Effects of snowmelt on phosphorus and sediment losses from agricultural watersheds in Eastern Canada

Snowmelt is the most important hydrological event in cold climates. However, snowmelt effects on suspended sediment (SS) and phosphorus (P) loss are poorly documented in Canada. Using two agricultural watersheds in Eastern Canada, this study aimed to quantify SS and P loss during the snowmelt period and to investigate how snowmelt contributes SS and P loss. Water samples were collected from the outlets of the Bras d’Henri watershed (BHW, 2007–2009) and Black Brook watershed (BBW, 2008–2009) and measured for SS and P concentrations. Hydrological parameters (precipitation, snow water equivalent, and runoff discharge), soil frozen status and soil temperature were also measured. Results revealed inter-annual variation of snowmelt conditions and SS and P losses in each watershed. The 2008 snowmelt in BHW and BBW mainly occurred on unfrozen soils, while the 2007 and 2009 snowmelts in BHW and 2009 snowmelt in BBW mainly on frozen soils. In BHW, 2008 snowmelt caused much higher median concentrations of SS, total P (TP), dissolved P (DP) and particulate P (PP) in stream water than 2007 and 2009; ratios of PP fractions in TP were variable with events but the median values were similar, suggesting both DP and PP important contrubutors to TP loss. In BBW, the median concentration of dissolved reactive phosphorus (DRP) in stream water was greater in 2008 snowmelt than in 2009 snowmelt; PP dominated TP loss. This study also suggests that soil state (i.e. frozen status) and rainfall were the most important factors influencing SS and P losses during snowmelt. Furthermore, snowmelt P export represented more than 20% of the total annual P export in BHW, and more than 12% of the annual DRP export in BBW. Thus, we strongly recommend adopting Best Management Practices (BMPs) that specifically target sediment and P loss during snowmelt.

Research highlights▶ This study is the first multi-year study on sediment and P losses in agricultural watersheds during snowmelt period in Eastern Canada; the only published study to date reported only one year of data. ▶ This study reports that phosphorus and sediment losses are major at snowmelt runoff in eastern Canada and that dissolved P fraction losses is significant which may have impacts on water quality and aquatic life. ▶ This study links the climate conditions, snowmelt runoff and surface water quality and shows that the inter-annual variability in climate conditions is very important for P and sediment losses. ▶ This study shows that it is fundamental to adapt agricultural BMPs to specifically mitigate and reduce soil erosion and nutrients loss caused by snowmelt runoff. In fact, most of the current BMPs target only the P and sediment losses occurring during the warm crop season.