Nutrients and Suspended Sediment Load Estimates for the Ishikari River Basin, Japan, Over a Decade

Abstract

The load estimation process for nutrients (nitrogen and phosphorus) and suspended sediment (SS) is complicated because of retransformation bias, data censoring, and non-normality. To obtain reliable unbiased estimates, the regression model Load Estimator (LOADEST) was applied to estimate total nitrogen (TN), total phosphorus (TP) and SS loads at five sites in the Ishikari River Basin, Japan, from 2000 to 2010. Coefficients of determination (R2) for the best-fit regression models for loads of TN, TP, and SS for the five sites ranged from 75.36 % to 92.37 %, suggesting the model for all three constituents successfully simulated the variability in constituent loads at all sites. Moreover, the estimated seasonal loads fluctuated widely during 2000 to 2010, with the greatest loads occurring in spring and the smallest loads occurring in winter. Accurately estimated loads are essential for effective water resources management efforts.