| To probe the state of water environment, eutrophication trend and the effect of nitrogen and phosphorus (P) in sediment on aqueous nutrients concentrations, the water quality, forms of phosphorus, sediment water interface diffusion fluxes and phosphorus release and adsorption of10lakes in west Jiangsu Province were studied in2010～2012. The research showed the results as follows:(1) As people’s awareness of environmental protection and harness force increasing, the trend of water pollution of some lakes in west Jiangsu Province was contained in some extent. However, most of the lakes were facing the problem of pollution becoming more serious in recent years. Regarding the changes of the water qualities of the lakes in west Jiangsu Province in recent years, the water qualities of Lake Luoma and Lake Xuanwu was getting better, of which the total nitrogen and the total phosphorus concentrations decreased. Most of the lakes are not in the up-to-up state yet, the total nitrogen (TN) concentration increased in Lake Hongze, Lake Gaoyou and Lake Gucheng, and the total phosphorus (TP) increased in Lake Shaobo and Lake Shijiu. The biological diversity of the lakes was declining. Based on the water quality monitoring data of major lakes in west Jingsu Province, the eutrophic levels of the lakes were evaluated by using comprehensive trophic state index, and the results showed that most of the lakes in west Jiangsu Province were in eutrophic state, of which the lowest eutrophic level was mesotrophication (47.04) in Lake Gucheng, and the highest eutrophic level was middle eutrophicaiton (61.65) in Lake Shaobo. And the water qualities of Lake Shaobo and Lake Hongze were worse than that of standard V, The other lakes were in the standards between IV and V. There was no eutrophication in lakes in Huaihe Basin; maybe it had some possible relationship with short period of exchanging water and hydraulic retention time. Due to the differences of geographical, hydrological and environmental conditions, there were different causes of changes in water environment in various lakes. The ratio of primary industry around the lakes decreased continuously. Conversely, the ratio of secondary industry and tertiary industry increased significantly, which was possiblely one of reasons that induced pollution for lakes. Compared to average amount of chemical fertilizer in Yangtze River Basin dereased annually, the average amount in Huaihe basin were increasing year by year. The average amount of chemical fertilizer in Huaihe basin keeping increasing may be one of reasons for pollution. The water quality of lakes in Jiangsu Proveince was mainly affected by upper river pollution, so the eutrophication degree was similar. Due to some lakes in Huaihe basin being upstream and downstream relationship, the amount of nitrients flxed into lakes carried by upper lakes and surrounding rivers were more than that lakes could self-purify, so it led to aggravate the level of eutrophication of lakes but not alleviate. Compared to the water quality of lakes in Huaihe Basin becoming worse, the water quality of lakes in Yangtze River basin was becoming better.(2) The content of TN and TP in sediments of Lake Luoma was relatively high. Sediments were sequentially extracted by the modified Ruttenberg’s method, and the result showed that inorganic phosphorus in sediments of the lakes was the major fraction of total phosphorus, but the proportion of bioavailable phosphorus was relatively low. Compared with the lakes in Huaihe Basin, the Fe-P was relatively high in sediments of lakes in Yangtze River basin, and it maybe resulted in the possibility of eutrophication in lakes in Yangtze River basin. The diffusion fluxes of lakes were mainly based on NH4+-N diffusion in west Jiangsu, and ions of most of the lakes diffused from overlying water to sediment, NO3--N was diffused from sediment to overlying water in lakes except for Lake Hongze, Lake Shijiu and Lake Xuanwu. The condition leaning to acidic (pH<4) or alkaline(pH>10) was beneficial to phosphorus release, and except for Lake Xuanwu, the least amount of phosphorus released form sediment was higher in acidic condition than that in alkaline condition. The amount of phosphorus adsorption was increasing with temperature increasing. Considering the phosphorus adsorption on native phosphorus polluted (NAP-polluted) sediments. All data of P adsorption on sediment samples collected from7lakes were fitted to the modified Langmuir model. And the values of the maximum adsorption capacity (Qm), phosphorus binding constant (k), native adsorbed exchangeable phosphorus (QNAP), were subsequently obtained. The results showed that the adsorption amount of P in Lake Hongze and Lake Xuanwu was relatively low, and the higher content of TP in the two lakes has possible relationship with the lower values of the maximum adsorption capacity. EPCo of Lake Hongze and Lake Gaoyou was higher than the content of phosphorus in interstitial water, and the two lakes were liable to release P from sediments. |
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