HGS RESEARCH HIGHLIGHT – Impacts of Climate Change and Different Crop Rotation Scenarios on Groundwater Nitrate Concentrations in a Sandy Aquifer
Saleem, S., Levison, J., Parker, B., Martin, R., & Persaud, E. (2020). Impacts of Climate Change and Different Crop Rotation Scenarios on Groundwater Nitrate Concentrations in a Sandy Aquifer. In Sustainability (Vol. 12, Issue 3, p. 1153). MDPI AG. https://doi.org/10.3390/su12031153
“Groundwater models were developed using HGS for the Norfolk site. The calibrated models were used to simulate reference (1986–2005) and future (2040–2059) surface water flows, groundwater elevations, and Nitrate-N concentrations in monitoring wells based on selected land use and climate change scenarios.”
Figure 1. Norfolk site: model domain boundary, elevation map, and land use map for Norfolk site for 2012. Red symbols indicate the positions of the monitoring wells (MWs) used in this study.
This study by researchers at the University of Guelph investigated the impacts of various crop rotation scenarios and climate change on groundwater nitrate concentrations in a 155 sq-km agricultural sub-watershed in Norfolk County, Ontario.
It is well established that groundwater nitrate concentrations can be tied to fertilizer application in agricultural settings. Nitrate is highly mobile, and groundwater discharge to streams can negatively impact watershed health, and climate change may exacerbate this issue. To better understand the dynamics of nitrate transport in agricultural watersheds a two-stage modelling approach was used. First, the root zone model called RZWQM2 was used to simulate detailed crop growth and nitrate leaching dynamics though the root zone. Then the integrated hydrologic modelling capabilities of HydroGeoSphere were harnessed to simulate regional groundwater/surface water flow. Three crop rotation scenarios were evaluated with RZWQM2, and the results were plugged into HGS models under three different climate change scenarios, for a total of nine simulations. The HGS model had nine layers and had a critical depth boundary applied at the watershed outlet boundary. Average rainfall and potential evapotranspiration data from 1990-2009 were used to calibrate the model. A key factor of the model was that rill storage was included and since groundwater flow and nitrate storage occur in unconsolidated shallow sand layers with high conductivities, rill storage was an important factor to consider.
“Water managers and land use managers can use the results of this study and future similar studies in other jurisdictions to inform water protection and nutrient management policies in rural contexts to protect water at the source.”
Figure 8. Groundwater elevation (masl) data for different climate change scenarios at (a) MW-04 and (b) MW-07 monitoring wells at the study site.
This research is relevant to water and land managers as climate change will change nutrient transport dynamics in the coming years, and the impacts to our water supply are extremely important to consider. Crops are normally selected based on past climate norms, but if farmers are not diligent, farming activities can be harmful to the watershed (e.g. resulting in algal blooms which can devastate aquatic ecosystems). Fertilizers can leech excess nutrients into the soil further leading to contamination after heavy rain events. Nitrogen and phosphorous can cause health and environmental problems, and considering 30% of Canadians rely on groundwater, it is crucial to protect it. The HGS model had nine layers and had a critical depth boundary applied at the watershed outlet boundary. Average rainfall and potential evapotranspiration data from 1990-2009 were used to calibrate the model. A key factor of the model was that rill storage was included and since groundwater flow and nitrate storage occur in unconsolidated shallow sand layers with high conductivities, rill storage was an important factor to consider.
The results of the HydroGeoSphere simulations showed that each climate change scenario resulted in less water availability compared to past decades. Additionally, nitrate concentrations were lower, especially when a corn-soybean-winter-red-wheat-clover rotation was used. That crop rotation scenario represents the best management practice that should be used to mitigate climate change impacts on nutrient transport. If a solely corn rotation or anything similar was used, groundwater nitrate concentrations may increase significantly compared to the reference period. In this study the corn-only rotation resulted in a 48% and 79% increase in two groundwater observation wells compared to the reference period.
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Abstract:
Nitrate in groundwater is a major concern in agricultural sub-watersheds. This study assessed the impacts of future climate and agricultural land use changes on groundwater nitrate concentrations in an agricultural sub-watershed (Norfolk site) in southern Ontario, Canada. A fully integrated hydrologic model (HydroGeoSphere) was used in combination with the root zone water quality model (RZWQM2) (shallow zone) to develop water flow and nitrate transport models. Three climate change models and three crop rotations (corn-soybean rotation, continuous corn, corn-soybean-winter wheat-red clover rotation) were used to evaluate the potential impact on groundwater quality (nine predictive scenarios). The selected climate change scenarios yielded less water availability in the future period than in the reference period (past conditions). The simulated nitrate nitrogen (Nitrate-N) concentrations were lower during the future period than the reference period. The continuous corn land use scenario produced higher Nitrate-N concentrations compared to the base case (corn-soybean rotation). However, the best management practices (BMP) scenario (corn-soybean-winter wheat-red clover rotation) produced significantly lower groundwater nitrate concentrations. BMPs, such as the one examined herein, should be adopted to reduce potential negative impacts of future climate change on groundwater quality, especially in vulnerable settings. These findings are important for water and land managers, to mitigate future impacts of nutrient transport on groundwater quality under a changing climate.