Study On Characteristics Of Phosphorus Release From Sediments Of East Dongting Lake And In-situ Control The Release Technology

The internal contamination would play a key role of eutrophication after external contamination load reduction. Studying on phosphorus actions in interface of sedime- nt-water is the key elements which helps find the mechanism of eutrophication, and it will provide guidance and theoretical basis for East Dongting lakes's governance and management. Meanwhile, the devepment of in-situ control technology of contamina- tion release from sediments of Lake has made a good progress in the past years. However, more studies need to be conducted about the systematic investigation of the technology and related mechanisms for its widely practical application.Taking East Dongting Lake sediments as the research object, the paper studied the disciplines of phosphorus release in interface of soil-water under the different of environmental factors including temperature, pH and Moisture content, and the effects of phosphorus release in interface of sediments-water under the different environ- mental conditions including temperature, pH, DO and Hydrodynamic, and the control effects of in-situ control technology for phosphorus release in sediments including aeration, zeolite capping and calcium nitrate in-situ treatment under the different environments in simulated laboratory conditions, which supported by The Water Sand Science And The Water Disaster Prevent And Control - Key Laboratory of Hunan Province"studies on distribution of water pollutants under effection of hydrodynamic in East Dongting Lake(2008SS06)"and"studies on characteristics of sediments and its release discip- lines in East Dongting Lake(2008SS05)"programs, The main finding are as following:First, the phosphorus release in interface of Sediment-PoreWater showed:⑴acidic and alkaline conditions conducive to the release of phosphorus in sediments to the pore water, and the releasing is followed by alkaline (pH9)> acidic (pH5) >neutral (pH7). Elevated pH can accelerate release of Fe-P and organic phosphorus, and lower pH is conducive to the release of Ca-P in sediments.⑵The higher the temperature, the faster the release of sediment phosphorus. When the temperature rise from 5℃to 25℃, the phosphorus concentrations in pore water will increase two-fold, and the forms of phosphorus in sediments transport and transfer faster, especially organic phosphorus release.⑶Lower moisture content can reduce sediment phosphorus release rates, but it can increas phosphorus concentration in pore water. The phosphorus concentration in pore water will increase 1.36-fold when the moisture content from 70% to 50%, but the release rate decreased by 1.7 times.Second, the phosphorus release in interface of sediment-overlying water showed:⑴When the pH value of water is 7, the phosphorus release is the smallest, reducing or increasing pH values will increase phosphorus release;⑵The higher ambient temperature of water, the greater impact on the release of phosphorus. The phosphorus concentration in overlying water can increase by 1.7-fold when the temperature rise from 5℃to 25℃.⑶The most significant factors of phosphorus release in sediments is Dissolved oxygen. Under anaerobic conditions,the phosphorus release is as 5.56 times as it under aerobic conditions.⑷The effects of phosphorus release in sediments for hydrodynamic is only a limited short-term action, the phosphorus concentration in water is not increase after the phosphorus in surface sediment and suspended solids release into water to a certain extent.Third, the in-situ control and its impact on phosphorus forms in sediments showed:⑴Under anaerobic condition, the control effects of phosphorus concentration in water was followed by calcium nitrate in-situ treatment > zeolite capping> untreated; and under aerobic condition, calcium nitrate in-situ treatment > zeolite capping > aeration≥untreated; and under hydrodynamic condition, calcium nitrate in-situ treatment >zeolite coverage>zeolite capping> aeration >untreated;⑵Zeolite capping and aeration can improve the ability of sediment in fixing phosphorus. The total content of sediment phosphorus increased by 20.5% and 19.6%, however, the calcium nitrate in-situ treatment can make phosphorus inverse into biological forms, and it increase the risk of internal P release.⑶The influence of zeolite capping and aeration for phosphorus forms in sediments is main effect surface sediment (1~2cm), and calcium nitrate in-situ treatment may be have an impact on migration and transformation of phosphorus forms in bottom (≥5cm) sediment.