Estimation of long-term external nutrient loading from watersheds to Lake Biwa by a combined rainfall-runoff model and loading-discharge curve approach
November 13th, 2020
Huu Le Tien, Kenji Okubo, Phuong Ho Thi, Mitsuyo Saito
Received 2020/06/02, Accepted 2020/08/08, Published 2020/11/13
Huu Le Tien1)2), Kenji Okubo2), Phuong Ho Thi3), Mitsuyo Saito2)
1) Graduate School of Environmental and Life Science, Okayama University, Japan
2) Faculty of Fisheries, University of Agriculture and Forestry, Hue University, Vietnam
3) School of Chemical, Biological and Environmental Technologies, Vinh University, Vietnam
External nutrient loadings to Lake Biwa were estimated using a combined tank model and loading-discharge curve approach. The model was applied to collective drainage basins of the lake’s Imazu (northwest), Hikone (northeast), and Otsu (south) areas. The hourly model was conducted using particular discharges from Kita (Ado) river, Takatoki (Ane) river, and Yasu River to obtain loading curves for phosphate (PO4) and silica (SiO2) by assimilating measured concentrations (2002–2003). The tank model was updated by adding an evapotranspiration routine and direct paths of groundwater discharges to the lake floor. The daily model was calibrated through analysis of water budget among the basin, inflow, lake and outflow, and then validated. The model was established and combined into a loading-discharge curve to determine the long-term external nutrient loadings entering the lake (1980–2017). Seasonal variation in nutrient loadings increased during spring and summer and decreased during winter. Annual phosphate-phosphorus (PO4-P) loading ranged from 217 to 296 tons yr–1 in the North Basin and 45 to 76 tons yr–1 in the South Basin, while SiO2 loading fluctuated from 16,027 to 32,655 tons yr–1 and 2,518 to 5,490 tons yr–1 in the North and South Basins, respectively.
Copyright (c) 2020 The Author(s) CC-BY 4.0