Groundwater monitoring of an open-pit limestone quarry: groundwater characteristics, evolution and their connections to rock slopes.

Groundwater flow and its geochemical evolution in mines are important not only in the study of contaminant migration but also in the effective planning of excavation. The effects of groundwater on the stability of rock slopes and other mine constructions especially in limestone quarries are crucial because calcite, the major mineral component of limestone, is moderately soluble in water. In this study, evolution of groundwater in a limestone quarry located in Chichibu city was monitored to understand the geochemical processes occurring within the rock strata of the quarry and changes in the chemistry of groundwater, which suggests zones of deformations that may affect the stability of rock slopes. There are three distinct geological formations in the quarry: limestone layer, interbedded layer of limestone and slaty greenstone, and slaty greenstone layer as basement rock. Although the hydrochemical facies of all groundwater samples were Ca-HCO3 type water, changes in the geochemical properties of groundwater from the three geological formations were observed. In particular, significant changes in the chemical properties of several groundwater samples along the interbedded layer were observed, which could be attributed to the mixing of groundwater from the limestone and slaty greenstone layers. On the rainy day, the concentrations of Ca2+ and HCO3- in the groundwater fluctuated notably, and the groundwater flowing along the interbedded layer was dominated by groundwater from the limestone layer. These suggest that groundwater along the interbedded layer may affect the stability of rock slopes.

Dissolved silicon in a lake-floodplain system: Dynamics and its role in primary production.

Dissolved silicon (DSi) is essential for aquatic primary production and its limitation relative to nitrogen (N) and phosphorus (P) facilitates cyanobacterial dominance. However, the effects of DSi on phytoplankton growth and community structure have yet to be fully determined in tropical lakes, particularly in relation to N and P. Therefore, this study investigated the role of DSi in Tonlé Sap Lake, Cambodia, a tropical floodplain system well known for its flood-pulse characteristics and high productivity. To that end, seasonal water sampling and in situ water quality measurements were performed around the floating villages of Chhnok Tru region. The concentration of DSi was significantly higher in the dry season than in the wet season at 16.3-22.1 versus 7.2-14.0 mg/L, respectively; however, both sets of measurements were comparable with lakes in other parts of the world. Meanwhile, the average molar ratio of TN:TP:DSi was 69:1:33 in the dry season and 39:1:24 in the wet season, which compared with the Redfield ratio of 16:1:16, suggested limitation of TP and DSi in both seasons. In addition, phytoplankton biomass in terms of chlorophyll-a was found to be a collective function of DSi, TN:TP, dissolved oxygen, and water temperature in both seasons. Taken together, these results suggest that DSi is affected by the annual hydrological cycle in the Tonlé Sap Lake flood-pulse ecosystem, serving as a secondary limiting nutrient of primary production during both the dry and wet seasons.

Datasets for the assessment of changes in the incidence, extents, and spatial patterns of inundations in the Cambodian Mekong Delta, based on a water level - flood link calculated from in-situ water levels, and Sentinel-derived inundation maps.

This brief contains the data needed to calculate and assess the robustness of a water level - flood link (WAFL) in the Cambodian Mekong Delta, which was used to analyze changes in the long-term behavior of Monsoon inundations in the region. The data comprises the WAFL raster (.tif) files for two zones in the delta. Zone A is located on the right bank of the Bassac River, a distributary of the Mekong. Zone B is bracketed between the Mekong River and the Bassac River. The WAFL was calculated by linking water levels measured by the Mekong River Commission (MRC) at the hydrological station in Koh Khel, with inundation maps derived from Sentinel-1 and -2 images taken between 2017 and 2021. The final WAFL raster files provides a basis for estimating inundation extents using in-situ water levels. Furthermore, this brief includes data used for the assessment of WAFL, including in-situ water level data and the extents of natural vegetation in the case study area in 1990, 2000, 2010 and 2020. The former was collected using a differential pressure logger. The latter was calculated from historical Landsat image composites. Finally, raster files representing the incidence and duration of inundations in the case study area before and after the year 2008 are provided. These were calculated based on the WAFL and the MRC water levels. For each area, before- and after-images are available, as well as a raster representing the change between the two. To simplify visualization and geographical location, shapefiles (.shp) of the study area and the location of the in-situ logger are also provided.