Unexpected nationwide nitrate declines in groundwater of Korea

Abstract

Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen 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, whereas the mean values also show a gradual decreasing trend. Non‐parametric 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 nitrogen 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.

Factors Controlling the Spatial Distribution and Temporal Trend of Nationwide Groundwater Quality in Korea

“…The climate is hot and humid in summer and cold and dry in winter. Average annual precipitation is 1200-1400 mm, 50-60% of which occurs in summer, and average annual air temperature is 10-16 °C [17]. The East Asian monsoon mainly affects the climate of the study area.…”

“…The data used in this study were from monitoring stations of GQMN installed in background regions. Groundwater quality depends on the location of monitoring stations [14,17]. Thus, we examined their locations with the different installation dates.…”

“…Using these data, we assessed the impact of land use on groundwater quality as well as the spatial distribution of groundwater hydrochemistry. For trend analysis, groundwater quality at each monitoring well was analyzed using a linear regression, which is a type of parametric analysis [14,17]. According to Central Limit Theorem, the sample All methods used to obtain groundwater samples, conduct preprocessing, and perform water quality analysis were complied with the ME regulations [21].…”

“…In a separate study [37], groundwater EC fluctuated within 240-320 µS/cm from 2008 to 2014 at 213 monitoring wells of NGMN. Lee et al [17] said that groundwater NO3 − showed the decreasing trends over the analysis period of 13 years (2001-2013) in 1628 out of total 2939 wells. In Korea, there are few studies on temporal variations in groundwater quality, and more attention is needed on it.…”

Factors affecting spatial pattern of groundwater hydrochemical variables and nitrate in agricultural region of Korea

“…causes human health problems such as blue baby syndrome and cancer in adults specially in the digestive tract (Powlson et al, 2008;World Health Organization, 2011;. The high concentration of NO 3 in groundwater is a severe problem in Korean agricultural areas (Lee et al, 2017). Monitoring groundwater contamination and identifying factors influenced the NO 3 concentration in groundwater are important steps to reduce contamination and manage groundwater quality.…”