Sediment Microbial Processes Research Articles

Biogeochemistry and microbiology of high Arctic marine sediment ecosystems—Case study of Svalbard fjords

AbstractFjord ecosystems of the high Arctic are distinct from fjords of temperate latitudes due to the influence of glaciers, icebergs, sea ice, and the permanently low temperatures. The sediment microbiology and biogeochemical processes were analyzed during an international research program with multiple field studies in Svalbard, situated between the Barents Sea and the Arctic Ocean. We here describe the physical and geochemical setting and the predominant microbiological processes in several fjords. Physiological studies of sediments and pure cultures show how the predominantly psychrophilic bacteria are adapted to the near‐zero temperature. The microbial communities include bacteria responsible for organic matter hydrolytic degradation, fermentation, and terminal oxidation to CO2. These processes drive the cycling of carbon, sulfur, iron, and manganese. The balance between the dominant sediment microbial processes changes along transects out through the fjords, reflecting the varying impact of the glacier‐derived rock flour, rich in metal oxides at the head, and the plankton‐derived, labile, marine organic matter at the mouth. Due to accelerated warming of Arctic ecosystems, glaciers are retreating with impacts on the physical, chemical, and biological functioning of the fjord sediment ecosystems.

Vegetation Loss Decreases Salt Marsh Denitrification Capacity: Implications for Marsh Erosion.

Salt marshes play a key role in removing excess anthropogenic nitrogen (N) loads to nearshore marine ecosystems through sediment microbial processes such as denitrification. However, in the Gulf of Mexico, the loss of marsh vegetation because of human-driven disturbances such as sea level rise and oil spills can potentially reduce marsh capacity for N removal. To investigate the effect of vegetation loss on ecosystem N removal, we contrasted denitrification capacity in marsh and subtidal sediments impacted by the Deepwater Horizon oil spill using a combination of 29N2 and 30N2 production (isotope pairing), denitrification potential measurements (acetylene block), and quantitative polymerase chain reaction (qPCR) of functional genes in the denitrification pathway. We found that, on average, denitrification capacity was 4 times higher in vegetated sediments because of a combination of enhanced nitrification and higher organic carbon availability. The abundance of nirS-type denitrifers indicated that marsh vegetation regulates the activity, rather than the abundance, of denitrifier communities. We estimated that marsh sediments remove an average of 3.6 t N km-2 y-1 compared to 0.9 t N km-2 y-1 in unvegetated sediments. Overall, our findings indicate that marsh loss results in a substantial loss of N removal capacity in coastal ecosystems.

The Chaoborus pump: Migrating phantom midge larvae sustain hypolimnetic oxygen deficiency and nutrient internal loading in lakes

Hypolimnetic oxygen demand in lakes is often assumed to be driven mainly by sediment microbial processes, while the role of Chaoborus larvae, which are prevalent in eutrophic lakes with hypoxic to anoxic bottoms, has been overlooked. We experimentally measured the respiration rates of C. flavicans at different temperatures yielding a Q10 of 1.44–1.71 and a respiratory quotient of 0.84–0.98. Applying the experimental data in a system analytical approach, we showed that migrating Chaoborus larvae can significantly add to the water column and sediment oxygen demand, and contribute to the observed linear relationship between water column respiration and depth. The estimated phosphorus excretion by Chaoborus in sediment is comparable in magnitude to the required phosphorus loading for eutrophication. Migrating Chaoborus larvae thereby essentially trap nutrients between the water column and the sediment, and this continuous internal loading of nutrients would delay lake remediation even when external inputs are stopped.

The impact of gamma radiation on sediment microbial processes.

Microbial communities have the potential to control the biogeochemical fate of some radionuclides in contaminated land scenarios or in the vicinity of a geological repository for radioactive waste. However, there have been few studies of ionizing radiation effects on microbial communities in sediment systems. Here, acetate and lactate amended sediment microcosms irradiated with gamma radiation at 0.5 or 30 Gy h(-1) for 8 weeks all displayed NO3 (-) and Fe(III) reduction, although the rate of Fe(III) reduction was decreased in 30-Gy h(-1) treatments. These systems were dominated by fermentation processes. Pyrosequencing indicated that the 30-Gy h(-1) treatment resulted in a community dominated by two Clostridial species. In systems containing no added electron donor, irradiation at either dose rate did not restrict NO3 (-), Fe(III), or SO4 (2-) reduction. Rather, Fe(III) reduction was stimulated in the 0.5-Gy h(-1)-treated systems. In irradiated systems, there was a relative increase in the proportion of bacteria capable of Fe(III) reduction, with Geothrix fermentans and Geobacter sp. identified in the 0.5-Gy h(-1) and 30-Gy h(-1) treatments, respectively. These results indicate that biogeochemical processes will likely not be restricted by dose rates in such environments, and electron accepting processes may even be stimulated by radiation.

Bacterial Diversity and Geochemical Profiles in Sediments from Eutrophic Azorean Lakes

In the Azores, the advanced trophic state of the lakes requires a fast intervention to achieve the good ecological status prescribed by the Water Framework Directive. Despite the considerable effort made to describe the phytoplankton growing on the water column, the lack of information regarding the microbial processes in sediments is still high. Thus, for the successful implementation of internal management actions, the present work explored the relationships between geochemical profiles and dominant members of the bacterial community in sediments from eutrophic Azorean lakes. Lake Azul geochemical profiles were quite homogeneous for all parameters, while in lake Furnas the total iron profile presented a peak below the aerobic layer. For lake Verde, the concentrations of all studied parameters (20 ± 2% loss-on-ignition; 2.10 ± 0.08 mg g−1 total phosphorus; 1.31 ± 0.50 mg g−1 total nitrogen; 8.06 ± 0.13 mg g−1 total iron) in the uppermost sediment layer were approximately two times higher than the ones in sediments from other lakes, decreasing with sediment depth. The higher amounts of phosphorus and organic matter in lake Verde suggested a higher internal contribution of phosphorus to eutrophication. The dominant members of the sediment bacterial community, investigated by denaturing gradient gel electrophoresis, were mostly affiliated to Proteobacteria phylum (Alpha-, Delta-, and Gamma-subclasses), group Bacteroidetes/Chlorobi and phylum Chloroflexi. The Cyanobacteria phylum was solely detected in sediments from lake Verde and lake Furnas that presented the highest amounts of nitrogen and phosphorus both in the water column and sediments, while the other phyla were detected in sediments from the three studied lakes. In conclusion, management measurers to achieve the good ecological status until 2015 should be distinct for the different lakes taking into account the relative magnitude of the nutrient sources and the bacterial diversity in sediments.

Thermophilic anaerobes in Arctic marine sediments induced to mineralize complex organic matter at high temperature

Marine sediments harbour diverse populations of dormant thermophilic bacterial spores that become active in sediment incubation experiments at much higher than in situ temperature. This response was investigated in the presence of natural complex organic matter in sediments of two Arctic fjords, as well as with the addition of freeze-dried Spirulina or individual high-molecular-weight polysaccharides. During 50 degrees C incubation experiments, Arctic thermophiles catalysed extensive mineralization of the organic matter via extracellular enzymatic hydrolysis, fermentation and sulfate reduction. This high temperature-induced food chain mirrors sediment microbial processes occurring at cold in situ temperatures (near 0 degrees C), yet it is catalysed by a completely different set of microorganisms. Using sulfate reduction rates (SRR) as a proxy for organic matter mineralization showed that differences in organic matter reactivity determined the extent of the thermophilic response. Fjord sediments with higher in situ SRR also supported higher SRR at 50 degrees C. Amendment with Spirulina significantly increased volatile fatty acids production and SRR relative to unamended sediment in 50 degrees C incubations. Spirulina amendment also revealed temporally distinct sulfate reduction phases, consistent with 16S rRNA clone library detection of multiple thermophilic Desulfotomaculum spp. enriched at 50 degrees C. Incubations with four different fluorescently labelled polysaccharides at 4 degrees C and 50 degrees C showed that the thermophilic population in Arctic sediments produce a different suite of polymer-hydrolysing enzymes than those used in situ by the cold-adapted microbial community. Over time, dormant marine microorganisms like these are buried in marine sediments and might eventually encounter warmer conditions that favour their activation. Distinct enzymatic capacities for organic polymer degradation could allow specific heterotrophic populations like these to play a role in sustaining microbial metabolism in the deep, warm, marine biosphere.

Effects of upwelling on short-term variability in microbial and biogeochemical processes in estuarine sediments from Elkhorn Slough, California, USA

We examined short-term variability in sediment microbial processes and biogeochem- istry in response to decreased irradiance accompanying an upwelling event. Potential nitrification, extractable nutrients, solid phase iron and pore water sulfide concentrations were measured several times at 3 locations in Elkhorn Slough, California, USA. Benthic fluxes of nitrate+nitrite, ammonium, phosphate, sediment oxygen consumption and denitrification from N2/Ar flux were also measured. Fog that was associated with upwelling in Monterey Bay reduced photosynthetically active radiation in Elkhorn Slough, which led to increased duration of water column hypoxia. Solid phase Fe 3+ con- centrations and potential nitrification rates declined while pore water sulfide increased over this period. While potential nitrification rates from this study are lower than rates from estuaries that do not experience hypoxia or anoxia, nitrifiers in Elkhorn Slough appear to be capable of adjusting to changing environmental conditions, specifically of tolerating low levels of sulfide. The nitrifying assemblage was similar to the community of ammonia-oxidizing bacteria and ammonia-oxidizing archaea that was previously reported from this system. Eutrophic shallow estuaries like Elkhorn Slough are delicately poised such that their sediment biogeochemistry responds quickly to relatively small changes in the light environment.

Effects of freeze–thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat

Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring (35)S sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.

Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat

BackgroundFood web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood.Methodology/Principal FindingsUsing an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1) Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2) Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution) correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments.Conclusions/SignificanceOverall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in the face of perturbations.

Effects of Imposed Salinity Gradients on Dissimilatory Arsenate Reduction, Sulfate Reduction, and Other Microbial Processes in Sediments from Two California Soda Lakes

Effects of Imposed Salinity Gradients on Dissimilatory Arsenate Reduction, Sulfate Reduction, and Other Microbial Processes in Sediments from Two California Soda Lakes

Eutrophication-driven sediment microbial processes can explain the regional variation in phosphorus concentrations between Baltic Sea sub-basins

Despite the ecological significance of microbial iron and sulphate reduction in aquatic environments, the processes involved have been poorly studied in Baltic Sea sediments. On the basis of indirect evidence, we conclude that the bottom sediments of the non-stratified and oligotrophic northernmost, and the poorly stratified and mesotrophic next northern, sub-basins of the Baltic have tolerated the external nutrient load rather well, as they are still in a state in which iron reduction and coupled cycling of iron and phosphorus prevail in the surface sediments. Since iron-reducing bacteria are unable to reduce ferric oxides completely, part of the iron-bound phosphorus may be permanently buried in the sediments. The good ability of the sediment to retain phosphorus results in low concentrations of phosphorus in water, a state that in turn promotes phosphorus limitation of primary production. In contrast, the sediments of the nutrient-loaded and stratified sub-basins, the Gulf of Finland (the most eutrophied sub-basin) and the Baltic Proper, appeared to have reached a state in which sulphate reduction is the dominant mineralisation pathway. Sulphate reduction followed by sulphide formation leads to efficient reduction of ferric oxides. Subsequently, iron-bound phosphorus dissolves into the pore water and is transported to the overlying water, whereas iron is buried as sulphides (uncoupled iron and phosphorus cycling). The capacity of sediments to retain phosphorus is limited; high amounts of bioavailable phosphate exist in the water column, primary production tends to be nitrogen limited and extensive blue-green algal blooms are common. We maintain that the decisive factors controlling the above regional distribution of iron and sulphate reduction are the flux of labile organic matter to the sediments and the variation in hydrodynamics. Sulphate reduction will be triggered when the flux of organic matter reaches a critical threshold value, resulting in anoxia at the sediment–water interface, followed by the collapse of benthic fauna and inhibition of iron re-oxidation. The only way to drive the sediments back into an iron-reduced state is to strongly reduce bioavailable nitrogen and phosphorus loading to the Baltic Sea, and thus the flux of labile organic matter to the sediments. Even so, recovery may also necessitate favourable hydrodynamic conditions.

Effects of Imposed Salinity Gradients on Dissimilatory Arsenate Reduction, Sulfate Reduction, and Other Microbial Processes in Sediments from Two California Soda Lakes

Salinity effects on microbial community structure and on potential rates of arsenate reduction, arsenite oxidation, sulfate reduction, denitrification, and methanogenesis were examined in sediment slurries from two California soda lakes. We conducted experiments with Mono Lake and Searles Lake sediments over a wide range of salt concentrations (25 to 346 g liter(-1)). With the exception of sulfate reduction, rates of all processes demonstrated an inverse relationship to total salinity. However, each of these processes persisted at low but detectable rates at salt saturation. Denaturing gradient gel electrophoresis analysis of partial 16S rRNA genes amplified from As(V) reduction slurries revealed that distinct microbial populations grew at low (25 to 50 g liter(-1)), intermediate (100 to 200 g liter(-1)), and high (>300 g liter(-1)) salinity. At intermediate and high salinities, a close relative of a cultivated As-respiring halophile was present. These results suggest that organisms adapted to more dilute conditions can remain viable at high salinity and rapidly repopulate the lake during periods of rising lake level. In contrast to As reduction, sulfate reduction in Mono Lake slurries was undetectable at salt saturation. Furthermore, sulfate reduction was excluded from Searles Lake sediments at any salinity despite the presence of abundant sulfate. Sulfate reduction occurred in Searles Lake sediment slurries only following inoculation with Mono Lake sediment, indicating the absence of sulfate-reducing flora. Experiments with borate-amended Mono Lake slurries suggest that the notably high (0.46 molal) concentration of borate in the Searles Lake brine was responsible for the exclusion of sulfate reducers from that ecosystem.

Ecosystem engineering: the impact of bioturbation on biogeochemical processes in marine and freshwater benthic habitats

In aquatic ecosystems, invertebrate bioturbation significantly influences microbial activities and biogeochemical processes in sediments by modifying water and sediment fluxes at the water-sediment interface. We apply the concept of ecosystem engineering to develop a qualitative general understanding of the role of bioturbation on microbial processes in different benthic environments. We hypothesized that the effects of the bioturbation mode (sediment reworking, biogenic structure building, bioirrigation) on microbial processes vary between diffusion- and advection-dominated benthic environments because bioturbation does not have the same influences on hydrological exchanges (and the flux of resources for micro-organisms living in sediments) at the water-sediment interface of the two systems. To test this hypothesis, we experimentally compared the influence of three bioturbation modes (fine-sediment reworking, U-shaped structure burrowing, and gallery-network burrowing) in a diffusion-dominated system (fine sediments/low interstitial flow rates) and an advectiondominated system (coarse sediments/advection of water in sediments). Our analysis demonstrated that bioturbation modes in the two systems had different impacts on microbial activities. For instance, U-shaped tube burrowing by animals increased O2 consumption in the diffusion- dominated system but produced the opposite effect in the advection-dominated system. The influence of bioturbation was also negatively related to interstitial flow rate, the bioturbation having a higher influence on O2 consumption in the diffusion-dominated system than in the advection-dominated system. According to our hypothesis, bioturbation modified microbial processes in sediments depend on the hydrological characteristics of the system. In the diffusion-dominated system, invertebrate bioturbation can produce water fluxes at the watersediment interface that may strongly influence microbial processes in sediments. In contrast, in the advectiondominated system, invertebrate bioturbation can only modify the water circulation patterns in sediments, moderately affecting microbial processes. Consequently, it is necessary to use a conceptual framework which takes into account the features of sediment habitats in order to allow a better prediction of bioturbation effects on sediment biogeochemistry. With this aim, the conceptual scheme of ecosystem engineers can be an organizing principle to integrate the complex relationships among physical habitat, bioturbation mode and microbial activity.

Sedimentary pyrite: A window into the microbial past

Early diagenetic pyrite forms as a result of microbial processes in sediments, but has received little attention as a potential source of microbial fossils. Sedimentary pyrite grains, Archean to Jurassic in age, were examined by scanning and transmission electron microscopy (TEM). Ion milling was essential for the preparation of electron transparent TEM samples. Most pyrite grains revealed coccoid, rod-shaped, and even filamentous features that are interpreted as microbial. Identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record. Combined with geochemical characterization, the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate-reducing communities. Sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on Mars.

Effect of redox conditions on MTBE biodegradation in surface water sediments.

Microbial degradation of methyl tert-butyl ether (MTBE) was observed in surface water-sediment microcosms under anaerobic conditions. The efficiency and products of anaerobic MTBE biodegradation were dependent on the predominant terminal electron-accepting conditions. In the presence of substantial methanogenic activity, MTBE biodegradation was nominal and involved reduction of MTBE to the toxic product, tert-butyl alcohol (TBA). In the absence of significant methanogenic activity, accumulation of [14C]TBA generally decreased, and mineralization of [U-14C]MTBE to 14CO2 generally increased as the oxidative potential of the predominant terminal electron acceptor increased in the order of SO4, Fe(III), Mn(IV) < NO3 < O2. Microbial mineralization of MTBE to CO2 under Mn(IV)-or SO4-reducing conditions has not been reported previously. The results of this study indicate that microorganisms inhabiting the sediments of streams and lakes can degrade MTBE effectively under a range of anaerobic terminal electron-accepting conditions. Thus, anaerobic bed sediment microbial processes may provide a significant environmental sink for MTBE in surface water systems throughout the United States.

Widespread potential for microbial MTBE degradation in surface-water sediments.

Microorganisms indigenous to stream and lake bed sediments, collected from 11 sites throughout the United States, demonstrated significant mineralization of the fuel oxygenate, methyl-tert-butyl ether (MTBE). Mineralization of [U-14C]MTBE to 14CO2 ranged from 15 to 66% over 50 days and did not differ significantly between sediments collected from MTBE contaminated sites and from sites with no history of MTBE exposure. This result suggests that even the microbial communities indigenous to newly contaminated surface water systems will exhibit some innate ability to attenuate MTBE under aerobic conditions. The magnitude of MTBE mineralization was related to the sediment grain size distribution. A pronounced, inverse correlation (p < 0.001; r2 = 0.73) was observed between the final recovery of 14CO2 and the percentage content of silt and clay sized grains (grain diameter < 0.125 mm). The results of this study indicate that the microorganisms that inhabit the bed sediments of streams and lakes can degrade MTBE efficiently and that this capability is widespread in the environment. Thus aerobic bed sediment microbial processes may provide a significant environmental sink for MTBE in surface water systems throughout the United States and may contribute to the reported transience of MTBE in some surface waters.

Effect of the seagrass Zostera capricorni on sediment microbial processes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 199:83-96 (2000) - doi:10.3354/meps199083 Effect of the seagrass Zostera capricorni on sediment microbial processes Jens W. Hansen2,*, James W. Udy1, Christine J. Perry1, William C. Dennison1, Bente Aa. Lomstein2 1Department of Botany, University of Queensland, Brisbane, Queensland 4072, Australia 2Department of Microbial Ecology, Institute of Biological Sciences, University of Aarhus, Bldg. 540, Ny Munkegade, 8000 Aarhus C., Denmark *Present address: National Environmental Research Institute, Vejlsøvej 25, 8600 Silkeborg, Denmark. E-mail: jwh@dmu.dk ABSTRACT: The effect of the seagrass Zostera capricorni on sediment microbial processes was studied in a tank experiment, where vegetated and unvegetated control sediments were incubated in 10 and 50% of incident light. Leaf and root-rhizome biomass, shoot density, and leaf productivity were significantly higher when plants were incubated in 50% than in 10% of incident light. Nitrogen fixation, sulphate reduction, and urea turnover in the Z. capricorni vegetated sediment were higher in the 50% than in the 10% light treatment and higher in the vegetated than in the unvegetated sediment. The stimulation of microbial processes in the Z. capricorni vegetated sediment took place in the rhizosphere, where nitrogen fixation and sulphate reduction in particular were stimulated. The sediment studies were supplemented by measurements of nitrogen fixation, sulphate reduction, and urea turnover by microorganisms associated with the roots and rhizomes of Z. capricorni. The rates of nitrogen fixation and sulphate reduction associated with root-rhizomes were up to 40- and 7-fold higher, respectively, than the highest respective sediment rates, whereas the root-rhizome associated urea turnover was lower than sediment rates. Nitrogen fixation and sulphate reduction associated with root-rhizomes could account for up to 39 and 4%, respectively, of the depth-integrated sediment rates. Nitrogen fixed by microorganisms associated with root-rhizomes could supply up to 65% of the nitrogen needed for plant growth. Further, it was estimated that 8 to 18% of the carbon fixed by Z. capricorni was released to the sediment by the roots and rhizomes. Urea turnover was suggested to be an important intermediate in the gross production of ammonium, and a low net production of ammonium indicated rapid internal nitrogen cycling within the sediment. KEY WORDS: Zostera capricorni · Sediment · Roots · Rhizomes · Microbial processes · Light Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 199. Publication date: June 26, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Geochemical and Microbial Processes in Sediments and at the Sediment-Water Interface of Acidic Mining Lakes

Geochemical and Microbial Processes in Sediments and at the Sediment-Water Interface of Acidic Mining Lakes

Rates of microbial processes in sediments

The following methods of measurement of sediment parameters are discussed: (1) rate of diffusional exchange of reactants and products across the sediment—water interface; (2) the concentration profiles of these reactants and profiles in the sediment, and (3) profiles and integrated rates of reactions in the sediment. The interaction of the processes of reaction and diffusion are illustrated using a simulation model. The effect of increasing organic loading (6.2, 37.2 and 62.0 mmol C m-2d-1), with organic matter distributed in three ways: close to the sediment surface, a linear gradient downwards or evenly mixed throughout the sediment. Predictable increases in anoxic processes occurred with increasing organic loading. There were higher diffusional losses of dissolved organic matter when organic degradation occurred close to the sediment—water interface. The model predicted that degradation of organic matter at depth could have the following effects: an increase in the depth of oxygen penetration, an increase in the ratio of CO2/O2, and an increase in nitrification and denitrification.

Mibrobes and microbial processes in sediments : Jones, J.G., 1985. Phil. Trans. R. Soc., (A)315(1531): 3–17

Mibrobes and microbial processes in sediments : Jones, J.G., 1985. Phil. Trans. R. Soc., (A)315(1531): 3–17