Effects of rainfall runoff on total nitrogen and phosphorus flux in different catchments of Dianchi Lake, Yunnan, China
滇池不同流域类型降雨径流对河流氮磷入湖总量的影响

This article focuses on analysis of status and characteristics of nutrient salts carried in typical rivers in the urban areas, the combination of urban and rural areas and the severely polluted agricultural areas by monitoring water quality and flow at outfall of rivers into lake after three rainfall events during early wet season in three different catchments of Dianchi Lake. The research result indicates that total quantities of nitrogen and phosphorus nutrients in the rivers into the lake in different catchments are generally controlled by rainfall process and characteristics of catchments, runoff flow and concentration of nutrient salts in runoff water. After three rainfall events, the maximum values of TP, KN, NH 3-N, NO 3-N and NO 2-N into lake appear in the river (Daqing river) at combination of urban and rural areas, with accumulated quantities of 11,374.3, 127,971.7, 85,365.4, 923.4 and 841.2 kg respectively, while the maximum unit area loadings of TP, KN, NH 3-N and NO 2-N into lake appear in the river (Wulong river) at urban area, with values of 535.7, 5,860.5, 3,821.9 and 24.6 kg/km 2. It is very complicated that the rainfall process influences the nitric and phosphoric nutrient salts which flow into Dianchi Lake by rivers in different typical catchments areas. Among the influencing factors, rainfall of the initial stage, rainfall frequency and rainfall intensity are very important. The runoff amount of nitric and phosphoric nutrient salts is controlled by changing curves of flux functional equation Q(t) and concentration functional equation C(t) finally during the rainfall process, with different conditions of dry time length, land use status, district draining status and properties of suspended particulate matter. So the total quantities of nitrogen and phosphorus nutrients in the rivers into the lake are different. Research reveals that the conception of total loading capacity in unit area in the rivers into the lake can simplify the calibration of important parameters of hydrological models and kinetics models which have all kinds of remove and transformation processes. The total amounts of nitrogen (counted as Kjedahl's N) in rivers into Dianchi Lake in unit area have such a sequence of Wulong river (5860.5kg/km 2)>Daqing river (1421.9kg/km 2)>Baoxiang river (129.0kg/km 2). The total quantities of phosphorus(counted as TP) in rivers into Dianchi Lake in unit area have such a sequence of Wulong river (535.7kg/km 2)>Daqing river (126.4kg/km 2)>Baoxiang river (22.2kg/km 2). The most highest total amounts of Kjedahl's N and TP in rivers into the lake appeared in the river at urban area and the most lowest total amounts appeared in the river at rural area. Although the amounts and concentration of NO 3-N and NO 2-N have been raised obviously, the amounts of NO 3-N and NO 2-N which flowed into Dianchi Lake in unit area are still the lowest. The amounts of NO 2-N observe a sequence of Wulong river (24.6kg/km 2)>Daqing river (9.35kg/km 2