Sediment Total Organic Carbon Research Articles

Spatial Distribution and Pollution Evaluation of Carbon, Nitrogen, and Phosphorus in Sediments of Zhushan Bay at Taihu Lake

To reveal the distribution characteristics of carbon, nitrogen and phosphorus in the sediments of Zhushan Bay at Taihu Lake, sedimentary columns were collected and sliced by 2 cm vertically from ten sampling points in three sections of Zhushan Bay. The content of total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) were determined for each slice to reveal their horizontal and vertical distribution. The results showed that:spatially, the content of TN, TP, and TOC increased in the surface sediments of Zhushan Bay from the open lake area to the bay, and inside the bay these indexes were significantly higher than in the open lake area (P<0.01). The content of TN, TP, and TOC in the surface sediments in the bay (section A) were 1.53 mg·g-1, 1.55 mg·g-1, and 11.31 mg·g-1, respectively, while in the surface sediments near the open lake (section C) they were only 0.75 mg·g-1, 0.57 mg·g-1, and 6.70 mg·g-1, respectively. Vertically, a feature of surficial enrichment was shown, and the contents of carbon, nitrogen and phosphorus in all three sections showed a decreasing trend with increase of depth. The contents of TN, TP and TOC in the surface sediments are 2-3 times, 2-5 times, and 2-3 times those in the bottom sediments, respectively. Generally, the average TP content in the sediment of Zhushan Bay is 0.93 mg·g-1, suggesting an apparent heavy pollution, while the average TN content is 1.11 mg·g-1 as slight pollution. According to the organic nitrogen index and comprehensive pollution index, the northern part of Zhushan Bay is suffering from heavy pollution, where the organic pollution is relatively strong. The TP pollution index is between 1.03 and 3.87, indicating heavy pollution in Zhushan Bay.

Dissolved Organic Matter Export from Surface Sediments of a New England Salt Marsh

Salt marshes sequester a large amount of carbon via sedimentation, but seasonal and climate change impacts on sediment carbon biogeochemistry are not well-understood. This study investigates the export of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) from New England salt marsh sediment seasonally and under possible expected drought conditions. Surface sediment total organic carbon (TOC) values shifted seasonally depending on the overlying dominant plant species suggesting that vegetation and inundation frequency and duration are key factors in sediment TOC fluctuations. Fall sediment samples leached more DOC than summer samples, were compositionally similar to the estuarine water column, and compositionally different from fresh plant matter. Thus, the seasonal TOC pulse incorporated into surface sediments could be a dominant source of DOC to the estuary in the fall and that summer contributions are presumed to be from upstream DOM sources based on optical properties. Sediments leached more DOC under drought than non-drought conditions due to induced cracking in the sediment enhancing organic matter degradation. This study suggests the majority of DOM exported laterally from salt marshes comes from surface sediments (versus plant matter) and that temperature and sea-level rise could affect seasonal and drought pulses of DOC from the marsh.

Methane distribution patterns along a transect of Lake Fuxian, a deep oligotrophic lake in China.

Freshwater ecosystems are recognized as one of the important natural methane (CH4) sources, but little is known about the emission hotspots and the effects of algal blooms on CH4 production in deep lakes. In this study, carried out from the littoral (S1), pelagic (S2-S4), and the deepest site (S5), water samples from different depths and sediment cores were collected along the transect of Lake Fuxian, a deep monomictic lake to investigate the spatial-temporal variations of CH4. Dissolved methane concentration observed at the oxic metalimnion was 37.5% and 19.5% higher than that those observed at the epilimnion and at the layer between 80 and 100 m depth, respectively. During the overturn period, the vertical distribution of CH4 in the water column was uniform, with an average concentration of 0.031 ± 0.007 μM in S2-S5. Statistical analysis indicated that the CH4 concentration in the water column was significantly higher in S1 than other sites along the transect during both sampling periods. Sediment CH4 concentration and methane production potential (MPP) were also significantly higher in S1 than in other sites. Along the sediment depth, the maximum MPP was observed at 6-8 cm in S1, but it moved up to the surface layer in S2-S5 in both sampling periods. In addition, stable carbon isotope analysis indicated that the surface sediments in the pelagic zone (S2-S5) mainly comprised autochthonous organic matters. In this zone, MPP had a significantly positive correlation with sediment total organic carbon (TOC) (R2 = 0.401, p < 0.01). In summary, we described the spatial and temporal distributions of CH4 in deep Lake Fuxian, littoral zones are CH4 emission hotspots that can contribute to the CH4 accumulation in the oxic metalimnion layer during the stratification period. In the pelagic zone, autochthonous organic matter was transported into the surface sediment after a massive algal bloom, representing another hotspot for CH4 production.

Dynamics and environmental importance of anaerobic ammonium oxidation (anammox) bacteria in urban river networks

Anaerobic ammonium oxidation (anammox) is recognized as an important bioprocess for nitrogen removal, yet little is known about the associated microbial communities in urban river networks which are intensively disturbed by human activity. In the present study, we investigated the community composition and abundance of anammox bacteria in the urban river network of Shanghai, and explored their potential correlations with nitrogen removal activities and the environmental parameters. High biodiversity of anammox bacteria was detected in the sediment of urban river networks, including Candidatus Brocadia, Scalindua, Jettenia, and Kuenenia. Anammox bacterial abundance ranged from 3.7 × 106 to 3.9 × 107 copies g−1 dry sediment based on 16S rRNA gene, which was strongly correlated to the metabolic activity of anammox bacteria (P < 0.01). A strong linkage between anammox bacteria and denitrifiers was detected (P < 0.05), implying a potential metabolic interdependence between these two nitrogen-removing microbes was existed in urban river networks. Sediment ammonium (NH4+) made a significant contribution to the anammox bacterial community-environment relationship, while anammox bacterial abundance related significantly with sediment total organic carbon (TOC) and silt contents (P < 0.05). However, no statistically significant correlation was observed between cell-specific anammox rate and the measured environmental factors (P > 0.05). In general, the community composition and abundance of anammox bacteria in different hierarchies of the river network was homogeneous, without significant spatial variations (P > 0.05). These results provided an opportunity to further understand the microbial mechanism of nitrogen removal bioprocesses in urban river networks.

Spatial and seasonal variability of sedimentary organic matter and its origin in an algal-blooming eutrophic lake

Abstract Knowledge of the origin of sedimentary organic matter (SOM) in lakes contributes to our understanding of the carbon cycle and provides valuable guidance for lake ecosystem management. To elucidate the changes in the spatial and seasonal origins of SOM in a eutrophic lake, we collected sediment at 31 sampling points in Lake Hachiro, northern Japan, in June and November of 2016 and April and June of 2017, and measured total organic carbon (TOC) and fatty acid biomarkers. We found that TOC and the origin of SOM showed both spatial and seasonal variations. TOC was relatively high in the eastern part of the lake and may reflect the hydrological conditions therein. The average TOC of sediment collected from the 31 sampling points increased from June to November 2016, concomitant with an increase in cyanobacterial fatty acids. A cyanobacterial bloom was observed in the water column from July to October of that year, and the input of cyanobacterial carbon to the sediment may explain the TOC increase during this period. We also detected an increase in TOC from November 2016 to April 2017, which coincided with increases in fatty acids of terrestrial and diatom origin. In this regard, we suspect that meltwater inflow during this period may have borne large quantities of terrestrial organic matter, and diatoms are known to predominate in Lake Hachiro during the spring. In contrast, from April to June 2017, we recorded decreases in TOC and all fatty acid biomarkers, with the exception of those derived from bacteria, indicating that decomposition processes prevailed during this period. Quantitative estimates indicated that, despite the spatial and seasonal variations, terrestrial organic carbon was the predominant carbon source in Lake Hachiro, even when the waters were eutrophic and algal blooms were present.

Organic Carbon in the Surface Sediments from the Intensive Mariculture Zone of Sanggou Bay: Distribution, Seasonal Variations and Sources

Mariculture has rapidly grown worldwide, which might greatly influence the biogeochemical cycle of organic carbon in coastal seas. In this study, several geochemical parameters, including grain size composition, sedimentary total organic carbon (TOC), total nitrogen (TN), stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions, were analyzed for surface sediments collected from different mariculture zones of Sanggou Bay and in different seasons. We investigated the composition and distribution of organic matter in surface sediments and further evaluated the contribution of mariculture activities to TOC sources. The TOC and TN contents (mass percentage) in the bay were in the range of 0.14% to 1.45% and 0.03% to 0.20%, respectively. The spatial distribution indicated that sedimentary TOC and TN contents in shellfish monoculture and shellfish-kelp polyculture zones were higher than in other mariculture zones, which might be related to grain size composition and mariculture organisms. Seasonal variations of TOC contents were observed in different mariculture zones. The TOC/TN atomic ratio (C/N), δ13C and δ15N were in the ranges of 5.97 to 10.97, −21.76‰ to −13.14‰ and 2.13‰ to 8.08‰, respectively, implying that sedimentary organic matter in Sanggou Bay was the mixture of marine phytoplankton, terrestrial and maricultural sources. A simple mixing model based on δ13C was applied and the results indicated that the relative contributions of organic carbon sources in Sanggou Bay followed the order kelp (36.6%) > marine phytoplankton (28.7%) > shellfish bio-deposition (23.8%) > terrestrial input (10.9%). Surface sediments in Sanggou Bay were dominated by mariculture-derived organic carbon, which on average accounted for 60.4% of TOC.

The Budget of Macrobenthic Reworked Organic Carbon: A Modeling Case Study of the North Sea

AbstractThe importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modeling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bidirectional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3‐D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is determined not only by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20–35% and in addition vertically diffuse 11–22% of the total budget of TOC in the uppermost 30‐cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the organic carbon cycling at the sediment‐water interface of continental margins.

Submarine canyons support distinct macrofaunal assemblages on the deep SE Brazil margin

Submarine canyons are common topographic features of continental margins where increased organic matter trapping and complex topography may enhance the abundance of benthic assemblages. This heterogeneity may result in differences in the composition of benthic assemblages and their diversity between canyon and nearby slope sediments. Here we studied and compared benthic macrofaunal assemblages of four submarine canyons and nearby slope transects (150–1300 m depth) on the E-SE Brazil margin (19–23 oS) along the Espírito Santo (ESB) and Campos Basins (CB). We asked if these submarine canyons would increase sediment total organic carbon (TOC) content and thus support higher abundances, lower diversity and dissimilar composition of macrofaunal benthic organisms if compared to open slope stations at similar depths. In general, we found limited support for a higher sediment TOC or macrofaunal abundances in canyons compared to slopes, although a steeper unimodal curve of TOC with depth in canyons was evidenced. Significant differences in sediment grain size and macrofaunal assemblages also occurred at spatial scales of basins, water depth and interactions between depth and environment (slope/canyon); highlighting the importance of intra-canyon heterogeneity processes. However, canyons and slope environments had significant differences in the structure of macrofaunal assemblages that were partially explained by water depth, TOC and mean grain size. The spatial heterogeneity within canyons and a variable proximity to continental runoff lead to a high dissimilarity of upper slope canyon assemblages indicating that these environments should be included in marine spatial conservation planning along Brazil’s EEZ in view of increasing offshore deep-sea exploration.

Level and distribution of nutrients in the hyporheic zone of Lake Taihu (China) and potential drivers.

To better understand the nutrient distributions in the hyporheic zone of a large shallow eutrophic lake (Lake Taihu) and the potential drivers, the total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) were investigated in March and December 2016. Spatial differences in the TN and TP contents existed in the hyporheic zone, particularly between the eastern and southern zones and the western and northern zones. The TOC/TN ratios in the western, northern, and central zones were mostly <8 and even reached 4, indicating that organic matter originated from aquatic organisms and algae, whereas those in the southern and eastern zones exhibited wide ranges, indicating complex pollution sources. The chloride depth profiles suggested that upwelling hyporheic flow potentially occurred in the southern, western, and northern zones, while alternating flow directions occurred in the eastern zone and no flow or weak flow occurred in the central zone. Compared to the 1st investigation, the TOC, TN, and TP in sediments in the 2nd investigation increased by 13%, 41%, and 87%, respectively, and these changes were mostly due to large hyporheic fluxes with high nutrient concentrations from shallow groundwater. The behavior of the hyporheic zone as an active pollution source/sink due to hyporheic flow should be considered in the comprehensive management of Lake Taihu. PRACTITIONER POINTS: Depth profiles of nutrients differed between sampling sites and between zones of Lake Taihu due to different pollution sources. Nutrients in sediment increased largely during winter compared to spring due to potential groundwater pollution through upwelling flow. No significant difference in sediment total organic carbon and ratios of C/N indicates a similar internal pollution source lake wide.

Past climate changes over South Korea during MIS3 and MIS1 and their links to regional and global climate changes

To test past climate change in central Korea in terms of latitudinal differences over the Korean Peninsula, we reconstructed relative abundances between C3 and C4 plants in Hanam area based on sedimentary total organic carbon isotope values (δ13CTOC) of a 2.8 m long trench in an archeological site and compared these data with climate changes at different latitudes of Korea. During marine isotope stage 3 (MIS3) corresponding to past 60,000–25,000 years, the millennial-timescale fluctuations of the δ13CTOC values in Hanam were more similar to those in Hongcheon located in the inner mountain area of central Korea than those in Cheollipo area in west coast of Korea. Periods with significantly decreased δ13CTOC values representing decreased C4 plants under wetter climates in these two inland areas are comparable with millennial-timescale Dansgaard–Oeschger (D-O) warming events recorded in Greenland ice cores, suggesting strong climatic teleconnection between East Asia and subpolar areas during the last glacial period. During MIS1 (Holocene), the changes in vegetation and climate in Hanam have been influenced by the long-term summer monsoon changes. Regarding past latitudinal change in aridity or humidity over Korea, during the middle Holocene, δ13CTOC values in areas of central South Korea gradually decreased, suggesting moving to a more humid climate. This is contrary to the increasing δ13CTOC values in southern South Korea indicating more dry climates. Furthermore, it is likely that there were two severe dry climates at different times at different latitudes (1000 cal BP in Hanam in northern South Korea and 2500 cal BP in Geoje in southern South Korea), suggesting possible different climate changes at millennial timescales over Korea.

Effects of fish cage culture and suspended oyster culture on macrobenthic communities in Xiangshan Bay, a semi-enclosed subtropical bay in eastern China

The impacts of fish cage culture and suspended oyster culture on macrobenthic communities were investigated in Xiangshan Bay, China, on a seasonal basis from January to October of 2015. Samples were collected from a fish cage farm, a suspended oyster farm, and two corresponding reference sites. Two-way ANOVA results showed that species richness, abundance, biomass, and Shannon–Wiener diversity differed significantly between the four different investigated areas, and different seasons as well. Cluster analysis showed that macrobenthic community composition in the fish and oyster culture areas significantly differed from that in the reference sites, respectively. Trophic structure of macrobenthos in the fish and oyster culture areas mostly clustered together owing to higher abundance and biomass of surface-deposit feeders and carnivores. The macrobenthic communities and feeding guilds correlated highly with environmental factors, such as bottom water chlorophyll a and nutrients, as well as sediment total organic carbon. Although integrated multi-trophic aquaculture is regarded as a suitable approach to coordinate desirable economic, social, and environmentally sustainable outcomes, coastal ecosystems may suffer from large-scale nutrient enrichment due to aquaculture and other human activities, which should not be considered in isolation.

Polybrominated Diphenyl Ethers (PBDEs) in Sediments of the Huron-Erie Corridor.

Polybrominated diphenyl ethers (PBDEs) were measured in 182 sediments from the Huron-Erie Corridor, North America. The median (5-95 percentile) Corridor ∑PBDE concentration was 1.03ng/g dry wt (0.25-13.48ng/g dry wt). Dry weight ∑PBDEs were elevated in U.S. waters of the Detroit River (US DR) and lowest in Canadian waters of Lake St. Clair (CA LSC). Sediment total organic carbon (TOC) explained some of the variation in ∑PBDEs, particularly in upstream waterbodies except for the Detroit River where local sources were apparent in the US DR and TOC-dilution occurred in CA DR. Canadian Federal Sediment Quality guidelines were exceeded at 19 stations, 14 occurring in the US DR. ∑Hazard Quotients (∑HQ) had a median (5-95 percentile) Corridor value of 0.46 (ND to 2.27). By strata, 43.2% of US DR stations had ∑HQ's greater than 1 while 21.3% of US SCR stations exceeded a value of 1.

Warming affects predatory faunal impacts upon microbial carbon cycling

Abstract Ocean warming and the loss of larger (often predatory) fauna are major threats to seabed (benthic) ecosystem functioning. Yet, we know little about the combined effects of warming and faunal species loss upon the marine carbon cycle. Using stable isotope pulse‐chase experiments, we tested how faunal species loss affects microbial carbon sequestration and retention in intertidal sediments, under both ambient and predicted future warming conditions (ambient +2°C), using the shore crab Carcinus maenas as a model predator. We traced the fixation and retention of a fixed dose of 13C‐labelled sodium bicarbonate within sediment organic matter and microbial biomass. Carcinus presence was associated with higher total organic carbon concentration within the mesocosm sediments. Temperature had no significant effect upon sediment total organic carbon concentrations. Temperature and Carcinus presence had no significant effect on polar lipid fatty acid (PLFA) concentrations within the sediment, which is a proxy for microbial biomass. Carcinus presence increased retention of 13C‐labelled carbon within the sediment organic matter pool under future warming conditions. Retention of the 13C‐label within the microbial PLFAs decreased significantly under future warming conditions. Changes in the relative abundance of PLFAs revealed increased contribution of microeukaryotes to the microbial community under ambient conditions, in the absence of Carcinus. PLFA profiles revealed significant changes in 13C‐label retention within the bacteria and microeukaryotes, driven by interactions between Carcinus presence and temperature. Given that temperature is a fundamental control on the metabolic activity of marine organisms (from bacteria to metazoans), we propose that interactions between faunal species loss and ocean warming will have a pronounced effect upon marine carbon budgets. A plain language summary is available for this article.

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.

Shifts in the anammox bacterial community structure and abundance in sediments from the Changjiang Estuary and its adjacent area

Anaerobic ammonium oxidation (anammox) is an important process in marine nitrogen cycle. In this study, diverse anammox bacteria were identified in the sediments of the Changjiang (Yangtze) Estuary and its adjacent area. Specifically, the community characters of anammox bacteria in the studied area were studied by quantitative polymerase chain reaction (qPCR), as well as 16S rRNA gene- and functional gene (hzo)-based Roche 454 sequencing. The abundance of denitrifying bacteria detected by the nirS gene was greater than that of anammox bacteria. 16S rRNA and hzo gene fragments affiliating with known anammox bacterial lineages were recovered, and the two major phylotypes belonged to the Candidatus Scalindua (Ca. Scalindua) genus, with >90% sequence similarity. A phylogenetic analysis detected the Scalindua and Brocadia genera together with some anammox-like bacterial clusters, which suggested a higher diversity in the studied ecosystem than in open ocean environment, where only Scalindua genus was detected. A redundancy analysis (RDA) showed that total organic carbon (TOC) and total nitrogen (TN) content in sediments significantly influenced anammox bacterial abundance of. Spearman correlation analyses confirmed that the spatial variation in anammox bacterial abundance was highly correlated with TOC (P<0.01) and TN (P<0.01) contents in sediments.

Reactive Iron and Iron‐Bound Organic Carbon in Surface Sediments of the River‐Dominated Bohai Sea (China) Versus the Southern Yellow Sea

AbstractFactors influencing reactive Fe cycling and its protection of organic carbon (OC) in sediments are poorly understood. Here we comparatively study Fe speciation and Fe‐associated OC (Fe‐OC) in surface sediments of the Bohai Sea (BHS) and southern Yellow Sea (SYS), two seas with common sediment sources but different depositional regimes. Though significant sequestration of highly reactive Fe (FeHR) is expected in the estuarine system stream from the river‐dominated BHS, this pool is, however, slightly enriched in the BHS sediments relative to their source material. This reconfirms a previous speculation of sedimentary FeHR enrichment in semi‐protected settings. Relative to the BHS, the SYS sediments are depleted of FeHR, despite common sediment sources of these two areas. Estuarine pre‐enrichment and subsequent redistribution of FeHR in the BHS, and aging of Fe‐bearing authigenic clays during transport from the BHS to the SYS are potential mechanisms for the depletion. The fractions (fFe‐OC) of Fe‐OC in total OC in sediments of the two seas are at the lower end for soils and sediments, indicating Fe being a minor “rusty sink.” 13CFe‐OC fractionations indicate preferential sequestration of terrestrial OC by Fe oxides in the BHS, in contrast with preferential retention of marine OC in the SYS. Different fractionations of 13CFe‐OC in the two seas are a net result of selective adsorption of OC by Fe oxides and selective stabilization of OC during Fe reductive dissolution. Preferential sequestration of terrestrial OC may exert an important influence on distribution and compositions of OC buried in the river‐dominated system.

Total organic carbon sensitivity to climate change from Lake Qinghai sediments at different time scales

湖泊沉积物总有机碳（TOC）含量通常作为表征流域和湖泊生产力的指标，在亚洲季风区也常常被当作夏季风的代用指标，被广泛应用于气候与环境变化研究.本文梳理了过去千年、全新世以及冰期-间冰期时间尺度上青海湖沉积物TOC的变化特征，并探讨了其指示气候变化的敏感性与有效性.结果表明，过去千年青海湖沉积物TOC含量与区域暖季温度和降水表现出较为一致的周期性波动.通过对比全新世区域夏季温度、基于孢粉的降水定量重建结果，以及湖泊水位、风沙活动反映的湿度状况等，发现不能简单地将青海湖沉积物TOC含量或沉积通量作为夏季风强度或者季风降水强度的代用指标.青海湖沉积物TOC含量在冰期和间冰期表现出巨大的差异，指示了冰期-间冰期时间尺度上较大的温度与降水变幅.因此，不同地域条件及不同时间尺度下，湖泊沉积物TOC对气候变化的敏感性不同，将湖泊沉积物TOC含量作为亚洲夏季风的代用指标需要特别谨慎，特别是在高寒气候区.;Total organic carbon (TOC) content of lacustrine sediments has been widely used in the climatic and environmental studies as a proxy of productivity in the catchment and lake water; it is also used as an index of monsoon precipitation in the regions dominated by the Asian summer monsoon. In the present paper, we summarized the variation characteristics of TOC in Lake Qinghai sediments at scales of past millennium, the Holocene and the glacial-interglacial; and discussed the sensitivity and applicability of TOC for indicating climate change. The results indicate that the variation of TOC in Lake Qinghai sediments during the past millennium is consistent with that of regional warm season temperature, as well as the precipitation. After compared with regional summer temperature, pollen-based precipitation reconstruction results, and moisture evolution inferred from water level of lakes and aeolian activity history, we found that TOC content or flux cannot be regarded as a reliable index of the intensity of summer monsoon or monsoonal precipitation during the Holocene. TOC content from Lake Qinghai during the Holocene and the last glacial were distinctly different, indicating huge difference of precipitation and temperature at the glacial-interglacial scale. Therefore, the sensitivity of TOC in lake sediments to climate change is different at different places or different time scales; it should be very careful to use lacustrine TOC as an index of Asian summer monsoon intensity, especially in the cold and high-altitude regions.

Effects of inlet excavation and climate oscillation on the ecosystem of a fishery lagoon in northern Japan

The chemical components and benthic foraminiferal assemblages in core sediments from Notoro Lagoon in northern Japan revealed the effects of artificial inlet excavation and the role of regional climate cycles on the shift of oxygen conditions in the lagoon basin. The materials analyzed were four sediment cores obtained from three basins in Notoro Lagoon using pushing-piston corers. An artificial inlet was excavated at the lagoon in 1977. Immediately after excavation, CNS contents in the sediment began to decrease, and benthic foraminiferal assemblages shifted due to high-oxygen seawater inflow. There was a 7-year transition before the lagoon environment and ecosystem were stable. After inlet excavation, the bottom environment and benthic foraminiferal assemblage of Notoro Lagoon were strongly influenced by short-term climate oscillations such as the Pacific Decadal Oscillation and Arctic Oscillation. Frequent short-duration peaks of oxygen-proxy foraminifera taxa and decreases in total organic carbon in sediment were confirmed between 1986 and 1998. This transition occurred because the spring air temperature and pressure over Notoro Lagoon were affected by the short-term climate oscillations, which have determined the timing of lake ice melt and the volume of oxygen-rich seawater inflow. As a result, bottom conditions and the benthic ecosystem of the Notoro Lagoon have shifted along with these regional climate changes.

An Approach to Predicting Sediment Microbial Fuel Cell Performance in Shallow and Deep Water

Here we present an approach to predicting sediment microbial fuel cell performance based on environmental conditions. Sediment total organic carbon and water temperature were found to be important determinants in predicting the power output from microbial fuel cells in shallow sediments (&lt;100 m) in San Diego. We extrapolated data from the in situ San Diego experiments to predict MFC performance in shallow sediments in other locations, namely the Gulf of Mexico and the Yellow Sea. Finally, using laboratory data of MFC performance in deep water (~1000 m) sediment samples, we extend our predictions to ocean sediments worldwide. We predict low power output from the deep sea (microwatts) relative to the shallow sediments (milliwatts), and attribute that to a possible lack of electrogenic bacteria in the sediments, lower sediment permeability, or a greater proportion of refractory organic matter reaching the bottom.

Assessment of the Geographical Detector Method for investigating heavy metal source apportionment in an urban watershed of Eastern China

Assessing heavy metal pollution in river sediments and identifying the key factors contributing to metal pollution are critical components for devising river environmental protection and remediation strategies to protect human and ecological health. This is especially important in urban areas where metals from a wide range of sources contribute to sediment pollution. In this study, the metal enrichment factor (EF) was used to measure the watershed distribution of Cu, Zn, Pb and Cd in sediments in the Wen-Rui Tang urban river system in Wenzhou, Eastern China. The Geographical Detector Method (GDM) was specifically evaluated for its ability to analyze spatial relationships between metal EFs and their anthropogenic and natural control factors, including densities of industry (DI), livestock (DL), service industries (DS), population (DP), and roads (DR), along with agricultural area (AG), sediment total organic carbon (TOC), and soil types (ST). Results showed that the watershed was highly contaminated by all metals with an EF trend of Cd ≫ Zn > Cu > Pb. The spatial distribution of EFs demonstrated high contamination of all metals in the southwestern region of the watershed where industrial activities were concentrated, and higher Cu and Zn concentrations in the northeastern region having a high density of livestock production. GDM results identified DI as the dominant determinant for all metals, while TOC and ST were determined to have a moderate secondary influence for Zn, Pb and Cd. Additionally, GDM revealed several additive and nonlinear interactions between anthropogenic and natural factors influencing metal concentrations. Compared to other correlation, multiple linear regression and geographically weighted regression, GDM demonstrated distinct advantages of being able to assess both categorical and continuous variables and determine both single and multiple factor interactions. These attributes provide a more comprehensive understanding of metal spatial distributions while avoiding multicollinearity issues when identifying significant contributing factors at the watershed scale.