Are Current Phosphorus Risk Indicators Useful to Predict the Quality of Surface Waters in Southern Manitoba, Canada?

Abstract

Many phosphorus (P) risk indicators have been developed to assess the risk of P loss from agricultural land to surface water. Most of these indicators are designed for land and climates where rainfall-induced erosion of particulate P from sloping landscapes is the main process of P transport. No indicators have been validated in the Canadian Prairies, where P losses are driven by snowmelt-driven runoff over nearly level landscapes and frozen soils. The objective of this project was to evaluate the relationship between water quality data for P from 14 watersheds and three existing P risk indicators for their potential use in the southern Manitoba prairie region of Canada. None of the indicators, including Birr and Mulla's P Index, a preliminary P risk indicator for Manitoba, and a preliminary version of Canada's National Indicator of Risk of Water Contamination by Phosphorus, was significantly correlated with mean concentrations of total P in water or P export per hectare. Although erosion risk was a significant factor influencing the value of these indexes, erosion risk was not correlated with either measure of P loss in these watersheds. Several other watershed characteristics, including average soil test P concentrations, livestock density, proportion of land in annual crops, and the land's inherent capability for agricultural production, were strongly correlated with P concentrations in water (r = 0.80***, r = 0.63**, 0.76***, and -0.70**, respectively). Therefore, these types of P risk indicators require modifications to estimate the risk of P loss under the soil, landscape, and climatic conditions of southern Manitoba.

Managing agricultural phosphorus for water quality protection: principles for progress

“…For example, in the semi-arid prairie province of Manitoba, Canada, P loads to water are very low (0.02 to 0.16 kg P ha −1 year −1 ), but concentrations of P in water (0.05 to 0.38 mg L −1 ) are well above eutrophication thresholds (Salvano et al 2009). As a result, while P loads do not appear to present a water quality problem in the Manitoba region, high P concentrations at times of greatest biological sensitivity can result in impairment.…”

Observed trends and future projections of precipitation and air temperature in the Lake Winnipeg watershed

“…To develop appropriate mitigation strategies for dealing with nutrient loadings, there is a need to improve scientific knowledge regarding the transport mechanism of non-point sources of nutrients from the landscape into the lake. Runoff from rainfall and snowmelt are generally found to be important in driving nutrient transport processes (Creed et al, 1996;Salvano et al, 2009) and the hydrologic regime of the LWW is dominated by spring snowmelt runoff, often occurring over frozen ground. Snowmelt runoff accounts for more than 80% of the total annual surface runoff in to Lake Winnipeg, despite the fact that snowfall only contributes one third of total annual precipitation in the LWW (Gray and Landine, 1988).…”

The effectiveness of small-scale headwater storage dams and reservoirs on stream water quality and quantity in the Canadian Prairies

“…This is the concern in the cold, dry agricultural landscapes of the Canadian Prairies, where (1) spring snowmelt is typically the primary runoff and nutrient loading event during the year, and (2) dissolved nutrients can dominate total nutrient loads in runoff waters, in both the spring and summer (Little et al 2007;Salvano et al 2009;Tiessen et al 2010). These environmental conditions are very different to those typically experienced in more humid regions of North America and Europe, where nutrient transport occurs predominantly through rainfall runoff and dissolved nutrient losses account for a small portion of the total loss.…”