Chen Jing'an

Spatial distribution, fractions, and potential release of sediment phosphorus in the Hongfeng Reservoir, southwest China

Abstract We investigated the spatial distributions of total phosphorus (P) and its fractions in the sediments from Hongfeng Reservoir, the largest man-made water body in southwest China, to reveal P sources to the reservoir and its pollution history. We sectioned sediment cores and measured P species concentrations, which increased progressively from relatively low concentrations at a depth of 20–30 cm to higher concentrations in upper sediment layers, reflecting an increase in P input that accompanied anthropogenic influences. P bound to metal oxides (NaOH-SRP) was the largest component of P in most core profiles, accounting for 34.6–67.2% of total P. The Yangchang River is the primary external P source to the reservoir and should be the focus of remediation efforts in the future. A batch P release experiment conducted using sediment cores showed that sediment P release was mainly caused by the transformation and/or desorption of NaOH–P and Residual–P under high temperature and low oxygen conditions. Large P release from sediments could affect the water quality of the reservoir in the future. Detailed knowledge of in situ microscale changes at the sediment–water interface is required to understand the migration of P fractions in the sediments.

The micro-scale investigation on the effect of redox condition on the release of the sediment phosphorus in Lake Hongfeng

In this paper,Lake Hongfeng,located in Guizhou Province,was chosen to study the release process of the sediment phosphorus under the natural,aerobic and anaerobic conditions. Microscale observation of the physical and chemical properties of sediment-water interface by microelectrode technology was used,together with traditional P-speciation analysis,to explore the P-releasing mechanisms. The results showed that under anaerobic conditions,the total content of phosphorus in the sediment in Lake Hongfeng decreased significantly,which was mainly caused by the reduction of NaOH-P and rest-P,indicating that the aerobic condition promoted the phosphorus release from sediments. The concentration of phosphate in the pore water of sediment increased greatly under anaerobic condition,and the trend was contrary to that under aerobic condition. Under the anaerobic condition,concentration of dissolved oxygen decreased and sulfate reduction was enhanced,which released NaOH-P from the sediment. Decrease of O_2 accelerated the sediment reducing processes and produced a large amount of H_2S,which combined with ferrous icon to form the precipitation-ferrous sulfide,resulting in release of NaOH-P( Fe-P) into the pore water. The conversion of aerobic to anaerobic condition could promote the release of rest-P by changing the distribution of p H value in the sediment as well as microbial activities. Under the anaerobic condition,anaerobic microorganisms could not only contribute to the sulfate reduction and H_2S production,leading to pH decrease,but also consume organic matter and convert organic phosphorus into inorganic phosphorus. The red-ox environment of sediment-water interface could affect the penetration depth of sediment-oxygen,pH distribution,microbial activity,sulfur cycle as well as organic matter degradation process,which controlled the speciation transformation and release of sediment phosphorus. Microelectrode technology,together with traditional P-speciation analysis,is an effective way to reveal the release mechanisms of sediment phosphorus as well as the control factors.

Sulfur Speciation in the Surface Sediments of Lakes from Different Regions, China: Characterization by S K-Edge XANES Spectroscopy

X-ray absorption near edge structure (XANES) spectroscopy affords the opportunity to determine redox status for element S in the aquatic ecosystems. However, there have been relatively few studies of S XANES spectroscopy in the terrestrial aquatic ecosystems. In this study, XANES technology was used to examine changes in S speciation in the sediments collected from Taihu Lake, Qinghai Lake, Dianchi Lake, Caohai Lake, and Hongfeng Lake located in distinct geological background areas of China. The results showed that sedimentary S in Qinghai Lake has a high proportion of sulfate averaged 88.9% due to physical weathering of watershed rocks, while deposited S in Taihu Lake has a high fraction of intermediate S (36.5%), which may be the response of the agricultural nonpoint source pollution in drainage basin. The three lakes located in Southwest China have similar composition characteristics of S species, indicating similar S sources including chemical weathering of carbonate and atmospheric deposition. 60–90% of S compounds in the surface sediments were in the form of sulfate and FeS. In deeper layers, the ratio of FeS2 and the intermediate S significantly increased, suggesting rapid processes of sulfate reduction and sulfide reoxidation with the increasing depths.