南方低山丘陵区小流域不同土地利用方式下面源污染分布特征

Non-point source pollution distribution characteristics under different land uses in small watershed in the hilly regions of south China

南方低山丘陵地区经水土保持综合整治后,水土流失得到了有效遏制,但面源污染问题依然突出。研究小流域面源污染的空间分布规律,对面源污染的治理尤为重要。以松溪河小流域为南方低山丘陵区典型代表,结合实地调研,选择小流域内最具有代表性的3种土地利用类型各自汇水范围内的水塘及松溪河下游和小流域出口处作为采样点,利用2016年6-11月采集的3次水样,分析不同土地利用类型对总氮(TN)、铵态氮(NH4+—N)、硝态氮(NO3-—N)、总磷(TP)空间分布的影响。结果表明:总氮是小流域水体主要污染物,小流域出口处总氮浓度最高,为0.90~3.15 mg/L;居民点和农田对小流域面源污染贡献最高,这是因为南方低山丘陵小流域近年来经济发展较快,社会经济活动频繁但基础设施建设相对滞后;硝态氮浓度与总氮浓度的空间分布特征较一致,硝态氮、铵态氮与总氮在时间上的变化趋势相同;小流域氮素面源污染受到降雨的显著影响,磷素面源污染受到施肥习惯的影响。

Soil and water loss has been effectively controlled by the comprehensive treatment of soil and water conservation in the hilly regions of south China,but the problem of non-point source pollution still exists. It is very important to study the spatial distribution of non-point source pollution in watersheds for the treatment of this kind of pollution. Taking the Songxi River Watershed as the representative of the hilly regions in south China,based on the field investigation,three representative land use types in watershed were selected as the sampling points,including the ponds within the catchment area,the downstream of Songxi River and the watershed outlet. The effects of different land use types on the spatial distribution of total nitrogen (TN),ammonium nitrogen (NH4+—N),nitrate nitrogen (NO3-—N) and total phosphorus (TP) were analyzed using water samples collected from June to November in 2016. The results showed that the total nitrogen was the main pollutant,and its concentration at the sampling point of the watershed outlet was the highest,ranging from 0. 9 to 3. 15 mg/L. Residential area and farmland contributed the highest to the pollution of small watersheds. Because the social and economic activities are frequent due to the fast economic development in these areas,but the infrastructure construction is relatively lagging behind. The spatial distribution characteristics of nitrate nitrogen concentration and total nitrogen concentration were consistent,and the time variation trend of nitrate nitrogen,ammonium nitrogen and total nitrogen was the same. It is found that nitrogen pollution in watershed is significantly affected by rainfall,and phosphorus pollution is affected by fertilization habits.