When most of the water in Manitoba’s ecosystem comes from snowmelt, typical best water management practices may not be the most beneficial
Some scientists are suggesting that some established water quality best management practices may have to be re-evaluated for their effectiveness under Manitoba conditions.
Many of the best management practices have been promoted across the Prairies over the last couple of decades were originally developed for ecosystems relying primarily on rainfall to replenish their annual water resources.
Manitoba’s ecosystem, however, relies largely on snowmelt as its water source. Prairie watersheds produce 80 to 90 per cent of their runoff during snowmelt, with minimal erosion, but with significant losses of dissolved forms of nutrients such as dissolved phosphorus.
This means it’s very challenging, but still vitally important to manage spring runoff from snowmelt in a way that maintains water and nutrients where they are needed most and keeps them from ending up in Prairie lake systems, where excess loading of nutrients such as phosphorus promotes the growth of algae and causes water quality problems.
New best practices
Specific best management practices (BMPs) need to be developed that are more applicable and effective under snowmelt runoff conditions, because the processes that contribute to water quality, erosion and water retention in Manitoba are not the same as for ecosystems that primarily rely on rainfall.
“BMPs have different effects on different issues, for example nitrogen versus phosphorus, in different environments, i.e. rainfall on sloping land versus snowmelt runoff on plains,” says Dr. Don Flaten of the Department of Soil Science at the University of Manitoba. “Our goal should be to improve overall environmental health, because focusing on a single issue, for example phosphorus loss, or a single BMP like zero-till increases the risk of simply exchanging one problem for another.”
It’s necessary to treat environmental health more like human health, say Flaten, by correctly diagnosing the problem in each individual case and then fine tuning effective remedies are based on specific circumstances and requirements. BMPs must take into account all the benefits and risk factors, rather than reaching for a quick-fix cure-all.
Revised BMPs might include re-evaluating or adapting zero-till systems, which do not help to prevent phosphorus losses during snowmelt runoff in the Manitoba environment.
In addition, research conducted in Manitoba, Vermont and Finland has shown that vegetated buffers are often ineffective and may even by counter-productive for removing phosphorus during snowmelt. Recent experiments conducted by Dr. Darshani Kumaragamage at the University of Winnipeg have shown that allowing ponded floodwater to accumulate on some of Manitoba’s agricultural soils for more than a few days can lead to dramatic increases in the release of phosphorus from soil to floodwaters.
Some traditional best management practices are not being questioned. For example, farmers should continue to aim for balanced phosphorus and avoid high soil test phosphorus levels by managing their inputs. Winter application of fertilizer and manure should be avoided.
But most importantly, farmers and policy-makers alike need to be more informed about all of the environmental and economic benefits and costs of different management practices so they can make better decisions about what will work best in their particular situation. †