Canadian prairie wetlands undergoing widespread degradation

Aerial imagery of prairie pothole wetlands. Credit, USFWS.The wetlands of Canada's prairie pothole region have long been recognized as a waterfowl factory for North America. However, in the 1980’s, with duck populations at record lows, wildlife managers suspected degradation or loss of those pothole wetlands as a major cause.

Now, in one of the first efforts of its kind, biologists have quantitatively assessed the status of Canadian wetlands on a large scale. Their findings indicate that high levels of impact combined with low recovery “clearly Prairie pothole region in North America.demonstrate the need for stronger wetland protection in prairie Canada.”

The study, published in Ecological Applications, followed trends of some 10,500 wetlands between 1985 and 2005 in the southern portions of the three Canadian prairie provinces: Alberta, Saskatchewan and Manitoba. Blake Bartzen and fellow researchers looked at impacts to the wetlands from agricultural activities such as cultivation and livestock grazing. They considered the wetlands to be recovered if the impacts had ceased.

The scientists, from the University of Saskatchewan and Canadian Wildlife Service, utilized multistate models with the widely-used mark-recapture program MARK to estimate transition probabilities in an elegant analysis. Their objective was  to assess “spatiotemporal variation in wetland impact rates” and determine how a suite of factors influence those rates.

They found that in all instances, rate of impact was far greater than that of recovery, often close to 10 times greater. Though results varied from province to province and other factors such as seasonal wetness, land use and wetland permanence, there was a clear message of widespread damage to wetlands.

Impacts on pristine wetlands, however, have declined over the twenty years. While this initially may sound encouraging, rate declines were likely because more than 90% of all wetlands had some form of agricultural impact.

Results varied by province with both impact and recovery rates being greater in Saskatchewan and Manitoba than Alberta. Impacts were less damaging in wet springs and highest in cultivated and pasture lands compared to natural grasslands and wooded areas. Wetland margins (natural vegetation surrounding the wetland) were more affected than wetland basins (the interior depression capable of holding water).

While many results are not surprising and may seem obvious, the study is an important contribution to wetland conservation in Canada. The ecological importance of wetlands is broadly recognized and their conservation has long been a management imperative, highlighted by the Ramsar Convention of 1971.

Yet over half the world’s wetlands have been lost by some measures and in Canada, where no inventory or monitoring program exists, quantitative trends have not previously been available. Thus, having this work as solid evidence should help wetland conservation in the region.

The study recommends preserving remaining pristine wetlands with additional focus on ephemeral wetlands and those in cultivated and pasture lands - much needed advice that should be heeded.

--by Ian Adams

Bartzen, B., Dufour, K., Clark, R., & Caswell, F. (2010). Trends in agricultural impact and recovery of wetlands in prairie Canada Ecological Applications, 20 (2), 525-538 DOI: 10.1890/08-1650.1