Search

Lake sediments are major sink for carbon and trace elements. Lake water and sediments need to be monitored continuously for environmental and geochemical explorations. In the present study, sediment characteristics, source and distribution of trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb and Zn) of Yercaud fresh water lake sediments, South India, situated at an elevation of 1515 m asl is presented. Twenty-five surface sediments were collected covering the entire expanse of the lake in a gridded pattern. Detailed chemical analyses reveal the following decreasing order of elements: Fe > Cu > Cr > Mn > Zn > Ni > Co > Pb. Geoaccumulation index, enrichment factor, contamination factor and pollution load index were calculated to evaluate the ecological impacts of these trace metals in the sediments. The index calculation indicates that all the trace elements were derived from natural process, but there are indications of anthropogenic activities. The study area was found to be highly contaminated with Cu, moderately contaminated with Cr and Co, considerably contaminated with Pb, Zn and Ni, and uncontaminated with Mn. The spatial distribution of the trace elements supports the strong association of sediment fine fraction and organic matter. The statistical principal component analysis also confirms that the concentration of Cr, Cu, Fe and Mn was mainly derived from the natural weathering and non-point agricultural sources. Pb and Zn arise due to the confluence of sewage effluents, traffic and boat activities. These elements need to be further evaluated for pollution control and prohibiting further deterioration in the Yercaud Lake. [ABSTRACT FROM AUTHOR]

Manganese ( Mn) and iron ( Fe)-enriched sediment layers were discovered in Lake Superior within, above and below the oxic-anoxic interface. While the role of bacteria in redox reactions with Mn is known to be significant, little information exists about indigenous microbial communities in many freshwater environments. This study examined the bacterial communities of Mn-enriched layers in Lake Superior to identify the potential Mn( II) oxidizers responsible for the formation of Mn oxides. Anaerobic Mn( II) oxidation occurring in the Mn-enriched layers at the oxic-anoxic interface was investigated using Mn( II)-enriched cultures. High-resolution microscopic and spectroscopic investigations provided evidence of the biogenic formation of Mn oxides on cell surfaces. Spectroscopic mapping confirmed high levels of Mn in structures resembling biogenic Mn oxides. These structures were observed in enrichment cultures and in Mn-enriched layer sediment samples, indicating the significance of biogenic Mn oxidation occurring in situ. 16S ribosomal DNA pyrosequencing was used to identify the bacteria potentially responsible for Mnoxide formation in the enrichment cultures and Mn-enriched layers, revealing that the Mn-enriched layer contains classes with known Mn( II)-oxidizing members. Pyrosequencing of bacterial cultures suggested that these bacteria may be Bacillus strains, and that anaerobic microbial-mediated Mn( II) oxidation contributes to the formation of the layers. [ABSTRACT FROM AUTHOR]

To investigate the influence of cyanobacterial blooms on phosphorus release across the sediment-water interface and the repair mechanisms of internal phosphorus by harvesting of cyanobacteria, a series of laboratory-based experiments were conducted.Microcystis aeruginosawas cultured in phosphorus-free BG11 medium containing sediments from different eutrophic water bodies. The culture solution was removed and the same volume of phosphorus-free BG11 medium was put into the system until theM. aeruginosahad died. Cyanobacterial density, pH and different phosphorus forms in culture solution and sediments after culturingM. aeruginosawere determined. The results showed that cyanobacterial blooms stimulated phosphorus release from the sediment to the overlying water for the sediment in the eutrophic water body. Phosphorus released from the sediment was assimilated byM. aeruginosaand no increase in water-soluble phosphorus was observed. Cyanobacterial blooms caused sharp increases in different phosphorus fractions of sediment with the exception of the phosphorite-type (Ca10-P). Cyanobacterial blooms decomposed iron minerals in the sediment yet there was no clear evidence to demonstrate a positive correlation between water-soluble phosphorus in the overlying water and iron bound phosphorus (Fe-P) in the sediment. These results indicated that harvesting of cyanobacteria might be a suitable method to eradicate cyanobacterial blooms and to limit phosphorus pollution under controlled external nutrient loads. [ABSTRACT FROM AUTHOR]

To advance the understanding of the spatial variability of sediment composition and its controlling factors in a large hydrologically closed lake, the spatial distributions in the mineralogy and geochemistry of 18 surface sediment samples along three transects across the deepest part of Lake Qinghai on the northeastern Tibetan Plateau were investigated. The data show (1) that the surface lake sediments are almost the same in the XRD patterns, (2) that the sediments do not have considerable changes in geochemical compositions along three transects and (3) that the standard deviations of the lake sediments are low in grain size, elemental abundances, δC and δO values of carbonates, and total organic carbon and nitrogen, with the exception of one sample (QH-11) from the westernmost part of the northern sub-basin. These characteristics indicate that the spatial variability of the surface sediment across Lake Qinghai is very low in geochemical and silicate mineralogical compositions, with limited differences in the chemical composition of carbonates associated with river water dilution. Sample QH-11 has anomalously high levels of MgO, a high carbonate content, and positive δC and δO values in bulk and fine-grained carbonates, probably because of the effect of calcareous tufa. Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai can be attributed to the flat topography of the lakebed and stable sediment provenances, the latter dominated by dust deposition and authigenic carbonates. The spatial uniformity and dominance of dust and authigenic aragonite of surface sediments across Lake Qinghai provide a potential record of the hydroclimate in the past, which is associated with changes in the Westerlies and the summer monsoons. [ABSTRACT FROM AUTHOR]

[Objective] The research aimed to study simulated method on the release of sediment pollutants in the Temple Lake. [Method] For existing pollution status of the Temple Lake, sediments and overlying water were sampled by the integrated device. Based on the technical route, through the orthogonal test, release processes of nitrogen and phosphorus from sediment were simulated, and their release speeds were estimated under different temperatures, pH and DO in the laboratory. Relationship between environmental factor and pollutant release was explored. [Result] The integrated device of sediment sampling and test had simple structure, cheap cost and easy operation, and sediment pollution test could be conducted without disturbing sediment after collecting sediment. Among the studied three impact factors, temperature had the maximum influence on contaminant release process, which should be considered as the important factor of future research. [Conclusion] Compared with routine research method of sediment contaminant release from other lakes, simulated method of contaminant release from sediment in the Temple Lake had many advantages, which was favorable for scientific research in latter period and actual lake control. [ABSTRACT FROM AUTHOR]

Abstract: More than 2300 sediment pore water distribution coefficients (K PCBi ds ) of 93 polychlorinated biphenyls (PCBs) were measured and modeled from sediments from Indiana Harbor and Ship Canal. K PCBi ds were calculated from previously reported bulk sediment values and newly analyzed pore water. PCBs in pore waters were measured using SPME PDMS-fiber and ∑PCB ranged from 41 to 1500 ng L−1. The resulting K PCBi ds were ∼1 log unit lower in comparison to other reported values. A simple model for the K PCBi d consisted of the product of the organic carbon fraction and the octanol–water partition coefficient and provided an excellent prediction for the measured values, with a mean square error of 0.09 ± 0.06. Although black carbon content is very high in these sediments and was expected to play an important role in the distribution of PCBs, no improvement was obtained when a two-carbon model was used. [Copyright &y& Elsevier]

The properties of plaques were different on the root surface of Potamogeton crispus planted in sediments from two different shallow lakes. Lake Tangxunhu sediment, with low pH, contained low organic matter, whereas Lake Yuehu sediment, with high pH, had high calcium deposits mixed with high organic matter. The contents of mineral elements in sediment of Lake Tangxunhu was lower than that of Lake Yuehu, except for iron (Fe) content, but the contents of mineral elements extracted by sodium dithionite-sodium citrate-sodium bicarbonate (DCB) from root plaques were higher in Lake Tangxunhu than those in Lake Yuehu, except for Fe. These element distributions on P. crispus root plaques were characterized by scanning electron microscope combined with energy-dispersive X-ray spectrometer and were consistent with the contents of mineral elements in sediment. The root plaque of P. crispus planted in Lake Tangxunhu sediment mainly contained silicon (Si) and Fe, and the content of Si was greater than Fe, which may be contributed to the formation of poly-silicic-ferric in the natural conditions. However, the root plaque of P. crispus planted in the sediment with higher calcium content of Lake Yuehu was rich in Fe, Si, phosphorus (P), and calcium (Ca). Due to oxygen secretion by plant roots, the root plaque has more Fe(PO) and a certain amount of Ca(PO). The ratio of magnesium (Mn) to Fe extracted by DCB from root plaque in Lake Tangxunhu sediment was 0.031 and 0.010 in Lake Yuehu sediment. In Lake Tangxunhu sediment, lower content of organic matter results in weak reducibility. Enhanced oxidation ability by oxygen secretion of P. crispus root could oxidize low-valent Fe and Mn into iron-manganese oxide, which leads to formation of iron-manganese plaque on the root surface. However, this case is different in Lake Yuehu sediment, where Fe and Mn can be reduced in high organic sediment and low-valent Mn can precipitate in the sediment in which pH is >8. Thus, low-valent Fe in Lake Yuehu sediment moves to the root surface of P. crispus, where it oxidizes into Fe oxide, i.e., Fe plaque. [ABSTRACT FROM AUTHOR]

Ferralsols upon ultramafic rocks are among the most Cr-enriched soils at the Earth surface. Weathering and erosion of these soils represents a major source of Cr for coastal sediments downstream of ultramafic settings. Although Cr mainly occurs as Cr(III)-bearing chromite and Fe-(hydr)oxides in Ferralsols upon ultramafic rocks, several evidences of oxidized Cr(VI) in relation with Mn-oxides have been reported. Regarding the high solubility and toxicity of this latter Cr species, a thorough characterization of Cr and Mn crystal-chemistry in tropical sedimentary settings downstream of Ferralsols upon ultramafic rocks is needed to evaluate the potential threat towards the biodiversity of these coastal environments. In this study, we determined Cr and Mn speciation across a shore-to-reef gradient in lagoon sediments downstream of one of the largest lateritized ultramafic regolith in New Caledonia that contains up to 5 wt% Cr 2 O 3. Chromium K-edge XANES data emphasized the absence of Cr(VI) and indicated a major hosting of Cr by chromite and clay minerals close to the shore, whereas Cr-bearing goethite dominated Cr speciation close to the reef. Manganese K-edge XANES data indicated a major hosting of Mn by clay minerals close to the shore, whereas Mn‑carbonates dominated Mn speciation close to the reef. The lack of Mn-oxides detection was considered to explain the absence of Cr(VI) in the studied sediments. This result thus suggests that, despite their shallow character that can favor occasional re-oxidation of the top-layer sediments upon re-suspension events, lagoon sedimentary settings downstream of Cr-rich Ferralsols upon ultramafic rocks appear rather favorable to Cr sequestration as the less mobile and less toxic Cr(III) form. However, the reverse trends observed from the shore to the reef between the chromite and goethite contributions to Cr speciation, as well as the decrease of the Cr/Ti ratio, suggest that a fraction of Cr could have been released towards the water column upon partial weathering of chromite to goethite during sediments transport across the shore-to-reef gradient. This latter point emphasizes the potential hazard that could still represent Cr for the exceptional biodiversity of tropical lagoon ecosystems downstream of Cr-rich Ferralsols, despite the absence of detectable Cr(VI). It thus calls for further studies aimed at better evaluating the stability of Cr(III)-bearing mineral phases upon early diagenesis in these shallow sedimentary settings. • Cr and Mn speciation change across the shore-to-reef gradient • Cr is only detected as the less mobile and toxic form, Cr(III). • The lack of Mn-oxides is considered as the main reason for the absence of Cr(VI). • Chromite weathering to Cr-bearing goethite from the shore to the reef is suspected. • Cr release during this suspected chromite weathering should be further investigated. [ABSTRACT FROM AUTHOR]