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Blue-green algae (CyanoHABs), photosynthetic bacteria that create a harmful aquatic environment, have been a trending issue on Taihu for over a decade. CyanoHABs adapt to varying climatic changes, which explains why the problem on Taihu still thrives. One major drive that keeps the algae is Sediment Oxygen Demand (SOD). In this paper, seasonal and spatial variations of SOD that contribute immensely to nutrient growth in Lake Taihu were done using the Environmental Fluid Dynamics Code (EFDC). The results were analyzed based on Nitrogenous SOD (NSOD) and Total SOD (TSOD). Summer results ranged from − 0.05754 to − 0.0826 (− 0.75658 to − 0.83902) (g/m2/day) and Winter values ranged from − 0.3022 to − 0.40171 (− 1.34486 to − 1.48856) (g/m2/day) indicate a gradual decrease in NSOD (TSOD) values respectively. Relatively higher values in summer are attributed to warmer surface water which sets up thermal stratification to increase the internal loading of nitrogen. Lower winter values are related to inverse stratification, where lower oxygen concentration decreases the SOD to trigger ammonium accumulation in the water column. NSOD (TSOD) values for Autumn results ranged from − 0.1039 to − 0.24786 (− 0.96251 to − 1.39454) (g/m2/day) and Spring values of − 0.43019 to − 0.35959 (− 1.48297 to − 0.54089) (g/m2/day). Transition seasons (i.e., Autumn and Spring) results are impacted by wind mixing that allows dissolved oxygen and nutrients in the whole water column. However, spring values depict a gradual increase in SOD value attributed to spring turnover and gradual stratification, which decrease nutrient concentration. In contrast, decreasing SOD values in autumn are related to mixing, but temperature decreases tend to increase nutrient concentrations. Carbonaceous sediment oxygen demand (CSOD), due to sulfide oxidation, presents high values from the difference between TSOD and NSOD. Based on the high values of CSOD, it is highly recommended that more research on eutrophic Taihu lakes would consider delving into CSOD. [ABSTRACT FROM AUTHOR]

We examined iron biogeochemistry in continental margin sediments along the western side of the Antarctic Peninsula (WAP) to explore the connections between iron redox cycling and other sediment biogeochemical processes, and to specifically examine the role of sediments as a source of iron to support Southern Ocean primary productivity. Total iron (Fe T) in WAP sediments ranged from ∼4 to 6 wt% Fe and showed no consistent depth variations. Total iron oxides (Fe Ox) represented ∼20–30% of Fe T in WAP surface sediments and was comprised of two types of materials: Fe ox1 , which is thought to contain amorphous, highly reactive, and poorly crystalline iron oxides such as ferrihydrite and lepidocrocite, and Fe ox2 , which is thought to contain magnetite and less reactive, more crystalline iron oxides such as goethite and hematite. Absolute and relative concentrations of Fe Ox declined with sediment depth, presumably due to reductive dissolution, and there was also a major depth change in the speciation of Fe Ox. Near the sediment surface ∼30% of Fe Ox was Fe ox1 , while below ∼30 cm Fe ox1 was almost completely consumed and therefore here virtually all Fe Ox was Fe ox2. Consistent with these observations, a simple reaction-transport model applied to the depth distributions of Fe ox1 and Fe ox2 iron in WAP shelf sediments suggested a ∼20-fold difference in the relative reactivity of these different oxides towards reductive dissolution (Fe ox1 > Fe ox2). At several stations profiles of pore water dissolved iron and solid phase Fe ox1 can be explained by steady state iron redox cycling. In contrast, profiles at other stations showed evidence of non steady-state iron redox cycling. Seasonal changes in the sediment organic carbon rain rate at these sites may explain this latter behavior. Differences in the behavior of iron at different sites may be related to the interplay between changes in sediment redox conditions and their impact on bioturbation and iron redox cycling. Sediment iron sources to the water column include dissolved iron (∼Fe2+) benthic fluxes as well as sediment resuspension processes that mix iron oxides (i.e., Fe ox1) found in surface sediments into the bottom waters. The impact these benthic iron sources will have on surface water iron concentrations (and eventually primary production) will depend on transport processes that move this iron from deeper waters to surface waters. They will also depend on chemical transformations in the water column that affect iron bioavailability. While sediment processes (in general) appear to be an important source of iron to Southern Ocean surface waters, there is large uncertainty in their magnitude. However, the results presented here demonstrate that the suspended sediment flux of amorphous iron oxides needs to be considered when discussing sediment iron sources to Southern Ocean surface waters. [ABSTRACT FROM AUTHOR]

The burial of organic carbon (OC) preserves paleoenvironmental archives and drives the evolution of Earth's biogeochemical cycles. While the impact of kinetic heterogeneity on OC preservation has been studied, the effects of sedimentation dynamics remain largely unknown. Here, we incorporate the expected stochastic variability in sedimentation rates into a reactive‐transport model, generate predictions for stratigraphic variability of OC burial efficiency, and compare the model outputs to field observations. We find that internal sedimentation dynamics profoundly influence OC preservation efficiencies and create autogenic signals that may obscure signals originated from external forcings. Simulations match observations in terms of power spectra when our model considers transient periods of erosion during net deposition, implying that the manifestation of sedimentation dynamics and their interactions with biogeochemistry in chemostratigraphic records are prevalent in nature. As sedimentary OC records reflect both internal variability and external forcing, they may be used as proxies for past depositional conditions. Plain Language Summary: In regions of sediment accumulation, the rates of deposition can vary in space and time even when factors like climatic conditions are kept constant. This type of "random" variability complicates the interpretation of the geologic record because many important chemical signals are affected by changes in sediment deposition rates. To explore the specific effects of random variability, we constructed a model with realistic, time‐varying sedimentation rates that tracks the burial and oxidation of organic matter. We chose organic matter because it is important to the global carbon cycle and is also commonly used to infer past environmental changes. We find that random changes in sedimentation rates can meaningfully impact organic matter burial and create patterns that look conspicuously like field observations interpreted as reflecting changes in environmental conditions. By predicting the patterns that can form randomly, our approach can help improve the interpretations of the geologic record. Key Points: Complex dynamics in sedimentation can profoundly influence organic carbon (OC) preservation efficiency, which has been largely overlookedAutogenic signals in OC burial can arise from sedimentation dynamics and may obscure signals originated from external forcingModel‐data comparison suggests the manifestation of sedimentation dynamics in chemostratigraphic records are prevalent in nature [ABSTRACT FROM AUTHOR]

Abstract Background Despite the widely recognized importance of aquatic processes for bridging gaps in the global carbon cycle, there is still a lack of understanding of the role of riverbed processes for carbon flows and stocks in aquatic environments. Here, we added a sediment diagenesis and sediment carbon (C) resuspension module into the SWAT-C model and tested it for simulating both particulate organic C (POC) and dissolved organic C (DOC) fluxes using 4 years of monthly observations (2014–2017) in the Tuckahoe watershed (TW) in the U.S. Mid-Atlantic region. Results Sensitivity analyses show that parameters that regulate POC deposition in river networks are more sensitive than those that determine C resuspension from sediments. Further analyses indicate that allochthonous contributions to POC and DOC are about 36.6 and 46 kgC ha−1 year−1, respectively, while autochthonous contributions are less than 0.72 kgC ha−1 year−1 for both POC and DOC (less than 2% of allochthonous sources). The net deposition of POC on the riverbed (i.e., 11.4 kgC ha−1 year−1) retained ca. 31% of terrestrial inputs of POC. In addition, average annual buried C was 0.34 kgC ha−1 year−1, accounting for only 1% of terrestrial POC inputs or 3% of net POC deposition. The results indicate that about 79% of deposited organic C was converted to inorganic C (CH4 and CO2) in the sediment and eventually released into the overlying water column. Conclusion This study serves as an exploratory study on estimation of C fluxes from terrestrial to aquatic environments at the watershed scale. We demonstrated capabilities of the SWAT-C model to simulate C cycling from uplands to riverine ecosystems and estimated C sinks and sources in aquatic environments. Overall, the results highlight the importance of including carbon cycle dynamics within the riverbed in order to accurately estimate aquatic carbon fluxes and stocks. The new capabilities of SWAT-C are expected to serve as a useful tool to account for those processes in watershed C balance assessment.

Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are 34S-enriched relative to coexisting sulfide, and experiments have produced 34S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography - inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in 34S relative to coexisting kerogen and porewater sulfide. We hypothesize that this 34S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon-sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary porewater. The 34S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.

Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are 34S-enriched relative to coexisting sulfide, and experiments have produced 34S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography - inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in 34S relative to coexisting kerogen and porewater sulfide. We hypothesize that this 34S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon-sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary porewater. The 34S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.

Abstract The degradation and loss of ecologically important wetlands has been a topical issue in the Great Lakes region, where 60–80% of the coastal wetlands have been lost since the 1800s. The present modeling study aims to guide the restoration efforts in Cootes Paradise marsh, one of the most degraded shallow wetlands in Southern Ontario. We use a process‐based eutrophication model designed to reproduce the biotic competition among multiple phytoplankton and macrophyte functional groups. Our primary focus is to offer guidelines for wetland restoration by characterizing the ecophysiological processes of the autotrophic assemblage, such as the nutrient uptake from the water column and/or the sediment pore waters, the relative ability to harvest light and fuel photosynthesis, and temperature control of the algal/macrophyte growth and basal metabolism. We predict that the additional reduction of external phosphorus loading in Cootes Paradise could induce an abrupt, non‐linear shift from the current turbid phytoplankton‐dominated state to a desirable clear macrophyte‐dominated state. The emergence of this critical (or tipping) point, where the shift to another ecological state may occur, can be accelerated by the presence of a thriving macrophyte community with an enhanced ability to sequester phosphorus. However, it may also be delayed by the presence of a suite of biogeochemical mechanisms (often referred to as “feedback loops”), such as the remobilization of legacy P due to sediment diagenetic processes, wind resuspension, bioturbation, hydraulic loading from local tributaries, water‐level fluctuations, and the leachable P pool of dead plant material that can be returned into the water column through senescence. Our study identifies the restoration actions required to minimize the likelihood of prolonged hysteresis and to facilitate a shift to a desirable ecological state in the foreseeable future. The areal expansion of aquatic vegetation will not only lead to the establishment of a thriving meadow and emergent vegetation community, but may also pave the way for submerged macrophytes through a suite of synergistic mechanisms. Additional point‐source loading reductions will facilitate the transition to an alternative stable clear macrophyte‐dominated state, but could also consolidate the future resilience of the marsh.

The degradation and loss of ecologically important wetlands has been a topical issue in the Great Lakes region, where 60–80% of the coastal wetlands have been lost since the 1800s. The present modeling study aims to guide the restoration efforts in Cootes Paradise marsh, one of the most degraded shallow wetlands in Southern Ontario. We use a process‐based eutrophication model designed to reproduce the biotic competition among multiple phytoplankton and macrophyte functional groups. Our primary focus is to offer guidelines for wetland restoration by characterizing the ecophysiological processes of the autotrophic assemblage, such as the nutrient uptake from the water column and/or the sediment pore waters, the relative ability to harvest light and fuel photosynthesis, and temperature control of the algal/macrophyte growth and basal metabolism. We predict that the additional reduction of external phosphorus loading in Cootes Paradise could induce an abrupt, non‐linear shift from the current turbid phytoplankton‐dominated state to a desirable clear macrophyte‐dominated state. The emergence of this critical (or tipping) point, where the shift to another ecological state may occur, can be accelerated by the presence of a thriving macrophyte community with an enhanced ability to sequester phosphorus. However, it may also be delayed by the presence of a suite of biogeochemical mechanisms (often referred to as "feedback loops"), such as the remobilization of legacy P due to sediment diagenetic processes, wind resuspension, bioturbation, hydraulic loading from local tributaries, water‐level fluctuations, and the leachable P pool of dead plant material that can be returned into the water column through senescence. Our study identifies the restoration actions required to minimize the likelihood of prolonged hysteresis and to facilitate a shift to a desirable ecological state in the foreseeable future. The areal expansion of aquatic vegetation will not only lead to the establishment of a thriving meadow and emergent vegetation community, but may also pave the way for submerged macrophytes through a suite of synergistic mechanisms. Additional point‐source loading reductions will facilitate the transition to an alternative stable clear macrophyte‐dominated state, but could also consolidate the future resilience of the marsh. [ABSTRACT FROM AUTHOR]

Background: Despite the widely recognized importance of aquatic processes for bridging gaps in the global carbon cycle, there is still a lack of understanding of the role of riverbed processes for carbon flows and stocks in aquatic environments. Here, we added a sediment diagenesis and sediment carbon (C) resuspension module into the SWAT-C model and tested it for simulating both particulate organic C (POC) and dissolved organic C (DOC) fluxes using 4 years of monthly observations (2014–2017) in the Tuckahoe watershed (TW) in the U.S. Mid-Atlantic region. Results: Sensitivity analyses show that parameters that regulate POC deposition in river networks are more sensitive than those that determine C resuspension from sediments. Further analyses indicate that allochthonous contributions to POC and DOC are about 36.6 and 46 kgC ha−1 year−1, respectively, while autochthonous contributions are less than 0.72 kgC ha−1 year−1 for both POC and DOC (less than 2% of allochthonous sources). The net deposition of POC on the riverbed (i.e., 11.4 kgC ha−1 year−1) retained ca. 31% of terrestrial inputs of POC. In addition, average annual buried C was 0.34 kgC ha−1 year−1, accounting for only 1% of terrestrial POC inputs or 3% of net POC deposition. The results indicate that about 79% of deposited organic C was converted to inorganic C (CH4 and CO2) in the sediment and eventually released into the overlying water column. Conclusion: This study serves as an exploratory study on estimation of C fluxes from terrestrial to aquatic environments at the watershed scale. We demonstrated capabilities of the SWAT-C model to simulate C cycling from uplands to riverine ecosystems and estimated C sinks and sources in aquatic environments. Overall, the results highlight the importance of including carbon cycle dynamics within the riverbed in order to accurately estimate aquatic carbon fluxes and stocks. The new capabilities of SWAT-C are expected to serve as a useful tool to account for those processes in watershed C balance assessment. [ABSTRACT FROM AUTHOR]

This paper presents the results of geoarchaeological and geochronological investigations at Con Moong Cave, North Vietnam. Beneath the published, terminal Pleistocene sequence, recent excavations have uncovered a ~5 m stratigraphic sequence containing flaked stone artifacts and sedimentary features that indicate extensive post‐depositional change. As the effects of tropical conditions on Pleistocene cave sediments are poorly resolved, a range of complementary techniques was selected to reconstruct the nature of on‐site sedimentation and occupation, while assessing the taphonomy of archaeological and palaeoecological materials. Our approach incorporates microstratigraphic, geochemical and sedimentological analyses, using optically stimulated luminescence (OSL) dating to estimate the time of sediment deposition in the cave. This case study has broad application to tropical zones worldwide. Sedimentation began in early Marine Isotope Stage (MIS) 4, while micromorphologically observed human occupation commenced before 42 thousand years ago (ka). By placing our results within the context of published, high‐resolution regional records of climate, we demonstrate that on‐site rhythms of Pleistocene occupation correlated with environmental changes in the region. During MIS 3, episodic abandonment of the site coincided with periods of drier conditions, while rapid climate fluctuations in MIS 2 corresponded with short‐lived occupation events and a switch to predominantly geogenic deposition in the cave. [ABSTRACT FROM AUTHOR]

Bioturbation promotes priming and total remineralization of sedimentary organic matter (Corg) in multiple ways. A primary local mode is the injection of reactive Corg from the water column, surface sediment, and mucus secretions into deposits. During feeding, burrowing, and construction activities by benthic fauna, labile substrates are brought into close association with more refractory material over a wide range of time scales, geometries, and depths, enhancing decomposition of the less reactive components (priming). One measure of these local interactions is the particle mixing coefficient, DB, which can be estimated from the averaged penetration of particle-reactive radionuclides into deposits. Patterns of DB in Long Island Sound, an estuarine system with well-defined sources of naturally occurring radionuclides, show consistent positive correlations between DB and total inventories of excess 234Th (t1/2 = 24 days) and 210Pb (t1/2 = 22 years) at local and basin scales. These correlations, maintained seasonally in the case of 234Th, demonstrate not only the penetration of plankton-derived, reactive Corg into deeper regions of deposits during bioturbation over monthly (∼5–10 cm) to decadal timescales (∼20–100 cm) but also the enhanced capture of labile substrates from the water column across basin scales into bioturbated patches as the intensity of reworking increases. In Long Island Sound, sedimentary Chl-a distributions and benthic nutrient regeneration (e.g., NH4+ fluxes) reflect these particle exchange processes. Basin and regional scale capture of labile substrates into bioturbated deposits can be generally demonstrated, for example, along the highly productive Cape Hatteras continental margin. Thus, total and net remineralization necessarily increase with the biogenic enhancement of the quantity of labile particulate substrate in deposits. This capture, intermixing, and close association of reactive and refractory substrates (reductant blending), and thus the optimization of priming potential, represent important, often overlooked, pathways by which bioturbation generates biogeochemical conditions conducive to maximum efficiency of remineralization.

Diagenetic effects on the magnetic mineralogy in marine sediments have long been investigated, including oxidation/reduction reactions, magnetic dilution, formation of iron sulfides and oxides, magnetization acquisition mechanisms and reliability of the paleomagnetic record. This study investigates diagenetic effects in low-oxygen depositional environments characterized by recent and past magnetic mineral dissolution zones. We analyze a marine sequence from the Alfonso Basin in the southern Gulf of California in which the topmost sediments show diagenetic effects marked by high magnetic enhancement factors. The susceptibility logs show high values at the top sediments with well-defined small amplitude low frequency fluctuations down core. Magnetic hysteresis loops indicate low coercivity saturation, characteristic of magnetites and low-tititanomagnetites with varying paramagnetic contributions. Intensity of natural remanent, isothermal and anhysteretic magnetizations and coercivity parameters show similar variation patterns with depth. The anhysteretic remanence intensity-susceptibility ratio shows an inverse correlation to magnetic susceptibility, indicating varying concentration of fine grained single domain and superparamagnetic particles. The magnetic logs record diagenetic changes and magnetite authigenesis, with preserved recent and old dissolution zones marked by enriched single-domain/pseudo-singledomain/multi-domain magnetite in between the dissolution fronts. The oxidation/reduction processes relate to climatic and water/sediment interface factors controlling the dissolution processes, which occur in the Alfonso Basin anoxic conditions. [ABSTRACT FROM AUTHOR]

Wilson, T. and DePaul, V., 2017. In situ benthic nutrient flux and sediment oxygen demand in Barnegat Bay, New Jersey. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay-Little Egg Harbor, New Jersey. The U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection, measured sediment oxygen demand (SOD) and benthic nutrient fluxes throughout Barnegat Bay, New Jersey. SOD was determined in situ using chambers equipped with optical dissolved oxygen sensors. The benthic nutrient fluxes of ammonia (NH3), nitrite + nitrate ( plus ions; here, referred to as NO32), soluble reactive phosphorous (SRP), and dissolved silica (SiO2) were measured with in situ equilibrium dialysis samplers. Measurements were made at nine stations around the periphery and at three mid-Bay locations from August 2012 to October 2013. The SOD ranged from −1.5 to −8.4 g of oxygen (O2) m−2 d−1. The SOD rates varied as a function of water temperature and followed the van't Hoff rate equation for change in reaction rate with temperature, with a temperature coefficient ( Θ) that varied among sites and averaged 1.083. The highest SOD rates in the bay were measured near the mouth of the Toms River embayment. Concentrations in the upper 1 m of sediment pore water were found up to 23 mg N L−1 for NH4+ and 6.7 mg P L−1 for SRP. Maximum measured fluxes into the overlying water were 3.0 × 10−2 g NH3-N m−2 d−1, 7.0 × 10−4 g NO32-N m−2 d−1, 1.9 × 10−3 g P m−2 d−1, and 3.6 × 10−3g SiO2 m−2 d−1. Using the measured benthic N and P fluxes, daily nutrient inputs derived from sediment recycling are shown to be comparable in scale to freshwater tributary inputs to the bay. [ABSTRACT FROM AUTHOR]

Deep-sea fans are well known depot centers for organic carbon that should promote sulfate reduction. At the same time, the high rates of deposition of unconsolidated metal oxides from terrigenous origin may also promote metal-reducing microbial activity. To investigate the eventual coupling between the iron and sulfur cycles in these environments, shallow sediment cores (< 50 cm) across various channels and levees in the Congo River deep-sea fan (~5000 m) were profiled using a combination of geochemical methods. Interestingly, metal reduction dominated suboxic carbon remineralization processes in most of these sediments, while dissolved sulfide was absent. In some ‘hotspot’ patches, however, sulfate reduction produced large sulfide concentrations which supported chemosynthetic-based benthic megafauna. These environments were characterized by sharp geochemical boundaries compared to the iron-rich background environment, suggesting that FeS precipitation efficiently titrated iron and sulfide from the pore waters. A companion study demonstrated that methanogenesis was active in the deep sediment layers of these patchy ecosystems, suggesting that sulfate reduction was promoted by alternative anaerobic processes. These highly reduced habitats could be fueled by discrete, excess inputs of highly labile natural organic matter from Congo River turbidites or by exhumation of buried sulfide during channel flank erosion and slumping. Sulfidic conditions may be maintained by the mineralization of decomposition products from local benthic macrofauna or bacterial symbionts or by the production of more crystalline Fe(III) oxide phases that are less thermodynamically favorable than sulfate reduction in these bioturbated sediments. Overall, the iron and sulfur biogeochemical cycling in this environment is unique and much more similar to a coastal ecosystem than a deep-sea environment. [ABSTRACT FROM AUTHOR]

Numerical modeling is an efficient and useful method for understanding the hydrodynamics and water quality responses to nutrient loading changes and other management in estuarine and coastal systems. In this study, the Environmental Fluid Dynamic Code (EFDC) was applied in the Famosa Slough, a small tidal marsh system in urban San Diego County, California, to analyze multiple management scenarios focusing on different aspects of controlling processes: watershed load reduction, macroalgae harvesting, dredging, and the combination of different options. In order to evaluate these management scenarios, a previous EFDC model was enhanced through modifying the model code to allow simulations of both benthic and floating macroalgae as separate state variables, and configuring a sediment diagenesis model to predictively represent the dynamic interactions between the watershed load and benthic nutrient flux. The model was calibrated and verified by comparing model predictions with the observed data of hydrodynamic and water quality parameters throughout 2008. The calibrated model was then applied to simulate the water quality response to various management scenarios. The simulated results showed that combining watershed nutrient load reductions and harvesting floating macroalgae can produce significant water quality benefits. The results provide useful information for hydrological ecosystem protection and can be used for determining cost-effective implementation actions in the future. [ABSTRACT FROM AUTHOR]

Sediment diagenesis can be a significant driver of oxygen depletion in lakes and may dramatically impact the hypolimnetic oxygen concentrations. In this study, our aim is to simulate sediment oxygen demand (SOD) dynamics under varying conditions of organic matter sedimentation and hypolimnetic oxygen levels. Specifically, we use a process-based sediment diagenesis model to identify the critical processes that regulate dissolved oxygen levels in the hypolimnion of the mesotrophic Lake Simcoe, Ontario, Canada. We quantify the spatial distribution of organic matter mineralization and subsequently assess the role of sediment oxygen demand in hypolimnetic oxygen depletion. Our model reinforces the notion that aerobic mineralization is a major diagenetic process that shapes sediment oxygen demand in the system. Our model confirms existing empirical evidence that SOD contribution to the hypolimnetic oxygen deficit is less than 30% in Lake Simcoe. Our analysis also sheds light on the potential drivers of the significant spatial heterogeneity of the sediment oxygen demand among Kempenfelt Bay, Cook’s Bay, and the main basin of Lake Simcoe, namely, the differences in primary production rates, the origins of the settling organic matter, the redistribution of sediments, and the oxygen concentration at the sediment–water interface due to differences in morphology and hydrodynamics. We conclude by arguing that the pace of the planned re-oligotrophication and the anticipated hypolimnetic oxygen improvements, induced by nutrient loading reductions, may experience short-term delays from years to several decades due to the potential effects of a number of feedback mechanisms across the sediment–water interface in Lake Simcoe. [ABSTRACT FROM AUTHOR]

Our study examines the relative importance of the causal linkages between exogenous total phosphorus (TP) loading and internal nutrient recycling with the water quality conditions in Lake Simcoe, Ontario, Canada. We enhance the mechanistic foundation of a simple TP mass-balance model, originally developed to guide the eutrophication management in the system. The structural improvements include the incorporation of macrophyte dynamics, the explicit representation of the role of dreissenids in the system, and the improved portrayal of the interplay between water column and sediments. Our model provides good agreement with the observed TP variability in the system during the study period (1999–2007). Consistent with empirical evidence, our model predicts that macrophyte uptake from the interstitial waters is responsible for a significant loss of P from the sediments. Our model also suggests that dreissenids filter a considerable amount of particulate P from the water column, but the effective clearance rate is significantly lower with a substantial amount of the filtered particles (> 85%) returned into the water column as faeces, pseudofeces or other metabolic excreta. P diffusive fluxes from the sediments account for about 30–35% of the exogenous P loading in Lake Simcoe. The sediments in the main basin are mostly driven by fast diagenetic processes of settling organic matter from the epilimnion, suggesting an internal P loading of 9.2 tonnes yr − 1 . Finally, our study attempts to explain the lack of distinct decreasing trends in ice-free TP concentrations after the invasion of dreissenid mussels, suggesting that the presence of active nutrient recycling pathways, potentially magnified by the particular morphological features and hydrodynamic patterns of Lake Simcoe, could counterbalance the direct effects of dreissenid filtration. [ABSTRACT FROM AUTHOR]

Our study presents a biogeochemical model that aims to reproduce the ecological processes shaping phytoplankton dynamics in the shallow hypertrophic lagoon of Albufera de Valencia (Spain). The model simulates two elemental cycles (N and P), two phytoplankton groups (cyanobacteria and non-cyanobacteria), and heterotrophic bacteria. First, we examine the capacity to reproduce the observed plankton patterns, while accommodating the uncertainty related to the external forcing factors of our model (hydraulic and nutrient loading, zooplankton grazing). Sensitivity analysis is also performed to identify the most influential parameters and therefore to shed light on the knowledge needed to solidify the model parameter specification. We subsequently utilize the calibrated model to assess the phytoplankton response to potential restoration actions; namely, the interplay between external nutrient loading reductions and variant flushing rates. The model successfully simulates a number of relevant water quality variables in the system, including total chlorophyll a , nitrate, ammonia, total nitrogen and total phosphorus. According to our sensitivity analysis, the credibility of the model as a management tool is primarily dependent upon the characterization of the phytoplankton growth strategies and associated settling rates. External P and N loadings are identified as the predominant driver of the system dynamics and their control should remain the main priority of local management efforts. Finally, we pinpoint future research directions that could advance our understanding of the ecosystem functioning, including an improved quantitative description of the seasonal variability of the hydraulic regime in the studied lagoon. [ABSTRACT FROM AUTHOR]

Current CE-QUAL-W2 mainly simulates hydrodynamics and eutrophication processes in the water column. The benthic sediment processes and sediment–water interactions have been neglected or very much simplified using zero-order and first-order rates. In this study a benthic sediment diagenesis module was developed and integrated into CE-QUAL-W2. Enhanced CE-QUAL-W2 was capable of simulating the dynamic releases of ammonium, nitrate, phosphorus, dissolved silica and dissolved methane from the sediment to the overlying water, as well as benthic sediment oxygen demand. The oxidation of sulfides is included for salt water sediments. The ability of CE-QUAL-W2 model to correctly predict sediment–water nutrient fluxes and sediment oxygen demand was evaluated against SedFlux and CE-QUAL-ICM models through a series of case studies. These case studies were chosen for representing various sedimentation and environmental conditions. The simulated sediment–water nutrient fluxes and sediment oxygen demand over time were generally in good agreement with these two model results for all data sets. The effect of benthic sediment diffusive thickness, particle mixing coefficients on nutrient releases from sediments and sediment oxygen demand were examined. Enhanced CE-QUAL-W2 model was also applied to the Lower Minnesota River for further evaluating its performance. This paper presents the sediment diagenesis module development, validation tests and application of the enhanced CE-QUAL-W2 model. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a transition metal that can be toxic to aquatic biota even at low levels. The adverse effects of Cd are of particular concern in waterbodies along the eastern margin of the Pacific Ocean, where anthropogenic inputs are superimposed on the naturally elevated oceanic concentrations. While the accumulation of Cd in marine bivalves is well documented, few studies have investigated the cycling of dissolved Cd in estuarine and coastal waters that are susceptible to Cd enrichment. Here we examine the temporal and spatial variations of dissolved Cd in the coastal waters of Salish Sea in the northeast Pacific, with a focus on the Strait of Georgia (SoG). We find that the distribution of dissolved Cd in the Salish Sea is largely governed by conservative mixing between the upwelled Pacific water and freshwater discharge from the Fraser River, with a biological overprint transferring some of Cd from surface to deep water. Anthropogenic loadings of Cd from municipal effluent are negligible compared to natural inputs. Spatially, dissolved Cd and salinity gradually decrease as the Pacific source water flows landward from Juan de Fuca Strait into the SoG. Time-series sampling in the southern SoG reveals a small but significant decrease of dissolved Cd concentrations in the SoG deep layer over a winter stagnation period. We attribute this decline to diffusive removal, as driven by Cd sulfide precipitation in suboxic porewaters. The intermittent stagnation of the SoG deep layer provides a natural "benthic chamber" to estimate elemental exchange between deep water and sediment on a basin-scale, which could be valuable for studying the biogeochemical cycling of other trace metals. • Conservative mixing largely governs the distribution of dissolved Cd. • Biological cycling transfers some Cd from surface to deep water. • Cadmium removal from deep water is likely driven by sediment diagenesis. • Cadmium loadings from municipal effluent are negligible compared to natural inputs. [ABSTRACT FROM AUTHOR]

Abstract: We carried out detailed magnetic measurements of the core (MD161/8) located in the vicinity of Site NGHP-01-10, where ~128m of hydrate is confirmed by drilling/coring, to understand the diagenesis of magnetic minerals in a gas hydrates/cold seep environment. The rock magnetic measurements along with SEM–EDS and XRD analyses show a zone of reduced magnetic susceptibility (zone 2) where most of the magnetic minerals are dissolved. The enhanced concentration of chromium reducible sulfur (CRS) in this zone suggests an intense pyritization process while isotopically depleted authigenic carbonates indicate sulfate reduction via anaerobic oxidation of methane (AOM). Therefore, the dissolution of magnetic minerals is attributed to the HS− released during AOM that has resulted in the reduction in the magnitude of magnetic parameters. Within zone 2, a zone of enhanced susceptibility (zone 2a) is observed between 17.68 and 23.6mbsf, and is located beneath the present day sulfate–methane transition zone (SMTZ). The frequency-dependent magnetic susceptibility and low temperature magnetic measurements suggest the abundance of fine grained superparamagnetic (SP) sized ferrimagnetic particles. The SEM–EDS and XRD analyses show the presence of greigite which occurs in interstices between the pyrite crystals. Such occurrence of greigite in sediments has important implications in the interpretation of paleomagnetic records. We evaluated the likely mechanism for the greigite formation in KG offshore basin and our data suggest that the formation of greigite may be related to either paleo-SMTZ or anaerobic oxidation of pyrite. It is unlikely that the formation of greigite can be explained by the downward diffusion of sulfide below the current depth of SMTZ. However, further investigations are required to ascertain the mechanism for the formation and preservation of greigite. [Copyright &y& Elsevier]

Abstract: A new sequential extraction scheme for iron, sulfide and organic carbon rich sediments was evaluated for iron partitioning in synthetic iron monosulfides, natural pyrite, schwertmannite and goethite and natural acid mine drainage contaminated sediments. This sequential extraction procedure enabled the following fractions to be distinguished: (1) water soluble, (2) exchangeable (monosulfides and carbonates), (3) low crystalline Fe(III)-oxyhydroxide, (4) crystalline Fe(III)-oxide, (5) organic matter, (6) sulfides (pyrite) and (7) residual. In soils or sediments where no carbonates are present step 2 can be used as the monosulfide fraction, which is recovered at 70%. Low crystalline Fe(III)-oxyhydroxides and crystalline Fe(III)-oxides are isolated in steps 3 and 4, respectively (>80%). Pyrite is completely isolated with HNO3 8M in step 7 (>99%). The application to sediments from a water reservoir affected by Acid Mine Drainage (AMD) indicated that Cu, Zn and Cd co-precipitate as sulfides (monosulfides and pyrite), whereas most of the S resulting from sulfate reduction is linked to the organic matter. Lead, As and Cr are mainly found in the low crystalline Fe(III)-oxyhydroxides and crystalline Fe(III)-oxides, and are released during their reduction. [Copyright &y& Elsevier]

Abstract: The shifts and extent of aquatic macrophyte-mediated P and N regeneration, crucial in the initial stages of ecosystem development, were investigated using immature sediments which were poor in organic matter, P and N, but rich in Fe and Mn, obtained from a five-year-old artificial pond ‘Chicken Creek’, in east Germany. During the decomposition of indigenous plant materials (Phragmites australis (Cav.) Trin. ex Steudel, Potamogeton natans L., Potamogeton pectinatus L.) in a laboratory experiment, the concentrations of P, ammonium (NH4 +), Fe and Mn in the sedimentary pore water increased with increasing fresh plant biomass amendments, and over time. Based on weighted average of the biomass added, there were no differences between species in the enrichment of pore water P (51- to 60-fold) and Mn (19- to 26-fold), compared to pure sediments. There was, however, a clear sequence in the NH4 + and Fe enrichment of pore water between control sediment and plant additions with P. pectinatus < P. natans

Skeptical views of the scientific value of modelling argue that there is no true model of an ecological system, but rather several adequate descriptions of different conceptual basis and structure. In this regard, rather than picking the single “best-fit” model to predict future system responses, we can use Bayesian model averaging to synthesize the forecasts from different models. Does the combination of several models of different complexity improve our capacity to synthesize different perceptions of the ecosystem functioning and therefore the value of the modelling enterprise in the context of ecosystem management? Our study addresses this question using a complex (14 state-variable) eutrophication model along with a simpler modelling construct that considers the interplay among phosphate, detritus, and generic phytoplankton and zooplankton state variables. Using Markov Chain Monte Carlo simulations, we calculate the relative mean standard error to assess the posterior support of the two models after considering the available data from the system. Predictions from the two models are then combined using the respective standard error estimates as weights in a weighted model average. The model averaging approach is used to examine the robustness of predictive statements made from our earlier work regarding the response of Hamilton Harbour (Ontario, Canada) to the different nutrient loading reduction strategies. In particular, we consolidate the finding that the existing total phosphorus goal (<17μgL−1) is most likely unattainable, and therefore we identify the most achievable ambient target under the most stringent (but realistic) nutrient loading reduction scenario. Finally, the discrepancy between the chlorophyll a predictions of the two models pinpoint the need to delve into the dynamics of phosphorus in the sediment–water column interface, as the internal nutrient loading can conceivably be a regulatory factor of the duration of the transient phase and the recovery resilience of the system. [Copyright &y& Elsevier]

Abstract: We examine the likelihood of delisting the Hamilton Harbour as an Area of Concern, if the nutrient loading reductions proposed by the Remedial Action Plan are actually implemented. Our analysis suggests that the chl a criterion of 10μgL−1 is achievable, but the water quality setting process should explicitly accommodate the natural variability by allowing for a realistic percentage of violations, e.g., exceedences of less than 10–15% of the weekly samples during the stratified period should still be considered as compliance of the system. The current epilimnetic total phosphorus criterion of 17μgL−1 is probably stringent and therefore a somewhat higher value (e.g., 20μgL−1) may provide a more realistic goal. Phosphorus dynamics in the sediment–water column interface need to be revisited, as the internal nutrient loading can conceivably be a regulatory factor of the duration of the transient phase and the recovery resilience of the Harbour. We also pinpoint two critical aspects of the system dynamics that invite further investigation and will likely determine our predictive capacity to assess compliance with the chlorophyll a criterion of 10μgL−1, i.e., the nutrient recycling mediated by the microbial food web and the structural shifts towards a zooplankton community dominated by large-sized and fast-growing herbivores. The latter prospect highlights the notion that the bottom-up (i.e., nutrient loading reduction) approach historically followed in the Harbour was sufficient to bring the system in its present state, but any further improvements should be viewed in the context of a combined bottom-up and top-down (i.e., alleviation of the zooplanktivorous pressure) control. [Copyright &y& Elsevier]

A new sediment profile imaging (SPI) instrument, CHEM-SPI, was developed for in situ two-dimensional measurements of biogeochemical solutes using fluorosensor foils in sediments and overlying waters. The CHEM-SPI system was used to simultaneously measure vertical sections of pH, O, and pCO distributions in subtidal, surface deposits of Long Island Sound, NY. Images are readily obtained in 5-15 min with inexpensive LED excitation and commercial grade digital cameras having typical pixel resolution of ~50-100 μm over areas >150 cm sediment. Seasonal examples of in situ deployments of the instrument revealed extensive horizontal and vertical heterogeneity of pH distributions. pH dynamics were associated with complex biogenic structures in the upper few centimeters of marine sediment and the pulsed input of organic matter during the spring bloom period. The pH beneath the sediment-water interface was dramatically depressed by the bloom input of organic matter but macrofaunal activity otherwise dominated pH variations in the bioturbated zone. The CHEM-SPI system allows direct quantitative confirmation of biogeochemical patterns previously inferred qualitatively from color patterns in visible SPI images. The instrument is sufficiently adaptable in design to accommodate new optical sensor foils for other chemical variables. [ABSTRACT FROM AUTHOR]

Abstract: Iodine and its radioisotope 129I have been successfully used to trace the origin of pore waters in submarine fluid escape structures because of their close association with organic material in deeply buried sediments. We report here halogen concentrations and 129I/I ratios for fluids of five mud volcanoes sampled along an E–W transect across the Gulf of Cadiz in the NE Atlantic Ocean. Concentrations of iodide and bromide increase consistently seaward accompanied by a decrease in 129I/I ratios from 6490×10−15 to 663×10−15. The exceptionally high 129I/I ratios at the near-shore locations reflect the presence of fissiogenic 129I, produced in situ by spontaneous fission of 238U within terrigenous sediments and released into pore water during clay mineral diagenetic processes. The observed 129I/I and halogen trends, together with similar changes in 87Sr/86Sr ratios, indicate a progressive seaward transition from inorganic-terrigenous to organic-marine fluid sources. Comparison of our results with literature data for varying geological settings reveals a general relationship between fissiogenic 129I, radiogenic 87Sr and the lithology or provenance of rocks and sediments, respectively. While 129I/I ratios in continental rock-hosted aquifers and terrigenous sedimentary systems are dominated by in situ production of fissiogenic 129I, iodine isotopes in oceanic settings or volcanogenic marine sediments reflect the release of ‘old’ iodine from deeply buried organic matter. The Gulf of Cadiz represents the full transition between these continental and oceanic 129I/I and 87Sr/86Sr end members. This is the first systematic investigation of fissiogenic 129I production in marine sedimentary environments. [Copyright &y& Elsevier]

Abstract: The ‘Chicken Creek’ artificial catchment area, Welzow-South, E Germany, created to study processes and structures of initial ecosystem development, discharges into a small experimental lake (A=3805m2, V=3992m3, z max=2.4m). This lake was man-made in 2005 and filled by natural surface runoff until January 2006. In summer 2006 and 2008, the actual development of sediments and the evolution of the phosphorus (P) cycle were studied. 19.7% of the original lake volume was filled by sediment within the first 3 years. A fine-grained sediment representing silt (6.3–63μm) accumulated at high accretion rates at the deepest point (200mma−1, 0–24mmweek−1) due to massive erosion in the catchment. The sediment is low in organic matter (2.5–5.2%) and total P (TP, 0.31–0.97mgg−1). Low amounts of P associated with degradable organic matter and surplus of metal hydroxides (Fe:P∼40, Al:P∼20) favor an efficient P binding and low dissolved P concentrations in pore water (1–107μgl−1). Hence, the mineral sediment quality and the low rates of P release (0.06mgm−2 d−1) revealed that a lake at an initial stage of development has essentially no sedimentary P cycle compared to eutrophic shallow lakes. However, the increasing emersed and submersed macrophyte growth will control further lake succession by intensifying the internal nutrient cycling. The macrophytes drive the evolution of a sedimentary P cycle by mobilizing and translocating P, by accumulating carbon and thus by stimulating microbial and redox processes. [Copyright &y& Elsevier]

Abstract: A one-dimensional vertical unsteady numerical model for diffusion-consumption of dissolved oxygen (DO) above and below the sediment–water interface was developed to investigate DO profile dynamics under wind waves and sea swell (high-frequency oscillatory flows with periods ranging from 2 to 30s). We tested a new approach to modelling DO profiles that coupled an oscillatory turbulent bottom boundary layer model with a Michaelis–Menten based consumption model. The flow regime controls both the mean value and the fluctuations of the oxygen mass transfer efficiency during a wave cycle, as expressed by the non-dimensional Sherwood number defined with the maximum shear velocity (Sh). The Sherwood number was found to be non-dependent on the sediment biogeochemical activity (μ). In the laminar regime, both cycle-averaged and variance of the Sherwood number are very low . In the turbulent regime, the cycle-averaged Sherwood number is larger . The Sherwood number also has intra-wave cycle fluctuations that increase with the wave Reynolds number (VAR(Sh) up to 30%). Our computations show that DO mass transfer efficiency under high-frequency oscillatory flows in the turbulent regime are water-side controlled by: (a) the diffusion time across the diffusive boundary layer and (b) diffusive boundary layer dynamics during a wave cycle. As a result of these two processes, when the wave period decreases, the Sh minimum increases and the Sh maximum decreases. values vary little, ranging from 0.17 to 0.23. For periods up to 30s, oxygen penetration depth into the sediment did not show any intra-wave fluctuations. Values for the laminar regime are small (≤1mm for μ =2000gm−3 d−1) and decrease when the flow period increases. In the turbulent regime, the oxygen penetration depth reaches values up to five times larger than those in the laminar regime, becoming asymptotic as the maximum shear velocity increases. [Copyright &y& Elsevier]

Abstract: In many anoxic sedimentary environments, the onset of sulfate reduction, and pyritization of detrital iron-bearing minerals, leads to a precipitous decline in magnetic mineral concentration during early diagenesis. The usefulness of the surviving paleomagnetic record in such environments is usually argued to depend on how much of the primary detrital magnetic assemblage survives diagenetic dissolution. Detailed rock magnetic and electron microscope analyses of rapidly deposited (~7 cm/kyr) latest Pleistocene–Holocene sediments from the continental margins of Oman (22°22.4′N, 60°08.0′E) and northern California (38°24.8′N, 123°58.2′W) demonstrate that pyritization during early diagenesis also leads to the progressive down-core growth of the ferrimagnetic iron sulfide greigite. Greigite growth begins with nucleation of large concentrations of superparamagnetic (SP) nanoparticles at the inferred position of the sulfate–methane transition, which can explain the apparently paradoxical suggestion that diagenetically reduced sediments contain enhanced concentrations of SP particles. Looping of hysteresis parameters on a “Day” plot records the dissolution of single domain (SD) (titano-)magnetite and the formation of SP greigite, which then slowly and progressively grows through its SD blocking volume and acquires a stable paleomagnetic signal. This looping trend is also evident in data from several published records (Oregon margin, Korea Strait, Japan Sea, Niger Fan, Argentine margin, and the Ontong–Java Plateau), indicating that these processes may be widespread in reducing environments. Our observations have profound implications for paleomagnetic records from sulfate-reducing environments. The paleomagnetic signal recorded by greigite is offset from the age of the surrounding sediments by 10''s of kyr, and ongoing growth of greigite at depth results in smoothing of the recorded signal over intervals of 10''s to 100''s of kyr. We therefore expect the presence of greigite to compromise paleomagnetic records in a wide range of settings that have undergone reductive diagenesis. [Copyright &y& Elsevier]

Abstract: Samples of particulate organic matter from the water column and anoxic Holocene sediment layers from the Small Meromictic Basin (SMB) in Ellis Fjord (eastern Antarctica) were analyzed to study the early incorporation of reduced inorganic sulfur species into highly branched isoprenoid (HBI) alkenes. HBIs were not detected in the water column samples taken during austral winter, whereas compounds containing the C25 HBI skeleton were abundant in all analyzed Holocene sediment layers. The structure of the C25:2 HBI alkene and its enriched stable carbon isotopic composition suggest that it is produced by a diatom or diatoms, probably belonging to the Navicula genus in the sea ice which covers the area most of the year. Within just 500 years of deposition, all of the HBI alkene was sulfurised. A mixture of products was formed, including components tentatively identified as a C25 HBI thiane and three S-containing dimers composed of two C25:1 HBI skeletons linked together by a sulfide bond. Most was, however, converted to polar S-containing compounds. The reaction rate for sulfurisation of the C25:2 HBI alkene is the highest observed so far in natural systems. Sterols and other lipids known to be prone to sulfurisation were not sulfurised. The reason for this is unclear. [Copyright &y& Elsevier]

Abstract: Copper and uranium may be closely associated metals in sedimentary basins in which “upstream” sediments have been diagenetically reddened (e.g., sediment-hosted stratiform copper (SSC) deposits and roll-type uranium deposits) and the immediate hosts of mineralization are adjacent reduced sediments. The timing of leaching is closely linked to the process and timing of reddening, with descending meteoric water providing the oxygen needed for the reddening process. To leach and transport copper, the low-temperature pore solution must evolve to a brine, and importantly, its Eh must decrease to moderately positive levels (0.1±0.1V). For uranium, a simple oxidized solution is sufficient. Given the parallel Eh paths for copper and uranium and their close associations with diagenetic reddening, the dominant metal in sediment-hosted stratiform copper or roll-type uranium deposits is probably related closely to the source mineral and/or rock constituents of the reddened sediments. [Copyright &y& Elsevier]

Searching for life when we do not know what it is like is at best a difficult task, and at worst, an exercise fraught with frustration and potential failure. In developing methods that will have general applicability, one must ascertain first what the general features of life might be that, when present, would provide strong inference of the presence of active life. We propose here that the tendency of life to be associated with energetic gradients, in fact to create its own gradients via the catalytic consumption of nutrients and oxidants, and the production of waste products, is one of the general features of active extant life. As life seeks out and creates such gradients, layered microbial communities, or LMCs, result that are in their own way, prima facie biosignatures. These LMCs are abundant, perhaps ubiquitous in physically stratified environments on our own planet. If energy flows through a given system, and if life has developed efficient catalytic methods to utilize this energy, then LMCs are predicted to be present. Here we discuss the general issues of what can be gleaned from the study of LMCs in terms of energy flow, carbon flow, and carbon storage in earthly ecosystems, as well as the philosophy of using LMCs as biosignatures in the search for life on Earth, and perhaps, in extraterrestrial sites. [ABSTRACT FROM AUTHOR]

Acidic mining lakes (pH<3) represent a big environmental issue in former lignite mining areas. The acidity status of such lakes is mainly governed by the fluxes and the turnover of iron. No data are known about the iron cycling at the sediment–water boundary in the littoral of acidic mining lakes. In order to study the microstratification of iron cycling at the sediment–water interface, existing microsensor and gel-probe techniques (diffusive equilibration in thin-films, DET) were adapted to the extreme conditions of a mining lake. Microprofiles of O2 and pH measured in situ by a profiler were compared with profiles measured in sediment cores immediately after sampling. The results indicate that microprofile measurements in cores from the littoral underestimate oxygen penetration into the sediment. Both advective pore water movement and pore water displacement during coring did influence concentration profiles. Measurement of sulfate and both ferric and ferrous iron was possible on a millimetre scale using DET. Based on different test measurements, a protocol for the application of gel probes for the analysis of iron and sulfate in acidic mining lakes was developed.The combination of microsensor and DET data allowed the characterisation and localisation of iron turnover on a millimetre scale. As an example, results from the littoral of Mining Lake 111 (Lusatia, Germany) are presented. Pore water gradients indicated a flux of ferric iron and sulfate from the water into the sediment. There were no indications of iron reduction or oxidation in the uppermost 6 cm of the sediment. A relative comparison of the fluxes revealed that the iron and sulfur fluxes were probably driven by the formation of jarosite directly in the sediment. [Copyright &y& Elsevier]