN g - 1 sediment. These slopes are consistent with a roughly monolayer coverage of organic matter on mineral grains (Weiler and Mills, 1965; Tanoue and Handa, 1979; Mayer et al, 1985). These data fit tightly to the regression line, and attempts to relate the residuals from the regression line to water depth were unsuccessful. This tight fit to the grain size regression suggests that the concentrations are n o t a s responsive to organic delivery variations as protein and chlorophyll levels.The re~uced sensitivityto organic input variations implies that carbon and nitrogen concentrations are 'buffered' by some grainsize-related factor. The S O M in these offshore stations is dominated by refractory material, as indicated by very slowly decreasing concentrations downcore (Mayer, unpublished data). This buffering at approximately a monolayer coverage of grain surfaces supports the suggestion of Suess and Mfiller (1980) that adsorbed organic matter is difficultto metabolize.
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Amino acids and proteins Amino acids occur in sediments in a variety of forms, ranging from minor contributions by free monomers to a dominance of polymeric forms such as fresh proteins and humified peptide material. This compound class represents the largest pool of nitrogenous material identified to date, although sedimentary amino acids often do not comprise the major fraction of sedimentary organic nitrogen. Strong acid hydrolysis, as used in this study, should liberate most if not all bound amino acids. Our protein technique, however, should measure only those larger polypeptides amenable to enzymatic hydrolysis; this measure should therefore represent a relatively labile component of the total amino acids. Total hydrolyzable amino acids contributed from 12 to 81% of the total nitrogen in these samples. These contributions may be higher by a factor of 10-20% if as much as all of the aspartic and glutamic acids were present as
300
asparagine and glutamine. These two latter amino acids lose amide nitrogen on acid hydrolysis and are analyzed as aspartic or glutamic acids. A significant fraction of asparagine and glutamine in soils has been found (Sowden, 1970). There was no strong surface area or depth control found on the amino acidnitrogen:total-nitrogen ratio. Instead, a significant inverse correlation was found with the total nitrogen concentration (Fig. 6). This decreasing fraction of nitrogen in identifiable amino acids with increasing total nitrogen may reflect either a real shift toward another form of nitrogen or an increasing humification of amino acids (with perhaps lower availability to acid hydrolysis) in samples with higher total nitrogen. This finding is consistent with that of Bordovskiy (1965), who noted an increasing humification of carbon and a lower acid hydrolyzability of the organic carbon with increasing carbon content in samples from the Bering Sea. The protein nitrogen constitutes a small fraction of the total nitrogen in these surficial sediments, ranging from 3 to 14%. This ratio shows a strong depth dependence (Fig. 7), indicating that the nutritional quality of organic matter decreases strongly with depth. Protein nitrogen forms a larger fraction 1.0-
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Fig. 6. Ratio of amino acid nitrogen to total nitrogen vs. total nitrogen for samples from open Gulf and estuarine sites.
0.20 "
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Fig. 7. Protein-nitrogen: total nitrogen vs. depth for open Gulf and estuarine sediment samples.
301
of the amino acid nitrogen, ranging from 10 to 24% at all but one site. An intertidal sediment, with high organic loading, had a ratio of 133%, i.e., there was apparently more protein than acid-hydrolyzable amino acids. The 33% discrepancy between the two measurements is probably due to a combination of factors such as incomplete estimation of amino acid nitrogen due to decomposition of some amino acids during acid hydrolysis and ignoring nitrogen contributions from asparagine and glutamine. It is also possible that we overestimate protein nitrogen through use of an inappropriate standard (see Mayer et al., 1986). The amino acid spectra of 30 samples from throughout the open Gulf and its estuaries showed a remarkable consistency (Fig. 8). The coefficient of variations (as per cent of means) of all of the major amino acids - those constituting > 5% of total residues - were < 11%, which is roughly the analytical variability. The overall spectra are similar to those found in a number of studies from North Atlantic sites (e.g., Degens and Mopper, 1976; Rosenfeld, 1979; Sargent et al., 1983; Henrichs and Farrington, 1987). There were, however, some significant trends among the estuarine and open Gulf sites. Basic amino acids were enriched in deeper Gulf of Maine sites relative to the estuaries, while the aromatic amino acids showed the reverse trend (Fig. 9). Histidine followed the basics trend, but is not included in this plot because other amino-containing material, such as amino sugars, co-elute with the histidine peak in our isocratic separation. Tyrosine dominated the aromatic trend, with concentrations averaging 3.8% of total residues in the estuaries and 0.61% in the open Gulf. This difference was also reflected in a decreased concentration of tyrosine in samples from the mouths of the estuaries relative to upstream sites. As this decrease occurred in both estuaries, it reflects some aspect of the estuarine environment, rather than an influence by 3O IJJ
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Fig. 8. Average amino acid spectra, with standard deviations, of 20 samples from the open Gulf of Maine and 10 samples from the estuaries. Compositions expressed as percentages of total residues.
302
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LYSINE + ARGININE
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Fig. 9. Basic amino acids (lysineplus arginine) vs. aromatic amino acids (tyrosine plus phenylalanine) for shallow ( < 70 m) and deep ( > 70 m) sites. terrigenous organic matter. There was also a higher proportion of methionine in the open Gulf relative to the estuarine samples. Among samples from the open Gulf, there were positive correlations between the chlorophyll concentrations and the fractions of leucine and glutamic acid. These correlations reflect the fact that these two amino acids are commonly enriched in plankton relative to sedimentary organic matter (Henrichs and Farrington, 1987). CONCLUSIONS Organic nitrogen derives from a mixture of terrigenous, macroalgal and planktonic sources. Macroalgal nitrogen is an important constituent of the nitrogen pool in estuaries and may comprise a small but detectable fraction of nitrogen in the deeper basins. Macroalgal transport into the deeper basins ol" the Gulf is consistent with the trapping of terrigenous macrophytic carbon in these sites. In both estuarine sites and deep basins there are apparently differing origins for the carbon and nitrogen components of the organic matter. Organic matter concentrations throughout the Gulf can be explained largely by variations in organic delivery rates, represented by water column depth, and grain size. The grain size dependence is consistent with a monolayer adsorption of organic matter which appears to inhibit the organic loss rate. Measures of total organic matter show greater control by grain size while measures of the labile component of organic matter, e.g., enzymatically hydrolyzable protein, are more dependent on the organic delivery rate. Acid-hydrolyzable amino acids and enzymatically hydrolyzable protein constitute generally minor fractions of total nitrogen, and protein is usually a minor fraction of amino acids. The total amino acid fraction is inversely related to the total nitrogen, which may reflect increasing humification of nitro-
303 gen in o r g a n i c a l l y e n r i c h e d s e d i m e n t s . T h e a m i n o acid s p e c t r a are r e m a r k a b l y h o m o g e n e o u s t h r o u g h o u t t h e Gulf; e x c e p t i o n s are h i g h e r a r o m a t i c a m i n o acids in t h e e s t u a r i e s a n d e n r i c h e d b a s i c a m i n o acids a n d m e t h i o n i n e in t h e o p e n Gulf. T h e i n f l u e n c e of r e c e n t l y d e p o s i t e d p l a n k t o n i c m a t e r i a l is e x p r e s s e d in a m i n o acid s p e c t r a b y e n r i c h m e n t of leucine a n d g l u t a m i c acid. ACKNOWLEDGMENTS T h i s w o r k w a s s u p p o r t e d b y g r a n t s f r o m t h e N S F ( I S P 8011448 a n d O C E 8700358), P e t r o l e u m R e s e a r c h F u n d , N O A A - S e a G r a n t ( R / L R F - 4 5 ) , a n d N S E R C . W e also t h a n k L. Schick, J. W a u g h , a n d E. L a n g t o n for t e c h n i c a l a s s i s t a n c e , D. S c h n i t k e r for s a m p l i n g a s s i s t a n c e , a n d P. J u m a r s for c o m m e n t s on the m a n u s c r i p t . T h i s is c o n t r i b u t i o n no. 204 f r o m t h e D a r l i n g M a r i n e Center.
REFERENCES Berner, R.A., 1982. Burial of organic carbon and pyrite sulfur in the modern ocean: its geochemical and environmental significance. Am. J. Sci., 282:451-473. Bordovskiy, O.K., 1965. Accumulation of organic matter in bottom sediments. Mar. Geol., 3: 33-82. Degens, E.T. and Mopper, K., 1976. Factors controlling the distribution and early diagenesis of organic matter in marine sediments. In: J.P. Riley and R. Chester (Editors), Chemical Oceanography. Academic Press, London, pp. 59-113. Hargrave, B.T., 1973. Coupling carbon flow through some pelagic and benthic communities. ,J. Fish. Res. Board Can., 30: 1317-1326. Hedges, J.I. and Mann, D.C., 1979. The lignin geochemistry of marine sediments from the southern Washington coast. Geochim. Cosmochim. Acta, 43: 1809-1818. Henrichs, S.M. and Farrington, J.W., 1987. Early diagenesis of amino acids and organic matter in two coastal marine sediments. Geochim. Cosmochim. Acta, 51: 1-15. Lyons, W.B. and Gaudette, H.E., 1979. Sediment geochemistry of Jeffreys Basin, Gulf of Maine: inferred transport of trace metals. Oceanol. Acta, 2: 477-481. Mann, K., 1982. Ecology of Coastal Waters. University of California Press, Berkeley, CA, 322 pp. Mayer, L.M., Macko, S.A., Mook, W.H. and Murray, S., 1981. The distribution of bromine in coastal sediments and its use as a source indicator for organic matter. Org. Geochem., 3: 37-42. Mayer, L.M., Rahaim, P.T., Guerin, W., Macko, S.A., Watling, L. and Anderson, F.E., 1985. Biological and granulometric controls on sedimentary organic matter of an intertidal mudflat. Estuarine Coastal Shelf Sci., 20: 491-503. Mayer, L.M., Schick, L.L. and Setchell, F., 1986. Measurement of protein in nearshore marine sediments. Mar. Ecol., Prog. Ser., 30: 159-165. Milller, P.J. and Suess, E., 1979. Productivity, sedimentation rate, and sedimentary organic matter in the oceans I. Organic carbon preservation. Deep-Sea Res., 26A: 1347-1362. O'Reilly, J.E. and Busch, D.A., 1984. Phytoplankton primary production on the northwestern Atlantic shelf. Rapp. P.-V. Reun. Int. Explor. Mer, 183: 255-268. Prahl, F.G. and Carpenter, R., 1984. Hydrocarbons in Washington coastal sediments. Est. Coastal Shelf Sci., 18: 703-720.
304 Premuzic, E.T., Benkovitz, C.M., Gaffaey, J,S.and Walsh, J.J., 1982. The nature and distribution of organic matter in the surface sediments of world ¢~eans and seas. Org. Geochem., 4: 63-77. Reichardt, W.T., 1987. Burial of Antarctic macroatgal debris in bioturbated deep-sea sediments. Deep-Sea Res., 34: 1761-1770. Rosenfeld, J.K., 1979. Amino acid diagenesis and adsorption in nearshore anoxic sediments. Limnol. Oceanogr., 24: 1014-1021. Sargent, J.R., Hopkins, C.C.E., Seiring, J.V. and Youngson, A., 1983. Partial characterization of organic material in surface sediments from Balsf~orden, northern Norway, in relation to its origin and nutritional value for sediment-ingesting animals. Mar. Biol., 76: 87-94. Sowden, F.J., 1970. Action of proteolytic enzymes on soft organic matter. Can. J. Soil Sci., 50: 233-241. Suess, E., 1980. Particulate organic carbon flux in the oceans - surface productivity and oxygen utilization. Nature, 288: 260-263. Suess, E. and Mtiller, P.J., 1980. Productivity, sedimentation rate and sedimentary organic matter in the oceans II. - Elemental fractionation. In: Biogeochimie de la Mati~re Organique h l'lnterface Eau-Sediment Matin. Colloq. Int. CNRS, pp. 17-26. Tanoue, E. and Handa, N., 1979. Differential sorption of organic matter by various sized sediment particles in Recent sediment from the Bering Sea. J. Oceanogr. Soc. Jpn., 35: 199-208. Tenore, K.R., 1983. Organic nitrogen and caloric content of detritus III. Effect on growth ot deposit-feeding polychaete, Capitella captitata. Est. Coastal Shelf Sci., 17: 733-742. Trask, P.D., 1939. Organic content of recent marine sediments. In: P.D. Trask (Editor }. Recent Marine Sediments. Am. Assoc. Petrol. Geol., pp. 428-453. Weiler, R.R. and Mills, A.A., 1965. Surface properties and pore structure of marine sediments. Deep-Sea Res., 12: 511-529. Whitney, D.E. and Darley, W.M., 1979. A method for the determination of chlorophyll-a in samples containing degradation products. Limnol. Oceanogr., 24: 183-186. Yentsch, C.M., HoUigan, P.M:, Balch, W.M. and Tvirbutas, A., 1986. Tidal stirring vs. stratification: Microalgal dynamics with:special reference to cyst-forming, toxin-producing dinoflageUates. In: J. Bowman, C.M. Yentsch and W.T. Peterson (Editors), Tidal Stirring and Plankton Dynamics, Springer-Verlag, Berlin, pp. 224-252.