EVALUATING LAND USE EFFECTS ON NITRATE CONCENTRATIONS IN GROUNDWATER AND RECEIVING STREAMS
Abstract:Agricultural, rural residential, and pastoral land uses give rise to separate impacts on water quality in receiving surface or groundwater systems through leachate percolation and recharge to shallow groundwater systems and the streams into which they discharge. Land use planners can benefit from a rapid method to evaluate water quality impacts due to these land uses. A method was developed to quickly and effectively assess the nitrate loading rates from surface application of fertilizer and from septic systems into local groundwater and surface water bodies. A range of expected loading rates can be used to assess the resulting groundwater and surface water nitrate concentrations from proposed development densities and land uses.
The methodology incorporates a water balance model to determine groundwater recharge based on local climate and soils conditions. A nitrate concentration in the aquifer recharge is computed using a mass balance approach that incorporates loading rates from the surface infiltration and septic system inputs of nitrate. A leachate/groundwater mixing model is then used to compute the resultant groundwater concentration from recharge of nitrate-containing leachate and from background nitrate conditions. In cases where groundwater discharges to surface water bodies, a groundwater/surface water mixing model is used to compute river or lake nitrate concentrations. The mass balance and mixing models are developed and implemented in a spreadsheet software package to provide a simple yet robust means to assess potential groundwater and surface water nitrate concentrations due to a range of loading rates.
This method was applied to a case study in central Minnesota to identify the acceptable housing densities being considered for new development that would meet state and federal water quality criteria for nitrate in the receiving waters. The effects of housing density were evaluated for two target populations: one home per two acres and one home per ten acres. Nitrate loading was calculated for a range of wastewater loading rates, agricultural nitrate loading rates, precipitation-based recharge, and soil denitrification rates. The analysis tool also was used to identify an acceptable housing density based on specified soil, recharge and wastewater loading characteristics for a potential housing development.
Document Type: Research Article
Publication date: 2007-01-01
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