Knowledge Bank

In the Western Lake Erie Basin, eutrophication is largely driven by nutrient loads from agricultural fields. Of these, some fields have accumulated phosphorus (P) concentrations above agronomic needs (legacy-P fields) and are of particular concern as they are expected to release greater loads of P. However, monitoring has shown that not all legacy-P fields pollute at increased rates. It is unknown why these variations occur, but one likely factor is soil texture. To examine this, soil textures were calculated using weighted-average areas of soil types within the contributing areas of nine legacy-P fields. Generalized linear models were then developed explaining P loss as a function of soil texture (either: sand, silt, or clay content) and soil test P concentrations. Both concentration and areal loading rates of dissolved reactive P (DRP) and total P (TP) were considered. The most accurate models included soil test P and silt, which together explained 0.82 of the variance in spring subsurface DRP concentrations and 0.93 of the variance of annual surface DRP concentrations. For comparison, models with sand were found to explain 0.65 of the variance in annual subsurface DRP loading, while those with clay were found to explain 0.60 of the variance in annual surface DRP loading. These initial results indicate the importance of silt as an indicator influencing loading rates from legacy-P fields. The models developed using soil test P and silt could help predict which legacy-P fields are likely to discharge greater loads to guide the location of management practices to better protect Lake Erie.