Surrogate measures for providing high frequency estimates of total suspended solids and total phosphorus concentrations
Surrogate measures like turbidity, which can be observed with high frequency in situ, have poten-tial for generating high frequency estimates of total suspended solids (TSS) and total phosphorus (TP) concen-trations. In the semiarid, snowmelt-driven, and irrigation-regulated Little Bear River watershed of northernUtah, high frequency in situ water quality measurements were recorded in conjunction with period ic chemistrysampling. Site-specific relations hips were developed using turbidity as a surrogate for TP and TSS at two moni-toring locations. Methods are presented for emplo ying censored data and for investigating categorical explana-tory variables (e.g., hydrolog ic conditions). Turbidity was a significant explanatory variable for TP and TSS atboth sites, which differ in hydrologic and water qual ity characteristics. The relation ship between turbidity andTP was stronger at the upper watershed site where TP is predominantly particulate. At both sites, the relation-ships between turbidity and TP varied between spring snowmelt and base flow conditions while the relation-ships between TSS and turbidity were consistent across hydrological conditions. This approach enables thecalculation of high frequency time series of TP and TSS concentrations previously unavailable using traditionalmonitoring approa ches. These methods have broad application for situations that require accurate characteriza-tion of fluxes of these constituen ts over a range of hydrologic conditions.