Observations of Nitrate Reduction in Pleistocene Aquifers
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Wells screened across multiple aquifers can provide pathways for the movement of surprisingly large volumes of groundwater to confined aquifers used for public water supply (PWS). Using a simple numerical model, we examine the impact of several pumping scenarios on leakage from an unconfined aquifer to a confined aquifer and conclude that a single inactive multi-aquifer well can contribute nearly 10% of total PWS well flow over a wide range of pumping rates. This leakage can occur even when the multi-aquifer well is more than a kilometer from the PWS well. The contribution from multi-aquifer wells may be greater under conditions where seasonal pumping (e.g., irrigation) creates large, widespread downward hydraulic gradients between aquifers. Under those conditions, water can continue to leak down a multi-aquifer well from an unconfined aquifer to a confined aquifer even when those multi-aquifer wells are actively pumped. An important implication is that, if an unconfined aquifer is contaminated, multi-aquifer wells can increase the vulnerability of a confined-aquifer PWS well.
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Abstract Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen fertilizer to croplands is one of the major sources of high nitrate content in groundwater. In this study, we analyse the nitrate concentrations in Korean groundwater based on data from groundwater quality monitoring wells ( n = 1,022–2,072), which were sampled twice annually over a recent 13‐year analysis period (2001–2013). We report that groundwater nitrate levels are decreasing, despite steadily increasing groundwater use. The maximum nitrate concentration decreased from 168.91 to 48.11 mg/L, whereas the mean values also show a gradual decreasing trend. Non‐parametric Mann–Kendall tests on nitrate concentrations also confirm the decreasing trend. The nitrate decrease is more clearly evident in agricultural groundwater as compared to domestic and drinking groundwaters. This decrease of nitrate in groundwater coincides with a large decline in nitrogen fertilizer application due to reduced cropland areas, more sustainable agricultural practices, and progressive improvement of sewage disposal services. This study proposes that the long‐term adoption of best practices in agriculture has had a positive impact on groundwater nitrate control.
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Groundwater is vulnerable to contamination by chemicals, including nitrate, which can pass through soil to the shallow groundwater systems. Nitrate-N is commonly used as an environmental indicator to trace the impact of anthropogenic activities on groundwater. An understanding of the fate of nitrate in groundwater is vital for managing risks associated with nitrate pollution to safeguard groundwater supplies. Hence, groundwater samples were collected in ninety wells of shallow groundwater systems of Kathmandu, Nepal including shallow tube wells, dug wells and stone spouts (locally called Dhunge Dharas). The samples were analyzed for nitrate-nitrogen (NO3-N), iron (Fe) along with pH and temperature. The nitrate-nitrogen and iron (Fe) concentrations ranged from 0.0 to 26.4 and 0.0 to 5.24 mg/L, respectively. An understanding of the relationship between nitrate and iron in groundwater is crucial to explore the mechanism of natural denitrification and its ability to reduce nitrate concentrations. In general, elevated nitrate concentrations were not found in sampled groundwater sources in study area where elevated iron concentrations were common. The observed negative correlations between nitrate and iron suggest that the nitrate in shallow groundwater is being consumed. Moreover, this study highlights the current status and trends of the nitrate and iron in shallow groundwater systems and their relationship to water depth and well types.
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