Background

In the Lake Winnipeg Basin, eutrophication of waters is of great concern and phosphorus (P) has been identified as the limiting nutrient. In most cases, the delivery and transport of P is associated with sediment, and thus most programs that focus on P in agricultural landscapes also address sediment sources and dynamics as the main vector of P.  There is great interest in the use of riparian areas as vegetated filters for sediment and P in runoff coming from agricultural land and riparian buffers are widely promoted through the prairie provinces and the rest of the country as a cost-effective Beneficial Management Practice (BMP) by Agriculture and Agri-Food Canada (AAFC) (i.e. Field Manual on Buffer Design in Canadian Prairies; Steward et al., 2010). 

The main design criteria for buffers is width, and most advice relates to buffer width considerations. However, recent studies in the USA and Europe (e.g. Owens et al., 2007) have identified that the strategic design and placement of buffers is fairly complex, such that simple, generic guidelines are likely to be inappropriate in many situations, and that topographic and vegetative features also need to be considered. Preliminary work by the project team in a 1-year LWBSF project (Lobb et al., 2012) demonstrated that the topography of buffers provided a mechanism for sedimentation and the deposition of P. Lobb et al. (2012) identified that it should be possible to manipulate the topography of such buffer “steps” to enhance their effectiveness in trapping sediment and P. However, we have yet to evaluate this through detailed field-based studies.

Most of the available information to date on buffer effectiveness and design comes from studies conducted in the USA and Europe (e.g. Owens et al., 2007). Few studies have evaluated buffer effectiveness in the Canadian Prairies and, in particular, the Lake Winnipeg Basin where: (i) soils are frozen during winter; (ii) buffer vegetation is dead or dormant; and (iii) snowmelt runoff is concentrated in a short time period. A study by Sheppard et al. (2006) found that the riparian buffer zones in the Lake Winnipeg Basin can act as sinks or sources of P, or be neutral in some cases. This is important, as it shows that riparian buffers could act as a source of P under certain situations and/or if not managed properly. Such a problem could be avoided and/or managed through a more comprehensive assessment of soil-P interactions in buffers and through managing buffer vegetation. Clearly, there is an urgent need to evaluate how buffers function in Canadian prairie landscapes, and determine ways to improve their efficiency in such environments.

Goals and Objectives

The goal of this project is to enhance the water quality of Lake Winnipeg and its tributaries through the effective use of riparian areas as filters of sediment and phosphorus from agricultural land. The objectives of the project are to: 1) to enhance our mechanistic understanding of how sediment and phosphorus move from agricultural fields into watercourses, and to determine if riparian buffers are net sinks or sources of phosphorus; 2) determine how buffer features can be manipulated to increase their filtering capacity; and 3) develop buffer design criteria to support their implementation and develop outreach materials for use by farm advisors and land managers.

References

Deeks LK, Duzant JH, Owens PN, Wood GA (2012). A decision support framework for effective design and placement of vegetated buffer strips within agricultural field systems. Advances in Agronomy 114, 225-248.

Lobb DA, Flaten D, Sheppard SC, Randall SJ, Owens PN, Caley KA (2012). Determining the Effective Use or Riparian Areas to Filter Sediments and Phosphorus. Final Report to Lake Winnipeg Basin Stewardship Fund, Environment Canada.

Owens PN, Duzant JH, Deeks LK, Wood GA, Morgan RPC, Collins AJ (2007). Evaluation of contrasting buffer features within an agricultural landscape for reducing sediment and associated phosphorus delivery to surface waters. Soil Use and Management 23, 165-175

Sheppard SC, et al. (2006) Runoff phosphorus retention in vegetated field margins on flat landscapes. Canadian Journal of Soil Science 86, 871-884

Stewart A, Reedyk S, Franz B, Fomradas K, Hilliard C, Hall S (2010). Field Manual on Buffer Design in the Canadian Prairies. AAFC, 55p.

Wood GA, Deeks LD, Duzant J, Owens PN, Morgan RPC, Collins AJ (2007) Strategic Design and Placement of Buffer Features for Trapping Sediment and Phosphorus. Final Report PE0205 to the UK Department for Environment, Food and Rural Affairs (DEFRA), London, UK.