Effects of sampling strategies and estimation algorithms on total nitrogen load determination in a small agricultural headwater watershed

Monitoring data collected from rivers are used to support assessments of the quality of the river environment andhelp decision makes formulate appropriate management plans. Therefore, accurate and precise estimates ofconstituentfluxes in streams and rivers are important. However, seasonal errors have not received enoughattention and the published results have rarely been verified by other methods. In this study, the error associatedwith sampling frequencies (3 daily, weekly, 2 weekly, 4 weekly, 6 weekly, 8 weekly) and seven load estimationalgorithms were examined. Seasonal and annual total N loads were estimated and wavelet coherence was used asa reference. In order to reduce the contingency of the results, three years data were used and total N (with17.53% particulate N, 58.70% NO3−-N and 23.77% other dissolved N fractions) was chosen to reflect waterquality parameters. Results indicated that 2 weekly sampling frequency and algorithm F (linear interpolation)are sufficient for evaluating the characters of annual total N load in Fengyu River Watershed with 5% RMSE(root-mean-square error). There was a large RMSE (3.97–44.66%) in summer with a high CV (coefficient var-iation) (35.2%) for total N concentration. These results can serve as a useful reference for decision makes whoneed to establish monitoring programmes in watersheds with similar characteristics.