Mapping of Seawater Intrusion into Coastal Aquifer: A Case Study of Pekalongan Coastal Area in Central Java

Seawater intrusion promotes the degradation of groundwater quality through excessive pumping activities or natural phenomena such as tidal floods which are popular with coastal areas. Pekalongan city is one of the areas affected by this phenomenon and was analyzed in this study with reference to the 1986 Ad Hoc Sea Water Intrusion (PAHIAA) Decree which classifies water into five based on salinity. This involved using the Integrated Distance Method (IDW) to map and applying the logarithmic equation to determine the dispersion relationship. The results showed seawater intrusion has already affected groundwater quality up to 6.52 km from the coastline for total dissolved solids and electrical conductivity and 7.22 km for chloride ion. The distribution of TDS, EC, and Cl- in the freshwater zone was also recorded to have reached 28.59 km2, 28.36 km2, and 23.95 km2 respectively. It is predicted that in 4 years, there would no longer be freshwater in Padukuhan Kraton Village due to decreasing groundwater quality caused by seawater intrusion. Furthermore, 23.03 km2 Pekalongan area which spread into 4.34 km2 to the West, 0 km2 to the South, 14.39 km2 to the North, and 1.28 km2 to the East of the district has also been affected and was discovered to be caused mainly by tidal flood from Bremi and Tirto rivers.

Groundwater quality assessment of a freshwater wetland in the Selangor (Malaysia) using electrical resistivity and chemical analysis

Groundwater quality of the Paya Indah Wetland (PIW) was targeted for the present study using integrated two-dimensional electrical resistivity imaging (ERI) and hydrochemical surveys. Electrical resistivity and the influence of variations in the lake level were investigated using daily water balance measurements, water sampling and geochemical analysis, and well-logging. The geoelectrical resistivity surveys comprised 14 resistivity traverses in the PIW. The resistivity surveys predicted the high-permeability areas separated in order to provide pathways for lake drainage. The resistivity inverse model showed that the freshwater zone is extremely clear. Chemical analyses of the groundwater samples obtained from seven boreholes from 2010 to 2013 were studied. The total dissolved solids and electrical conductivity were represented as being less than 500 mg/L and 600 μmhos/cm, respectively, and freshwater was therefore indicated. The lake water level was proportionate to rainfall fluctuation with the level measured in 2010. The soil and groundwater confirmed there to be fresh and brackish water zones in the study area, this result being obtained from ERI and the hydrochemistry of the groundwater samples.

River regulation alters drivers of primary productivity along a tropical river-estuary system

Worldwide, rivers continue to be dammed to supply water for humans. The resulting regulation of downstream flow impacts on biogeochemical and physical processes, potentially affecting river and estuarine productivity. Our study tested the hypothesis that primary production in the downstream freshwater reaches of a dammed river was less limited by light and nutrients relative to downstream estuarine primary production. In a tropical dryland Australian river estuary, we found that water-column primary productivity was highest at freshwater sites that had lowest light attenuation. Nitrogen may also have limited primary productivity. Below the freshwater zone was a region of macrotidal mixing with high concentrations of suspended soil particles, nutrients and chlorophyll a, and lower but variable primary productivity rates. Light controlled productivity, but the algal cells may also have been osmotically stressed due to increasing salinity. Further downstream in the estuary, primary productivity was lower than the freshwater reaches and light and nutrient availability appear to be a factor. Therefore the reduced magnitude of peak-flow events due to flow regulation, and the resulting decrease in nutrient export, is likely to be negatively impacting estuarine primary production. This has implications for future development of dams where rivers have highly seasonal flow.