Characteristics and distribution of low molecular weight organic acids in the sediment porewaters in Bosten Lake, China

The composition and vertical profiles of low molecular-weight organic acids （LMWOAs） and the contribution of them to dissolved organic matter （DOM） in sediment porewaters in Bosten Lake, Xinjiang, China were investigated. The results showed that total concentration of LMWOAs was up to 94.5 μmol/L and their proportion in DOM was 5.6%, suggesting that LMWOAs were important chemical components in DOM in lake sediment porewaters. Among the seven LMWOAs, pyruvic and acetic acid had the highest concentrations with 26.30 and 8.31 μmol/L, accounting for 51.4% and 14.92% of LMWOAs, respectively. Trifluoroacetic and sorbic acid had the lowest concentrations, indicating that the compositions of LMWOAs in relative reducing environments were largely different from those reported in glacier, atmosphere and soils. The concentrations of lactic, acetic, formic, sorbic and oxalic acid decreased with increasing depth, probably relating to stronger microbial activities in the initial stage of early diagenesis. Trifluoroacetic acid was mainly anthropogenic with its concentration, showing a diusive trend from the surface to bottom sediments. The concentrations of lactic acid and nitrate generally showed a consistent profile. The increasing concentration of pyruvic acid in the vertical profile was just opposite to that of sulfate, revealing a significant negative relationship between them. Oxalic acid remained constant except for an obvious peak at 6 cm depth. The results indicated the diversities in sources and behaviors for various LMWOAs during early diagenesis in sediments.

In-situ formation of perylene in lacustrine sediments and its geochemical significance

To identify the possible sources and formation mechanism of perylene in sediments,temporal trends of perylene and other polycyclic aromatic hydrocarbons,as well as the organic matters,were analyzed in sediment cores from Dianchi Lake and Sihailongwan Maar Lake in China.Significantly high concentrations of perylene were observed in both cores and increased gradually with the sediment depth.Source identification suggested that perylene in both cores were of primarily diagenetic origin,other than the anthropogenic inputs.Both terrigenous and aquatic organic matters could be the source of perylene in sediments and diagenetic formation of perylene in sediment is kinetically controlled by the microbial activities under anaerobic conditions.All evidence points to the fact that the formation of perylene in sediment should be an index of the microbial activities and environmental conditions,other than the source of specific organic matters or precursors.In addition,we should be cautious when using any geochemical indicators involving the microbial alternation.

A 60-year sedimentary record of natural and anthropogenic impacts on Lake Chenghai,China

Recent sediments from Lake Chenghai, China, were investigated at high temporal resolution to trace both natural and anthropogenic effects on the lake using total organic carbon （TOC）, total nitrogen （TN）, total phosphorus （TP）, organic phosphorus （Po）, inorganic phosphorus （Pi） and organic carbon and nitrogen stable isotopes （~13Corg and 615N） in a 137Cs-dated sediment core. The results indicated that the sedimentary record covers the last 60 years, during which the lake had undergone apparent changes in nutrient sources and productivity in response to nutrient loading. Prior to the late 1980s, the nutrient contents in sediments mainly originated from algae and lake productivity was relatively stable. Since the late 1980s, increasing TOC, TN and TP concentrations together with the change of 613Corg and 615N suggested anthropogenic perturbations in nutrient loading and lake productivity. Endogenic nutrients derived from algae and anthropogenic inputs were two important sources of sedimentary nutrients. The anthropogenic nutrients mainly originated from the discharge of industrial wastewater and artificial cultivation of Spirulina after the middle 1980s, and domestic wastewater discharged from Yongsheng County since 1993.

Sedimentary record of polycyclic aromatic hydrocarbons in Lake Erhai,Southwest China

The temporal distribution of polycyclic aromatic hydrocarbons （PAHs） was investigated in a sediment core from Lake Erhai in Southwest China using gas-chromatography/mass spectrometry （GC/MS） method. The total organic carbon （TOC） normalized total PAHs concentrations （sum of US Environmental Protection Agency proposed 16 priority PAHs） ranged from 31.9 to 269 ixg/g dry weight （dw）, and were characterized by a slowly increasing stage in the deeper sediments and a sharp increasing stage in the upper sediments. The PAHs in the sediments were dominated by low molecular weight （LMW） PAHs, suggesting that the primary source of PAHs was low- and moderate temperature combustion processes. However, both the significant increase in high molecular weight （HMW） PAHs in the upper sediments and the vertical profile of diagnostic ratios pointed out a change in the sources of PAHs from low-temperature combustion to high-temperature combustion. The ecotoxicological assessment based on consensus-based sediment quality guidelines implied that potential adverse biological impacts were possible for benzo（ghi）perylenelene and most LMW PAHs. In addition, the total BaP equivalent quotient of seven carcinogenic polycyclic aromatic hydrocarbons （BaA, CHr, BbF, BkF, BaP, DBA and INP） was 106.1 rig/g, according to the toxic equivalency factors. Although there was no great biological impact associated with the HMW PAils, great attention should be paid to these PAH components based on their rapid increase in the upper sediments.