Assessment of Sediment Delivery and Nutrient Export As Indicators of Soil Sustainability.

Soil erosion is an ongoing global agricultural crisis. Quantifying and tracking soil erosion and sediment export from agricultural watersheds is a key component for evaluating long-term sustainability. Our study used Revised Universal Soil Loss Equation soil erosion estimates and concentration of total suspended solids in-stream (determined through relationships with in-stream turbidity measurements) to estimate sediment delivery to an Eastern Iowa stream from a 780 ha watershed in 2015. Furthermore, we quantified soil organic carbon (SOC), nitrogen (N), and phosphorus (P) storage within the plow layer of our study area and used our estimated soil loss values to determine particulate nutrient export to the stream. These values were compared to in-stream nutrient sensor data in order to quantify the proportion of N and P in-stream coming from soil erosion compared to other sources. Results indicate that soil erosion in 2015 was approximately 7.5 Mg ha^-1. Sediment export to the stream was determined to be 279 kg ha^-1 and the sediment delivery ratio was estimated to be 3.7%. SOC, N, and P stocks were 40, 2.5, and 1.8 Mg ha^-1, respectively. Approximately 0.01% of total SOC, N, and P were lost from the plow layer in 2015. This study identifies long-term risks to watershed sustainability and water quality associated with soil erosion which directs watershed managers towards Best Management Practices that may more effectively reduce export of soil and nutrients while increasing the sustainability of an essential agricultural industry.