基于偏最小二乘模型的河流水质对土地利用的响应

流域土地利用类型变化是影响河流水质的重要因素之一.为探究子流域尺度土地利用与河流水质之间的相互关系,本文基于太子河流域遥感影像和水质数据,采用偏最小二乘模型(partial least squares,PLS),分析不同土地利用类型对流域水质的影响程度.选取7个不同子流域土地利用类型面积百分比作为自变量X,总氮(TN)、硝酸根离子(NO_3~-)、氯离子(Cl-)与硫酸根离子(SO_4~(2-))这4个水质参数浓度值作为因变量Y,构建了土地利用类型与河流水质数据的偏最小二乘模型,并使用其余子流域数据对构建的模型进行验证.结果表明,太子河流域不同子流域土地利用类型与河流水质指标TN与NO_3~-之间线性关系显著,决定系数R~20.62.其中,耕地面积变化对水体中TN浓度变化影响明显,居民及工矿建设用地面积变化则对水体中NO_3~-浓度变化影响强烈.但对于Cl-和SO_4~(2-)来说,土地利用类型对其浓度大小有一定影响,但并不是最主要的影响因素.虽然太子河流域未利用地面积百分比极小(1.13%),但是未利用地面积变化对水质参数有较显著影响(影响系数0.24).

Modeling of Water Quality Response to Land-use Patterns in Taizi River Basin Based on Partial Least Squares

Land use change in river basin is one of the most significant factors that influence river water quality. Based on remote sensing images and river water quality data of Taizi River Basin, partial least squares (PLS) model was applied to explore the relationship between water quality and land use patterns at sub-watershed scale. In this study, PLS model was established by using the percentage of area of land use patterns from seven different sub-watersheds as the variables and the concentrations of four water quality parameters as the observations. The established model was further tested with the data from other sub-watersheds in Taizi River Basin. The results indicated that total nitrogen (TN) and nitrate (NO₃^-) were significantly associated with land use types in Taizi River Basin with determination coefficient (R²) greater than 0.62. As for chloride (Cl^-) and sulfate (SO₄^2-), measured values and fitted values had a relatively low fitting precision (R²<0.5), which meant land use pattern was not the main factor affecting the concentrations of Cl^-and SO₄^2- in river water. Meanwhile, river water quality had a strong correlation with the percentage of area of unused land at the sub-basin scale (influence coefficient>0.24), although unused land area in the Taizi river basin was small.