Sulphate reduction and sulphur cycling in lake sediments: a review

1. The concentration of sulphate is low in lakes and sulphur cycling has often been neglected in studies of organic matter diagenesis in lake sediments. The cycling of sulphur is, however, both spatially and temporally dynamic and strongly influences many biogeochemical reactions in sediments, such as the binding of phosphorus. This review examines the control of sulphate reduction and sulphur cycling in sediments of lakes with different trophic status. 2. The factors that control the rate of sulphate reduction have not been identified with certainty in the various environments because many factors are involved, e.g. oxygen and sulphate concentrations, temperature and organic matter availability. 3. Sulphate reduction is less significant under oligotrophic conditions, where mineralization is dominated by oxic decomposition. The supply of organic matter may not be sufficient to support sulphate reduction in the anoxic parts of sediments and, also, sulphate availability may control the rate as the concentration is generally low in oligotrophic lakes. 4. There is a potential for significant sulphate reduction in eutrophic lakes, as both the availability of organic matter and sulphate concentration are often higher than in oligotrophic lakes. Sulphate is rapidly depleted with sediment depth, however, and methanogenesis is generally the most important process in overall carbon mineralization. Sulphate reduction is generally low in acidic lakes because of low sulphate availability and reduced microbial activity. 5. It is still unclear which of the forms of sulphur deposits are the most important and under which conditions burial occurs. Sulphur deposition is controlled by the rate of sulphate reduction and reoxidation. Reoxidation of sulphides occurs rapidly through several pathways, both under oxic and anoxic conditions. Only a few studies have been able to examine the importance of reoxidation, but it is hypothesized that most of the reoxidation takes place under anoxic conditions and that disproportionation is often involved. The presence of sulphide oxidizing bacteria, benthic fauna and rooted macrophytes may substantially enhance oxic reoxidation. Deposition of sulphur is generally higher in eutrophic than in oligotrophic lakes because of a number of factors: a higher rate of sulphate reduction, enhanced sedimentation of organic sulphur and less reoxidation as a result of reduced penetration of oxygen into the sediments, a lack of faunal activity and rooted macrophytes.     

Performance of two laboratory‐scale horizontal wetlands under varying influent loads treating artificial sewage

The performance of two laboratory‐scale horizontal subsurface‐flow constructed wetlands(CWs) treating artificial sewage in response to varying influent components and loads was investigated. Acidification with a pH of 3.0 was detected under an organic carbon load of 100 mg/day, which further inhibited the activity of the denitrification process. With an increase in the carbon load to 240 mg/day, the pH was significantly elevated to 6.0. However, a negative effect of sulphide as a product of sulphate reduction was observed on the removal of ammonium, the plants (Juncus effusus), and the organic carbon degradation. With a produced sulphide concentration of about 3.5 mg/L, the ammonium removal decreased from 100% to 30% under an inflow load of 100 mg/day, and the number of healthy stalks of J. effuses was reduced from about 14 000/m² to less than 6000/m². The removal of organic carbon decreased from 94% to 68% under an influent load of 240 mg/day, when the sulphide concentrations reached up to about 8–10 mg/L. The production of sulphide was not immediately controlled by stopping the inflow sulphate load to remove the negative effect of the sulphide toxicity, thus indicating an immobilization of the deposited reduced sulphur compounds. Moreover, the effect of a nitrate dosage on the sulphide control was also examined, but was shown to be only evident under the conditions of a low organic carbon input.     

The importance of sediment phosphorus release in the restoration of very shallow lakes (The Norfolk Broads,England) and implications for biomanipulation

Phosphorus release from the sediments of very shallow lakes, the Norfolk Broads, can be as high as 278 mgP m^-2 d^-1. These high rates are associated with high total sediment Fe:P ratios and occur when sulphide from sulphate reduction removes Fe(II) from the pore water. There is also evidence that bioturbation from benthic chironomids can enhance phosphorus release rates, particularly in sediments low in total iron. The release of phosphorus from the sediments of these lakes is delaying restoration following the control of phosphorus from sewage discharges. Biomanipulation is being used in these lakes to create clear water and re-establish aquatic macrophytes. This removal of fish has allowed larger populations of benthic chironomid larvae to develop which may result in an increase in the rate of phosphorus release and changes to the pore profiles of dissolved phosphorus, soluble iron and free sulphide.     

Microbial decomposition of organic matter in the bottom sediments of small lakes of the urban landscape (Lithuania)

Bacterial abundance and the rates of sulfate reduction (SR) and total organic matter decomposition (D_total) were studied in the bottom sediments of nine lakes in the vicinity of Vilnius (Lithuania) during the ice-free seasons of 2006–2009. During the spring mixing of the water, aerobic processes of organic matter decomposition prevailed in the bottom sediments of most lakes, while anaerobic processes predominated (up to 80–90% D_total) in summer and early autumn. SR rates in the bottom sediments made up 0.16–2.6 and 0.09–2.0 mg S^2?/(dm³ day) for the medium-depth and shallow lakes, respectively. The highest numbers of sulfate-reducing bacteria (up to 10⁶ cells/cm³) and SR rates were observed in summer. SR rate in mediumdepth lakes increased with development of anaerobic conditions at the bottom and elevated sulfate concentrations (up to 96.0 mg/dm³). In shallow lakes, where O₂ concentration at the bottom was at least 6.7 mg/L, SR rates increased with temperature and inflow of fresh organic matter, especially during cyanobacterial blooms. The average SR rates in the bottom sediments of the lakes of urbanized areas were 4 times higher than in the shallow lakes of protected areas. Accumulation of organic matter and its intensive decomposition during summer may enhance the processes of secondary eutrophication of these small and shallow lakes.     

Bacterial oxidation of sulphide under denitrifying conditions

Anoxic H2S oxidation under denitrifying conditions produced sulphur and sulphate in almost equal proportions by an isolated Thiobacillus denitrificans. Under nitrate reducing conditions the rate of sulphide oxidation was approximately 0.9 g sulphide/g biomass h. Nitrate was reduced to nitrite and accumulated during sulphide oxidation. Above 100 mg nitrite/l, the sulphide oxidation rate declined and at 500 mg/l it was totally arrested. The optimum pH for the anoxic sulphide oxidation was around 7.5. Concentrations of sulphate 1500 mg/l and acetate 400 mg/l had no effect on anoxic sulphide oxidation.     

Biotechnological process for sulphide removal with sulphur reclamation

A new biotechnological process for sulphide removal is proposed. The process is based on the oxidation of sulphide into elemental sulphur, which can be removed by sedimentation. In this study it was found that elemental sulphur and sulphate are the main oxidation products of the biological sulphide oxidation. The settling characteristics become worse as the sulphide concentration increases, due to polysulphide formation. The start-up phase of this biological system is very short; Only four days are needed to reduce the sulphide concentration of 100 to 2 mg/l at a HRT (Residence time) of 22 minutes. Also some environmental factors were evaluated. The optimal pH is situated in the pH-range 8.0–8.5. Significantly lower conversion rates are found at pH = 6.5 to 7.5 and pH = 9.0, while at pH = 9.5 the sulphide oxidation capacity of the system detoriates. The process temperature was 20°C, although the optimal temperature is situated in the range 25–35°C. No substrate inhibition of sulphide was found at sulphide concentrations up to 100 mg/l.     

Sulphur metabolism in Thiorhodaceae. II. stoichiometric relationship of CO2 fixation to oxidation of hydrogen sulphide and intracellular sulphur inChromatium okenii

Stoichiometry of sulphide and intracellular sulphur oxidation in connection with CO₂ fixation was studied inChromatium okenii. The equipment used was a special stirred cuvette with a rapid-sampling arrangement, which allowed short-time experiments with illuminated bacterial suspensions under anaerobic conditions. Turnover of the sulphur compounds is controlled by a linear CO₂ fixation rate which amounts to 0.069µmoles of CO₂/min mg of cell protein at light saturation. Van Niel's equations for bacterial photosynthesis could be confirmed for short periods under the condition that sulphate is produced during increase of intracellular sulphur; i.e., oxidation of sulphide and of intracellular sulphur do not occur consecutively but simultaneously. The full oxidation rate of intracellular sulphur starts after complete consumption of sulphide. The time during which sulphide is oxidized to intracellular sulphur amounts to 1/3–1/4 of the time necessary for the complete quantitative oxidation of the sulphide to sulphate.     

Biotic conversion of sulphate to sulphide and abiotic conversion of sulphide to sulphur in a microbial fuel cell using cobalt oxide octahedrons as cathode catalyst

Varying chemical oxygen demand (COD) and sulphate concentrations in substrate were used to determine reaction kinetics and mass balance of organic matter and sulphate transformation in a microbial fuel cell (MFC). MFC with anodic chamber volume of 1 L, fed with wastewater having COD of 500 mg/L and sulphate of 200 mg/L, could harvest power of 54.4 mW/m², at a Coulombic efficiency of 14%, with respective COD and sulphate removals of 90 and 95%. Sulphide concentration, even up to 1500 mg/L, did not inhibit anodic biochemical reactions, due to instantaneous abiotic oxidation to sulphur, at high inlet sulphate. Experiments on abiotic oxidation of sulphide to sulphur revealed maximum oxidation taking place at an anodic potential of −200 mV. More than 99% sulphate removal could be achieved in a MFC with inlet COD/sulphate of 0.75, giving around 1.33 kg/m³ day COD removal. Bioelectrochemical conversion of sulphate facilitating sulphur recovery in a MFC makes it an interesting pollution abatement technique.

     

Sulfate-Reducing Bacteria in Gypsum Karst Lakes of Northern Lithuania

Microbiological studies were performed in three small gypsum karst lakes in northern Lithuania, most typical of the region. Samples were taken in different seasons of 2001. The conditions for microbial growth in the lakes are determined by elevated content of salts (from 0.5 to 2.0 g/l), dominated by SO ₄ ^2? and Ca²⁺ ions (up to 1.4 and 0.6 g/l, respectively). The elevated sulfate concentration is favorable for sulfate-reducing bacteria (SRBs). Summer and winter stratification gives rise to anaerobic water layers enriched in products of anaerobic degradation: H₂S and CH₄. The lakes under study contain abundant SRBs not only in bottom sediments (from 10³ to 10⁷ cells/dm³) but also in the water column (from 10² to 10⁶ cells/ml). The characteristic spatial and temporal variations in the rate of sulfate reduction were noted. The highest rates of this process were recorded in summer: 0.95–2.60 mg S^2?/dm³ per day in bottom sediments and up to 0.49 mg S^2?/l per day in the water column. The maximum values (up to 11.36 mg S^2?/dm³) were noted in areas where bottom sediments were enriched in plankton debris. Molecular analysis of conservative sequences of the gene for 16S rRNA in sulfate-reducing microorganisms grown on lactate allowed them to be identified as Desulfovibrio desulfuricans.     

Sulphate reduction in the hypolimnion and sediments of Lake Kinneret, Israel

1. Lake Kinneret is a warm (13–30°C) monomictic lake. Between January and June a heavy annual bloom of the dinoflagellate Peridinium gatunense dominates phytoplankton biomass (250 g m^?2). At the beginning of the summer, degradation and decomposition of the Peridinium biomass occurs, serving as a trigger for intense sulphate reduction in the hypolimnion and sediments. 2. The rates of sulphate reduction in the sediments varied seasonally from 12 to 1700 nmol SO₄.^?2 reduced cm^?3 day^?1 in December and July, respectively. The availability of organic matter and sulphate is high in June after the crash of the Peridinium bloom and the beginning of stratification and is lowest in December before overturn. 3. Sulphate concentrations in the hypolimnion range between 0.52 mM and 0.20 mM during mixing (January-April) and before overturn (December), respectively. The depletion in sulphate in the hypolimnion is stoichiometrically correlated to the increase in sulphide. The lake is not depleted of sulphate at any time, so the sulphate reduction process in Lake Kinneret is not limited by sulphate concentrations except in the sediments just before overturn.     

Sulphur isotope rations in late and early Precambrian sediments and their implications regarding early environments and early life

The stable isotopes of sulphur are fractionated in equilibrium and unidirectional processes in the earth's crust and biosphere. By far the most important of these processes occur in the biological sulphur cycle characterized by the activity of sulphur oxidizing and reducing microbiota. In particular, the dissimilatory reduction of sulphate to hydrogen sulphide by anaerobic bacteria leads to isotope effects of from 0 to 60, the magnitude of the effect depending largely on metabolic rates. Actual isotope ratio (^{3 4}S) patterns in sediments depends, therefore, on environmental conditions and the nature of sulphate reservoirs during reduction. Sulphur isotope ratios can and have been used to trace environmental conditions, sources, and modes of formation of certain Phanerozoic deposits.These studies which have been extended to late and early Precambrian sediments provide a potential source of information about very early sediment deposition environments and early life. Recent carbon and sulphur isotope data for the low grade metamorphosed banded iron-formations of the Michipicoten area in Ontario (2.7 b.y. old) provide strong evidence for the existence of autotrophic organisms and reducing bacteria in late Archean times.Sulphur isotope ratios (^{3 4}S) have now been obtained for samples from the Isua area of West Greenland. The ^{3 4}S of the Isua sediments (3.7 b.y. old), including the various facies of the banded iron-formations, have a very narrow spread with their mean close to zero C.D.T. (0.45 ± 0.5). This comes extremely close to the respective means yielded by the Isua tuffaceous amphibolites (+0.3±0.9) and by the somewhat younger, 3.1 to 3.7×10⁹ yr, basaltic Ameralik dykes of the region (+0.6±1.1).These results indicate a complete absence of isotopic evidence for sulphate reducers in the Isua sediments (early Archean) in contrast to the banded iron-formations of the late Archean, where ^{3 4}S varies from –2-to +20Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.Contribution No. 90 of the McMaster Isotopic, Nuclear and Geochemical Studies Group.     

Correlation of viable cell counts,metabolic activity of sulphur-oxidizing bacteria and chemical parameters of marine sediments

Viable counts of aerobic and anaerobic chemotrophic sulphur-oxidizers as well as phototrophic sulphur bacteria were determined in sediment samples taken from two different areas along the Baltic Sea shore which were known to regularly develop sulphidic conditions. Depth profiles of bacterial cell counts were correlated with concentration profiles of chloride, sulphate, sulphide, nitrate and phosphate in the pore water of these sediments and with potential activities of nitrate reduction, thiosulphate transformation and sulphate formation. The data revealed a complex multilayered structure within the sediments. Sulphide was released into the water from sediments of both sampling areas, but it was found that light and the availability of oxygen significantly reduced this amount. In the highly reduced sediment at Hiddensee, the highest numbers of phototrophic and chemotrophic sulphur-oxidizers were found near the sediment surface. Therefore, it was concluded that the combined action of both groups of bacteria most efficiently oxidizes reduced sulphur compounds in the top layers of the sediments. Nitrate may replace oxygen as final electron acceptor and will support oxidation of sulphide, in particular when oxygen and light are limiting.     

Microbial destruction of organic matter in the bottom sediments of Lithuanian lakes

The rates of the processes of bacterial sulfate reduction (SR) and total destruction of organic matter (D_total) were studied in the bottom sediments (BS) of 14 lakes in Lithuanian national and regional parks in the summers of 1998–2002. Anaerobic processes accounted for an average of 92% of D_total in the depressions of deep-water lakes; for the sediments of shallow lakes, high rates of oxygen uptake were noted. The SR rate in different lakes varied from 0.09 to 2.60 mg S^2?/(dm³ day). At low sulfate concentrations (13.3–70.6 mg S-SO ₄ ^2? /dm³), characteristic of the BS of freshwater ecosystems, the main factor that affected the SR rate in the BS of the lakes studied was the content of readily available organic matter; only in special cases, was it affected by a change in the sulfate ion concentration. In shallow lakes, temperature-dependent activation of sulfate-reducing bacteria and their inhibition by acidification of the environment were recorded. The contribution of SR to D_total was 0.2 to 11.0%.     

Chemical water quality studies in the Central Patagonian Region of Chile following the eruption of Volcan Hudson

In February/March, 1993, a range of water-quality variables were measured in nine freshwater lakes at different locations in Region XI, Chile. Seven of the lakes, situated between the Rio Ibanez (46 °08S) and Lago Lapparent (46 °14S), are characterised by low concentrations of minerals and nutrients, similar to the oligotrophic lakes of the Araucanian district of Chile (39 °S to 42 °S).Sulphate concentrations were disproportionately high at each of these sites and it is proposed that this results from the deposition of volcanic ash following the eruption of Volcan Hudson in August, 1991. The concentration of sulphate found in a ninth lake well to the north of the ash deposition zone was 35 fold lower than those typically measured within the main study area.Lago Lapparent is a large blue lake receiving glacial sediments, that forms the southern boundary of the area studied. Concentrations of minerals and nutrients found at this site were generally even lower than those found in the other seven lakes within the area. Organochlorine pesticides were not detected at any of the sites after solid phase extraction of 250 ml water samples.     

Optimization of sulphur production in a biotechnological sulphide-removing reactor

A new biotechnological process for sulphide removal is proposed. The principle of this process is that sulphide is converted into elemental sulphur, which can be removed by sedimentation. In this article, investigations on the optimization of the sulphur production are reported. It seems that less than 10% sulphate is produced at low oxygen concentration, when the sulphide concentration in the reactor exceeds 10 mg/L. At sulphide concentrations higher than 20 mg/L only 5% of the incoming sulphide is converted to sulphate even at high oxygen concentrations. An immobilized biomass on recticulated polyurethane produced more sulphate than a free cell suspension at the same oxygen and sulphide concentration.     

DsrL mediates electron transfer between NADH and rDsrAB in Allochromatium vinosum

Dissimilatory sulphite reductase DsrAB occurs in sulphate/sulphite-reducing prokaryotes, in sulphur disproportionators and also in sulphur oxidizers, where it functions in reverse. Predictions of physiological traits in metagenomic studies relying on the presence of dsrAB, other dsr genes or combinations thereof suffer from the lack of information on crucial Dsr proteins. The iron–sulphur flavoprotein DsrL is an example of this group. It has a documented essential function during sulphur oxidation and was recently also found in some metagenomes of probable sulphate and sulphite reducers. Here, we show that DsrL and reverse acting rDsrAB can form a complex and are copurified from the phototrophic sulphur oxidizer Allochromatium vinosum. Recombinant DsrL exhibits NAD(P)H:acceptor oxidoreductase activity with a strong preference for NADH over NADPH. In vitro, the rDsrABL complex effectively catalyses NADH-dependent sulphite reduction, which is strongly enhanced by the sulphur-binding protein DsrC. Our work reveals NAD⁺ as suitable in vivo electron acceptor for sulphur oxidation in organisms operating the rDsr pathway and points to reduced nicotinamide adenine dinucleotides as electron donors for sulphite reduction in sulphate/sulphite-reducing prokaryotes that contain DsrL. In addition, dsrL cannot be used as a marker distinguishing sulphate/sulphite reducers and sulphur oxidizers in metagenomic studies without further analysis.     

Biogeochemistry of microbial mats under Precambrian environmental conditions: a modelling study

Microbial mats have arguably been the most important ecosystem on Earth over its 3.5 Gyr inhabitation. Mats have persisted as consortia for billions of years and occupy some of Earth's most hostile environments. With rare exceptions (e.g. microbial mats developed on geothermal springs at Yellowstone National Park, USA), today's mats do not exist under conditions analogous to Precambrian habitats with substantially lower oxygen and sulphate concentrations. This study uses a numerical model of a microbial mat to investigate how mat composition in the past might have differed from modern mats. We present a numerical model of mat biogeochemistry that simulates the growth of cyanobacteria (CYA), colourless sulphur bacteria (CSB), and purple sulphur bacteria (PSB), with sulphate‐reducing bacteria (SRB) and heterotrophic bacteria represented by parameterized sulphate reduction rates and heterotrophic consumption rates, respectively. Variations in the availability of light, oxygen, sulphide, and sulphate at the upper boundary of the mat are the driving forces in the model. Mats with remarkably similar biomass and chemical profiles develop in models under oxygen boundary conditions ranging from 2.5 × 10^?13 to 0.25 mm and sulphate boundary concentrations ranging from 0.29 to 29 mm , designed to simulate various environments from Archean to modern. The modelled mats show little sensitivity to oxygen boundary conditions because, independent of the overlying oxygen concentrations, cyanobacterial photosynthesis creates similar O₂ concentrations of 0.45–0.65 mm in the upper reaches of the mat during the photoperiod. Varying sulphate boundary conditions have more effect on the biological composition of the mat. Sulphide generated from sulphate reduction controls the magnitude and distribution of the PSB population, and plays a part in the distribution of CSB. CSB are the most sensitive species to environmental change, varying with oxygen and sulphide.