洱海西部灌排沟渠水质特征及土地利用的影响

Water quality characteristics of irrigation and drainage ditches in western Erhai Lake Basin and the effect of land uses

灌排沟渠径流是洱海氮、磷营养盐输入的主要来源。2020年秋季,研究选取洱海西部2个汇水区,分析了降雨条件下汇水区和沟渠子汇水区2个空间尺度下沟渠水质的变化特征,以及土地利用对沟渠水质的影响。结果表明:沟渠水质表现出显著的空间差异性,其中双隐汇水区东南部沟渠化学需氧量(COD)较高,为5.68~20.49 mg/L,北部沟渠总氮(TN)浓度较高,为1.04~1.44 mg/L,总磷(TP)浓度自东向西递减,氨氮(NH_(3)-N)浓度整体较低;万阳汇水区南部沟渠COD较高,为5.02~14.22 mg/L,TN浓度整体较低,环洱海和中部靠北沟渠TP和NH_(3)-N浓度整体偏高。冗余分析结果表明,村镇、农田是沟渠TP和NH_(3)-N的主要来源,秋季库塘未被利用的蓄水也可能对沟渠水质造成影响,林草地面积占比与沟渠水质呈负相关,但由于占比小和空间分布原因,对入海污染负荷的削减效用较小。洱海西部应加强灌溉用水循环利用,完善环湖截污工程,以减少灌排沟渠退水和农村生活污水对洱海水质的影响。

The runoffs from irrigation and drainage ditches are the major sources of nitrogen and phosphorus of Erhai Lake.In the Autumn of 2020,two catchments in the western Erhai Lake Basin were selected to analyze the change characteristics of ditch water quality in catchment scale and sub catchment scale under the rain condition,as well as the impact of land use on ditch water quality.The results indicated that the water quality of the ditches presented obvious spatial variation.In Shuangying catchment,the chemical oxygen demand(COD)of the ditch runoff was relatively high in the southeast,which ranged from 5.68-20.49 mg/L,and that of total nitrogen(TN)of the ditches in the north was relatively high,which ranged from 1.04-1.44 mg/L.The total phosphorus(TP)concentration decreased from east to west,and ammonia nitrogen(NH_(3)-N)concentration was generally low in the catchment.In Wanyang catchment,the COD concentration of the ditch runoff was relatively high in the south,which ranged from 5.02-14.22 mg/L,and the TN concentration was generally low,and the TP and NH_(3)-N concentrations were generally high in the ditches around Erhai Lake and north of the central part.The redundancy analysis indicated that the farmland and village were the major source of TP and NH_(3)-N in the ditch runoff.The unutilized water storage in ponds and wetlands may cause the ditch water quality pollution in the Autumn.The grass and forest land area presented negative relationship with the ditch water quality,but due to the low proportion and spatial location,it had little effect on reducing the pollution load into the sea.To reduce the impact of irrigation and drainage ditch backwater and rural domestic sewage on Erhai Lake,measures should be taken to strengthen the recycling of irrigation water,and improve the sewage interception project around the lake.