Environmental Chemistry of Lakes and Reservoirs - American

10 Retention of Sulfur in Lake Sediments

Downloaded by UNIV OF TEXAS AT DALLAS on July 12, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0237.ch010

N. R. Urban Lake Research Laboratory, Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG/ETH), CH-6047 Kastanienbaum, Switzerland

Measurements of S cycling in Little Rock Lake, Wisconsin, and Lake Sempach, Switzerland, are used together with literature data to show the major factors regulating S retention and speciation in sediments. Retention of S in sediments is controlled by rates of seston (planktonic S) deposition, sulfate diffusion, and S recycling. Data from 80 lakes suggest that seston deposition is the major source of sedimentary S for approximately 50% of the lakes; sulfate diffusion and subsequent reduction dominate in the remainder. Concentrations of sulfate in lake water and carbon deposition rates are important controls on diffusive fluxes. Diffusive fluxes are much lower than rates of sulfate reduction, however. Rates of sulfate reduction in many lakes appear to be limited by rates of sulfide oxidation. Much sulfide oxidation occurs anaerobically, but the pathways and electron acceptors remain unknown. The intrasediment cycle of sulfate reduction and sulfide oxidation is rapid relative to rates of S accumulation in sediments. Concentrations and speciation of sulfur in sediments are shown to be sensitive indicators of paleolimnological conditions of salinity, aeration, and eutrophication.

S U L F U R FULFILLS MANY DIVERSE ROLES in lakes. As the sixth most abundant element in biomass, it is required as a major nutrient by all organisms. For most algae, S is abundant in the form of sulfate in the water column; however, in dilute glacial lakes in Alaska (J) and in some central African lakes (2) low concentrations of sulfate may limit primary production. Sulfur also serves the dual role of electron acceptor for respiration and, in reduced forms, source of energy for chemolithotrophic secondary production. Net sulfate reduction can account for 10-80% of anaerobic carbon oxidation in lakes (3-5), and hence this process is important in carbon and energy flow. Sulfate reduction, whether associated with uptake of sulfate and ineorpo-

0065-2393/94/0237-0323$ 12.75/0 © 1994 American Chemical Society Baker; Environmental Chemistry of Lakes and Reservoirs Advances in Chemistry; American Chemical Society: Washington, DC, 1994.


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ration into biomass (assimilatory reduction) o r w i t h anaerobic r e s p i r a t i o n (dissimilatory reduction), generates a l k a l i n i t y . I n m a n y d i l u t e lakes this source of alkalinity is i m p o r t a n t as a means o f n e u t r a l i z i n g acid d e p o s i t i o n (e.g., 6, 7). Sulfide p r o d u c e d t h r o u g h d i s s i m i l a t o r y sulfate r e d u c t i o n c a n alter t h e c y c l i n g a n d availability o f nutrients, trace metals, a n d radioisotopes (e.g., 8-10) as w e l l as b e toxic to organisms. I n a d d i t i o n to d i r e c t a n d i n d i r e c t effects o f sulfur, a d d i t i o n a l processes are m e d i a t e d b y s u l f u r - u t i l i z i n g bac teria. S u l f a t e - r e d u c i n g bacteria may b e capable of m e t h y l a t i n g trace metals such as m e r c u r y a n d t i n , o x i d i z i n g methane, a n d l i m i t i n g m e t h a n e p r o d u c t i o n b y c o m p e t i t i o n for electron donors (e.g., 11-14). T h e n u m e r o u s possible c h e m i c a l a n d b i o l o g i c a l reactions o f sulfur together w i t h t h e effects o f these reactions o n n u m e r o u s other elements r e n d e r the c y c l i n g o f S i n lakes b o t h important and complex. S e d i m e n t profiles o f t h e forms a n d rates o f a c c u m u l a t i o n o f sulfur have b e e n u s e d i n b o t h freshwater a n d m a r i n e systems as indicators o f past c o n ditions. O v e r geologic times, sulfate r e d u c t i o n has p l a y e d a major role i n g o v e r n i n g the carbon a n d oxygen balance of the atmosphere a n d i n r e g u l a t i n g global climate (e.g., 15-19). T h e r e c o r d o f these c h a n g i n g c o n d i t i o n s is p r e s e r v e d i n t h e p y r i t e deposits i n m a r i n e sediments. C h a n g i n g c o n d i t i o n s of salinity, p r i m a r y p r o d u c t i v i t y , a n d oxygenation o f b o t t o m waters are s i m i l a r l y r e c o r d e d i n s e d i m e n t profiles of sulfur species a n d isotopic c o m p o s i t i o n (e.g., 20-22). I n lake sediments, changes i n sulfur content a n d speciation have b e e n i n t e r p r e t e d as i n d i c a t i v e of changes i n t r o p h i c status (e.g., 23-25), inputs o f acid d e p o s i t i o n (e.g., 26-30), a n d inputs o f salt water (21). Interpretation of s e d i m e n t stratigraphy can b e c o m p l i c a t e d b y diagenetic reactions that alter the o r i g i n a l p r o f i l e . F o r instance, reactions o f sulfur w i t h organic matter have b e e n s h o w n to alter stratigraphie records o f organic b i o m o l e c u l e s (e.g., 31-33). S u c h diagenetic alterations can l e a d to erroneous interpretations o f s e d i m e n t a r y profiles. D i f f u s i o n o f sulfate into sediments can lead to zones of sulfur i n c o r p o r a t i o n that are not contemporaneous w i t h s e d i m e n t d e p o s i t i o n i n the same zones (e.g., 2 1 , 2 8 , 34). O r g a n i c sulfur f r o m p l a n k t o n can b e transformed into inorganic forms (e.g., 3 5 - 3 8 ) . C l e a r l y , a t h o r o u g h u n d e r s t a n d i n g o f t h e processes c o n t r o l l i n g r e t e n t i o n o f sulfur i n sediments as w e l l as an u n d e r s t a n d i n g o f diagenetic transformations w i t h i n sediments are prerequisites for i n t e r p r e t a t i o n o f stratigraphie records o f sulfur i n lake sediments. T h i s chapter uses n u m e r o u s measurements o f sulfur speciation i n lake sediments a n d recent research to clarify the factors that regulate r e t e n t i o n of sulfur i n lake sediments, t h e possible diagenetic alter ations, a n d the areas o f u n c e r t a i n t y that c o n t i n u e to i m p e d e o u r a b i l i t y to i n t e r p r e t s e d i m e n t stratigraphy.

Forms, Abundance, and Patterns of S in Sediments S u l f u r t y p i c a l l y is e n r i c h e d i n lake sediments ( 3 0 0 - 6 4 , 0 0 0 μg/g) relative to crustal materials ( 3 0 - 2 7 0 0 μg/g; 39, 40) a n d surface soils ( 5 0 - 2 0 0 0 μg/g;

Baker; Environmental Chemistry of Lakes and Reservoirs Advances in Chemistry; American Chemical Society: Washington, DC, 1994.


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41-45). I n some lakes S content a n d S : C ratios can exceed values t y p i c a l of m a r i n e sediments (46, 47), although this abundance tends to b e t h e ex c e p t i o n rather than the r u l e (9, 20). I n 53 o f 72 lakes for w h i c h data are available, concentrations o f S are h i g h e r i n surface (recent) sediments than i n d e e p e r (background) sediments. T h i s contrast has b e e n v a r i o u s l y attrib u t e d to e u t r o p h i c a t i o n , air p o l l u t i o n , a n d diagenesis (e.g., 7, 23-27, 29, 30, 48, 49). Differences i n s e d i m e n t a r y S content a m o n g lakes have b e e n at t r i b u t e d to differences i n lake-water sulfate concentrations, s e d i m e n t i r o n content, a n d s e d i m e n t organic c a r b o n content (24, 26, 30, 50, 51). H o w e v e r , none o f these factors i n d i v i d u a l l y can r e l i a b l y p r e d i c t t h e S content o f lake sediments ( F i g u r e 1). I n lake sediments sulfur exists i n b o t h organic a n d inorganic forms. Inorganic species i n c l u d e H S , i r o n monosulfides (i.e., those w i t h F e : S ratios close to 1, i n c l u d i n g amorphous F e S , (hydro)troilite, m a c k i n a w i t e , p y r r h o tite, a n d greigite), p y r i t e or marcasite, a d s o r b e d o r d i s s o l v e d S O / , e l e m e n t a l sulfur (S°), polythionates, a n d a variety o f soluble i o n i c species ( S 0 ~ , S 0 ~, S„~, a n d S 0 ~ ) . I n saline lakes g y p s u m o r a n h y d r i t e m a y be present. T h e d o m i n a n t species t y p i c a l l y are t h e monosulfides a n d p y r i t e . M o n o s u l f i d e s are i d e n t i f i e d analytically b y d e c o m p o s i t i o n w i t h n o n o x i d i z i n g acid a n d f r e q u e n t l y are c a l l e d acid-volatile sulfides (AVS). P y r i t e a n d S ° f r e q u e n t l y are analyzed together b y the c h r o m i u m - r e d u c t i o n t e c h n i q u e o f Z h a b i n a a n d V o l k o v (52) a n d r e f e r r e d to j o i n t l y as c h r o m i u m - r e d u c i b l e sulfur ( C R S ) . O r g a n i c S c o m p o u n d s are f o u n d a m o n g p r o t e i n s , polysaccharides, a n d l i p i d s ; t h e y i n c l u d e thiols, disulfides, t h i o p h e n e s , thiolanes, sulfones, a n d sulfoxides. Several volatile species exist [ d i m e t h y l sulfide ( D M S ) , m e t h a n e t h i o l ( M S H ) , a n d c a r b o n y l sulfide ( C O S ) ] , a n d m a n y species r e m a i n to be i d e n t i f i e d . A n a l y t i c a l l y , organic S f r e q u e n t l y is d i v i d e d into t w o groups: c a r b o n - b o n d e d S a n d ester sulfates. C a r b o n - b o n d e d S m a y b e a n a l y z e d b y desulfurization w i t h R a n e y n i c k e l , b u t this i n c l u d e s a v a r i e t y o f f u n c t i o n a l groups. Questions r e m a i n about the specificity a n d c o m p a r a b i l i t y o f h y d r i o d i c a c i d r e d u c t i o n a n d a c i d h y d r o l y s i s , the t w o t e c h n i q u e s u s e d to ana l y z e ester sulfates (41, 53, 54). Because o f a lack o f suitable analytical t e c h n i q u e s , most o f t h e organic S i n sediments has not b e e n c h a r a c t e r i z e d . 2

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A w i d e variation is o b s e r v e d i n relative a n d absolute abundances of different S species i n lake sediments. T h e fraction o f s e d i m e n t a r y S i n inorganic forms ranges f r o m 0 to 9 9 % . T h e relative i m p o r t a n c e o f A V S a n d C R S , the d o m i n a n t inorganic species, also varies w i d e l y (ratios o f A V S : C R S range f r o m 0.01 to 100). C o n c e n t r a t i o n s o f free H S greater than 100 μιτιοΙ/L occur o n l y i n pore waters i n lakes w i t h extensive o r p e r m a n e n t l y anoxic h y p o l i m n i a (e.g., 55, 56). E l e m e n t a l S occurs i n l o w c o n centrations; i n o r g a n i c - r i c h sediments the concentrations t y p i c a l l y are less than 5 μιτιοΐ/g (25, 27, 30). I n m o r e i n o r g a n i c sediments o r i n sediments u n d e r layers o f S - o x i d i z i n g bacteria, concentrations o f S° c a n reach 280 μΐΏθΙ/g (27, 56, 57). Thiosulfate, polythionates, a n d polysulfides are reactive intermediates present i n l o w concentrations (57, 58). E s t e r sulfates t y p i c a l l y 2



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Figure 1. Data from the literature indicate that S concentrations in surface lake sediments are poorly correlated with A, lake-water sulfate concentrations (104 lakes); B, sediment carbon content (78 lakes); or C, sediment iron content (22 lakes). Sulfur concentrations in lake sediments typically are lower than concentrations in marine sediments of comparable carbon content (upper line in B). The lower line in Β represents the average C:S ratio (55) reported in seston (59, 72, 27, 56, IS). Most of the lake sediments reported in the literature have more iron than sulfur. (Data are from references 24-30, 34, 48-51, 55-57, 59-61, 71, 104, 112, 199, 205, 222, and 223.)

Lakewater [SO^ "] ( μ ι η ο Ι / L )

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represent 3 0 - 6 0 % of the total organic S (51, 59-61). T h i s chapter seeks to identify c o m m o n patterns o f S speciation a n d the e n v i r o n m e n t a l variables a n d processes responsible for t h e m .


Processes Causing Observed Patterns Storage of sulfur i n lake sediments results f r o m c y c l i n g of S i n the lake water a n d postdepositional diagenetic processes i n sediments. T h e major features of S c y c l i n g i n lakes are w e l l k n o w n . S u l f u r is a m a c r o n u t r i e n t ; uptake b y p h y t o p l a n k t o n a n d subsequent b u r i a l of organic S i n sediments o c c u r i n a l l lakes (23, 62, 63). Putrefaction o f organic S releases H S (as w e l l as trace amounts o f other S gases; 64-66) that is e i t h e r fixed i n sediments as i r o n sulfides, lost to the atmosphere v i a diffusion o r e b u l l i t i o n , o r o x i d i z e d . A p a r t f r o m d e p o s i t i o n of organic matter, sulfate r e d u c t i o n is the o t h e r major source of S f o u n d i n sediments. D i s s i m i l a t o r y s u l f a t e - r e d u c i n g bacteria use S Ô ~ as an electron acceptor to p r o d u c e H S . A s for H S p r o d u c e d i n algal d e c o m p o s i t i o n , this r e d u c e d S m a y be e i t h e r f i x e d i n sediments as i r o n sulfides o r organic c o m p o u n d s , o r it m a y b e r e o x i d i z e d b y o x y g e n , m e t a l oxides, o r bacteria. A large n u m b e r o f bacterial types (green, p u r p l e , c o l orless, a n d blue-green) that can oxidize H S have b e e n r e c o g n i z e d for some t i m e (e.g., 67-69). T h e amounts a n d patterns o f S forms i n sediments w i l l d e p e n d , therefore, o n relative rates of seston d e p o s i t i o n , sulfate r e d u c t i o n , putrefaction, r e c y c l i n g to the lake water, a n d diagenetic i n t e r c o n v e r s i o n s o f S species. 2

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Deposition, Putrefaction, and Recycling of Seston Sulfur. U p take b y algae a n d subsequent s e d i m e n t a t i o n is a major flux of S w i t h i n lakes. S u l f u r is r e q u i r e d b y organisms for f o r m a t i o n o f p r o t e i n s , structural p o l y saccharides, sulfolipids, osmotic regulators, a n d c o e n z y m e s . C o n c e n t r a t i o n s of S i n algae vary considerably ( < l - 2 0 mg/g corresponds to C : S ratios (mass basis) o f 2 2 - 2 7 2 ; 70, 71 ), b u t do not appear to be i n f l u e n c e d b y concentrations of S 0 ~ i n lake water ( I , 72). A significant fraction o f algal S occurs i n n o n p r o t e i n forms such as sulfate esters (59, 73-75), b u t there has b e e n n o systematic study of the structure a n d f u n c t i o n of these c o m p o u n d s i n freshwater algae. S u l f u r generally is taken u p b y algae as sulfate, a l t h o u g h bacteria a n d some b l u e - g r e e n algae can u t i l i z e h y d r o g e n sulfide (76). I n most lakes sulfate is not a l i m i t i n g n u t r i e n t , a n d concentrations o f sulfate i n the water are not greatly affected b y algal g r o w t h . Q u a n t i t i e s taken u p b y p l a n k t o n generally are less than 6 % of the sulfate p o o l i n the water c o l u m n (73, 77). Some fraction o f p l a n k t o n i c S is released i n t h e water c o l u m n as H S or other volatile S c o m p o u n d s (65, 66), a n d t h e r e m a i n d e r settles to t h e sediments, w h e r e it is c a l l e d seston. K i n g a n d K l u g (73) calculated that particulate matter (seston) c o l l e c t e d i n s e d i m e n t traps h a d lost 6 0 - 7 5 % o f the p r o t e i n S present i n algae. A l t h o u g h n o change i n S content o r c o m 4

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position was n o t e d a m o n g seston samples c o l l e c t e d f r o m traps at 5-, 8-, a n d 15-m depths i n S o u t h L a k e (59), L o s h e r (56) m e a s u r e d a large progressive decrease i n total S content f r o m p l a n k t o n (8 mg/g) to seston c o l l e c t e d at 4 0 - m d e p t h (6 mg/g) to seston c o l l e c t e d at 150-m d e p t h (4 mg/g) i n L a k e Z u r i c h . R e l a t i v e p r o p o r t i o n s of c a r b o n - b o n d e d S d e c l i n e d i n this sequence, a n d c o n t r i b u t i o n s f r o m inorganic a n d ester S increased. E x i s t i n g m e a s u r e ments of S i n seston c o l l e c t e d i n s e d i m e n t traps (herein t e r m e d seston deposition) show a m u c h smaller range of S concentrations than i n algae ( 0 . 4 - 1 4 mg/g; 27, 59, 62, 72, 78), b u t a large range i n C : S ratios ( 9 - 1 0 5 mass basis). F l u x e s of S i n seston d e p o s i t i o n ( 3 1 - 2 6 6 m m o l / m p e r year; 59, 72, 73) thus are c o n t r o l l e d b y the m a g n i t u d e of p r i m a r y p r o d u c t i o n , r e c y c l i n g of S w i t h i n the water c o l u m n , a n d the u n k n o w n factors r e g u l a t i n g S content of seston.


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D e c o m p o s i t i o n of seston a n d r e c y c l i n g of sulfur f r o m sediments r e m a i n p o o r l y u n d e r s t o o d . A s s u m i n g that there is no source except seston for the organic S i n sediments, K i n g a n d K l u g (73) calculated that 7 5 % of p r o t e i n S, 4 2 % of ester S, a n d 4 6 % of total S was m i n e r a l i z e d i n sediments of W i n t e r g r e e n L a k e . O n the basis of s i m i l a r mass-balance calculations, 4 3 % of ester S a n d 2 6 % of total S was estimated to b e m i n e r a l i z e d i n S o u t h L a k e (59) a n d 6 0 % of total S i n L a k e M e n d o t a (25). T h e a s s u m p t i o n that a l l organic S i n sediments is d e r i v e d f r o m seston is not v a l i d i n m a n y lakes because m u c h s e d i m e n t S is d e r i v e d from the reaction of sulfide w i t h organic matter (72, 79, 80); thus the foregoing estimates p r o b a b l y u n d e r e s t i m a t e the extent of r e c y c l i n g . C o r r e c t i n g for other sources of organic S, B a k e r et a l . (72) estimated that 8 0 % of total seston S is r e m i n e r a l i z e d i n L i t t l e R o c k L a k e . N o estimates of hydrolysis of sulfate esters are c o r r e c t e d for i n situ f o r m a t i o n (cf. 79). D i r e c t m e a s u r e m e n t of putrefaction is p r o b l e m a t i c . I n laboratory m i crocosms i n w h i c h r a d i o l a b e l e d ( S) algae w e r e a l l o w e d to settle a n d decay o n top of lake sediments, a net release of less than 5 % of the S to the w a t e r c o l u m n was o b s e r v e d , a n d a l l release o c c u r r e d w i t h i n the first 2 weeks (38). H o w e v e r , o n g o i n g m i c r o b i a l uptake of sulfate f r o m the w a t e r c o l u m n m a y have o b s c u r e d f u r t h e r release. M a x i m a l p o t e n t i a l rates of cystine degradation w e r e estimated b y Jones et a l . (81) to range f r o m 0.001 to 50 μιτιοΙ/L p e r day i n B l e l h a m T a r n sediments a n d b y D u n n e t t e (82) to range f r o m 28 to 47 μιηοΙ/L p e r day i n sediments f r o m two lakes. S i m i l a r m e a s u r e m e n t s of potential rates o f hydrolysis o f sulfate esters (83) t r e m e n d o u s l y o v e r e s t i m a t e d the rates calculated b y mass balance to o c c u r i n sediments of W i n t e r g r e e n L a k e (73). A b e t t e r u n d e r s t a n d i n g of putrefaction is n e e d e d to p r e d i c t re t e n t i o n a n d concentrations of S i n sediments. 35

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Sulfate Reduction. D i s s i m i l a t o r y sulfate r e d u c t i o n , anaerobic res p i r a t i o n w i t h sulfate as the t e r m i n a l e l e c t r o n acceptor, is p e r f o r m e d b y relatively f e w genera of bacteria (84). M a n y bacteria a n d algae are able to


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r e d u c e sulfate for purposes o f assimilation, a n d several genera are able to r e d u c e e l e m e n t a l S, S 0 ~ , a n d S 0 ~ . S u l f a t e - r e d u c i n g bacteria m a y use a variety o f e l e c t r o n donors, i n c l u d i n g sugars, fatty acids, a n d h y d r o g e n (4, 1 3 , 8 4 - 8 8 ) . Q u a n t i t a t i v e l y , acetate a n d h y d r o g e n are the most i m p o r t a n t o f these donors (4, 13, 87, 89, 90).


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Sulfate r e d u c t i o n yields less energy than r e s p i r a t i o n w i t h oxygen, n i trate, manganese, o r i r o n as t h e t e r m i n a l e l e c t r o n acceptor. H e n c e , t h e r m o d y n a m i c s p r e d i c t that i t s h o u l d occur o n l y after alternate e l e c t r o n acceptors have b e e n r e d u c e d to l o w concentrations b u t above t h e zone o f methanogenesis (91). R e c e n t l y , h o w e v e r , aerobic sulfate r e d u c t i o n was r e p o r t e d (92, 93). M o r e typically, oxygen a n d nitrate are c o n s u m e d w i t h i n sediments above 0 . 5 - 1 0 c m , t h e d e p t h at w h i c h sulfate is c o n s u m e d . L o w availability o f solid-phase i r o n a n d manganese oxides can result i n r e d u c t i o n of these species i n the same zone as sulfate r e d u c t i o n (e.g., 94, 95). K i n e t i c s of substrate uptake, m i c r o b i a l g r o w t h , a n d mass transfer as w e l l as t h e r m o d y n a m i c s d e t e r m i n e w h e t h e r sulfate r e d u c t i o n w i l l occur together w i t h other modes of anaerobic r e s p i r a t i o n . H i g h affinity for b o t h carbon substrates and electron acceptors allows i r o n - r e d u c i n g bacteria to c o m p e t i t i v e l y e x c l u d e sulfate reducers (96, 97) a n d also allows sulfate reducers to o u t c o m p e t e methanogens (4, 13, 87). T h e s e c o m p e t i t i v e interactions are i m p o r t a n t not only because they p r o m o t e extensive anaerobic degradation of organic matter (84, 89), b u t also because they d e t e r m i n e the diffusive flux o f sulfate into sediments b y r e g u l a t i n g the d e p t h at w h i c h sulfate r e d u c t i o n occurs (4, 90). Occurrence and Rates of Sulfate Reduction. Sulfate r e d u c t i o n is w i d e s p r e a d i n lakes, as e v i d e n c e d b y d e p l e t i o n o f sulfate i n s e d i m e n t p o r e waters. P o r e - w a t e r profiles s h o w i n g d e p l e t i o n of sulfate have b e e n p u b l i s h e d for m o r e than 35 lakes (e.g., 98, 99). A n absence o f sulfate d e p l e t i o n i n p o r e waters does not indicate an absence of sulfate r e d u c t i o n . Sulfate d e p l e t i o n was n o t e v i d e n t i n pore waters o f M c N e a r n e y L a k e , b u t stable isotope measurements i n d i c a t e d that l o w rates o f sulfate r e d u c t i o n must o c c u r (I). Sulfate d e p l e t i o n was n o t e d i n 15 o f 17 lakes i n northeastern N o r t h A m e r i c a and N o r w a y (80, 98), b u t uptake o f S 0 ~ o c c u r r e d e v e n i n t w o lakes i n w h i c h n o sulfate d e p l e t i o n was o b s e r v e d . Sulfate p r o d u c t i o n a n d r e d u c t i o n can occur c o n c u r r e n t l y , a n d the f o r m e r m a y exceed the latter. 3 5

4

2

Sulfate r e d u c t i o n occurs i n b o t h littoral a n d pelagic sediments. C o o k et al.(JOO) calculated b y mass balance that S r e t e n t i o n i n e p i l i m n e t i c sediments exceeded that i n h y p o l i m n e t i c sediments. R u d d et a l . (98) also f o u n d h i g h e r rates o f uptake o f S 0 " i n littoral sediments. I n L i t t l e R o c k L a k e , rates of sulfate r e d u c t i o n i n intact cores w e r e l o w e r i n sandy littoral s e d i m e n t s than i n o r g a n i c - r i c h pelagic sediments, b u t rates i n shallow bays r e c e i v i n g h i g h leaflitter inputs w e r e comparable to rates i n pelagic sediments (101). 3 5

4

2

R e p o r t e d rates o f sulfate r e d u c t i o n range over n e a r l y 3 orders o f m a g n i t u d e (Table I). A l l measurements r e p o r t e d i n Table I are actual, not p o -


330


Table I. Measurements of Sulfate Reduction Rates in Lake Sediments Sulfate Reduction Rate nmol/cm per day 1

System


Meromictic lakes Faro E u trophic lakes Mendota Wintergreen

5-42 50-600 458

Third Sister Sempach Maggiore Lugano Braband Mesotrophic lakes Washington Oligotrophic lakes Lawrence Little Rock Estuaries, shallow seas, continental shelf

1.6-100 6-190 38-69 8500

mmoll m per year

2

References 55

36-^1200

85 78 73 82 this studv 104 104 58

5580 2560 900-13,000 2000 1200

1.73

43

90

71 0-1680

0-5480

4 101

1-10,000

73-160,000

103

NOTE: All reported measurements are actual, not potential, rates measured with S . Blank spaces mean that no data are available. a,

tential, rates; carrier-free S 0 ~ was u s e d i n all cases w i t h o u t a d d i t i o n o f u n l a b e l e d S 0 ~ . M o s t measurements r e p o r t e d i n Table I are f r o m a single date, a n d some o f the v a r i a b i l i t y m a y reflect seasonal or t e m p e r a t u r e differences a m o n g sites. H o w e v e r , no seasonal variation was o b s e r v e d i n L i t t l e R o c k L a k e (101), W i n t e r g r e e n L a k e (78) or L a k e M e n d o t a (85). C o m p a r a b l e m e t h o d o l o g y was used b y all investigators r e p o r t e d i n T a b l e I; w i t h the exception of Jorgensen (58), all investigators m e a s u r e d r e d u c e d S o n l y i n A V S rather than i n C R S . Results of F o s s i n g a n d Jorgensen (102) a n d m e a surements i n L a k e S e m p a c h ( U r b a n , u n p u b l i s h e d data) a n d L i t t l e R o c k L a k e (101) indicate that v e r y little S is i n c o r p o r a t e d into p y r i t e d u r i n g short incubations (

Environmental Chemistry of Lakes and Reservoirs - American

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