| Dianchi Lake is the most important plateau shallow water lake in China , which is now facing serious eutrophication. Lakeside zone is a very significance ecotone between aquatic ecosystem and terrestrial ecosystem to maintain biodiversity , adjust matter and energy flow , purify water quality , reduce pollution and other functions . Lakeside zone is the natural defense of lake and an important component of the lake ecosystem .This paper was part of the fifth subject of the tenth " five years " subject of water treatment , " the study on water environment technology of Lake Dianchi river and demonstration engineering " and the state basic research and development key subject, " the study on evolution of lake water environment quality and baseline " . In order to know the current conditions and mechanisms of eutrophication of Dianchi lakeside zone , it was necessary to study deeply on present situation and spatial distribution characteristics of nutrient in lakeside zone .The overlying water and sediments sample were collected from 34 sites of Dianchi lakeside zone . The research on present situation and nutrient content of carbon , nitrogen , and phosphor in overlying water and sediments of lakeside zone was carried out . The distribution characteristics of phytocenose , spatial distribution characteristics and existing forms of nutrient was analyzed . The relativity of carbon , nitrogen , and phosphor content in sediments and the process of accumulation and conversion were also studied . The potential impact of nutrients to the eutrophication course , the characteristics of both endogenous and exogenous load and the mechanism of eutrophication was posted for offering reasonable scientific evidence accordance to the ecosystem rehabilitation . It also provided proposal on eutrophication and water pollution control for typical shallow water lake in China . The conclusion was summarized as following :1. Dianchi lakeside zone with serious damage to wetlands , biological species with a sharp decrease , the biodiversity recession destroyed the ecological functions of lakeside zone . Plant species had becomed fewer and fewer , a large number of aquatic plants was extinct; phytocenose aera was shrinkage , the growing depth of plant becomed more and more shallow . The number of fish species in Dianchi Lake also declined .2. The concentration of TN and TP in overlying water of Dianchi lakeside zone were separately 5.82mg/L and 0.74mg/L . Based on evaluation standard for the eutrophication , the nutritive index of TN and TP in 34 sites of lakeside zone were all above 60 , individual sites in excess of 100 . The ratio TN/TP in overlying water was 7.82 , higher than the critical value of 7.2 . So phosphorus was the nutrient element which restricted primary productivity of the water body and blocked the eutrophication course of the lake .3. The variation of C N P content in surface sediments of different regions was large . The content of TN was among 109.31mg/kg～7220.38mg/kg , with the average value of 1713.58mg/kg . The content of NH4+-N and Org-N was higher , with the average value of 1177.05mg/kg and 1478.69mg/kg separately . The content of NO3--N in sediments was lower . TP content ranged at 790.27mg/kg～4181.45mg/kg , with the average value of 2062.78mg/kg . TP was mainly componented by I-P (inorganic phosphorus) and Org-P . I-P content was more than Org-P in the proportion of TP , accounting for 68.33% of TP . I-P as mainly componented by Ca-P ( calcium phosphorus ) and Fe/Al-P (iron / aluminum-bound phosphorus ) . Ca-P was the major component of I-P , so the risk of phosphorus release resulting from conditions acidification should be considered . The distribution of TOC (total organic carbon ) content in sediments was different between Caohai and Waihai . The content of TOC in Caohai lakeside zone sediments was higher than in Waihai as a whole . The average content of TOC in Caohai and Waihai was separately 76.94g/kg and 16.56g/kg . The content of Caohai was 4.49 times for Waihai. The content was lower in east coast than in west . Because the different geological environment , pollution sources and degree in different regions , the vertical distribution characteristics of C N P content in the 16 sites were different.4. The ratio TOC/TN in surface sediments of Dianchi lakeside zone ranged at 6.78-80.36 with the average value of 25.77 . TN and TOC in sediments had obvious positive correlation and the correlation quotiety was 0.83 . The ratio TOC/TP ranged at 3.09～84.01 with the average value of 21.28 . TOC and TP had positive correlation , but the linear relation was not good , with the correlation quotiety of 0.57 , which indicated that the existence forms of phosphorus in the sediments of Dianchi lakeside zone were complex . The ratio TN/TP in surface sediments ranged at 0.15～2.17 with the average value of 0.76 and the ratio of Caohai was more than Waihai.In Dianchi lakeside zone , the nutrients in sediments were much richer than in water . Therefore , it is an important measures to control the release of nutrients in sediments for eutrophication of Dianchi Lake . |
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