QUANTITATIVE EVALUATION OF WATER POLLUTANT LOAD FROM KINOKAWA RIVER BASIN BY HIGH-FREQUENCY WATER QUALITY OBSERVATION
Keywords:
Pollutant loads, River water quality, Total nitrogen, Flooding, Kinokawa river basinAbstract
In the Kinokawa river basin, as same as other watersheds around the world, excess runoff of
nutrients to the ocean mainly due to human activities has become an environmental issue. This study conducted
high-frequency total nitrogen (TN) and total phosphorus (TP) monitoring at several monitoring posts set
downstream of the Kinokawa river in the Kii peninsula, Japan in order to evaluate water pollutant load from
the basin quantitatively. The water sampling has been conducted about 90 times for over a year from May in
2018 at the monitoring posts. In the calm or the drought periods, TN and TP concentrations at Kinokawa river
mouth were basically about 0.8 ~ 1.1 mg/L and under 0.05 mg/L, respectively. However, TN concentrations
was exceeded 5.0 mg/L after one of the most intense storms, it was shown the TN concentration had a tendency
extremely to rise rapidly in flooding condition. This tendency was similar in TP. The result of pollutant load
analysis showed that 65% of the nitrogen load and 80 % of the phosphorus load from the basin was generated
during a few and heavy flooding which were included in 5 % flow exceedance probability. These results imply
it is essential that to understand and to predict how nutrients runoff in short-term during flooding events in
order to accurately grasp long-term nutrient runoff amount.