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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]

This study was conducted to reveal the trends of the air temperature and soil temperature for 51 years (1960-2010) and their relationship in four of Korea's largest metropolitan cities (Seoul, Incheon, Busan and Daejeon). Also, the trends of the air and soil temperatures between the studied metropolitan cities and a rural area (Chupungryong) were compared to examine the effect of urban heat. Among the metropolitan cities, the long-term mean soil temperatures (depth 0.0, 0.5, 1.0, 1.5, 3.0, 5.0 m) were lowest (13.34-14.80 °C) in Seoul and highest (16.24-16.54 °C) in Busan, which is mainly the effect of the latitude. The soil temperature exponentially increased with depth in the three cities except for Busan and was closely related to the air temperature. The soil temperatures responded well to the air temperature change (maximum correlation coefficients 0.88-0.98) but this response was slightly delayed with depth. The air and soil temperatures increased at the rates of 0.24-0.40 and 0.11-0.73 °C/decade, respectively, for the period. The increasing rate of the soil temperature was the largest in Daejeon as 0.39-0.73 °C/decade, which was almost 2-4 times greater than those of the other cities (0.11-0.40 °C/decade), and it rose with depth. The increase of the soil temperature was coincident with the increase of the air temperature, which indicates that the soil temperature was largely affected by the increasing of the air temperature. In contrast, the increase in air temperature in Chupungryong (0.06 °C/decade) was significantly lower than in the metropolitan cities. In addition, the increase of the soil temperature in the rural area (0.13 °C/decade) was also much lower than that in the inland cities (0.20-0.27 °C/decade) while it showed no substantial difference from that in the coastal cities (0.11-0.15 °C/decade). Therefore, it is inferred that the soil temperature of the metropolitan cities increased with the increase of the air temperature due to global warming as well as the anthropogenic urban heat. [ABSTRACT FROM AUTHOR]

The spatial synoptic classification (SSC) scheme is a daily weather-type classification scheme that is widely used in climatological and epidemiological investigations. We investigated the modification effect of temperature on respiratory disease-related hospital admissions (RAs) in children based on the SSC type. Data on RAs among children aged ≤ 19 years were collected from the National Inpatient Sample (NIS) database between 2011 and 2015 in Seoul, Korea. In this time-series study, we used Poisson generalized linear models allowing for over-dispersion, with stratification by season and each of the seven distinctive SSC types (Dry moderate [DM], Dry polar [DP], Dry tropical [DT], Moist moderate [MM], Moist polar [MP], Moist tropical [MT], and Transition [T]). We investigated the modification effects of temperature by SSC type through seasonal stratification, adjusting for other meteorological conditions, air pollution, and time trends, and considered the delayed effect for up to four consecutive days. We reported the relative risk percentage change with 95% confidence intervals (CIs) of RAs for every 1 °C increase in ambient temperature, by season and SSC type. Of the 8346 RAs overall investigated between 2011 and 2015, there were 5271 [63.2%] RAs in children aged 0–4 years. Overall, on majority of the days, the SSC types were DM (665 days [36.4%]), and DP (371 days [20.3%]). With regard to seasons, the different SSC types were distributed as follows: spring, DM (193 days [42.0%]); summer, MT (193 days [42.0%]); fall, DM (241 days [53.0%]); and winter, DP (228 days [50.6%]). A stronger association between RAs and temperature was observed overall (1.28% [95% CI; 0.04%, 2.53%]), and in spring (2.10% [0.62%, 3.60%]). According to SSC type, increased associations between RAs and temperature were detected with DM (2.20% [0.47%, 3.97%]) condition during spring and DT (2.41% [0.22%, 4.64%]) during fall. In addition, on re-categorizing the SSC types from a temperature or humidity standpoint, a modified association was observed especially in children aged ≤ 4 years and 5–9 years during spring. Using temperature variability to distinguish seasonal characteristics, we found that the relationship between temperature and RAs in children varied by SSC type. Application of the SSC scheme as an integrative approach may assist in gaining an understanding of seasonal characteristics and health effects due to temperature change. • The spatial synoptic classification (SSC) system is widely used in epidemiology. • We investigated the modification effect of temperature by SSC type. • The study focused on respiratory disease-related pediatric hospital admission (RA). • Temperature increases were associated with an increased RA rate. • The effect was modified by season, SSC type, and age. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogeologic and hydrochemical data for subway tunnel seepage waters in Seoul (Republic of Korea) were examined to understand the effect of underground tunnels on the degradation of urban groundwater. A very large quantity of groundwater (up to 63 million m3 year−1) is discharged into subway tunnels with a total length of 287 km, resulting in a significant drop of the local groundwater table and the abandonment of groundwater wells. For the tunnel seepage water samples (n =72) collected from 43 subway stations, at least one parameter among pathogenic microbes (total coliform, heterotrophic bacteria), dissolved Mn and Fe, NH4 +, NO3 −, turbidity, and color exceeded the Korean Drinking Water Standards. Locally, tunnel seepage water was enriched in dissolved Mn (avg. 0.70 mg L−1, max. 5.58 mg L−1), in addition to dissolved Fe, NH4 +, and pathogenic microbes, likely due to significant inflow of sewage water from broken or leaking sewer pipes. Geochemical modeling of redox reactions was conducted to simulate the characteristic hydrochemistry of subway tunnel seepage. The results show that variations in the reducing conditions occur in urban groundwater, dependent upon the amount of organic matter-rich municipal sewage contaminating the aquifer. The organic matter facilitates the reduction and dissolution of Mn- and Fe-bearing solids in aquifers and/or tunnel construction materials, resulting in the successive increase of dissolved Mn and Fe. The present study clearly demonstrates that locally significant deterioration of urban groundwater is caused by a series of interlinked hydrogeologic and hydrochemical changes induced by underground tunnels. [Copyright &y& Elsevier]