Estimating regional nutrient criteria for streams and rivers is a key step toward protecting river water quality and restoring the health of aquatic ecosystems. Using a multivariable statistical analysis technique, nutrients were identified as the main factor influencing the degradation of the benthic macroinvertebrate community. Three chemical methods (the reference stream distribution approach, all-streams distribution approach and Y-intercept approach) and one biological method (the stress-response approach) were applied to evaluate the nutrient thresholds in the Qing River basin. The reference stream distribution approach and all-streams distribution approach were based on calculating a predetermined percentile of reference streams and all-streams water quality data set, respectively. The Y-intercept approach was based on determining the influence of human activity on water quality by linear regression models. The biological method was based on the response of the benthic macroinvertebrate community structure to changes in water quality. The chemical thresholds were 0.750–1.288 mg/L for total nitrogen (TN) and 0.035–0.046 mg/L for total phosphorus (TP); the biological thresholds were 1.050–1.655 for TN and 0.052–0.101 for TP. The results from the chemical approaches were verified using the biological method, resulting in preliminarily recommended thresholds of 1.000 mg/L TN and 0.040 mg/L TP in the Qing River system.
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机译：估算河流和河流的区域养分标准是保护河流水质和恢复水生生态系统健康的关键一步。使用多变量统计分析技术，养分被确定为影响底栖大型无脊椎动物群落退化的主要因素。三种化学方法（参考水流分配方法，全流分配方法和Y截距方法）和一种生物方法（应力响应方法）被用于评估清河流域的营养物阈值。参考流分配方法和全流分配方法分别基于计算参考流和全流水质数据集的预定百分位数。 Y拦截方法基于线性回归模型确定人类活动对水质的影响。生物学方法基于底栖大型无脊椎动物群落结构对水质变化的响应。总氮（TN）的化学阈值为0.750–1.288μmg / L，总磷（TP）的化学阈值为0.035–0.046μmg / L； TN的生物学阈值为1.050–1.655，TP的生物学阈值为0.052-0.101。化学方法的结果已使用生物学方法进行了验证，得出清河系统中初步推荐的阈值为1.000 mg / L TN和0.040 mg / L TP。
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