Optimal estimates for dissolved and suspended particulate material fluxes in the Yangtze River, China

Accurate estimate of riverine material fluxes in dissolved and suspended particulate forms is a fundamental issue in monitoring water environments of large basins. Here we collected sub-daily observations of dissolved pollutants (NO₃^--N, NH₄⁺-N, and DOC) and daily data of suspended sediment (SS) at eight gauging stations with controlling areas varied from 694,700 to 1,705,400 km² located in the Yangtze River basin of China, and selected optimal estimates for both dissolved and suspended particulate material fluxes from five time-averaging methods and two regression methods. The results showed that time-averaging methods generally performed better in estimating dissolved pollutants, while regression methods were more applicable for suspended particulate materials. Compared with the selected optimal methods, the conventional method generally overestimated material fluxes by 0.09-49.75% in most cases. Longer sampling interval and smaller controlling area often led to larger uncertainty in estimation and critical values of sampling interval and controlling area were generally found to be 10-20 days and 1.3 million km² in the Yangtze River basin.