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 O2 accelerated the sediment reducing processes and produced a large amount of H2S, 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 pH value in the sediment as well as microbial activities. Under the anaerobic condition, anaerobic microorganisms could not only contribute to the sulfate reduction and H2S production, leading to pH decrease, but also consume organic matter and convert organic phosphorus into inorganic phosphorus. The redox 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. © 2016 by Journal of Lake Sciences.