不同时空尺度下土地利用对洱海入湖河流水质的影响

土地利用与入湖河流水质的关系存在时空差异。以洱海西部入湖河流及其小流域为研究对象,综合空间分析和数理统计手段,探讨两者随空间尺度和时间变化的关系,结果表明:选取的小流域、河岸带30m缓冲区、河岸带60m缓冲区和河岸带90m缓冲区4种尺度下,对入湖河流水质影响显著的土地利用类型为建设用地和植被(包括林地和牧草地),影响最大的空间尺度为小流域尺度,河岸带30m缓冲区次之;小流域尺度下,建设用地面积百分比与入湖河流COD和TP浓度呈正相关,植被面积百分比与NH_4~+-N浓度呈负相关,响应土地利用的主要水质指标为TN和TP,回归调整系数分别为0.624和0.579;季节性关联分析表明建设用地与COD、NH_4~+-N、TP的回归关系在雨季强于旱季,植被与COD、TP的回归关系在雨季强于旱季,雨季建设用地和植被面积变化引起COD浓度变化更快。在流域管理中,针对植被覆盖率低、建设用地占比高的白鹤溪和中和溪应重点加强雨季土地利用管控,增加植被覆盖率,合理开发建设用地。

Impact of land use on the water quality of inflow river to Erhai Lake at different temporal and spatial scales

Relationships between land use and water quality of rivers flowing into lake vary spatially and temporally. These variations were analyzied using spatial analysis and mathematical statistical methods for the inflow rivers and their subcatchments on the western side of the Lake Erhai basin. The results indicated that the land use types influencing river water quality significantly were construction and vegetation land at four spatial scales (subcatchment, and 30m, 60m, and 90m riparian buffer zones). Vegetable land included forest, grassland and shrub land. The greatest impact occurred at the subcatchment scale, followed by the 30m riparian buffer zone. At the subcatchment scale, the amount of construction land was positively correlated with COD and TP concentrations of the inflow rivers. The amount of vegetation land was negatively correlated with NH₄⁺-N concentration, and the main water quality indexes corresponding to land use were TN and TP, with 0.624 and 0.579 adjusted regression coefficients, respectively. Seasonal correlation analysis suggested that the regression relationships between construction land and COD, NH₄⁺-N, and TP concentrations during the wet season were stronger than those in the dry season, and the regression relationships between vegetation land and COD and TP concentrations were also stronger during the wet season than those in the dry season. COD concentration change caused by variation in construction land and vegetation land variation occurred more rapidly during the wet season than those in the dry season. During river basin management, particular attention should be paid to land use control during the wet season for the Baihe and Zhonghe Rivers, whose watersheds have a lower proportion of vegetation land and a higher proportion of construction land. Vegetation coverage should be increased, whereas the effects of land development should be studied adequately before implementation.