Quantifying phosphorus loads from legacy-phosphorus fields

Authors: BROOKER, MICHAEL - THE OHIO STATE UNIVERSITY; D'AMBROSIO, JESSICA - THE OHIO STATE UNIVERSITY; KALCIC, MARGARET - UNIVERSITY OF WISCONSIN; King, Kevin; LABARGE, GREG - THE OHIO STATE UNIVERSITY; ROE, BRIAN - THE OHIO STATE UNIVERSITY; STOLTZFUS, NATAN - THE OHIO STATE UNIVERSITY; SAGE, SAM - THE OHIO STATE UNIVERSITY; CROW, RACHELLE - THE OHIO STATE UNIVERSITY; WILSON, ROBYN - THE OHIO STATE UNIVERSITY; WINSTON, RYAN - THE OHIO STATE UNIVERSITY; MARTIN, JAY - THE OHIO STATE UNIVERSITY

Submitted to: Journal of Great Lakes Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2024
Publication Date: 10/4/2024
Citation: Brooker, M.R., D'Ambrosio, J., Kalcic, M., King, K.W., Labarge, G., Roe, B., Stoltzfus, N., Sage, S., Crow, R., Wilson, R.S., Winston, R.J., Martin, J. 2024. Quantifying phosphorus loads from legacy-phosphorus fields. Journal of Great Lakes Research. Article 102446. https://doi.org/10.1016/j.jglr.2024.102446.
DOI: https://doi.org/10.1016/j.jglr.2024.102446

Interpretive Summary: Excess phosphorus loading from agricultural watersheds continues to drive development of harmful and nuisance algal blooms in Lake Erie. Water quality, from fields or fields containing a significant area with elevated phosphorus concentrations, also referred to as legacy field/sources were compared to fields with phosphorus concentrations in the agronomic range to see if they disproportionately contributed more phosphorus loading. Phosphorus losses tended to increase with an increase in soil test phosphorus but the increase was not significant, suggesting that other factors beyond soil test phosphorus are important in controlling phosphorus loss. These findings are important for understanding the controls and transport mechanisms for nutrient movement in artificial (tile drained) watersheds. The findings are also important for researchers, conservationists, extension, and practitioners as they develop, assess, and implement conservation practices aimed at addressing nutrient transport.

Technical Abstract: Agricultural nutrient loss is a major contributor to eutrophication across the world. In the western basin of Lake Erie, phosphorus (P) from agricultural lands is the primary driver of recurrent harmful algal blooms. To reduce the magnitude of future blooms, targets have been set for total and dissolved reactive P (TP/DRP) loads during the Mar-Jul and annual periods. Meeting these targets can be accelerated by targeting management to fields with the greatest P loads. As soil P (STP) is correlated with greater risk of P loss, a public-private partnership previously recruited legacy-P fields with elevated-STP for monitoring in accordance with a regional edge-of-field network including fields with agronomic STP (agronomic-P) to assess the effect of the recruitment criterion on P loading rates. Though not statistically significant, stronger effects were generally associated with Mar-Jul DRP loading rates. DRP loading rates were greater from legacy-P fields than agronomic-P fields (p=0.19, g=0.54). The effect of total volume discharged (3% Mar-Jul, 11% annual) from legacy-P fields dampened this effect. This was affirmed by a stronger effect, though marginally significant, on subsurface DRP concentrations (p=0.08, g=0.83). Beyond this effect, STP exhibited significant correlations with P concentrations in surface (R2 0.22-0.33) – except Mar-Jul TP – and subsurface (R2 0.22-0.46) discharge. This study demonstrated a limited effectiveness of STP alone in identifying fields with greater P loads. Further analysis will need to identify other factors that can explain the variance in P loads so that the recruitment process for targeted management can be revised and improved.