Relationship between Agricultural Land Use and Spatial Heterogeneity in Quality of Water Resources in Haean Basin of Korea.

In the Republic of Korea, Haean basin is the largest agricultural area in Soyang watershed which is drinking water source for more than 20 million people residing in Seoul metropolis. It is important to investigate any factor affecting the stream or groundwater quality, especially nitrate () concentration in Haean basin which can affect drinking water quality of Soyang watershed. For this purpose, multiple environmental tracers were studied, including major ions and stable isotopes of water (δ²H and δ¹⁸O). Stream and groundwater samples were collected from six predominant agricultural land uses located at different elevation points in the study area. Fields with high fertilizer amounts at intermediate to low elevation using flood irrigation method, had contaminated water. Mixing model of chloride (Cl⁻) and δ¹⁸O indicated groundwater recharge from precipitation and lateral inflow from fields at intermediate to low elevation, regarding solute inputs. Another mixing model and δ¹⁸O defined the existence of lateral inflow of agricultural water in fields at low elevation. The highest water contamination was found in ginseng fields located at high, intermediate, and low elevation, for (68.79 mg/L), exceeding the World Health Organization standard of 50 mg/L in groundwater. This explains that anthropogenic agricultural practices (high fertilizer amounts and flood irrigation) through precipitation and lateral inflow of agricultural water recharge processes, are the major source of groundwater contamination in Haean basin. After anthropogenic inputs, elevation complexity has played a role in spatial heterogeneity of in stream and groundwater. Findings of this study presents a need to focus on ginseng fields and their agricultural practices to maintain stream and groundwater quality of nearby aquifer. [ABSTRACT FROM AUTHOR]