水稻种植对中亚热带红壤丘陵区小流域氮磷养分输出的影响

以湖南省长沙县的脱甲流域(高水稻种植面积比例)和涧山流域(低水稻种植面积比例)为研究对象,对比研究红壤丘陵地区典型农业流域水稻种植对河流水体氮磷浓度和输出强度的影响.连续16个月的监测结果表明,脱甲和涧山流域河流水体均存在比较严重的养分污染,尤其是氮污染;对比两个流域,脱甲流域河流水体的氮磷浓度水平和水质恶化程度均高于涧山流域.从养分组成来看,脱甲流域河流水体中氮以铵态氮为主(占总氮的58.5%),而涧山流域主要是硝态氮(占总氮的76.1%).脱甲流域中可溶性磷占总磷比例为47.1%,高于涧山流域的37.5%.从养分浓度变化的时间动态而言,两个流域河流中各形态氮素水平在1~2月和7月较高,而可溶性磷和总磷在5~6月和10~12月出现两个峰值.由于两个流域河道径流主要集中在水稻种植期间的4~10月,脱甲流域河流中较高的氮磷养分浓度意味着潜在的氮磷流失风险.脱甲流域月平均总氮输出通量为1.67 kg·(hm2·月)-1,总磷为0.06 kg·(hm2·月)-1,均高于涧山流域的0.44 kg·(hm2·月)-1和0.02kg·(hm2·月)-1.考虑到两个流域的气候、地形地貌、土壤类型、农田耕作方式相似而只是水稻种植面积比例不同,因此,在该地区传统的水稻栽培管理模式下,较高面积比例的水稻种植对流域河流水体环境存在潜在威胁.

Impact of Rice Agriculture on Nitrogen and Phosphorus Exports in Streams in Hilly Red Soil Earth Region of Central Subtropics

The research selected the Tuojia catchment and Jianshan catchment in Changsha County, Hunan Province, to comparatively study the effects of rice agriculture on the nitrogen and phosphorus concentrations and exports in streams in the typical agricultural catchments of the hilly red soil earth region. The monitoring of 16 months suggested that, there was a moderate stream nutrient pollution in both Tuojia and Jianshan catchments, especially for nitrogen pollution. Comparing the two catchments, the nitrogen and phosphorus concentrations were higher and the water quality was worse in the Tuojia catchment than that in the Jianshan catchment. From the nutrient composition of view, ammonia nitrogen was the main species of total nitrogen in the Tuojia catchment (accounting for 58.5% of total nitrogen), while it was nitrate nitrogen in the Jianshan catchment (accounting for 76.1% of total nitrogen). The proportion of dissolved phosphorus in total phosphorus was 47.1% in the Tuojia catchment, higher than the proportion of 37.5% in the Jianshan catchment. From temporal variations of nutrient dynamics of view, concentrations of all forms of nitrogen were higher during January to February and in July, respectively, and total phosphorus and dissolved phosphorus were higher during May to June and during October to December. Since the stream discharge in the catchments concentrated during the rice growing period from April to October, the higher nutrient concentrations during the period suggested potential risks of nitrogen and phosphorus losses. The total nitrogen mass flux was 1.67 kg·(hm²·month)^-1 and TP was 0.06 kg·(hm²·month)^-1 in the Tuojia catchment, which were greater than the 0.44 kg·(hm²·month)^-1 and 0.02 kg·(hm²·month)^-1 in the Jianshan catchment. Given the similar climate, geomorphology, soil type and cultivation patterns but the different area proportion of rice agriculture between two catchments, results suggested that, under the traditional crop management in hilly red soil earth region of central subtropics, the higher area proportion of rice agriculture has the potential to degrade stream aquatic environment.