Hydrogeochemistry of the New Jersey Coastal Plain

Chemical Geology, 33 (1981 ) 23--44 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

23

HYDROGEOCHEMISTRY OF THE NEW JERSEY COASTAL PLAIN 2. T r a n s p o r t a n d D e p o s i t i o n o f I r o n , A l u m i n u m , D i s s o l v e d O r g a n i c M a t t e r , a n d Selected Trace E l e m e n t s in S t r e a m , G r o u n d - a n d E s t u a r y Water

D.A. CRERAR, J.L. MEANS*', R.F. YURETICH *~, M.P. BORCSIK, J.L. AMSTER, D.W. HASTINGS, G.W. KNOX, K.E. LYON and R.F. QUIETT

Department of Geological and Geophysical Sciences, Princeton University, Princeton, N.J. 08544 (U.S.A.) {Received September 3, 1980; revised and accepted April 23,1981 )

ABSTRACT Crerar, D.A., Means, J.L., Yuretich, R.F., Borcsik, M.P., Amster, J.L., Hastings, D.W., Knox, G.W., Lyon, K.E. and Quiett, R.F., 1981. Hydrogeochemistryof the New Jersey Coastal Plain, 2. Transport and deposition of iron, aluminum, dissolved organic matter, and selected trace elements in stream, ground- and estuary water. Chem. Geol., 33: 23--44. The geochemical controls on the transport and deposition of iron, organic carbon, and certain trace elements have been examined in bogs, streams, groundwater and estuaries of the New Jersey Coastal Plain. Surface waters are unusually dilute (total dissolved solids ~ 25 ppm) and acidic (pH 4--5) and contain relatively high concentrations of organic C and Fe. Liquid chromatographic analyses show that from 10 to 70% of total "dissolved" Fe (< 0.2 ~m) in river water is associated with dissolved organic carbon (DOC), which is primarily humic and fulvic acid, presumably as organo-metallic complexes. A significant proportion of the streamborne Fe and AI is colloidal or particulate (> 0.2 um) Fe-oxyhydroxide or -oxyhydroxides admixed with insoluble organic material. The proportion of organically-complexed Fe present varies seasonally with the DOC content of the water. These stream waters are near saturation with respect to amorphous Fe(OH)3; groundwaters are uniformly undersaturated with respect to amorphous Fe(OH3). Both stream and groundwaters are near saturation with respect to halloysite, slightly supersaturated with respect to gibbsite, and highly supersaturated with respect to kaolinite. Bog iron deposits are common in streams and swamps where Fe precipitation is catalyzed by ironoxidizing bacteria. Fe and AI precipitate rapidly within both estuaries, with ionic strength rather than increased pH exerting the prime control on estuarine deposition. Estuarine floccules contain very little or no organic matter, suggesting that inorganic Fe- and Al-oxyhydroxides are the primary precipitates. The high contents of "dissolved" (< 0.2 um) Fe and Al suggest that both are either organically complexed or in the form of small (< 0.2 urn) oxyhydroxide colloids in the estuaries.

Present addresses: *' Batelle--Columbus Laboratories, 505 King Avenue, Columbus, OH 43201, U.S.A. .2 Department of Geology and Geography, University of Massachusetts, Amherst, MA 01003, U.S.A.

0009-2541/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company

24 INTRODUCTION

The geochemical controls on the movement of iron, trace elements, and organic carbon in natural waters are topics of continuing interest (cf. Beck et al., 1974; Picard and Felbeck, 1976}. This study explores the behavior of some trace constituents in the surface and groundwaters of the New Jersey Coastal Plain. The sediments of this region, briefly discussed in Part I (Yuretich et al., 1981; see also Owens and Sohl, 1969; Minard et al., 1974; Crerar et al., 1979~ range in age from Late Cretaceous to Pleistocene and consist largely of poorly-consolidated marginal-marine sands and clays. The quartz sands and gravels of the Pliocene Cohansey Formation crop out over most of the study area, which is characterized by low topographic relief, poorly developed soils, pineand cedar-dominated vegetation and extensive lowland bogs and streams. This region, known locally as the Pine Barrens or Pinelands, is sparsely populated and remains largely unaltered by human activity. The waters of the Pine Barrens are unusually dilute, with total dissolved solids (TDS) averaging ~ 25 ppm. Many of the major components of surface waters are introduced by rainfall or precipitation. This paper focuses on those constituents that are derived mainly from sediments and vegetation such as dissolved silica, Fe, A1, various trace elements and organic carbon. Particular emphasis is placed on transport mechanisms of trace components, including chemical speciation of various inorganic and organo-metallic complexes, equilibria governing Fe and Al solubilities, relative importance of dissolved and suspended loads, and the chemical nature of dissolved humic substances. METHODS

Sampling techniques and field analyses During the period 1976--1978, stream- and estuary-water samples were collected at intervals of approximately one month along both Cedar Creek and the Mullica River (Fig. 1). Groundwaters were also sampled periodically at eleven observation wells installed by the U.S. Geological Survey within the Mullica River drainage basin (Fig. 1}. In all cases samples were collected in polyethylene bottles previously cleansed with 1:10 Ultrex ® ultrapure concentrated HNO3 for at least 10 hr. Groundwater wells were flushed 10--20 min before sampling. Eh, pH and temperature were measured directly in the field. Corrected Eh was calculated from temperature and measured Eh, following Langmuir (1971). Eh measurements were usually stable and reproducible, probably due to the relatively high concentration of dissolved Fe and concomitantly high redox capacity.

25

N

\

0 10 I MILES I

CAMDEN

DOVE R O 0 ~ L ~ ' ~

J ATLANTIC CI]Y

• STREAM • GROUNDWATER • ESTUARY

Fig. 1. Stream, groundwater and estuary sampling sites. See Yuretich et ai. (1981, fig. 1, p. 2 in this issue} for a general index map.

Laboratory analyses Aliquots o f each sample were filtered through 0.2-pm Nucleopore membranes within several hours after collection. Considerable care was taken to minimize trace-metal c o n t a m i n a t i o n by cleaning glassware in a metal-free acid-bath, soaking in 1:10 Ultrex ® HNO3, and then t h o r o u g h l y rinsing with d o u b l y distilled water prior to use. Both filtered and unfiltered samples were acidified to pH < 2.0 with c o n c e n t r a t e d Ultrex ® HNO3 prior to analysis. Total dissolved solids (TDS) were determined by evaporating 1 1 of filtered sample to dryness. Evaporated residue was analyzed for organic carbon on a Leco ® carbon-sulfur analyzer. Si was analyzed in filtered.samples on a Perkin-Elmer ® model 603 atomic-absorption flame s p e c t r o p h o t o m e t e r ; Fe, A1, Mn, Zn, Cu, Pb and Cd concentrations were determined using the HGA2000 graphite furnace a t t a c h m e n t to this instrument. C1- was measured by specific ion electrode. Humic acid (HA) and fulvic acid (FA) in u n t r e a t e d water samples were separated and purified using a pr oc e dur e adapted from Rashid and King

26 (1969). Unfiltered samples, either unconcentrated or preconcentrated on a rotoevaporator or by lyophi!ization, were acidified to pH 1 with concentrated HC1. HA precipitated out of solution overnight and was separated from FA by filtration through a 0.2-um Nucleopore ® membrane. HA was air
Cedar Creek Mullica River

Groundwater Cedar Creek estuary Mullica River estuary

pit

~';h (mVi

4.7 54~i (3.9-.- 5.:') ~ (4,t I . - 7 1 3 ) 5.1 513 (,t.2--5 9) (375--635) 4.5 ,iS l (4.3--4.9) (274--593) (4.67- 770) (382-£,53) (4.63--R I()~ ( 4 0 5 - - 6 4 3 )

n.a. = not analyzed. * F r om Part 1 (Yuretieh et al., 198 '. J

TDS (ppml

DOC ( p p m, •0 2 ~rn)

T o t a l Fe (a g,'kg)

"Dissolved" Fe (ag/kg - (3.2 a m

22.8 ( 16.2 - 2 7 5 } 28.1 (202-34.3) 47 (28--99) (54--31,800) (35 - 2 5 4 5 3 ~

2.2 (0.77 - 3 . 7 ) 2.6 (1.1-.4.8) 1.2 (0.6--2.9) n.a. n.a.

200 (66--380) 2300 (500--4,210) 520 (50--2,780) n.a. n.a.

90 (21--3t0; 330 (12---~40) 510 (50--2,870) ( 5. 160) (63--420)

1

27 JEM ® Model IOOB scanning electron microscope equipped for energy-dispersive X-ray analysis, using a computerized Kevex ® model 7000 X-ray energy analytical system. Samples of bog and stream waters were tested for presence of iron-oxidizing bacteria both by microscopic examination (using Nomarski ® interference optics at 1200 power), and in several cases using species specific culture media as described by Crerar et al. (1979). ANALYTICAL RESULTS Table I summarizes the results of the chemical analyses of stream, groundand estuary waters. Averages and ranges are listed here, the complete data set being available in the report by Means et al. (1981). The Mullica River water contains generally greater concentrations of Fe, Al, DOC and the trace elements analyzed than Cedar Creek. Total (unfiltered) Fe and A1 stream-water values are highly variable and depend on where in the water column the sample was taken. Stream bottoms are coated with an Feand Al-rich flocculent material, so samples collected close to the b o t t o m will contain greater total Fe and Al contents. Groundwaters analyzed contained up to ~ 3 ppm Fe and ~ 5 ppm A1. Unlike the stream waters, filtration removed little Fe and Al in the groundwaters. Trace elements detected comprised mainly Mn and Zn and traces of Cu, Pb and Cd. Seasonal trends were observed in stream waters, with Eh being lower and pH slightly higher in the summer than in the winter. Similarly, total dissolved solids (TDS), dissolved organic carbon (DOC), and dissolved Fe typically reach highest values during summer months. Surface waters are generally tea-colored during the growing season, and become almost colorless during the winter; color ranges from roughly 3--150 Pt--Co units over the course of a year (Rhodehamel, 1973). In Cedar Creek, TDS content is low at 20--25 ppm. Also these waters are unusually free of suspended material, as total filterable solid content (> 0.2 pm) is generally no more than several ppm. TDS content of the Mullica River

Total AI (ug/kg)

"Dissolved" AI (ug/kg <:0.2 urn)

92 (44--340) 250 (98--910) 1,960 (210--4,980) n.a. n.a.

54.2 (9.17--]10) 76.7 (26--140) 1,680 (18--4,980) (22--120) (16 180)

Total (ug/kg) Mn

Zn

Cu

Pb

Cd

Si

6.1 (2.6.8.4) 19.6 13--30.2} 49.8 (7.9--211) 12.3 (6.0--26.0) 26.8 (17.9--36.0)

,t.8 (1.2- 10.1) 9.5 (1.5--29.0) 19.6 (0.9--80.3) 7.3 (4.8--9.2) 21.9 (16.4--27.9)

0.6 (0.1-1.6) 0.9 (0.1--2.3) 1.7 (0.4 2.9) 4..t (1.9--14.7) 4.3 (1.2. 12.2)

0.4 (<0.1'~'}.9) 1.7 (0.4--7.3) 1.2 (0.3--3.0) 1.7 (0.9..7.8) 2.0 (1.0--7.5)

0.1 (.:0.1--0.2) 0 1 (0.1--0.31 0.4 (0.1--1.2) ha.

4,000* (2,800-.-,t,800) 4,600 (3,900--6,200) 2,960 (1,000 8,300) ~ 5,000

ha.

~9,000

28 is only slightly higher at ~ 30 ppm. Here the total filterable solids content is significantly greater (at 5--15 ppm), and consists predominantly of flocculated organic material and amorphous Fe-oxyhydroxides. DISCUSSION: STREAM- AND GROUNDWATER

Inorganic constituents Concentrations and sources of the components Na +, K ÷, Mg ~+, Ca :" , SiO:, C l , SOl', PO~- and NO~ in streams and precipitation have been discussed in Part I (Yuretich et al., 1981). With the exception of silica, which approaches saturation relative to quartz, these components are introduced primarily by precipitation. The remaining inorganic constituents listed in Table I are presumably derived from underlying glauconitic sediments. Hydrologic data indicate that streams in this area are fed almost entirely by underlying aquifers, There is evidence, for example, of both lateral and vertical groundwater movement into the Mullica River (Lang, 1961; Lang and Rhodehamel, 1962; Crerar et al., 1979). It has been estimated that groundwater baseflow supplies roughly 89% of all river discharge throughout the study area, with the remaining 11% coming from surface runoff (Rhodehamel, 1970). Average annual precipitation is 1140 mm; approximately half of this is lost to evapotranspiration. Although it is possible that some proportion of trace metals such as Pb and Cd could be anthropogenic, the similarity in composition of ground- and surface waters suggest that human influence is not of major significance. Furthermore, the relative order of trace-element abundances in underlying glauconites which we have analyzed parallels that of the stream- and groundwaters (Table I), following the general sequence: Fe ~ Al > Zn ~ Mn > Cu ~ Pb ~ Cd. The observed metal content of the Mullica River was consistently higher than Cedar Creek as shown by the overall averages in Table I. This may be attributed to greater relative base flow in the Mullica and southern streams (table III in Yuretich et aI., 1981, p. 12 in this issue). Theoretical equilibrium solubilities of amorphous Fe(OH)3 and of the Albearing phases kaolinite, halloysite, gibbsite and amorphous AI(OH)3 were calculated from thermodynamic data, using two c o m p u t e r programs. The program input variables are pH, Eh, Cl-, F-, SO~-, <0.2-~m Fe and A1, dissolved Si and ionic strength. Activity coefficients for all species are computed from an extended Debye--Hiickel equation. In all, the equilibrium concentrations of 24 aqueous Fe and 15 aqueous Al species are determined. The calculations and free-energy data used are described in greater detail in Means et al. (1981). Using these c o m p u t e r codes, the total concentrations of all calculated Fe and A1 species may be compared with observed values as a test for degree of saturation in both metals. Note that no consideration of possible organic

29 complexing is included in the calculated solubilities which are therefore minimum values only. In fact, one intent of these calculations is to infer the presence of organic complexes and small Fe- and Al-bearing colloids from calculated saturation levels. Supersaturation with respect to the most so!,uble solid phase [amorphous Fe(OH)3 and AI(OH)3] based on purely inorganic equilibria may be interpreted to imply the presence of organic complexes and colloids. Table II lists average measured/computed solubility ratios and standard deviations for groundwaters and both rivers. On the average, Cedar Creek appears slightly undersaturated and the Mullica River appears slightly supersaturated with respect to amorphous Fe(OH)3. This difference is probably due to the slightly higher average pH of the Mullica River coupled with higher metal concentrations. Groundwaters tested are uniformly undersaturated in Fe. For the Al-phases, both rivers are slightly undersaturated with respect to halloysite, roughly saturated relative to gibbsite, and supersaturated in kaolinite. A1 solubility ratios are significantly higher in the Mullica River than in Cedar Creek, presumably for the same reasons that cause the difference in Fe solubility ratios. Groundwaters are apparently supersaturated in Al relative to all three minerals. Since surface waters seem roughly saturated in both Fe and A1, it is also possible that if organic complexing were considered these waters might in fact be slightly undersaturated. The relative importance of organic complexing is considered in the following text. In the case of Fe, a measured/theoretical solubility ratio significantly greater than 1.0 is interpreted to indicate the presence of small o x y h y d r o x i d e colloids and/or organic Fe species in the "dissolved" {<0.2 pm) Fe analyses TABLE II Average degrees of saturation of stream and groundwaters in Fe and AI with standard deviations (in parentheses), ignoring organic complexing Site

Cedar Creek Mullica River Groundwater

Cedar Creek estuary Mullica River estuary

Measured/computed concentration ratio Fe, relative to amorphous Fe(OH)3

AI, relative to halloysite

A1, relative to gibbsite

AI, relative to kaolinite

0.26 (0.34) 2.98 (4.35) 0.060 (0.060) 37.4 (67.2) 7.8 (8.1)

0.17 (0.19) 0.81 (0.78) 1.42 (1.52) 2.5 (2.0) 1.1 (0.7)

0.66 (0.73) 3.26 (3.21) 4.14 (3.26i 10.3 (8.3) 4.5 (3.0)

5.06 (7.17) 31.6 (33.8) 40.26 (41.02) 105.8 (86.0) 44.0 (33.0)

30 in Table I. This interpretation is substantiated by the data presented below on organo--metallic interactions and colloid size distribution in Pine Barrens surface waters. Similar observations and explanations have also been offered by other investigators (e.g., Jones et al., 1974). The same interpretation can be applied to the apparent supersaturated conditions relative to amorphous Fe(OH)3 in the Cedar Creek and Mullica River estuaries (Table II).

Organic constituents DOC is an important constituent of both surface- and groundwaters in the, study area {Table I}; it represents mainly humic and fulvic acids. While DO(: averages 2.5 ppm in streams, concentrations up to 30 ppm in adjacent swamps were measured. These high levels of organic matter account for the characteristic tea color of surface waters on the Coastal Plain {e.g., Lamar, 1968; Beck et al., 1974}. Assuming that organic c o m p o u n d s such as humic and fulvic acids contain ~ 5 0 wt.% C, then organic components actually account for ~ 2 0 % of the TDS in Pine Barrens river waters.

Organo--metallic interactions The relative organic molecular-weight distributions and the importance of organo--Fe associations in river samples were determined, using the GFC procedure developed previously {Means et al., 1977}. Representative GFC elution profiles are shown in Fig. 2. The blue dextran peak denotes the highest molecular-weight fractions not retarded by the gel. The UV absorbance peak monitors relative concentration of soluble organic' matter with molecular weight decreasing to the right. The superimposed histograms show dissolved Fe concentrations determined for each molecularweight fraction. Additional profiles are compiled by Means et al. (1981). Fig. 2. shows that no fractionation occurred with gel G-10 in the sample from Cedar Creek. When passed through gel G-15, the sample exhibited some fractionation, and fractionation increases progressively with the higher gels, most materials being lighter than the exclusion limit of gel G-50 (~ 10,000 MW units for dextrans). In all GFC separations, Fe profiles closely paralleled organic carbon. Inorganic Fe species are strongly retarded and even adsorbed by Sephadex ® gels (Plumb and Lee, 1973; Means et al., 1977). Comparing the amount of Fe eluted in the first (or large molecular weight} peak of G-IO with the total quantity loaded onto the column gives the ratio of organic to inorganic Fe species. The authors' results indicate a significant association between dissolved Fe (< 0.2 pm filtered) and humic substances in surface water. In samples containing 20--30 ppm DOC, 60--70% of the total dissolved Fe is associated with organic carbon, presumably as organo-metaUic complexes. At DOC concentrations on the order of 2--5 ppm, which are typical of Pine Barrens stream waters, 10--20% of the total dissolved Fe is organically complexed. The present authors were unable to evaluate the extent of association between organic substances and other trace metals such as A1, Pb, Cu, Mn, Zn and Cd

31 = r,,

w ~9 Z

-~ ~1'~

CEDAR CREEK BOG 6 78

TF" \,

G. I

o

=,

o~

~.~\

--UV ABSORBANCE .... BLUEDEXTRAN rrhFe

~Z '¢D /~

,", z

.° :

G.15

,.,G2~ r]

k

G 50

L~"-~.-Y-~--T4o

5o

so ELUTION

DECREASING

I _I~ 7o

8o

VOLUME

9o

,oo

,,o

(ml]

MOLECULAR

WEIGHT

Fig. 2. Gel filtration chromatography elution profiles for Cedar Creek bog water.

because of their low concentrations in filtered samples. However, a qualitative correlation between A1 and DOC was observed in GFC profiles and it is reasonable to expect some association, particularly for A1, Pb and Cu, which are known to form especially strong complexes with organic acids (Irving and Williams, 1948; Schnitzer and Kahn, 1972). Chemical composition and structure The chemical composition and structure of the dissolved organic substances present were investigated by elemental analysis, functional group titrations and IR spectrophotometry. As noted above, GFC studies indicate that the DOC substances are predominantly high-molecular-weight compounds. Filtered water samples were purified by dialysis to remove low-molecular-weight organic and inorganic constituents. HA and FA fractions were separated as described previously. H A / F A ratios from both Cedar Creek and Mullica River averaged 0.7. Elemental compositions of the HA and FA are shown in Table IIL Note that Pine Barrens HA and FA display relatively high C/H and O/C contents, suggesting a higher than normal degree of aromatization (Kononova, 1966) and a relative enrichment in oxygen-bearing functional groups. Thus Pine Barrens HA and FA would be expected to demonstrate stronger than normal metal-binding capacities and greater than normal aqueous solubilities. Analyses of the functional group content of the HA and FA are summarized in Table IV. Total acidity is higher than that of average soil HA and FA tabulated by Schnitzer and Kahn (1972) and more consistent with the acidity of dissolved organic matter (DOM) reported by Beck et al. (1974) from coastalplain rivers in Georgia. The present authors attribute some of the scatter in

32

P~

P~

•~

D--

Q;

© CO

0

O

Q;

0

s~

O

oj .o °~

°~

°.

Q;

~Q

p.

< E~

Q;

p.

p.

33 TABLE IV Acid functional group analyses on humic and fulvic acids from Pine Barrens rivers Sample

Total acidity (meq/g)

Carboxyl (meq/g)

Phenolic hydroxyl (meq/g)

Mullica River tributary humic acid (HA) Mullica River tributary fulvic acid (FA) Cedar Creek upstream fulvic acid (FA) Cedar Creek downstream fulvic acid (FA)

12.4

5.2

7.2

8.9

2.2

6.7

10.3

1.9

8.4

27.1

6.5

20.6

total acidities to variations in sample preparation. The sample taken downstream on Cedar Creek was dialyzed for 3 weeks compared to only 2--3 days for the others. This longer dialysis period may have removed more organically b o u n d cations, restoring a greater proportion of functional groups to their acid form. This suggests that the dialysis step may be considerably more crucial to such analysis than previously considered. IR spectra of representative HA and FA samples (Fig. 3) resemble spectra previously reported from similar environments {Stevenson and Goh, 1971; Schnitzer and Kahn, 1972; Beck et al., 1974}. The prominent bands in the IR spectra may be assigned as follows: broad band at 3400 cm -~, O--H and to a lesser extent N--H stretching; shoulder peak at 2850--2950 cm -~, aliphatic C--H stretching; strong band at 1700--1720 cm -~, C=O stretching in carboxyl and ketone groups; peak at 1640 cm -~, aromatic C=C, hydrogen-bonded

4.000

3,500

3.000

2.500

FREOUENCY

2.000

1.500

1.000

( C M "1 )

Fig. 3. Infrared spectrographs of fulvic (1 and 2) and humic acids (3 and 4) from the Mullica River.

34

quinone carbonyl C=O stretching, also C O O carboxylate; small peak at 1375 cm -t, COO" carboxylate or aliphatic C--H; and broad peak around 1200 cm -~, C--O stretch of alcohol, phenol, carboxyl acids, etc.(Rashid, 1971; Schnitzer and Kahn, 1972; Beck et al., 1974). Comparison of the IR spectra of Pine Barrens humic and fulvic acids suggests some compositional differences (Fig. 3). HA spectra show greater absorption at 2850--2950 cm "~ (C--H stretching) than FA, indicating that Pine Barrens HA is more aliphatic than FA, which is consistent with other data {Stevenson and Goh, 1971; Beck et al., 1974). In addition, Pine Barrens FA has proportionately greater absorption in the 1600--1650 cm -~ and 1350--1375 cm ~ (COO-} and less absorption in the 1700--1720 cm-l(C=O in ketones, carboxyl groups; C=C stretching) regions of the spectrum. This suggests that a greater proportion of total C=O functional groups in FA are present as quinone or carboxylate metal complexes, whereas relatively more of the C=O in HA o(:curs as ketone or acid-form carboxylic functions (Levesque and Schnitzer, 1967; Schnitzer, 1968; Rashid, 1971}. This interpretation is supported by the data of Schnitzer and Kahn (1972}, which illustrates much higher (ketone C=O)/(total C=O) ratios in soil HA than in FA. Furthermore, a greater proportion of carboxyl groups in FA may occur as carboxylate--metal complexes because of the greater metal-holding capacity of FA relative to HA (Stevenson and Butler, 1969}.

Particulate and colloidal fractions River-water samples were filtered successively through Nucleopore ® filters of decreasing pore size, and the filtrate at each step was analyzed for Fe and A1 as described above. Duplicate samples were ultracentrifuged, and the supernatant was analyzed for both metals. Typical results (Table V; see also Table I} clearly indicate that significant fractions of river-borne Fe and Al are colloidal, with the most dramatic decrease in concentration observed after Whatman ® filtration. The percentage removed by ultracentrifugation corresponds roughly to the cumulative 0.2-tam filtration. Lamar (1968), Perhac {1972}, and Boyle et al. (1977) have also shown that a significant fraction of river-borne Fe is typically colloidal in size. For example, Boyle et al. (1977) TABLE V A m o u n t o f F e a n d Al remaining a f t e r filtration and u l t r a c e n t r i f u g a t i o n (ug/kg) for s a m p l e s c o l l e c t e d at L a n o k a H a r b o r o n N o v e m b e r 2, 1979

Fe Al

Untreated

Whatman ® No. 5 0

12.0 t~m

8.0 ~ m

2.0 ~m

185 114

158 82

151

151 75

141 73

35

found that ~ 75% of the Fe in Mullica River samples which passed through a 0.45-pm membrane was removed by ultracentrifugation or refiltration through 0.1- and 0.05-pm membranes. However, in our analyses more than 50% of the total Fe and A1 present is not removed by ultracentrifugation or by filtration down to even 0.03 p m (Table V). Thus it would appear that a significant proportion of the total Fe and Al is present in a truly dissolved state - -either as organic complexes or as inorganic species such as Fe 2÷. A separate set of samples was filtered first through 12-~m Nucleopore ® membranes, then successively through 0.2- and 0.03-~m membranes. Examination of filtered residues by scanning electron microscopy (SEM) and energydispersive X-ray analysis (EDA) showed a high proportion of ferric hydroxide particles with trace of (presumably coprecipitated) Al, at sizes exceeding 12 pm. Typical particles in the 0.2--12-pm range contained slightly more A1 and Si and less Fe. Only traces of Fe and no A1 could be detected on particles in the 0.03--0.2-um fraction, which give no major EDA-identifiable peaks and are thus presumed to be predominantly organic. Clearly the composition of particulates in these waters varies considerably with size.

Bog iron deposition Stream beds and swamps throughout the study area are typically coated with freshly precipitated iron oxides, and thicker deposits of bog iron are common. The bog iron consists of unconsolidated to massive limonite, impregnating sands, silts and gravels, and was mined from the 1700's to 1850's (Bayley, 1910; Braddock-Rodgers, 1930; Pierce, 1957; Starkey, 1962). The geochemistry of these deposits has been described in detail elsewhere (Crerar et al., 1979), and is only briefly outlined here. It is generally thought that bog iron forms by precipitation of ferric oxides when Fe-charged groundwaters surface, oxidize and lose CO2. In the Pine Barrens, Crerar et al. (1979) have argued for a more complicated process requiring bacterial catalysis. Their argument is based on the following observations: (1} Surface waters and freshly precipitated oxides harbor an abundant

0.2 ~m

0.08 ~m

0.03 ~m

Ultracentrifugation

121 58

104 56

100 53

113 71

36 microflora of iron-oxidizing bacteria including Thiobacillus ferrooxidans, Leptothrix ochracea, Crenothrix polyspora, Siderocapsa geminara, Metallogenium or Gallionella sp., and possibly Naumanmlla and Toxothrix sp. (2) Bacteria-like microscopic structures are preserved throughout the bog iron itself. (3) Iron precipitation is markedly seasonal, being most pronounced in warmer months when bacterial counts are highest. (4) Fe is actually less saturated in shallow than in deep groundwaters sampled from this area. (5) Abiotic oxidation of ferrous to ferric ion is almost impossibly slow at the acidic pH of these surface waters. However, oxidation rates can be increased up to six orders of magnitude by microbial activity (Stumm and Lee, 1961; Singer and Stumm, 1970). (6) The bog iron is strongly depleted in trace metals relative to the water from which it is precipitating, suggesting a mechanism (such as enzymatic bacterial catalysis) which is highly selective for Fe. DISCUSSION: THE ESTUARINE ENVIRONMENT

Trace metals and organic--metallic interactions From September 1976 to April 1978 we monitored Fe, A1, Mn, Zn, Cu, Pb, Cd, Si and C1 concentrations together with Eh and pH at five different stations in the Cedar Creek estuary and at three sites in the estuary of the Mullica River. Trace metals other than Fe and A1 are slightly more concentrated in estuary than in river waters (see Table I). These concentrations remain relatively uniform throughout the estuary and may be attributed in part to increased human activity at nearby marinas and residences. Si also remains relatively constant at ~ 5 ppm, varying little from its concentration in rivers. On the other hand, both "dissolved" (0.2-/~m Nucleopore ® filtered) Fe and A1 decrease dramatically with increasing Cl concentration o u t into each estuary -- see also Coonley et al. (1971) and Boyle et al. (1977). Theoretical equilibrium solubilities of Fe relative to amorphous Fe(OH)3 and of Al relative to gibbsite, kaolinite and halloysite were calculated for various estuarine conditions, using the same methods described for river water. These calculations demonstrate that estuary waters are generally supersaturated in both metals, unlike their associated rivers (see Table II). The degree of supersaturation varies with Eh, pH and ionic strength within each estuary, but is usually around 1--2 orders of magnitude. Since the calculations consider only inorganic species, it is possible that most of the estuarine Fe and A1 less than 0.2/~m in size is organically complexed or present as small o x y h y d r o x i d e and organo-metallic colloids.

37 The flocculation of Fe and Al in the estuarine environment The flocculation of stream-borne dissolved and colloidal materials within estuaries has been the subject of m a n y recent investigations. Coonley et al. (1971) and Boyle et al. {1977) showed that up to 96% of river-water Fe is flocculated in the Mullica River estuary. Sholkovitz (1976) used mixing experiments to illustrate the removal of Fe, Mn, A1, P and humic substances from Scottish river waters. More recently, it has been shown that Cu, Ni, and to a lesser extent, Co and Cd are removed along with colloidal humic substances and hydrous iron oxides (Sholkovitz, 1978) in Scottish estuaries. Similar flocculation of Fe has been observed in the Gulf of St. Lawrence (Bewers et al., 1974), the Beaulieu estuary, southern England (Moore et al., 1979), Chesapeake Bay (Carpenter et al., 1975), and in several southeastern U.S.A. localities (Windom et al., 1971; Windom, 1975). Even though there is a b u n d a n t evidence for the removal of Fe in estuaries, the exact flocculation mechanism remains unclear. Sholkovitz (1979) attributes variations in the chemistry of the suspended load in the Tay estuary, Scotland to sedimentological and hydrological processes, rather than chemical ones. Windom et al. {1971) suggest that dissolved Fe is precipitated as oxyhydroxides with increasing pH. Others propose that increased ionic strength is the prime control (Ong and Bisque, 1968; Ong et al., 1970; Sholkovitz, 1976; Boyle et al., 1977). These last four papers also suggest that organic matter plays an important role in the removal of Fe and other metals an explanation that is not substantiated by the authors' studies. The authors' field data, like that of Coonley et al. (1971) and Boyle et al. (1977), for the Mullica River estuary clearly demonstrate that "dissolved" (<0.2 gm) Fe is being removed at a rate far beyond that predicted by simple mixing with seawater. The same observation holds for Fe in Cedar Creek and for A1 in both the Mullica River and Cedar Creek (e.g., Fig. 4). The present authors have tested various mechanisms for removal of Fe and A1 in estuary waters, using mixing experiments similar to those of Eckert and Sholkovitz (1976). Varying concentrations of CaC12, MgC12, or NaC1 were added to unfiltered Mullica River samples collected upstream from any saltwater influence. Additional samples containing no electrolyte were adjusted to pH 8.3 with NaOH to compare the relative effect of pH and ionic strength. Several samples were left completely untreated as blanks. After several days a rust-colored precipitate collected in those samples to which salt had been added, while no visual change was apparent in the blanks and pH-adjusted samples. Unfiltered supernatant was carefully drawn off from each sample and analyzed for Fe, Al and organic carbon. Typical results of such mixing experiments for Fe and Al are illustrated in Fig. 5. Results for both metals are similar, although initial concentrations of A1 are considerably lower. The 1:2 salts MgC12 and CaC12 cause more rapid removal of trace metals than NaC1, and the rate of flocculation increases rapidly at relatively low ionic strength, leveling out at higher concentrations. -

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39 The above field and laboratory data support previous observations that Fe, A1 and Mn are precipitated as destabilized colloids when river waters mix with seawater. Whereas Fe and A1 are approximately saturated or undersaturated in river water, both metals become markedly supersaturated in the adjoining estuaries and should precipitate from solution as o x y h y d r o x i d e flocs. Previous studies have concluded that most of the "dissolved" Fe in the Pine Barrens consists of mixed iron oxide--organic matter colloids, and that flocculation of Fe in the estuary is caused when hydrophilic and negatively-charged Fe-organic colloids react with seawater cations to form hydrophobic colloids, which then precipitate (Sholkovitz, 1976; Boyle et al., 1977). The mixing experiments of Sholkovitz (1976) and of this study show clearly that ionic strength, as opposed to pH, is the principal cause of Fe and A1 removal. However, in all the mixing experiments involving Pine Barrens water conducted thus far, almost all of the dissolved Fe and A1 are removed while only ~0--20% o f the dissolved organic matter (DOM) is flocculated. A second question concerns the physical and chemical state of "dissolved" (<0.2 pm) Fe in Pine Barrens surface waters before it empties into the estuaties. Previous investigators have observed that river-borne "dissolved" Fe consists almost entirely of mixed iron oxide--organic matter colloids. The filtration, GFC and SEM data presented above suggest that abundant mixed oxide-organic colloids do exist, but also that a significant proportion of Fe and A1 in Pine Barrens waters may be truly dissolved. For example, over 50% of the Fe and Al in the samples analyzed was not removed by filtration down to even 0.03 pm (Table V). GFC data suggest that only 10--20% of the <0.2 pm Fe in normal Pine Barrens stream waters (containing 2--~ ppm DOM) was organically-complexed; the other 80+% appeared to be present as a cationic species. In fact, the theoretical solubility data for Fe and Al predict significant concentrations of the species Fe 2÷ and A13+ in these acidic waters. The picture that is emerging is that Fe and A1 in the <0.2-pm size fraction of natural waters comprise a complex mixture of species, including organic com. plexes, o x y h y d r o x i d e colloids, oxyhydroxides admixed with organic colloids~ and true inorganic solution species such as Fe 2. and Al 3÷. The total concentration and relative abundances of these species depend on the water chemistry, the most important variables being pH, Eh, and the chemical composition of the DOM present. In typical, unaltered Pine Barrens stream water < 0.2-pm Fe appears to be ~ 45% dissolved inorganic species, 10% soluble organic complexes, and 45% colloidal o x y h y d r o x i d e and oxyhydroxides admixed with colloidal organic matter. Filtered A1 appears to be ~ 45% dissolved inorganic species and 55% o x y h y d r o x i d e and o x y h y d r o x i d e plus colloidal organics. Some of the A1 is probably organically complexed (e.g., see Reuter and Perdue, 1977), though this was not confirmed in our GFC analyses. Upon entering the estuary, dissolved inorganic Fe and A1 become supersaturated and precipitate as colloids or larger flocs. Pre-existing o x y h y d r o x i d e colloids grow in size and flocculate, and the least soluble organics such as the higher-molecularweight humic acids with higher C/O ratios also flocculate. Therefore the DOM,

40 Fe and Al t h a t precipitate are n o t nece~arily chemically associated with each other, but they do appear to be removed by a c o m m o n mechanism -- flocculation by electrolyte. The flocculation of Fe, Al and DOM may also affect the chemical behavior of other trace metals. For example, Sholkovitz (1978) reports that varying amounts of Cu, Ni, Co, Cd and Mn are removed in several Scottish estuaries. In this case the basic removal mechanism appears to be sorption onto the precipitating humic acids and Fe- and Al-oxyhydroxides. The present authors conclude that estuarine flocculation processes vary from estuary to estuary. Certain elements may quantitatively precipitate in one estuary, but remain in solution in another. The species and amounts of trace elements that flocculate will depend upon the chemistry of the river and estuary water, especially the Eh, pH, and the chemical composition of DOM present. The chemical composition of Pine Barrens DOM is important in that only the least-soluble organic constituents flocculate. The more soluble species remain in solution in even full-strength seawater. In the Amazon River, humic acid comprises less than 10% of total DOM. 60--80% of the humic acid precipitates in the estuary while other organic components remain in solution. This represents a removal of only 3--6% of the total DOM (Sholkoritz et al., 1978). In the Pine Barrens, humic acid comprises ~40% of the total DOM; however, only ~ 25% of the HA, or ~ 10% of total DOM is removed in the estuary. Even though 40% of the DOM is humic acid, Pine Barrens HA contains somewhat more oxygen than is typical for other localities (Table III), giving it greater aqueous solubility. In other settings, such as watersheds draining chernozems or chestnut soils, one might expect the flocculation of nearly all of the humic acid present. Humic acid from these settings is generally depleted in oxygen and is therefore less soluble. Finally, even though most Fe flocculates in the estuarine zone, surprisingly little is incorporated into b o t t o m sediments. Coonley et al. (1971) analyzed sediment cores from the Mullica River estuary and concluded that most ferric precipitates must be carried out to sea by tidal currents. It is not known how far this material travels nor how much ultimately reaches the open ocean. Furthermore, the dominance of colloidal material calls into question the published residence times of metallic elements in the oceans. Boyle et al. {1977) have identified a number of problems involved in calculating the mean residence time or Fe in seawater from primary river input. These objections are supported by the present data, and may be extended to include AI and possibly other metallic elements. Almost all stream-borne Fe and A1 flocculates within estuaries. It is n o t y e t known what fraction of this precipitate ultimately reaches the open ocean. The behavior of many other trace metals may follow t h a t of Fe and Al, being also governed to varying degrees by adsorption and coprecipitation reactions (e.g., Jenne, 1968; Turekian, 1977}. Hence oceanic residence times of Fe and Al as well as associated trace metals cannot be accurately calculated from river input data at the present time.

41

SUMMARY AND CONCLUSIONS The Pine Barrens region of the New Jersey Coastal Plain includes the largest tract of forest and one of the largest water reserves on the east coast of the U.S.A. between Boston and Washington, D.C. The area is largely undeveloped, and its waters are for the most part pristine and unpolluted. Drainage basins are underlain throughout by the comparatively uniform sands and gravels of the Pliocene--Miocene Cohansey and Kirkwood Formations. Because of the relative simplicity of the overall system, the waters of this region lend themselves well to geochemical study and interpretation. This paper and Part 1 of the series (Yuretich et al., 1981) cover the major geochemical controls on the complete hydrologic system including precipitation, surface, ground- and estuary waters. In this study we have measured baseline concentrations of Fe, A1, Cd, Cu, Pb, Zn, Mn and organic carbon in groundwater, stream and estuary samples. Glauconite-bearing formations of Early Tertiary and Late Cretaceous ages which underlie the area appear to be the most likely source of trace metals in these waters. Solubility calculations suggest that streams and groundwaters are roughly saturated or undersaturated in Fe and A1 with respect to amorphous Fe(OH)3 and gibbsite, and that estuaries are generally 1--2 orders of magnitude supersaturated in both metals. About half of the stream-borne Fe and Al is carried as filterable colloidal particles of oxyhydroxides or oxyhydroxide mixed with organic material. The natural organic substances which together with Fe give Pine Barrens stream waters their striking tea-brown color consist primarily of humic and fulvic acids with a somewhat higher than normal oxygen content and degree of aromatization. Gel filtration chromatography analyses of typical surface waters (2--5 ppm organic C) show that from 10% to 20% of the total dissolved Fe is associated with humic substances. This figure increases to 60--70% in waters containing over 10 ppm dissolved organic carbon. Iron precipitates in swamps and streams of this area as thin o x y h y d r o x i d e coatings and flocs and also as more massive limonitic bog iron deposits. At least five species of Fe-oxidizing bacteria actively catalyze precipitation of these deposits. Field analyses and laboratory mixing experiments have shown that Fe and A1 are precipitated quantitatively within the estuaries. Only a small proportion of total dissolved organic carbon is removed in the same environment. Coagulation by electrolytes such as NaCl, MgC12 and CaC12 is the principal control on flocculation. The flocculation of stream-water'constituents is now a widely observed phenomenon. However, the a m o u n t and type of materials that are precipitated depend on stream and estuary water chemistry, especially Eh, pH, and the chemical composition of the DOM present.

42 ACKNOWLEDGEMENTS

The authors wish to thank Kemble Widmer and the New Jersey Bureau of Geology and Topography for encouragement and support of this research. Beryl Baldwin provided much appreciated assistance with the many chemical analyses. The authors also thank C. Melton and J. Ogden for providing the SEM--energy-dispersive X-ray analyses. Battelle's Columbus Laboratories supported the preparation of the final manuscript.

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44 Singer, P.C. and Stumm, W., 1970. Acidic mine drainage: the rate-determining step. Science, 167: 1121--1123.

Starkey, Jr., J.A., 1962. The bog ore and bog iron industry of South Jersey. Bull. N.J. Acad. Sci., 7: 5--8. Stevenson, F.J. and Butler, J.H.A., 1969. Chemistry of humic acids and related pigments. In: G. Eglinton and M.T.J. Murphy (Editors), Organic Geochemistry, Springer, New York, N.Y., pp. 534--557. Stevenson, F.J. and Goh, K.M., 1971. Infrared spectra of humic acids and related substances. Geochim. Cosmochim. Acta, 35: 471--483. Stumm, W. and Lee, G.F., 1961. Oxygenation of ferrous iron. Ind. Eng. Chem., 53: 1 4 3 146. Truesdell, A.H. and Jones, B.F., 1974. WATEQ, a computer program for calculating chemical equilibria of natural waters. J. Res. U.S. Geol. Surv., 2: 233--248. Turekian, K.K., 1977. The fate of metals in the oceans. Geochim. Cosmochim. Acta. 41~ 1139--1144. Windom, H.L., 1975. Heavy metal fluxes through salt-marsh estuaries. In: L.E. Cronin (Editor), Estuarine Research, Vol. 1. Academic Press, New York, N.Y., pp. 137--152. Windom, H.L., Beck, K.C. and Smith, R., 1971. Transport of trace metals to the Atlantic ocean by three southeastern streams. Southeast. Geol., 12: 169--181. Yuretich, R.F., Crerar, D.A., Kinsman, D.J.J., Means, J.L. and Borcsik, M.P., 1981. Hydrogeochemistry of the New Jersey Coastal Plain, 1. Major-element cycles in precipitation and river water. Chem. Geol., 3 3 : 1 - - 2 1 (this issue).