Abstract
Agricultural irrigation leachate is often the largest source for aquifer recharge in semi-arid groundwater basins, but contamination from fertilizers and other agro-chemicals may degrade the quality of groundwater. Affected communities are frequently economically disadvantaged, and water supply alternatives may be too costly. This study aimed to demonstrate that, when addressing these issues, environmental sustainability and market profitability are not incompatible. We investigated the viability of two low impact crops, alfalfa and vineyards, and new recharge basins as an alternative land use in recharge buffer zones around affected communities using an integrated hydrologic, socio-geographic, and economic analysis. In the southern Central Valley, California, study area, alfalfa and vineyards currently constitute 30% of all buffer zone cropland. Economic analyses of alternative land use scenarios indicate a wide range of revenue outcomes. Sector output gains and potential cost saving through land use conversion and resulting flood control result in gains of at least $2.3 billion, as compared to costs of $0.3 to $0.7 billion for treatment options over a 20 year period. Buffer zones would maintain the economic integrity of the region and concur with prevailing policy options. Thus, managed agricultural recharge buffer zones are a potentially attractive option for communities facing financial constraint and needing to diversify their portfolio of policy and infrastructure approaches to meet drinking water quality objectives.
Highlights
While other factors contribute to groundwater nitrate concentrations [8,14,15], the proportion of the total area covered by cropland, pasture, and well-drained soil are often prominent determinants of risk of nitrate leaching to groundwater [16,17,18], report a positive relationship between the amount of residual soil mineral N at harvest and the concentration of upper groundwater NO3 concentrations
In 24 developing communities (DCs) the maximum measured nitrate level exceeds the Maximum Contaminant Level (MCL), in 16 DCs at least one well has an average NO3 concentration that is above the MCL, in 2 DCs, the median measured nitrate level among all wells exceeds the MCL
Given the pressing water quality circumstances in this region, we have explored the potential of establishing recharge buffers zones of 1000 m around developing communities to ameliorate very high drinking water
Summary
In California, nearly 6000 liters per capita per day are used to produce food crops; over 70% of this is dedicated to irrigation [4]. Synthetic N fertilizers account for more than 187 Tg·yr−1 (77% of all N produced by humans), up from 156 Tg·yr−1 in 1995; the remainder has its origin in manure and leguminous crops [7,8,9]. Nitrogen is applied to crops in organic form (Norg), as ammonium (NH4), or as nitrate (NO3). In whatever form it is applied, soil microorganisms generate NH4 or NO3, which can be synthesized by living organisms, including the target crop [10]. Improved plant nutrition and newly developed crop varieties have resulted in dramatic increases in agricultural production in recent decades, which in turn has enabled improved human nutrition and food security [11]
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