Sediment Survey Research Articles

Evaluation of Nutrients Mass Balance on the Weirs in the Mid-lower Nakdong River Basin

The construction of artificial weirs as part of the Four Major Rivers Restoration Project is expected to result in the Nakdong River Basin having the characteristics of closed water bodies and properties of water quality that convert suspended components into soluble ones due to a long retention time, thereby leading to the continuous deterioration of water quality. In this regard, this study investigated the changes of water quality on four weirs in the mid-lower Nakdong River Basin. In addition, it examined the organic matters and nutrient salts affecting the water quality, established mass balance with respect to the nutrient salts, and analyzed the load accumulations of each weir to present the directions for water quality management. With regard to the water quality, the items of BOD and COD, T-N and NH4-N, and T-P and PO4-P showed similar tendencies, and most of the items exhibited high concentrations from July to September. Furthermore, it was confirmed that the concentrations of the water quality items were high in Dalseong Weir and Hapcheon-Changnyeong Weir. In July, most of the weirs showed the greatest difference of DO in the surface layer and deepwater layer, while the DO concentration of the deepwater layer dropped below 4.0 mg/L in all four weirs. The sediment survey showed that the SS, T-N, and T-P have a larger amount of sediment in the aphotic zone than in the photic zone, and the amount of sediment per unit area was greatest in Dalseong Weir. According to the sediment release survey results, the release concentration was high in July, which was due to the effects of high water temperature and low DO concentration. T-N was eluted mostly from Dalseong Weir and Gangjeong-Goryeong Weir, and T-P was eluted mostly from Dalseong Weir and Hapcheon-Changnyeong Weir. Among the mass balance, nitrogen balance showed the highest amount of accumulation in Gangjeong-Goryeong Weir (6109 kg/d), and phosphorus balance showed the highest amount of accumulation in Changnyeong-Haman Weir (447 kg/d). These results are expected to be utilized as important materials for setting the management directions for each weir.

Anomalous geochemical fields of ore elements of the South Tatarian sedimentary basin (Tatar Strait, Sea of Japan)

Introduction. Currently, sea territories for production and exploration of hydrocarbon raw materials and ore deposits have been increased. Geochemical survey of seafloor sediments is of great interest among direct methods for finding deposits. One of the most important objects for such work is the Tatar Strait, in the territory of which high concentrations of useful elements can be found. Purpose of the work: to study the geochemical characteristics of seafloor sediments of the South Tatarian sedimentary basin in order to identify possible ore fields within its territory. Methods and materials. The chemical composition of seafloor sediments was analyzed, according to which maps of geochemical fields were constructed using the ArcGis program. The results of the chemical assays are obtained from the Delta Olympus X-ray fluorescent spectrometer. The number of samples obtained is 62. Results. The contents and redistribution of 21 chemical elements on the studied area were studied. Only five elements have geochemical anomalies or elevated contents that may indicate possible ore deposits: Ti, Zr, Mn, V, S. The main zones of concentration of these elements are in the shelf and bathyal areas. The characteristics of distribution of these elements over the area of the South Tatarian sedimentary basin are given and anomalous geochemical fields are identified. Conclusions. The presence of geochemical indicators of placers of titanium raw materials confined to the river fans of the Tokhtinka, Zhulman, Nemi, Ptichya and to the mechanical barrier in the region of Sovgavan uplift has been established. Promising zones of hydrocarbon concentration due to the high sulfur contents in the zone of the dynamic influence of faults (mainly fissure displacement) along the boundaries of the Terneysky trough in its western and eastern regions have been identified.

Discrepancy in the responses of diatom diversity to indirect and direct human activities in lakes of the southeastern Tibetan Plateau, China

Abstract Both global warming and human impacts are inimical to the maintenance of biodiversity across the planet. Although there is some consensus regarding the probable responses of biodiversity changes under different global change scenarios, the factors controlling biodiversity on regional scales are unclear. Using surveys of lake-bed surface sediments and an analysis of diatoms from six lake cores across 116 lakes in the southeastern Tibetan Plateau of China, we investigated (i) changes in diatom richness and (ii) β diversity and its components at various spatial and temporal scales. β diversity partitioning revealed that the most important factor affecting changes in diatom communities was species turnover across both spatial and temporal scales. This finding indicates that conservation planning requires a regional approach that focuses on multiple lake systems. Temporal changes in the trend of β diversity were shown to result from changes in nestedness components. The results showed that climate warming and indirect human impacts caused the decline of species nestedness, thereby increasing biodiversity, while the intensification of direct human activities caused species nestedness to rise, resulting in concomitant loss of biodiversity. Since nestedness is often related to ordered species gain/loss dynamics, the results suggest that species gain slows down in lakes affected indirectly by human activities, while species loss accelerates in lakes subjected to direct human impacts. Thus, we predict that species richness will continue to decline across this vast region in the future.

Origin and depositional characteristics of supported conglomerates

Abstract The origin and depositional characteristics of supported conglomerates in the Mahu Sag, Junggar Basin, Xinjiang, China, are examined. Based on the terminological comparison, modern sedimentary survey and core description, the initial connotation and similarities and differences in definition between supported conglomerates and other similar concepts are discussed, the modern sedimentary environment in which supported conglomerates develop is analyzed, and the sedimentological characteristics of supported conglomerates formed in different depositional environments revealed by the cores of Mahu conglomerate oil field in the Junggar Basin are described. The supported conglomerate is similar in texture to grain supported conglomerate and openwork conglomerate but has differences from them, so it is suggested to keep the term “supported conglomerate”, but the formation mechanism of supported conglomerate needs to be re-examined. Through field survey of modern sediments in Baiyanghe alluvial fan, Huangyangquan alluvial fan, and Wulungu Lake in Xinjiang, it is found that supported gravels not only formed by flooding events but also by sieving, avalanching, fluvial sorting as well as wind and wave reworking in the depositional environments such as inter-mountain creek, colluvium fan, gravel channel on gobi and the fan surface, lake beach, delta front, subaerial debris flow and subwater grain-flow etc. Supported gravels could form supported conglomerate after being buried. Supported conglomerates of seven different origins have been recognized in the cores of the Triassic and Permian stratum of Mahu Depression, Junggar Basin, namely, supported conglomerates in gravel channel deposits, in wind reworked channel deposits, in gravel beach bar deposits, in wave reworked delta front deposits, in mouth bar deposits and in debris flow deposits respectively. The study shows the supported conglomerates may be formed by a single depositional event or by multi-events during the post-depositional sedimentary reworking and even in diagenesis stage. Through flume experiment, numerical simulation, empirical model and modern sediment survey, infiltration process of gravelly channel can be reconstructed and the primary pore structure of supported gravel can be estimated. Statistics on physical properties of various types of reservoirs in Triassic Baikouquan Formation of Mahu oilfield show that granule conglomerate and pebbly conglomerate have higher porosity and permeability, while the cobble and coarse pebble conglomerate have lower permeability, which indicates that the supported gravels are easy to be reworked by post depositional filtration and diagenesis, and thus decrease in porosity and permeability.

Cumulative effects of channel correction and regulation on floodplain terrestrialisation patterns and connectivity

One of the main drivers of overbank fine deposition and floodplain formation is the hydrological connectivity between the channel and the floodplain. Channel correction (i.e., groyne field construction within the main flow channel and secondary channel disconnections) and flow regulation can typically lead to a disconnection of riverine floodplains and disturbances that directly affect terrestrialisation. Channel correction and flow regulation can sometimes occur successively, and it is challenging to distinguish the roles of each. This work attempts to assess the respective effects of two phases of channel regulation (correction versus flow regulation) on floodplain terrestrialisation by comparing three bypassed reaches of the Rhône, France (Pierre-Bénite, Péage-de-Roussillon and Donzère-Mondragon). We applied a transversal methodology coupled with GIS analysis (old maps, Orthophotos, DEM's, etc.) to understand processes of channel-planform evolution, conducted a sediment survey (metal rod) to assess floodplain terrestrialisation, and performed sediment sampling (manual auger) to obtain surface sediment metal content levels (X-ray Fluorescence and Inductively Coupled Plasma Mass Spectrometry). We found a general trend of channel narrowing within the three reaches, among which approximately 40% was found to be associated with correction works while 20% was attributed to flow lowering caused by channel bypassing. The number of flowing channels in all sections declined significantly, and local anabranching reaches evolved into very stable single thread channels. Overbank sedimentation declined significantly over the period, with very high sedimentation levels observed immediately after correction works and with very low sedimentation levels observed after diversion. We also found overbank flooding (in the number of days per year) decreased while fine sediment thickness increased. Similarly, the highest concentrations of metals (Zc, Pb, and Cu) were found to be associated with a low connection frequency and vice versa. When similar 2-staged terrestrialisation patterns are observed in all three reaches, they differ in chronology and driving factors because of their longitudinal positioning and specific local conditions.

An Exploration Study of the Kagenfels and Natzwiller Granites, Northern Vosges Mountains, France: A Combined Approach of Stream Sediment Geochemistry and Automated Mineralogy

Following a regional reconnaissance stream sediment survey that was carried out in the northern Vosges Mountains in 1983, a total of 20 stream sediment samples were collected with the aim of assessing the regional prospectivity for the granite-hosted base and rare metal mineralisation of the northern Vosges magmatic suite near Schirmeck. A particular focus of the investigation was the suspected presence of W, Nb and Ta geochemical occurrences in S-type (Kagenfels) and I-S-type (Natzwiller) granites outlined in public domain data. Multi-element geochemical assays revealed the presence of fault-controlled Sn, W, Nb mineralisation assemblages along the margins of the Natzwiller and Kagenfels granites. Characteristic geochemical fractionation and principal component analysis (PCA) trends along with mineralogical evidence in the form of cassiterite, wolframite, ilmenorutile and columbite phases and muscovite–chlorite–tourmaline hydrothermal alteration association assemblages in stream sediments demonstrate that, in the northern Vosges, S-type and fractionated hybrid I-S-type granites are enriched in incompatible, late-stage magmatic elements. This is attributed to magmatic fractionation and hydrothermal alteration trends and the presence of fluxing elements in late-stage granitic melts. This study shows that the fractionated granite suites in the northern Vosges Mountains contain rare metal mineralisation indicators and therefore represent possible targets for follow-up mineral exploration. The application of automated mineralogy (QEMSCAN®) in regional stream sediment sampling added significant value by linking geochemistry and mineralogy.

A retrospective analysis on changes in sediment flux in the Mississippi River system: trends, driving forces, and implications

PURPOSE: The Mississippi River is the largest river in the USA and one of the most regulated rivers in the world. Understanding fluvial sediment flux changes in the Mississippi River system has critical implications for future sustainable development and management strategies. MATERIALS AND METHODS: We obtained annual runoff and suspended sediment series from the United States Geological Survey (USGS) Data Series. Here, we investigated temporal trends and historical phases of fluvial sediment flux, while also quantifying the driving forces of changes in sediment loads in the Mississippi River system using a sediment identity approach and the sediment survey records. RESULTS AND DISCUSSION: Since the earliest estimates (initially 400–500 Mt year⁻¹), land-ocean sediment reduction in the Mississippi River system has displayed two temporal phases, decreasing from 350 Mt year⁻¹ during 1952–1962 to 200 Mt year⁻¹ during 1963–2009. The decline in land-ocean sediment flux was the result of an increase in precipitation and water yield capacity being outweighed by a decrease in sediment concentration. It is estimated that a total of 24 Gt of sediment was trapped by dams and reservoirs from 1985 to 2015, while the amount of sediment reduction by soil conservation is estimated to be 15 Gt in the USA. We can deduce that reservoir construction was the dominant driver (~ 62%) influencing land-ocean sediment flux from the Mississippi River system during 1985–2015. During 1950s–1960s, reservoirs played an overwhelmingly primary role in reducing riverine sediments. In the Missouri River basin, the largest contributor of sediment to the lower Mississippi River, we found a dominant role (> 53%) of reservoirs on tributaries in trapping sediments. The decrease in land-ocean sediment flux has caused degradation of the Mississippi River delta. CONCLUSIONS: Human activities are the main factors influencing changes in land-ocean sediment flux. Therefore, there is an urgent need of a basin-wide strategic plan to maximize the benefits and minimize the risks in order to achieve sustainable management of the drainage basin and river delta.

Geochemical Footprint of Megacities on River Sediments: A Case Study of the Fourth Most Populous Area in India, Chennai

An intensive surface sediment survey was carried out over 24 locations from the upstream to downstream sections of two large rivers (Adyar and Cooum) in Chennai (India) during the February dry season of 2015. Trace element concentrations were assessed on a <63 µm fraction using the Geoaccumulation Index (Igeo) and the newly proposed Geochemical Urban Footprint Index (GUFI), which can be performed to determine the pollution status of any megacity river influenced by urban development. The sediment quality of Chennai’s rivers was also compared to worldwide megacity pollution using sediment quality guidelines (SQGs), and a new megacity pollution ranking was determined. The Igeo results indicate that the Chennai rivers studied are strongly to extremely polluted regarding trace element content of sediment. Silver (Ag), Cadmium (Cd) and Mercury (Hg) are the most significant tracers of urban contamination. Chromium (Cr) concentrations show an industrial contamination gradient in relation to levels of other trace elements (As, Cu, Ni, Pb, and Zn) at the Chennai megacity scale. The GUFI ranges from moderate to extreme contamination, particularly in the downstream stretches of the two rivers. This spatial trend is related to various point sources and identified at specific sampling stations, with a lack of identifiable buffer zones. According to the worldwide comparison of megacity pollution, Chennai is ranked in fifth position. The present position can be attributed to a number of explanations: a population explosion associated with the unplanned growth of the city and non-controlled point sources of pollution in Chennai’s waterways.

Assessment of organic and metallic contamination in the surface sediment of Monastir Bay (Eastern Tunisia): Spatial distribution, potential sources, and ecological risk assessment.

To investigate the current environment status in Monastir Bay (Tunisia), surface sediments from 32 stations were assessed for heavy metal and organic matter concentrations, and the results were compared with values of natural metal content, marine sediment quality standards, and other results concerning sediments from other Mediterranean coasts. The study of their spatial distributions refined by complementary approaches, including potential ecological risks determined through the enrichment factor, geo-accumulation index, contamination factor, potential ecological risk index, pollution load index, and principal component analysis, showed a significant impact of multiple anthropogenic sources. Moderate pollution of sediments, particularly by Ni and Cu, was also observed. Moreover, TOC values showed that the northern part of Monastir Bay is characterized by high levels of sediment organic matter because of the presence of fish farm cage. This baseline study can be used to establish background values for future sediment surveys.

Microbial metatranscriptomic investigations across contaminant gradients of the Detroit River

Microbial community function in freshwater sediments is influenced by the presence and persistence of anthropogenic pollutants, yet simultaneously imposes significant control on their transformation. Thus, microbes provide valuable ecosystem services in terms of biodegradation and bioindicators of compromised habitats. From a remediation perspective it is valuable to leverage the suite of microbial genes at the transcriptional level that are active in either natural versus stressed environments to provide insight into the cycling and fate of contaminants. Metatranscriptomic analysis of total bacterial and archaeal messenger RNA (mRNA) is a useful tool in this facet and was applied to sediments sampled from the Detroit River; a binational Area of Concern (AOC) in the Great Lakes. Previously established sediment surveys and modelling delineated the river into contaminant gradients based on concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and metals. Differential expression analysis through DESeq2 revealed that microbial transcripts associated with nitrate reduction, methanogenesis, and beta-oxidation were significant in legacy polluted sediments and linked with energetic pathways key in the generation of cellular currencies (acetyl-CoA, succinyl-CoA). Gluconeogenesis and polyester synthesis also showed high abundance in contaminated regions, along with increased expression of stress response genes and transposons, despite decreases in community α-diversity. Aromatic cleavage genes were detected, but in low abundance across the contaminant gradient. These results suggest that microbial communities within the Detroit River exploit unique anabolic and catabolic pathways to derive and store energy from legacy organic contaminants while simultaneously recruiting stress-response and gene transfer mechanisms to cope with xenobiotic pressures. By coupling well-resolved chemical datasets with metatranscriptomics, this study adds to the spatial understanding of in-situ microbial activities in pristine and perturbed freshwater sediments.

SPECTRAL IMAGING AND CLAY DETECTION IN LATGALE LAKES

The survey of lake sediments is complex, time consuming and costly process with risks to human health. Additionally, manually obtained sediment samples provide incomplete data about a survey region. In turn, remote sensing methods are cost-effective and can provide continuous data about a survey region. Therefore, authors decided to perform a pilot experiment with a remote sensing method in order to detect clay sediments deposited in lakebeds. The evaluated method is the analysis of spectral images of Sentinel-2. Pearson coefficient and C4.5 datamining methods were applied for data analysis. Survey objects are Latgale lakes with and without clay sediments. The pilot experiment showed, that spectral imaging of lake water is not applicable method to detect definitely clay sediments in lakes, however, research results provide ideas about indirect methods, which must be studied in the future.

Study on visual control system of acoustic in situ measurement technology for survey of seafloor sediment

A new kind of visual acoustic measurement system was developed to obtain the acoustic characteristics of seabed sediment and the working state of in situ measuring equipment in real time. The control unit of the system structure is mainly made up of the underwater control unit and the deck control unit. In comparison with similar traditional systems, the system can transmit the working video image, the measured acoustic data and the waveform synchronous from the underwater control equipment to the deck control unit through the connecting cable. Apart from self-contained in situ measurement, the working modes of it include visual online real-time control. In order to guarantee the stability and measurement precision of the video control system, the process control of in situ measurement was strictly tested in the experimental tank. In 2017, sea trials of the in situ measurement system was carried out in the South China Sea. In the process, data related to measurement, including the acoustic velocity and attenuation coefficient of the seabed sediment, were obtained as well. The results from sea trials show that the control process of the visual system is intuitive, reliable and accurate, and therefore it can be popularized and applied.

Flux of organic carbon burial and carbon emission from a large reservoir: implications for the cleanliness assessment of hydropower

Accurately quantifying the budget of carbon sources and sinks in hydropower reservoirs is important for evaluating the cleanliness of hydroelectricity. However, current research on carbon emissions from reservoirs has rarely taken into account the organic carbon (OC) buried in sediment. Only greenhouse gas emissions from the water-air interface at reservoirs have been examined, which would result in an overestimation of the greenhouse effect of reservoirs. In November 2017, this study investigated the distribution of sediment in the Hongfeng Reservoir (HFR) in southwest China, a typical large hydropower reservoir, by using an underwater seismology monitoring system. We estimated the flux of OC into sediment using the results of a sediment survey and a dataset compiled from references. Our results show that, the HFR retained 200,715 t of OC in the sediment since its impounding after dam construction to the sampling year of 2017, when the average burial flux was 3,521 t-C a−1 (106 g C a−1) and the modern burial flux was 5,449 t-C a−1. After excluding the exogenous OC, the modern valid carbon sink of the sediment was 4,632 t per year. Under the current state of the reservoir, taking the modern valid carbon sink value, the carbon emissions from the reservoir’s surface, and the discharge water from the dam into consideration, the net carbon sink of the HFR is found to be 1,098.9 t-C a−1. If the hydroelectricity generated by the reservoir is converted to a carbon sink, then the total net carbon sink becomes 12,972.9 t-C a−1. This work argues that both reservoir sediment and hydroelectricity are important carbon sinks and both should be included in assessments of the greenhouse effects of reservoirs.

Examination of Sediment Dynamics Based on the Distribution of Silica Fluxes and Flood Sediments in the Otoishi River Related to the Northern Kyushu Heavy Rain Disaster, July 2017

The heavy rain disaster occurred in July 2017, in northern Kyushu, Japan. The river environment greatly changed due to sediment moving accompanied by erosion. It is important regarding disaster prevention to localize watersheds where sediment transportation is active. In this study, the sediment dynamics were discussed on the basis of our investigation about the stored sediment, water-flow, and silica fluxes from sub-basins. As a result, the sediment survey revealed that many sediments consist of sand or gravel and were moved secondarily by water-flow. By the hydrological survey, it was confirmed that the trend of the dissolved silica concentrations varied between the right and the left bank tributaries. It was suggested that the left bank tributaries have a various process of water-flow. Considering the distribution of collapsed slopes, the right bank tributaries have more collapsed slopes than the left bank tributaries. As suggested by the results, the range of the silica flux is wider at the left bank tributaries because the sedimentation shows various distributions. On the other hand, the right bank tributaries were estimated topographically stable since the value of the silica flux is about the same.

Characteristics of sediment affecting monomethylmercury accumulation in benthic fish of the Mekong Delta.

The Mekong River Delta (Vietnam) is a flat, low-lying area formed by a dense network of main tributaries of the Tien and Hau Rivers, providing a nourishing habitat for aquatic organisms. A sediment survey of the total mercury (Hg), monomethylmercury (MMHg), and geochemical variables was carried out from the coast to 131 km upriver to establish an overview of the environmental factors affecting the bioaccumulation of Hg and MMHg in delta fish. The survey results revealed that the total Hg (12-90 ng g-1 ) and MMHg (0.014-1.5 ng g-1 ) concentrations were in the range of uncontaminated sediment. Statistical analysis using various geochemical factors demonstrated that sediment MMHg concentrations and fractions of MMHg over total Hg in sediment were higher at sites with higher total organic carbon (TOC) and total nitrogen sites. The current levels of TOC in Mekong Delta sediment are relatively low (0.2-1.5%); however, expanding dam constructions and aquacultures related to salinity intrusion are reinforcing the carbon burial rate by increasing the fine fractions. Based on the positive relationship found between MMHg and TOC in sediment, proper management efforts are necessary to reduce MMHg production in the Mekong River Delta sediment. Environ Toxicol Chem 2019;38:503-510. © 2018 SETAC.

Impact of water-sediment regulation on the transport of heavy metals from the Yellow River to the sea in 2015

Variations in particulate and dissolved heavy metal (Cu, Co, Ni, Zn, Pb, Cr, Cd and As) concentrations and fluxes as well as their response to the Water-Sediment Regulation Scheme (WSRS) process in 2015 were studied based on a daily water and sediment survey at Lijin gauge. The results showed that the water and sediment flux increased rapidly in the first stage of the WSRS, which was characterized by high water discharge and suspended sediment concentration (SSC). The suspended sediment was coarser than the natural state, while the particulate and dissolved heavy metal contents increased. In the second stage, the SSC decreased rapidly followed by a gradual reduction in water discharge, the suspended sediment became even coarser and both the particulate and dissolved metal contents showed a decreasing trend. The heavy metal flux during the WSRS period accounted for 42%–54% of the total year, and the transport form was dominated by the particulate form. Dissolved metal contents were affected by the release of heavy metals derived from the channel in the lower reaches, while particulate heavy metals mainly came from erosion of the riverbed and their contents were much lower than Xiaolangdi reservoir sediment. Heavy metal transportation was influenced significantly by the WSRS process. Changes in sediment flux resulted in significant differences in the flux of heavy metals and the distribution of metals in different transport forms between the first and second stage of WSRS.

A combined approach using spatially-weighted principal components analysis and wavelet transformation for geochemical anomaly mapping in the Dashui ore-concentration district, Central China

Sometimes geochemical anomalies linked with buried mineral deposits are too weak to be recognized by conventional methods. In this study, element concentration data from a stream sediment survey were subjected to a combined method of SWPCA (spatially-weighted principal components analysis) and WT (wavelet transformation) to derive a geochemical anomaly model for epithermal Au deposits in the Dashui ore-concentration district. The SWPCA was applied as a data integration method to extract information related to mineralization in the geochemical data. The WT was applied as a powerful tool for recognizing mineralization related anomalies in a complex geochemical field and for enhancing weak anomalies from background. The SWPCA–WT geochemical anomaly model indicated high favorability values for the known mineral occurrences and out-performed PCA–WT and SWPCA models. The SWPCA–WT geochemical model generated in this study provides a robust guide for further gold exploration in the Dashui ore-concentration district.

Spatially and temporally variable sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

Shallow-sea hydrothermal systems are ideal for studying the relative contributions to sedimentary sulfur archives from ambient sulfur-utilizing microbes and from fluxes of hydrothermally derived sulfur. Here we present data from a vent field in Palaeochori Bay, Milos, Greece using a suite of biogeochemical analytical tools that captured both spatial and temporal variability in biotic and abiotic sulfur cycling. Samples were collected along a transect from a seagrass meadow to an area of active venting. The abundance and isotopic composition of sulfide captured in situ, together with geochemistry from sedimentary porewaters and the overlying water column and solid phase sulfide minerals, record evidence of ephemeral activity of microbial sulfate reduction as well as sulfide oxidation. The sulfur and oxygen isotope composition of porewater sulfates indicate active sulfate reduction within the transition zone between the vents and seagrass, rapid recycling of biologically produced sulfide within non-vent sediments, and reoxidation of abiotic sulfide within the vent field. A phylogenetic survey of sediments also indicates the pervasive presence of a suite of putative sulfur-metabolizing bacteria, including sulfate reducers and sulfide oxidizers, many of which can utilize intermediate valence sulfur compounds. The isotopic composition of pyrite in these sediments consistently records a microbially influenced signature (δ34Spy of −4.4 to −10.8‰) relative to the hydrothermal endmember (δ34S ~ + 2.5‰), independent of distance from the vent source. The narrow range of pyrite δ34S across sediments with a highly variable hydrothermal influence suggests that physical mixing (e.g., by storm events) homogenizes the distribution of biogenic and hydrothermal Fe-sulfides throughout the region, overprinting the spatially and temporally variable interplay between biological and hydrothermal sulfur cycling in these environments.

Impoundment intensity determines temporal patterns of hydrological fluctuation, carbon cycling and algal succession in a dammed lake of Southwest China

Hydrological control of lakes has been increasingly practiced in many parts of the world, however, the long-term ecological impact of hydrological regulation and their dependence on lake impoundment intensity has been rarely examined. We combined a spatial survey of surface sediments with sediment core analyses to quantify the limnological changes over the last two centuries for an oligo-mesotrophic lake, which was dammed in 1957 and reinforced during 1987–1990, respectively. A water depth inference model constructed from surface sediment clay components was applied to a well-dated sediment core for water level reconstruction. The inferred water depth increased from 6.2 ± 0.9 m to 8.7 ± 1.7 m after dam construction and further to 13.6 ± 2.6 m after dam enforcement, resulting in an increase in the magnitude of water level fluctuation (WLF). Accordingly, bulk sediment C/N ratio and median grain size spiked in ∼1957 and ∼1990, respectively, reflecting a large input of terrestrial sources due to impoundment. With a consistent loss of littoral zone and benthic diatoms over time, a significant decrease in C/N ratio and an abrupt depletion of carbon isotopic signal suggested a shift of carbon transfer towards a pelagic pathway after ∼1990. While there was a significant increase in algal production since ∼1990, the accumulation rate of carbon and nitrogen burial displayed an accelerating drop since ∼1957, reflecting a diluting effect derived from expanding water storage. Furthermore, there was a significant increase in both the ratio between inorganic and organic carbon fluxes and sediment burial of inorganic carbon, reflecting enhanced degradation and low storage of aquatic organic carbon in stratified deep waters since ∼1990. Hydro-morphological variables were found to exert strong impact on diatom communities, with an increasing interplay with nutrient and climate variables over time. While there existed a significant shift of diatom composition in ∼1960, species richness and community dissimilarity showed a significant decrease when water depth was raised to above ∼10 m or the magnitude of WFL was above ∼2 m. Thus, our sediment surveys provide evidence on the significant impact of lake regulation on hydro-morphology, carbon burial and ecological shift over time, as well as its stronger interaction with other forcing with increased impoundment intensity.

Phosphorus Contents Re-visited After 40 Years in Muddy and Sandy Sediments of a Temperate Lagoon System

Worldwide, coastal water bodies suffer from anthropogenically elevated nutrient inputs, which led to eutrophication. Sediments in eutrophic systems are assumed to be an important internal nutrient source. The total phosphorus (TP) concentration (mg g-1 dry mass) is widely used as a proxy for the sediment nutrient load. 2-D distribution maps of TP concentrations are used for management plans, where areas of high TP values are marked in red. However, the sediment density is lowered at increasing water content, which can lead to different TP stocks per g m-2. The aim of this study was, to do a re-evaluation of TP concentrations and stocks in the model ecosystem of the Dars-Zingst Bodden chain, a typical lagoon system of the southern Baltic Sea. Sediment cores were taken at eight stations along transects from shallow to deeper parts of the lagoon. Samples were analyzed for TP, water and organic content, as well as density. This data set was compared to results from a sediment survey during the time of highest nutrient inputs (40 years ago) at the same sampling stations. TP concentrations from 40 years ago and today were in the same range. The highest TP concentrations (up to 0.6 mg TP g-1 dry mass) were found in the deeper basins and lowest concentrations in the shallow areas of the lagoon (down to 0.05 mg TP g-1 dry mass). However, normalization over dry bulk density reversed some results. The highest TP stocks (up to 5 g TP m-2) were then found in the shallow areas and lowest stocks (down to 0.2 g TP m-2) in the deeper parts of the lagoon. Some stations did not exhibit any differences of TP at all, even after including the dry bulk density. These findings suggest that there seems to be no up-, or downward trend in nutrient concentrations of sediments even after 25 years of reduced external nutrient inputs. Furthermore, TP stocks point to possible diffuse P entry pathways that counteract external nutrient reductions. These findings can have an impact on possible countermeasures for ecosystems rehabilitation, like sediment removal or nutrient reductions in the adjacent land.