This study analyzed the hydrochemical characteristics and microbial communities of karst water in Samcheok, Korea, and compared water quality results to identify the seasonal characteristics and hydrogeological connectivity of the study areas of Hamaengbang-ri, Gyogok-ri, Yeosam-ri, and the downtown area of Samcheok. Field survey and water quality analysis were performed in July 2019, February 2020, and April 2020. Hydrochemical analysis of karst water (groundwater and surface water) showed that most samples were comprised of Ca-HCO₃ and that water–rock interactions were a dominant factor compared to precipitation and evaporation (crystallization). For seasonal characteristics, water–rock interactions appeared more active in the dry season than in the rainy season. Calcite weathering was dominant in the dry season, whereas dolomite weathering dominated the rainy season. Moreover, the saturation indexes for the dry and rainy seasons were less than and greater than 0, respectively, corresponding to an unsaturation (oversaturation) state; thus, white precipitate distributed in the study areas was deposited in the rainy season. Finally, as a result of analyzing the hydraulic characteristics between regions, hydrogeological similarities were identified between Hamaengbang-ri and Yeosam-ri, and between Gyogok-ri and downtown Samcheok, which suggested hydrogeological connectivity between each of the pairs.

Karst regions cover approximately 10% of the Korean Peninsula and are highly vulnerable to contamination. In this study, five field surveys were conducted between 2017 and 2019 to examine the monthly and seasonal changes in the hydro-environment of a characteristic karst region in Samchoek, South Korea. During the surveys, a total of 24 surface water samples were collected and analyzed for field water quality parameters, major and minor ions, and stable isotopes. The results indicate that the water quality in the study area is significantly affected by precipitation. Overall, the water was classified as a Ca-Mg-HCO₃ type, and correlation analysis of the major ions detected in the water samples indicates that the inflow of nitrate to the surface water originated from agricultural activities in the region. Furthermore, variations caused by climate were verified using the relationships between the various ions. In addition, high precipitation rates during the rainy season cause the active exchange of surface material, which was verified using stable isotope outliers. The results provide a scientific basis for studying the connectivity of water systems in complex karst hydrogeological regions and can aid future sustainable management of water resources in these regions.

카르스트 수리지질학은 복잡한 유동 과정을 겪으며 수화학 및 수리연결성을 파악하기 어려운 도전적인 분야 중 하나이다. 이 연구는 동굴 유출수와 하천수의 수화학 특성을 규명하고 싱크홀이 다수 발달된 카르스트 지역에서 새롭게 제안된 추적자 시험을 통해 동굴과 싱크홀을 통한 수리적 연결성을 밝혀내는 것이다. 강원도 삼척시의 하천수와 동굴 유출수의 수화학은 대부분 CaSUP2+/SUP와 HCO₃SUP-/SUP가 높은 농도로 나타나는데 탄산염암의 용해로 인한 것으로 판단된다. 그러나 지하수의 CaSUP2+/SUP와 HCO₃SUP-/SUP의 농도는 하천수와 동굴 유출수에 비해서 낮은 조성으로 나타난다. 이는 하천수와 동굴 유출수에 영향을 주는 천부지하수의 경우 지표 지질의 영향을 받고, 심부지하수의 경우 부정합으로 존재하는 변성암의 영향을 받는 것으로 추정된다. 연구지역의 서쪽에 위치한 유역은 지하수 관정 및 하천수가 없는 유역으로 기존의 추적자 시험의 적용은 불가능하다. 따라서 연구지역 내에 발달된 거대한 싱크홀을 통한 형광광물 추적자 시험을 하였다. 주입된 형광광물 추적자는 설치장소로부터 903 m 이격되어 있는 동굴 유출수로 발원하는 하천에서 발견되었다. 추적자는 짧은 시간 안에 유역을 넘어 유출되었으며 0.8-9 cm/s 속도로 이송되었을 것으로 추정된다. 이 연구를 통해 카르스트 지역의 수화학 특성을 이해하고, 또 카르스트 지역의 특이한 수리적 연결성 및 지하수 유동 속도를 추정할 수 있다.

The effects of the unpredictability of the flow system in a karst area, with respect to bacterial communities in the aquatic environment, were evaluated. Bacterial communities from two different types of flow conditions (spring and sinkhole) were characterized and compared in the karst area. Proteobacteria, Bacteroidetes, and Verrucomicrobia were the major phyla present in the sampled spring and sinkhole waters. The water samples from the spring points were heavily loaded with Actinobacteria, especially Firmicutes, which accounted for 4.3% of the bacterial content. Furthermore, Actinobacteria were prevalent in some water samples, serving as indicators of the effects of seawater inundation. The richness and diversity of bacterial species were evaluated at the spring and sinkhole water points. The spring waters showed a higher bacterial richness and diversity compared to the sinkhole waters. Our results provide valuable information for the evaluation and investigation of microbial compositions in karst areas, which are characterized by heterogeneous hydrological conditions. The microbial species in karst areas are already exposed to changing hydrogeological conditions, and are likely to be confronted with future changes; thus, their spatiotemporal variations reflect the shifting baselines of physicochemical and ecosystem processes.