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Title: Upland and in-stream controls on baseflow nutrient dynamics in tile-drained agroecosystem watersheds

Author
item FORD, WILLIAM - University Of Kentucky
item King, Kevin
item Williams, Mark

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2017
Publication Date: 1/25/2018
Publication URL: https://handle.nal.usda.gov/10113/5894523
Citation: Ford, W.I., King, K.W., Williams, M.R. 2018. Upland and in-stream controls on baseflow nutrient dynamics in tile-drained agroecosystem watersheds. Journal of Hydrology. 556:800-812.

Interpretive Summary: Nutrient loss from crop production agriculture continues to plague waterbodies worldwide. Much emphasis has been focused on nutrient losses associated with storm events. However, in low gradient artificially drained areas, baseflow can also represent a significant period for nutrient transport. Long-term (10 years) nutrient loss measured in tributaries and main stem segments of the Upper Big Walnut Creek Watershed in central Ohio was determined to be seasonal and controlled by either upland, in-stream,or a combination of upland and in-stream controls and differed for nitrogen and phosphorus. The findings highlight the need to consider the temporal variability with respect to nitrogen and phosphorus loss as well as both upland and in-stream management and treatment technologies needed to address nutrient loss from crop production agricultural watersheds.

Technical Abstract: Controls on baseflow nutrient concentrations in agroecosystems are poorly characterized in comparison with storm events. However, in landscapes with low residence times (e.g., rivers and reservoirs), baseflow nutrient concentration dynamics during sensitive timeframes can drive deleterious environmental conditions downstream. This study assessed upland and in-stream controls on baseflow nutrient concentrations in a low-gradient, tile-drained agroecosystem watershed. We conducted time-series analysis using Empirical Mode Decomposition of seven decade-long nutrient concentration time-series in the agricultural Upper Big Walnut Creek watershed (Ohio, USA). Four tributaries of varying drainage areas and three main-stem sites were monitored and nutrient grab samples were collected weekly from 2006-2016 and analyzed for dissolved reactive phosphorus (DRP), nitrate-nitrogen (NO3-N), total nitrogen (TN), and total phosphorus (TP). Statistically significant seasonal fluctuations were compared with seasonality of baseflow, watershed characteristics (e.g., tile-drain density), and in-stream water quality parameters (pH, DO, temperature). Findings point to statistically significant seasonality of all parameters with peak P concentrations in summer and peak N in late winter-early spring. Results suggest that upland processes exert strong control on DRP concentrations in the winter and spring months, while coupled upland and in-stream conditions control watershed baseflow DRP concentrations during summer and early fall. Conversely, upland flow sources driving streamflow exerts strong control on baseflow NO3-N, and in-stream attenuation through transient and permanent pathways impacts the magnitude of removal. Regarding TN and TP, we found that TN was governed by NO3-N, while TP was governed by DRP in summer and fluvial erosion of P-rich benthic sediments during higher baseflow conditions. Findings of the study highlight the importance of coupled in-stream and upland management for mitigating excess nutriente conditions during environmentally sensitive timeframes.