Water Quality Monitoring Design for Precise River Load Estimation

― A case study in a small forested catchment using autosamplers ―

Abstract

In a small forested catchment (12.14 ha), both periodic (every two days) and flow-proportional sampling (every five mm aliquot of cumulative discharge) of stream water quality were conducted in 2016 using autosamplers to estimate annual stream loads. Bulk deposition was also measured. A total of 16 water quality parameters were assessed, including soluble and particulate matter. The results of the load estimates still showed large uncertainties for particulate matter, such as several times of point estimates, even with a large number of flow-proportional samples of 183 elements per year, and an acceptably small uncertainty for soluble matter. Such large uncertainties found for particulate matter were attributed to erratic and irregular variations in water quality. For particulate matter, periodic sampling with a two-day interval did not to provide an uncertainty of acceptable magnitude.