Near-surface soils as a source of phosphorus in snowmelt runoff from cropland

Citation

Wilson, H., Elliott, J., Macrae, M., Glenn, A. (2019). Near-surface soils as a source of phosphorus in snowmelt runoff from cropland, 48(4), 921-930. http://dx.doi.org/10.2134/jeq2019.04.0155

Plain language summary

• snowmelt P concentrations are highest where surface soil P (0-5cm) is elevated
• increased concentrations of snowmelt P also occur when soil moisture is higher
• differences in total P export with snowmelt are primarily controlled by snowpack
• reductions of P export challenging for soil with high water holding capacity
• increased monitoring of surface soil P will aid in targeting of mitigation efforts

Abstract

© 2019 The Author(s) and Her Majesty the Queen in Right of Canada, as represented by the Minister of Agriculture & Agri-Food Canada. This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). In northern regions, a high proportion of annual runoff and phosphorus (P) export from cropland occurs with snowmelt. In this study, we analyze 57 site-years of field-scale snowmelt runoff data from 16 small watersheds draining fine-textured soils (clay or clay loam) in Manitoba, Canada. These fields were selected across gradients of soil P (2.4 to 26.7 mg kg−1, 0- to 15-cm Olsen P), tillage intensity (high frequency to long-term no-till), and fertilizer input. The strongest predictor of flow-weighted mean concentrations of total dissolved P (TDP) in snowmelt runoff was Olsen P in the top 5 cm of soil (r2 = 0.45, p < 0.01). Residual variation in this relationship related positively to volumetric soil moisture and negatively to water yield. Although Olsen P levels were relatively consistent from year to year, suggesting control by long-term fertilization and tillage history, Olsen P stratification (ratio of 0-5/0-15 cm) increased with rates of fertilizer application. Particulate P (PP) comprised <34% of total P on average, and concentrations were not well predicted by soil or management characteristics. Loads of PP and TDP exported during snowmelt were primarily a function of water yield and size of accumulated snowpack; however, residual variation in the TDP relationship correlated positively with both soil moisture and Olsen P. Retention of runoff water on the landscape could reduce loads, but careful management of near-surface soil P is required to prevent snowmelt runoff losses of P at the source and to reduce the potential for the eutrophication of downstream aquatic ecosystems.

Publication date

2019-01-01