The contribution of rain‐on‐snow events to nitrate export in the forested landscape of south‐central Ontario, Canada

Abstract

Abstract:Rain-on-snow (ROS) events have the potential to contribute significantly to nitrate (NO 3 -N) export from forested catchments, but have received relatively little research attention. This study assesses the importance of ROS events for NO 3 -N export across 18 catchments in south-central Ontario, Canada, that receive the same annual and seasonal N deposition, but encompass a range of physiographic characteristics. Winter (December to February) NO 3 -N export was calculated from 1982 to 1987, a period when streams were sampled on average every 3Ð3 days for NO 3 -N analysis. ROS events contributed a similar proportion of total winter NO 3 -N export across all catchments (median proportion of NO 3 -N from ROS events D 55%). There was considerable variation in the total magnitude of winter NO 3 -N export from these catchments, ranging from 0Ð01 to 0Ð4 kg/ha. Analysis of relationships between NO 3 -N export and physiographic characteristics indicated that NO 3 -N export varied with till coverage, wetland coverage and slope. Catchments with more till coverage, less wetland coverage and steeper slopes may be able to sustain hydrological linkages with the stream channel during the winter, contributing to higher NO 3 -N export. An analysis of one catchment over a longer time period revealed that years with higher maximum winter temperatures had more ROS events than cooler winters (p < 0Ð001; r 2 D 0Ð48). As climate projections for this region include increased winter temperatures and more winter precipitation falling as rain, ROS events may increase in the future, raising concerns about increased NO 3 -N loading to surface waters.

Hydrogeological controls on spatial patterns of groundwater discharge in peatlands

“…Preferentially stronger flow paths are thus concentrated at the break in land surface slope (Blume et al, 2013;Casson et al, 2010;Cherkauer and McKereghan, 1991;McBride and Pfannkuch, 1975;Rosenberry et al, 2010;Winter, 1981). Previous work proposes that seepage flux decreases exponentially with distance from the shore of a lake (Cherkauer and Zager, 1989;McBride and Pfannkuch, 1975), which is qualitatively confirmed by our data.…”

Rain-on-snow events over North America based on two Canadian regional climate models

“…A positive correlation of ROS days with elevation and a negative correlation with increasing air temperatures for New York State, US, for the 2004-2012 period were reported by Pradhanang et al (2013). Winters with higher maximum temperatures had more ROS events than cooler winters due to more rainfall occurrences, for the case of south-central Ontario, Canada, for the 1971-2001 period (Casson et al 2010). Similarly, an increase in winter ROS events with warmer air temperatures for the northern Eurasian high-latitude regions was reported for the 1936-1990 period (Ye et al 2008).…”

“…Therefore, it is very important to evaluate how these events will evolve in a future warming climate at regional scale. ROS events have significant impacts on various sectors such as the cold region environment and ecosystem (Putkonen and Roe 2003;Putkonen et al 2009;Rennert et al 2009;Casson et al 2010) and water resources, particularly for flood forecasting and risk management (Leathers et al 1998;Sui and Koehler 2001;McCabe et al 2007;Pradhanang et al 2013;Surfleet and Tullos 2013;Freudiger et al 2014).…”

Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

“…Snow also allows solutes to accumulate in the soil (Kurian et al 2012) leading to pronounced fluxes when the snow melts. Watersheds throughout the Northeast USA export more than 85% of the annual NO 3 -loss during winter (Mitchell et al 1996), with most of this export occurring during spring snowmelt (Campbell et al 2005), but mid-winter melt events and rain-on-snow events can also influence winter NO 3 -loads to streams (Casson et al 2010). Individual rain-on-snow events can contribute as much as 40% of annual NO 3 -export from forested watersheds in southeast Canada, and the contribution of rain-on-snow events to annual and winter NO 3 -loads has generally increased in recent decades (Eimers et al 2007).…”