川中丘陵区农业源头沟渠反硝化速率特征及其影响因素

Denitrification Variations and Influencing Factors in Agriculture Headwater Ditch in the Hilly Area of Sichuan Central Basin

农业源头沟渠是连接农田排水与河流的重要通道,对农业非点源污染物具有很高的削减作用。反硝化作用是沟渠水体氮污染去除最彻底的机制,但目前相关研究缺乏。利用改进的乙炔抑制法研究川中丘陵区农业源头沟渠沉积物反硝化作用的速率、季节变化及影响因素,以期为长江上游农业水环境保护提供新的思路。结果表明:1)农业源头沟渠沉积物反硝化速率变化范围在0.31~43.11mg·m^(-2)·h^(-1)之间,平均值为10.45mg·m^(-2)·h^(-1);2)沟渠反硝化速率具有明显的季节差异,冬季沟渠沉积物反硝化速率普遍偏低,而夏季则具有较强的反硝化作用,不同季节的反硝化速率大小顺序为:夏季>春季>秋季>冬季;3)沟渠反硝化作用受水文条件、水体沉积物碳氮浓度等因素影响。其中,水文条件不同的区域反硝化速率的大小顺序为:间歇滞水区>干湿交替区>常年淹水区;沉积物和上覆水NO-3-N,DOC浓度与反硝化速率之间具有显著的正相关关系。总体来说,川中丘陵区农业源头沟渠具有较高的反硝化速率,通过增加碳源或改善水文条件能有效地促进沟渠沉积物的反硝化作用,从而极大地提高农业源头沟渠对非点源氮污染的截控能力。

Agricultural headwater ditch with high nitrogen removal efticiency is an important channel connects agricultural drainage and rivers. Denitrification is the most important mechanism of nitrogen removal in the water. However, relative researches in agri- cultural headwater ditch were lack. Seasonal variations and influencing factors of agricultural headwater ditch denitrification in the Hilly Area of Central Sichuan Basin were investigated by the method of amended acetylene inhibition technique with the objective to offer new ideas for the water quality protection in the upper reaches of Yangtze River. Results indicated that： 1） Denitrification rate of sediment in agricultural headwater ditch ranged from 0.31~43.11 mg· m ^-2· h^-1 with an average of 10.45 mg · m ^-2· h^-1; 2） Seasonal variations of denitrification in sediment in agricultural headwater ditch were obviously. Higher denitrification rate was found in summer than the rate in winter; 3） Denitrification in agricultural headwater ditch sediment affected by hydrology, the con- centration of carbon and nitrogen in sediment. The denitrification rate in intermittent flooding area was highest, followed by the dr- ying-wetting alternating area, the perennial flooding area. Denitrification rate positively related with NO3-N and DOC in sediment and water. It could be concluded that denitrification can be improved by adding carbon sources and changing hydrological conditions in agricultural ditches, which will be conducive to the control of non-point nitrogen pollution in the upper reaches of Yangtze River.