[Analysis on the forms and release potential of nutrients in sediments from lakes in the West Jiangsu Province].

To probe the effect of nitrogen and phosphorus (P) in sediment on aqueous nutrient concentrations, forms of phosphorus, sediment water interface diffusion fluxes and phosphorus release and adsorption of 10 lakes in the west Jiangsu province were studied. 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 northern Jiangsu, the Fe-P was relatively high in sediments of lakes in southern Jiangsu. The diffusion fluxes of lakes were mainly based on NH4(+) -N diffusion in the west Jiangsu, and ions of most of lakes diffused from overlying water to sediment, NO3(-) -N 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 increase. Considering the phosphorus adsorption on native phosphorus polluted (NAP-polluted) sediments. All data of P adsorption on sediment samples collected from 7 lakes were fitted to the modified Langmuir model. And the values of the maximum adsorption capacity (Q(m)), phosphorus binding constant (k), native adsorbed exchangeable phosphorus (Q(NAP)), were subsequently obtained. The results showed that the adsorption amount of P in Lake Hongze and Lake Xuanwu was relatively low, which were liable to release P from sediments.

[Regional heterogeneity of lake eutrophication effects in China].

Although biomass of algae (Chl-a) were in variant levels between different lake regions in China under the same nutrients conditions, it demonstrated that efficiencies of TN/TP used by algae had regional differences. In order to clarify the differences, curve estimation in SPSS was used to analyze the linear relationship between Ig Chl-a and Ig TN/lg TP. The slopes of these linear equations were identified as the efficiencies of TN/TP used by algae. The slopes of linear equations from Mengxin Plateau, Yungui Plateau, Northeast Mountain-Plain, lower reach of Yangtze River Plain and North Plain were 1.002, 0.817, 0.761, 0.545, 0.250, orderly. The efficiencies of TN used by algae ranged from the highest to the lowest were lower reach of Yangtze River Plain, Yungui Plateau, North Plain, Northeast Mountain-Plain, Mengxin Plateau, and the slopes of linear equations were 1.401, 1.058, 0.447, 0.239, 0. 099, respectively. Consequently, in Northeast Mountain-Plain, Mengxin Plateau the efficiencies of TP used by algae were higher than those of TN, and in Yangtze River Plain, Yungui Plateau, North Plain, the efficiencies of TN used by algae were higher than those of TP. On the other hand, in order to describe the effects of algae on transparency in different lakes, the relationships between Chl-a and SD were analyzed. The results showed that in Yungui Plateau the effect of algae on transparency was the most obvious as the variation of SD explained by Chl-a was the highest, and Northeast Mountain-Plain, Mengxin Plateau and North Plain followed. However, in lower reach of Yangtze River Plain, the relationship between Chl-a and SD was not significant.

[Effects of land management measures on nutrients emission].

The SWAT model, coupled with a GIS, was applied to simulate the effects of fertilizer application, contour planting and returning land for farming to forestry on nutrients discharges. The results showed that when nitrogen fertilizer of agricultural land increased from 630 to 955 kg/hm2, and phosphorus fertilizer increased from 200 to 300 kg/hm2, nitrogen and phosphorus nutrient emissions have shown a growing trend. Nitrate nitrogen loads reached to 3 776.59 kg which increased 19.7% and the rate of changes was the largest. The change rate of inorganic phosphorus was the smallest which increased only 2.7%. The impact of emission loads on nitrogen and phosphorus was the smallest if contour planting was adopted. When slope farmland which slope is greater than 25% all returned land for farming to forestry, the emission loads of various forms of nitrogen and phosphorus decreased, organic phosphorus decreased 16.3% among them. Organic nitrogen, ammonia nitrogen and inorganic phosphorus compared with before returning land for farming to forestry, decreased 22.7%, 25.4% and 27.9% respectively. In small basin of Zhangjiachong, returning farmlands to forests and reducing the amount of chemical fertilizer on the slope farmlands which slopes are larger than 25% have played a prominent role.

[Simulation of nonpoint source pollution load in Maoping River watershed].

The nitrogen and phosphorous transport in the Maoping River watershed was modelled using the SWAT model, which simulates the water cycle and the transformation of nutrients. The model was first calibrated by comparing the observed and the simulated data from May to October 2004, and then validated. The Nash-Sutcliffe coefficient (R2), the mean square root error (RMSE) and the relative error(CV) were used to test the agreement between observed and simulated data. The validated model was then be used to simulate the nutrients load in Maoping River watershed. The Nash-Sutcliffe coefficient of flow, nitrogen and phosphorous was 0.71, 0.51 and 0.62 with the minimum relative error 1.8%, 1.1% and 10% respectively. Despite achieving the relatively lower resemblance between observed and simulated phosphorous and nitrogen load the model showed good agreement in simulating runoff. The results showed that 102.5t nitrogen and 9.46t phosphorous entered intoYangtze River during May to October 2004. One of the important reason that caused the water quality deterioration can be attributed to the nonpoint source pollution.