Critical nitrogen load in small-scale watershed: an analysis of natural and anthropogenic factors

Abstract. Nitrogen is one of the main nonpoint source pollutants from agricultural lands in most of the watersheds in the US that can lead to over-nutrition of the downstream ecosystems. In order to evaluate the impacts of the changes in natural and anthropogenic stressors on the response of an agricultural watershed, a high resolution (30 x 30 m cells) PRZM-3 model for the Willow Creek watershed in Fort Cobb Reservoir Experimental Watershed located in south-central in Oklahoma was developed from 2002 to 2014. Different crops, fertilizer application schemes, management practices, and rainfall patterns were used to create a matrix of cell-based scenarios to determine the critical recurrence concentration of nitrogen in the watershed. Preliminary results showed that crop type and fertilizer application timing could largely affect the concentration of nitrogen in the main waterways of the watershed. Based on the results, not only can we better understand the relationship between the nitrogen load and the related natural and anthropogenic factors, but can also formulate measures that can mitigate the impacts of changes in environmental stressors on agricultural production and the environment.