The Characteristic Of Carbon And Nitrogen Leaching And Associated Environmental Health Effect In Subtropics Watershed In Red Soil Area

Nutrient loss has been identified as a major factor in the degration of surface water quality through its role in eutrophication and soil and water loss, and there is increasing concern regarding the control of nutrient loss from various sources. In resent study, the area of soil and water loss in red soil region is 264.97 km2,0.08% of the whole nation, and amount of nutrient flowaway with the soil and water loss. Red soil area suffers from big threat of soil and water loss and water pollution. So, well understand the hydrological pathway of carbon and nitrogen loss of red soil is crucial for water pollution and soil and water loss control. In this study, we selected a little watershed, Xiangxi watershed, and monitored its rainfall traits and the variation of carbon and nitrogen in sediment. Results:(1) In the monitoring period, the total rainfall is 1349.80 mm with 271098.50 m3 rainoff. The statistical results of 2013-2014 indicate that the rainfall events are all concentrate on May to August. Rainfall of July is the highest which total rainfall reaches 336 mm. (2) Carbon and nitrogen concentrations in the watershed are positively correlated with the farming activities and the discharging of temperature in dry season. The concentration of TN range from 0.52 mg/L to 4.96 mg/L, DTN range from 0.33 mg/L to 1.43 mg/L, mainly consist of No3--N, and DOC range from 6.99 mg/L to 11.70 mg/L. (3) Bimodal state of C, N concentrations are appeared in rainy season and following with the increase of rainfall, the peak concentrations are all appeared in the fertilization period of double cropping rice. The peak value of TN, DTN and DOC is 8.89 mg/L,5.12 mg/L,4.79 mg/L,2.96 mg/L,14.22 mg/L and 10.55 mg/L, respectively. (4) The main form of TN in upper dry season is PN, and then replaced by DTN which controls the tendency of TN in rainy season, completely. Nitrate makes big contribution to DTN. However, ammonium nitrogen and nitrate as main components of DTN alternately in rainy season. (5) In the monitoring period, the total input of nitrogen is 12368.74-14155.74 kg and the total output is 609.20 kg. (6) TN and effective nitrogen content in sediment are 414.70-899.60 mg/L and 17.50-58.90 mg/L, respectively. Effective nitrogen accounts 3-10% of TN with the similar change rules. (7) The experiment of sediment N release and variance analysis show that temperature is the key factor. (8)Strong applicability and reliability is shown on basin runoff simulation with SWAT model.