Among-site variability in environmental and management characteristics: Effect on nutrient loss in agricultural tile drainage

Authors: Hanrahan, Brittany; King, Kevin; MACRAE, MERRIN - University Of Waterloo; Williams, Mark; Stinner, Jedediah

Submitted to: Journal of Great Lakes Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2020
Publication Date: 2/25/2020
Citation: Hanrahan, B.R., King, K.W., Macrae, M.L., Williams, M.R., Stinner, J.H. 2020. Among-site variability in environmental and management characteristics: Effect on nutrient loss in agricultural tile drainage. Journal of Great Lakes Research. 46(3):486-499. https://doi.org/10.1016/j.jglr.2020.02.004.
DOI: https://doi.org/10.1016/j.jglr.2020.02.004

Interpretive Summary: Nitrogen (N) and phosphorus (P) are applied as fertilizers to enhance crop growth in agricultural systems across the Midwestern United States, as well as others around the world. When fertilizers are applied in excess of crop needs, N and P accumulate in fields and are susceptible to loss through subsurface tile drainage systems. Excess N and P then enter adjacent streams and are eventually transported to downstream water bodies where they can negatively impact water quality. In the Laurentian Great Lakes region, specifically, harmful and nuisance algal blooms (HNABs) occur annually in Lake Erie and are primarily caused by nutrients transported from agricultural fields. Furthermore, previous work has shown that N and P loss is significantly greater from agricultural fields in the US portion of the Lake Erie Basin (LEB) compared with fields located in the Canadian (CA) portion of the LEB. The goal of this study was to compare environmental and management characteristics across 30 sites located in Indiana and Ohio, US and southwestern Ontario (CA) in order to determine the relationship between these characteristics and N and P loss. We found that fertilizer management practices and soil properties of sites varied along a latitudinal and longitudinal gradient in the LEB. However, these broad-scale patterns (i.e., spatial gradients in characteristics) were not related to N and P loss from agricultural tile drainage. Instead, the unique combination of environmental conditions and management practices at an individual site more strongly controlled the amount of N and P transported from fields. These findings are important for scientists, producers, and resource managers because they highlight the important interaction between soil properties, environmental conditions, and management decisions that can control N and P loss from agricultural fields. Results here demonstrate that nutrient loss differences between the US and Canada are likely related to contrasting fertilizer management strategies (build and maintain vs. sufficiency). This study also shows that controls on N and P loss differ and draws attention to the need for further research that includes details soil analyses. Overall, site- and nutrient-specific management remains critically important when addressing water quality issues.

Technical Abstract: Water quality issues, including harmful and nuisance algal blooms (HNABs), related to nitrogen (N) and phosphorus (P) exported from agricultural lands persist in the Great Lakes region. Previous work examining N and P loss from agricultural fields in portions of the United States (US) and Canada (CA) that drain into Lake Erie, specifically, consistently indicate greater losses from fields in Indiana and Ohio, US compared with those in southwestern Ontario, CA. The primary objective of this study was to examine variation in environmental and management characteristics from 30 sites (US: n=28, CA: n=2) located along a spatial gradient in the Lake Erie Basin and subsequently determine the influence of among-site variation on edge-of-field N and P losses. Using principal component analyses (PCA), we found that among-site variation was predominantly controlled by broad-scale patterns in fertilizer management practices and soil properties, however, N and P loss metrics were largely unexplained by these gradients. As such, fine-scale variability and the interaction of environmental and management characteristics at individual sites more strongly influenced N and P loss than spatial position within the watershed. Ultimately, these results further emphasize the importance of site- and nutrient-specific management plans that are needed to mitigate N and P losses from agricultural fields.