紫色土流域次降雨条件下碳、磷非点源输出过程及其流失负荷

The dynamic process of carbon and phosphorus losses by runoff and associated loss load in a farmland-dominated watershed of purple soil region

通过对位于川中丘陵区的紫色土流域在次降雨过程中溶解态有机碳(DOC)和不同形态磷素的输出进行动态监测,分析降雨过程DOC和P输出负荷,并探讨降雨径流对C、P迁移和水环境的影响。研究结果表明:(1)3次降雨共产生地表径流20399.8 m3,碳、磷输出负荷为83.19 kg和5.1 kg,次降雨过程径流C、P输出动态差异较大,其中径流DOC浓度随降雨历时的延长而降低,随后迅速升高,在达峰值后逐渐降低并趋于平稳。(2)降雨径流过程中磷素迁移主要以颗粒态(PP)为主,磷酸盐(PO3-4-P)是径流溶解态总磷(DTP)的主要存在形式,3次降雨PP输出负荷分别为1167.491、1891.331、984.74 g;PO3-4-P输出负荷分别为108.37、338.8、167.79 g。(3)3次降雨径流DOC输出浓度分别为3.37、4.77、6.97 mg/L,总磷(Total phosphorus,TP)输出浓度分别为0.11、0.43、0.74 mg/L;次降雨径流C/P比分别为192、48和42.1,相比于暴雨而言,大雨和中雨带来的水质问题需引起关注。

Rain has been identified as a major factor causing phosphorus （P） and dissolved organic carbon （DOC） loss, particularly in agricultural landscape. More application of chemical fertilizer and unreasonable agricultural management intensified the loss. In addition, rain also made great contribution to water pollution, such as eutrophication which degraded the surface water quality and threatened the hydrosphere ecosystem. The aim of this study was to monitor the dynamics of carbon and phosphorus losses under different rainfall events in Yanting, Sichuan Province, China （105027 E, 31 16 N） from July to August in 2012, then to better understand the processes and mechanisms of the dissolve organic carbon （DOC） and P loss, and to evaluated the effect of environment on purple soil area as well. The results showed that the total discharge of all of the rainfall events was 20399.8 m3 and the transport load of carbon and P was 83.19 kg and 5.1 kg, respectively. The higher rainfall resulted in the bigger loss load. Furthermore, the DOC and total phosphorus （TP） output dynamics were significantly different among the three types of rainfall. For example, the pattern of DOC concentration in the runoff is not consistent with the discharge of runoff, which showed that the concentration went down with the time length of rainfall first, and then sharply up, after it achieved the peak value, it decreased gradually and then tended to remain at a level. The order of peak values of total phosphorus （TP） appeared in the runoff was 20th Jul 〉20＇h Aug 〉30th Aug. The particular phosphorus （PP） transported by surface flow in all kinds of rainfall types was the main form of P during runoff, while phosphate phosphorus （PO34--P） occupied the main position of dissolved total phosphorus （DTP）. The transport load of PP under each rainfall event was 1167.491,1891.331,984.74 g while that of PO34--P was 108.37,338.8,167.79 g, respectively. The export concentration of DOC and TP in runoff under different rainfall events was 3.37,4.77,6. 97 mg/L and 0.11,0.43,0.74 mg/L, respectively. One of the targets to evaluate the effectiveness of P is C/P ratio. In general the lower C/P ratio will lead to the higher effectiveness of P. In each rainfall events the ratio was 192, 48 and 42.1, respectively, which indicated that the chance of water pollution caused by big and middle rainfall types was much higher. In conclusion, the effective control measures should be taken to reduce the loss of P and carbon in this pluvial region, and more attentions should be given to big and middle rainfall types.