TY - JOUR
T1 - Estimation of long-term external nutrient loading from watersheds to lake biwa by a combined rainfall-runoff model and loading-discharge curve approach
AU - Tien, Huu Le
AU - Okubo, Kenji
AU - Thi, Phuong Ho
AU - Saito, Mitsuyo
N1 - Funding Information:
This work was supported by the Grant for Encourage-E ment of Students, Okayama University (No. 7772). We thank Okayama University graduate students for sample collection and M. Murakami for data compilation during the research process.
Publisher Copyright:
© The Author(s) 2020.
PY - 2020
Y1 - 2020
N2 - 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.
AB - 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.
KW - Lake Biwa
KW - Loading-discharge curve
KW - Long-term external loading
KW - Rainfall-runoff model
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U2 - 10.3178/hrl.14.143
DO - 10.3178/hrl.14.143
M3 - Article
AN - SCOPUS:85096395789
VL - 14
SP - 143
EP - 149
JO - Hydrological Research Letters
JF - Hydrological Research Letters
SN - 1882-3416
IS - 4
ER -