| Xiang Jiang is the mother river of Hunan province, and increasing, serious pollution of Xiang Jiang river has been paid much attention by the society. The nitrogen pollution of water has been mainly caused by agricultural non-point source pollution. A general analysis of the temporal and spatial variation characteristics of nitrogen in Xiang Jiang river and Dong Ting lake, and study on the amounts of rational nitrogen application of rice, can provide scientific foundation for avoiding eutrophication of water in Xiang Jiang river, inhibit nitrogen pollution in water, and select a better prediction technique of nitrogen concentration in Xiang Jiang river, and can also offer a new method for the pollution control and management. The main research contents and results from our studies are as follows.The annual variation characteristics of water environmental indexes (water temperature, pH value, dissolved oxygen) and total nitrogen, ammonia nitrogen, nitrate nitrogen of water in Xiang Jiang river and Dong Ting lake were analyzed and the results showed that, the water temperature and dissolved oxygen value in Xiang Jiang river and Dong Ting lake had obviously seasonal characteristics, and the change of pH value was not significant from April of 2006 to March of 2007. The concentrations of ammonia nitrogen, nitrate nitrogen and total nitrogen of water in Xiang Jiang river were 0.03～1.76 mg/L,0.02～1.68 mg/L and 1.11～7.62 mg/L respectively, and the concentrations of ammonia nitrogen, nitrate nitrogen and total nitrogen of water in Dong Ting lake were 0.03～1.56 mg/L,0.04～1.72 mg/L and 0.04-9.81 mg/L respectively. The effect of agricultural non-point source pollution on total nitrogen concentrations of the Xiang Jiang river and Dong Ting lake was higher with the peak values appearing in July and August. There was significant correlation between total nitrogen concentrations and water temperatures of AoZhou, QiaoKou sections in Xiang Jiang river and WanZi lake, MuPing lake in Dong Ting lake. There existed significantly, negative correlation between ammonia nitrogen concentrations and water temperatures of AoZhou, QiaoKou and LuJiao sections in Xiang Jiang river and WanZi lake, MuPing lake in Dong Ting lake. There was significant correlation between NH4+-N concentrations and dissolved oxygen values of AoZhou, QiaoKou and LuJiao sections in Xiang Jiang river.The annual variation characteristics of water environmental indexes and ammonia nitrogen, nitrate nitrogen, total inorganic nitrogen concentrations of water in Xiang Jiang river were analyzed and the results showed that, the changes of ammonia nitrogen, nitrate nitrogen and total inorganic nitrogen concentrations of water in Xiang Jiang river were 0.01～1.50 mg/L,0.02～1.28 mg/L,0.26～2.29 mg/L respectively during years of 1990～2005 and the nitrate nitrogen concentration was observed to be increased a little annually. In most of the years monitored, the average annual concentration of nitrate nitrogen was higher than that of ammonia nitrogen. There was no significant correlation between total inorganic nitrogen, nitrate nitrogen concentrations and water environmental indexes.The catchment area of Xiang Jiang mainstream from Guiyang to Hengshan was the main focus of our studies, and we adopted the grey system forecast model, triple exponential smoothing forecast model, fuzzy linear regression forecast model and BP neural network forecast model, which could efficiently describe nonlinear regularities of water body, to identify the relationship between the total nitrogen concentration and related factors. Based on the predicted and monitored values of total nitrogen concentrations, the prediction precision was assessed with seven indexes including root mean squared error, average error, average absolute error and so on. The BP neural network was found to be the best model to predict the water total nitrogen concentration and all the relative errors were less than 20% of the difference between predicted and measured values and the qualified rate of prediction was 100%.Our studies on the correlation between the fertilizer input per unit arable area and the non-point source TN load of anthropogenic activity contribution to Xiangjiang river showed that they had obvious linear relationship and the coefficient of correlation was 0.899. moreover, the studies on the effects of different fertilization treatments on total nitrogen loss with runoff,it showed that There was very significant correlation between them and the linear equation is y=0.0087χ+3.5248 (r=0.9585,p=0.0036).Based on controlled nitrogen fertilizer application amount and application method to increase the nitrogen use efficiency in agriculture production, the combined application of organic and inorganic fertilizers and ecological and economical nitrogen application for rice were studied. The results from combined application of organic and inorganic fertilizers in the rice field experiment demonstrated that, the yield from combined application was 135.00-562.00 kg/hm2 higher than that from pure nitrogen application treatment, with an increase of 9.87～23.68%. The effect of combined application of organic and inorganic fertilizer on yield of rice was bigger, and the highest yield of rice among the five combined application treatments was from the 50% organic fertilizer and 50% inorganic fertilizer treatment with a yield of 7050.00 kg/hm2. The average nitrogen accumulation amount, nitrogen recovery percent and nitrogen agriculture rate of the 60% organic fertilizer and 40% inorganic fertilizer treatment were the highest, and they were 124.25 kg/hm2,31.44%,20.91% respectively. The results of ecological and economical nitrogen application experiment in the field showed that, the economical nitrogen application of rice cultivation in Xiang Jiang valley was 132.31 kg/hm2. Based on the estimate of the environmental cost of nitrogen application in rice cultivation between GuiYang and HengShan sections of Xiang Jiang river, it could be concluded that the best nitrogen application amount for the ecological and economical nitrogen benefit is 129.31 kg/hm2.
|
PDF Full Text Request