Non-point sources of pollution from cultivated lands in river districts and their contribution to water bodies along the North Han River Basin in Korea

Abstract

Cultivated lands within the river district are likely non-point sources of pollution that could be directly discharged into rivers and lakes, as well as identified as significantly risky areas for pollutant run-off during floods. In this study, major non-point sources in surface run-offs, from cultivated lands within the river districts, and their effects on the bodies of water in North Han River Basin were examined. It was found that pollutant concentrations in the run-offs from farms appeared to be generally higher than in the run-offs from paddies. Initial concentrations of pollutants during rainy seasons were usually higher than the medians of their concentration ranges, though not necessarily the highest. The unit loads of BOD from cultivated lands within river districts, which were proposed in this study for the first time in Korea, were 4.56, 3.35, and 10.26 kg/km2/year for paddies, farms, and greenhouses, respectively. Likewise the unit loads of total nitrogen (TN) were proposed as 1.54, 8.11, and 5.59 kg/km2/year for paddies, farms, and greenhouse, respectively. Meanwhile, the unit loads of Total phosphorus (TP) were 0.71, 2.79, and 1.11 kg/km2/year for paddies, farms, and greenhouses, respectively. The unit loads for both BOD and TP from paddies and farms in the North Han River basin were higher than those provided by the Ministry of Environment. It was largely attributable to the regional characteristics of the cultivated area, within the river district, that is adjacent to the water system. Three priority standard watersheds, which were believed to contain higher non-point sources of pollution than other standard watersheds, were recommended to undergo restoration. The sum of the discharged total loads per unit area for BOD, TN, and TP from these three standard watersheds (i.e. NHR M2, NHR1, and NHR M) was 71.8, 71.5, and 73.0%, respectively. Restoring cultivated lands within river districts into grasslands could effectively reduce the total load of TP rather than BOD and TN. Therefore, converting cultivated lands within river districts back to grasslands can be an alternative in effectively reducing pollution in bodies of water.