Water quality sampling methods may bias evaluations of watershed management practices

Abstract

Accurate measurement of the discharge of total suspended solids (TSS) from watersheds is complicated by the extreme temporal variability of suspended solid concentrations during periods of high stream flow. Consequently, TSS loads estimated from data collected at different temporal frequencies may differ in accuracy and precision. Moreover, there remains a need for optimal sampling methods which yield the highest possible accuracy for the least effort. We investigated the effect of sampling frequency on estimations of TSS loads and retention within a restored stream in Maryland, USA. We found that coarser temporal sampling methods can lead to erroneous conclusions of restoration efficacy with poor accuracy and precision in estimates of sediment retention. Additionally, we synthesized 28 years of continuous turbidity-based TSS data from Europe and North America to assess the effect of sampling frequency. Our synthesis suggests that flow-paced composite sampling may be the most accurate and precise sampling method. This method is also economical, requiring analysis of only one sample per week. Thus, the flow-paced method may be a potential solution to economize and standardize water quality monitoring.