Correlations between catchment-scale farm infrastructure densities and stocking rate to stream nutrient concentrations in dairy-dominant catchments

Nitrogen and phosphorus pollution is a critical environmental issue that causes eutrophication of water bodies. High concentrations of these nutrients primarily come from agricultural areas and are driven by catchment characteristics such as climate, hydrology, topography, geology, land use, and land cover. In addition to these factors, specific farming practices – particularly, the use of dairy farm infrastructure and management of stocking rate – also influence stream nutrient concentrations. However, the extent of the influence of specific farming practices and their relative importance in determining nutrient concentrations in waterways remain unknown. In this paper, we used data from an agriculturally-intensive dairy farming region to investigate these relationships. We used statistical analyses and modelling to determine relationships between concentrations of ammonium (NH₄⁺), filterable reactive phosphorus (FRP), nitrogen oxides (NOx), total phosphorus (TP), and total nitrogen (TN) with 26 predictors which include farm infrastructure density and stocking rate. We found that farm infrastructure and operational characteristics such as effluent pond density, dairy shed density, and stocking rate are consistently important predictors that influence concentrations of NH₄⁺, FRP, NOx, TP, and TN during both wet and dry weather periods. This paper has shown that in addition to established factors such as land use and land cover, specific farming practices also play a role in influencing stream nutrient concentrations. By identifying key infrastructure and stocking rate as drivers of stream nutrient concentrations, this research emphasized the need for targeted management strategies to mitigate the impacts of agricultural activities on water quality.