In situ high-frequency measured turbidity can potentially be used as a surrogate for riverine phosphorus (P) concentrations to better justify the effectiveness of nutrient loss mitigation measures at agricultural sites. We explore the possibilities of using turbidity as a surrogate for total phosphorus (TP) and particulate phosphorus (PP) in four snowmelt-driven rivers draining agricultural clayey catchments. Our results suggest slightly stronger relationship between in situ measured turbidity and PP than between turbidity and TP. Overall, linear TP and PP regressions showed better error statistics in the larger catchments compared with their sub-catchments. Local calibration of the in situ sensors was sensitive to the number of high P concentration discrete water samples. Two optional calibration curves, one with and one without influential data, resulted in a 17% difference in the estimated mean TP concentrations of a snowmelt storm contributing 18% of the annual discharge volume. Accordingly, the error related to monthly mean TP estimates was the largest in spring months at all sites. The addition of total dissolved phosphorus (TDP) improved the model performance, especially for sites where the TDP/TP ratio is large and highly variable over time. We demonstrate how long-term discrete samples beyond sensor deployment can be utilized in the evaluation of the applicability range of the local calibration. We recommend analysing the validity of P concentration estimates, especially during high discharge episodes that contribute substantially to annual riverine nutrient fluxes, since the use of surrogates may introduce large differences into the P concentration estimates based on selected local calibration curves.

中文翻译：

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高频测得的浊度作为北方地区河流中磷的替代物：适当的选择和紧急情况。

现场测得的浊度可潜在地用作河流磷（P）浓度的替代物，以更好地证明减少农业地点营养物流失措施的有效性。我们探索了使用浑浊度代替四根融雪驱动河流排出农业黏性流域的总磷（TP）和颗粒磷（PP）的可能性。我们的结果表明，现场测得的浊度和PP之间的关系比浊度和TP之间的关系稍强。总体而言，线性TP和PP与子集水区相比，回归显示较大集水区的误差统计更好。原位传感器的本地校准对高P浓度离散水样品的数量敏感。两条可选的校准曲线（一条带有影响数据，一条没有影响数据）导致融雪风暴的估计平均TP浓度相差17％，占年排放量的18％。因此，与春季平均TP估算有关的误差在春季所有月份都是最大的。总溶解磷（TDP）的添加改善了模型性能，特别是对于TDP / TP比率很大，并且随时间变化很大。我们演示了如何将超出传感器部署范围的长期离散样本用于评估本地校准的适用范围。我们建议分析P浓度估算值的有效性，尤其是在大流量排放事件中，这对每年的河流养分通量有很大贡献，因为使用替代物可能会根据选定的本地校准曲线将较大的差异引入P浓度估算值中。