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To study the hyporheic exchange driven by a single peak flood‐induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real‐time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of "Botan" (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine‐type) and its change rate v (cosine‐type), and was proportional to the polynomial of them q∝ (ω∙h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs. [ABSTRACT FROM AUTHOR]

There are some weaknesses in the methodology of original paper "Informal landfill contributes to the pollution of microplastic in the surrounding environment" published in Environmental Pollution. We commented on the groundwater sampling procedure that affect the calculated concentrations of microplastics in groundwater. Important information related to the description of sampling wells, informal landfill, and the exact description of sample collection method are missing. In addition, significant data related to the groundwater like water level, flow direction, and velocity have been skipped, which are fundamental in groundwater related studies. There should be a clear diagram of landfill location and sampling wells in the landfill, for appropriate understanding of microplastics (MPs) pollution in surrounding environment of a landfill. [ABSTRACT FROM AUTHOR]

We examined groundwater and stream water interaction in the Inbuk stream, Korea, using various approaches including hydrologic, thermal, hydrochemical, and isotopic methods. For this purpose, we installed four piezometers (IYHW1-4) in the streambed at 10 m interval across the stream and at depths of 0.90 to 1.54 m. We monitored water levels and water temperatures every hour using automatic transducers at the piezometers and in the stream (IYSW1) from September 2013 to April 2014. We also analyzed chemical and isotopic compositions for the hyporheic waters, stream water, and nearby groundwater in early September and late November in 2013. The water levels and hydraulic gradients revealed that three (IYHW1, 2, and 4) of the piezometers were in upwelling conditions for most of the monitoring period, except for the earliest short period (considered to be the wet season), whereas one piezometer (IYHW3) showed a reverse behavior, indicating that the gaining was dominant in the dry period. The mean calculated influx to the stream was 3.04 × 10 cm/sec. Observed temperatures of stream water, hyporheic waters, and groundwater also revealed that stream water was downwelling in the early monitoring period (wet season), whereas the groundwater was generally upwelling in most of the resting period, which is consistent with the water level interpretation. Chemical composition analysis indicated that most of the waters were Ca-HCO type for both seasons. However, no distinctive difference between chemical compositions of water without substantial seasonal variation negated any inference on the flow conditions. The mixing ratios computed from oxygen and hydrogen isotopic compositions indicated that losing conditions were dominant in the wet season, whereas gaining conditions prevailed in the dry season. The interpretations of stream water and groundwater interactions based on these different methods are relatively consistent for this study area, indicating that such combined methods will be very useful in enhancing understanding of groundwater and stream water interaction. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine groundwater responses before and after the November 15, 2017 Pohang earthquake (Mw=5.4) in a coastal area of Korea. The earthquake caused devastating damages to many buildings in the city. For this study, groundwater monitoring data (water level, electrical conductivity, water temperature) were obtained for January 2016 to February 2018 from the national groundwater monitoring stations, the rural groundwater monitoring wells, and the seawater intrusion monitoring wells and they are located within 25 km from the epicenter. There are eight national groundwater monitoring stations (PSG, PYI-D, PYI-S, PGB-D, PGB-S, PJH, PDH, PGR), five rural groundwater monitoring wells (PH1, PH2, PH3, PH4, PH5) and four seawater intrusion monitoring wells (GG1, GG2, YI1, YI2). Six of the monitored wells showed groundwater level decreases of 9–81 cm and two of them exhibited a recovery to the previous level within three days while the remaining wells did not. And six monitoring wells showed EC changes to the earthquake with -1,274–161 μS/cm. In addition, three wells showed discernible groundwater temperature fluctuations of -0.2–0.3oC. Here, we found the magnitude of groundwater level change is decreasing with distance of the monitoring wells from the epicenter. Some detailed analyses on the relationship between the responses and a variety of hydrogeological parameters deserve a further study. This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (No. 20183010111860) and by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2015R1A4A1041105). [ABSTRACT FROM AUTHOR]

Seasonal fluctuation in groundwater level (below the ground surface) and water quality variables are mainly attributed to climatic conditions, soil characteristic, drainage method, and management practices. Groundwater degradations and high nitrate values have taken considerable attention in the Republic of Korea. Water management practices needs to be based on results of monitoring of groundwater level and water quality variables. We studied spatial variations based on temporal fluctuations of groundwater level (GWL), and water quality parameters including pH, electrical conductivity (EC), and nitrate (NO3). These contents were monitored from year 2011 to 2014 in 70 groundwater wells of an agricultural region in Korea. The monitoring of contents was done in field and collected data after laboratory analysis, was analyzed by using geostatistical modeling and mapping techniques. Seasonal variations in GWL during the period of four years of monitoring were ranged 2.91–5.17 m and 2.80–4.08 m in wet and dry seasons, respectively. The variations in pH value for the same period ranged 6.55–7.50 and 6.69–7.82 in wet and dry seasons, respectively. The fluctuations in EC values ranged 125–604 μg/cm and 80–272 μg/cm in wet and dry seasons, respectively. The values for NO3 in groundwater ranged 12.87–34.40 mg/L and 9.46–38.80 mg/L during the wet and dry seasons. The GWL shows strong spatial dependence, while pH and EC show strong to weak spatial dependence. The groundwater NO3 shows partial spatial dependence with decreased values in 2014 compared to the values in 2011. This finding is attributed to improved agricultural practices and change in land use pattern from white radish and cabbage to orchards and ginseng fields. This work was supported by the National Research Foundation of Korea (NRF) grant, funded by the Korean government (MSIT) (NRF-2015R1A4A1041105) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2018R1D1A1B07047200). [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal flow process can maximize the denitrification capacity of riparian zones downstream of reservoirs. • Denitrification is reaction- instead of transport-limited when the hydrograph wave amplitude/duration ratio is high. • Riparian nitrogen removal has a strongly positive correlation to return/infiltration time ratio of solutes. Flood waves generated by reservoir discharge play a crucial role in the potential for riparian denitrification downstream. The efficiency of nitrogen (N) removal from river water by riparian zones is typically enhanced with greater wave amplitude (A) and duration (T). However, a knowledge gap exists with respect to the impact of flood waves on N removal when considering a fixed-value integral over time of flood waves (IOFW). This study explored N transport and transformation in the riparian zone downstream of the dammed Inbuk River, Korea under various wave conditions with a fixed IOFW. The results revealed a logarithmic enhancement in solute infiltration into the riverbank with an increasing wave amplitude/duration ratio (A / T ratio). The solute residence time within the riparian zone displays an initial increase followed by a decrease with the increment in the A/T ratio. We identified a threshold for the wave A/T ratio that maximizes riverine N removal by the riparian zone, a phenomenon observed across various dammed rivers. Our findings indicated that riparian denitrification is reaction time-limited when the wave A/T ratio exceeds the threshold; contrarily, it becomes transport capacity-limited. Additionally, we observed a significant relationship between the net nitrate removal and the return/infiltration time ratio of water (r2 = 0.93, p < 0.05). The research results contribute to a better understanding of the impact of water level fluctuations on the N cycle in riparian zones, and provide valuable insights for developing sustainable reservoir operation strategies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Numerical method to delineate hyporheic zone depth using CAD analysis was proposed. [•] To evaluate adequacy of the proposed method, sensitivity analysis was performed. [•] The hyporheic zone depth was little influenced by hyporheic water flux shapes. [•] Estimated hyporheic zone depth of the method is comparable with that of tracer test. [•] The proposed method has an advantage even when hyporheic flux shape is ambiguous. [Copyright &y& Elsevier]

Summary: The Korean Ministry of Construction and Transportation (MOCT) and the Korean Ministry of Environment (MOE) manage the National Groundwater Monitoring Stations (NGMS) and the Groundwater Quality Monitoring Stations (GQMS) under Article 17 of the Groundwater Act. Under the same legislation, local government will install or designate an additional 10,000 monitoring wells as Subsidiary Groundwater Monitoring Stations (SGMS) by 2011. However, a standard for the installation and management of the SGMSs has not yet been developed. This study focuses on the development of a model for the determination of optimal monitoring frequencies during the manual measurement of the SGMSs. The groundwater level time series for the 81 deep and shallow monitoring wells making up the NGMSs were analyzed using an AR(p) model, and a harmonic series model was then made for the determination of groundwater level sampling frequency in the SGMSs. The result showed that the average sampling frequency necessary for groundwater level monitoring is about once every 8.9 days. Moreover, it indicates that water level sampling needs to be performed more frequently in steeply inclined sites, deep wells, and in monitoring wells belonging to an AR(2) rather than an AR(1) model. [Copyright &y& Elsevier]