Internal Phosphorus Of Chagan Lake Release And Impact On Eutrophication In Low Temperature Period

Eutrophication has developed into global ecological crisis, it is harmful for theecological balance of aquatic and a serious threat to human survival and development.The external sources of pollution were controlled and eliminated gradually.Phosphorus in the shallow lake sediments become internal pollution sources foreutrophication, instead of external sources of pollution. Phosphorus in sedimentreleases not only at nomal temperature and high temperature period, but also at lowtemperature period. It has became an important factor for eutrophication in the lakesof north of China. However, the geochemical processes of internal phosphorusmigration and transformation at the sediment-water interface are still lack, especiallythe knowledge of role of chemical environment and the microorganisms on theprocess at low temperature period. A typical northern shallow lake–Chagan Lake inthe west of Jilin Province was chosen as the study object. Based on the hydrochemicalcharacteristics of Chagan Lake and the distribution characteristics of N and P at lowtemperatures period, the temporal and spatial variation in forms of P fractions in thesediment were investigated and analysed, with SMT analytical methods recommendedby the EU. The mechanisms of P migration and transformation and process at thesediment-water interface was analysed using the aquatic microcosms system, alsothe impact of the biological effects, physical and chemical effects. Effects of P releasein sediment in notrhtern shallow lakes to the eutrophication were studied, based on thechlorophyll-a and algae in the distribution of Chagan Lake at the low temperature.The process of P released from sediment can be described by a desorption-kineticsmodel. It built a trophic level index （TLI） to evaluate the level of Chagan Lakeeutrophication. The results of this study provided theoretical and technical support forthe sediment nutrient control and eutrophication control in northern lakes.The hydrochemical characteristics of Chagan Lake as well as the temporal andspatial distribution of different forms of N and P were investigated in low-temperature.The pH ranged from9.35to9.40and the Chagan Lake’s characteristics was highturbidity, high hardness and high salinity. HCO₃^-and Na⁺were main anion and cation，ion content characteristic was Na⁺>Mg²⁺>Ca²⁺>K⁺，HCO₃^-> Cl^-> CO₃^2->SO₄^2-. Thehydrochemicaln of Chagan Lake is Bicarbonate-Na-I type. The concentration ofvarious ions at low temperature was higher than the nomal temperature. The distribution of ions concentration was northwest lower than southeast in lake becauseof the supply of water, geological conditions and other factors. In the case ofagricultural activities stopped surrounding Chagan Lake at low temperature, noexternal phosphorus input Chagan lake. The forms of N and P had a highconcentration in water, because of internal pollution in sediments of Chagan Lake.NH₄⁺-N was the primary form of nitrogen and TDP was the primary form ofphosphorus. TN and TP has more than average levels of eutrophication in the criticalconcentration, but thanks to the low temperature, the high turbidity and the lowconcentration of PO43-, which were not conducive to the propagation of algae, andChagan Lake hasn’t appear the bloom of algae. The area of high concentrations ofNH₄⁺-N and NO2-N were shrinking year by year. The concentration of TP and TDPalso showed a decreasing trend.On the basis of the advantages and disadvantages of the existingsediment-collecting distributors, and the practical problems encountered in thesampling process, a portable sediment sampler with independent intellectual propertywas invented. The collector can facilitate the collection of sediment samples ofdifferent textures, greatly improves the sampling efficiency. Significantly reduce theworkload and intensity of work of researchers at the same time, improve the accuracyof the sample collection and keep the sediment sampling original state. It is able toavoid sample polluted and broken when them are transfered to a storage container.The distribution of various forms of P in the sediment surface and bottom ofChagan Lake was investigated by SMT method. The result showed that the IP was themain form of P in sediment and the Ca-P was the main form of IP. The phosphate inthe surrounding high calcium soil of Chagan Lake gradually transformed into awater-soluble calcium phosphate as the environmental conditions changed, withsurface runoff into Chagan Lake and re-settlement. The re-settlement Ca-P insediment was highly significant correlation of TP. The high concentration area of P inthe sediment was in southwest. The various forms of P content increased withincreasing depth in sediment in vertical direction. It showed that the external input ofP pollution gradually reduced in recent years.The distribution of algae in Chagan Lake in low temperature and the factors thataffect algal species composition were studied. The Chagan Lake algae species wereCyanophyta, Chlorophyta, Bacillariophyta and Euglenophyta in low temperature.Blue-green algae prefer alkaline water and high cell storage ability of phosphorus, which are conducive to blue-green algae instead of diatoms and green algae becomethe dominant at low temperature period. It became a potential threat to eutrophicationin Chagan Lake. But the lower water temperature, lighting conditions, aquatic plantsand aquatic animals preying and other reasons inhibited excessive propagation ofalgae such as cyanobacteria and restrictions risk of eutrophication. By correlationanalysis of algae with N, P, low temperature of Chagan Lake algae distribution andconcentration, the result showed algea had no ralitionship with N, but significantcorrelation P. Chagan Lake is phosphorus controlling lake.The mechanisms and the influencing factors of P migration and transformation inChagan Lake sediment at low temperature were studied. The P in sediment was stillable to sustained releasing in the presence or absence of illumination and DO, and itmade the content of the overlying water TP sustained increase. Because of Ca-Pcontent in the sediments was most, desorbed phosphorus was most from Ca-P. It wasanaerobic and non-illumination conditions that easily lead to eutrophication, becauseof the release rate of various forms of P in the sediments greatly under thisenvironmental conditions. The chlorophyll-a and P had a significant correlation withillumination. The proliferation of algae reduce the P content in water, and thus speedup the release of P in sediment, meanwhile P release is material basis for algaeproliferation. The raito and the quantity of P release was effected by DO, pH,illumination. The control of sediment phosphorus release is key condition to inhibiteeutrophication in Chagan Lake.P desorption kinetics of Chagan Lake sediment and eutrophication were analysed.Using water static simulation method in the laboratory to study the desorption kineticswith the content of phosphorus, desorption time （t） and water/soil ratios （W） at lowtemperature. A simple desorption kinetics model could be created, as=0.01700.3751.493, which be used to describe the process of phosphorusdesorption in Chagan Lake sediment at low temperature. It built a trophic levelindex（TLI） model to assess the eutrophication, the results showed that: from2009（TLI=28.56）to2011（TLI=30.19）, the nutritional level of Chagan Lake isoligotrophic into moderate eutrophication. The risks of eutrophication in Chagan Lakeexist.