Assessing the Effectiveness of a Holding Pond to Intercept Farm Yard Runoff in Manitoba.

Runoff from confined livestock sites often contains elevated concentrations of nutrients, which can have a detrimental effect on the ecology of downstream lakes and rivers if it is allowed to enter surface watercourses.  In western Canada, producers are encouraged to construct holding ponds (or runoff retention ponds) to intercept farmyard runoff and prevent excess nutrients from reaching stream systems.  However, little information is available regarding the overall effectiveness of these structures under local climatic conditions.  Therefore, the quantity and quality of the runoff into a small (two-cell) holding pond constructed downstream of a winter cattle feeding/containment area was intensively monitored over a four-year period. 

Although the yard site (2.1 ha) was only about 1 % of the total area of the watershed, approximately 4 % of the total basin (206 ha) runoff was generated in the yard.  Nutrient concentrations and loading in the runoff from the yard site were considerably greater than those measured elsewhere in the watershed.  Maximum concentrations of nitrogen (N) and phosphorus (P) measured were 543 and 40 mg L^-1, respectively; while annual loadings of N and P from the yard site averaged 80 kg N ha^-1 and 12 kg P ha^-1.  Overall, the holding pond was estimated to reduce total and dissolved N and P transport in the watershed by 10 to 40 %.  However, the potential impact of the holding pond was assessed assuming that all nutrients intercepted by the holding pond would have otherwise been transported directly out of the watershed.  This assumption likely resulted in an overestimation of the impact of the pond.  Nonetheless, our results show that the holding pond is an effective BMP for reducing nutrient loading to downstream water bodies and deserves consideration when developing watershed management plans for this region of Canada.