Kideok D. Kwon

Current water uses, related risks, and management options for Seoul megacity, Korea

Megacities worldwide face various challenging tasks associated with expanding populations and land exploitations; these include securing water supplies, appropriate operating of wastewater treatment/disposal, and the mitigation of natural hazards triggered by anthropogenic activities. Seoul megacity, Korea, where over ten million people populate, is not an exception to the issues. In this study, we examine water resources, their uses, and issues associated with them, specifically climate change, urban flooding, underground water seepage, and land subsidence in Seoul. The changing climate of this city manifests itself in a sharp escalation in air temperature. Increased torrential rainfall causes repeated human casualties from urban floodings, which are exacerbated by expanding impervious surface. The increasingly large interannual variability in precipitation makes it more difficult to take proper actions to secure water supplies. Despite a large annual budget being devoted to producing tap water from the Han River, only about 5% of the population drinks the tap water. Underground transport routes (subway lines) and high storied buildings with deep foundations produce high volumes of underground water seepage, and most of the valuable water resources are dumped without being reused. Underground water seepage also triggers a decline in groundwater levels and elevates the possibility of land subsidence. Recent increases in land subsidence and road sinks in the city are mostly related to old sewer lines and heavy underground work. In this study, we discuss options toward supporting sustainable urban water management in Seoul.

Unexpected nationwide nitrate declines in groundwater of Korea

Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen (N) fertilizer to croplands is one of the major sources of high nitrate content in groundwater. In this study, we analyse the nitrate concentrations in Korean groundwater based on data from groundwater quality monitoring wells (n=1,022–2,072), which were sampled twice annually over a recent 13-year analysis period (2001–2013). We report that groundwater nitrate levels are decreasing, despite steadily increasing groundwater use. The maximum nitrate concentration decreased from 168.91 to 48.11 mg/L, while the mean values also show a gradual decreasing trend. Nonparametric Mann-Kendall tests on nitrate concentrations also confirm the decreasing trend. The nitrate decrease is more clearly evident in agricultural groundwater as compared to domestic and drinking groundwaters. This decrease of nitrate in groundwater coincides with a large decline in N fertilizer application due to reduced cropland areas, more sustainable agricultural practices, and progressive improvement of sewage disposal services. This study proposes that the long-term adoption of best practices in agriculture has had a positive impact on groundwater nitrate control.