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New evidence of the effectiveness of buffers

The beneficial effects of forested riparian buffers along small watercourses are already well known: the stabilization of banks and improved water quality are only two examples. New studies by the Ministère des Ressources naturelles et de la Faune du Québec (MRNF) have found two new beneficial effects on wildlife. On the one hand, forested riparian buffers lower the temperature in summer enough to provide a proper environment for brook trout. They also reduce muskrat abundance, which is useful because these rodents damage the banks and increase water turbidity.

The studies, carried out under the agricultural component of the St. Lawrence Plan for Sustainable Development (SLP), addressed some of the SLP Agriculture Coordination Committee’s objectives with respect to biodiversity in rural watercourses. The MRNF is a partner of this committee.

Lowering lower temperature

In the first study (Influence de l’ombrage produit par la végétation riveraine sur la température de l’eau), MRNF researchers worked on two agricultural and forest watercourses in the Chaudière-Appalaches region, the Boyer River and the Petite Sainte-Marguerite River. For six months (from June to November), they recorded the water temperature by taking readings every two hours using thermographs installed in various segments of the rivers, some shaded and others unshaded.

Watercourse with forested riparian buffers Photo: Geneviève Bourget

The results showed significant differences of 1 to 2°C between the shaded stations and those along the bare embankments. The warmer the temperature and the slower the water flow (during low-flow periods), the wider the gap. According to the researchers, a difference of 1 to 2°C can determine whether or not a watercourse is conducive to the presence of a sensitive species like the brook trout, which cannot survive at temperatures in excess of 25 or 26°C.

Watercourse with shrub buffers Photo: Geneviève Bourget

The researchers reached the conclusion that “the planting of a riparian vegetation border that is sufficiently tall and dense to shade watercourses that run through farms would appear to be a simple and effective measure for maintaining a satisfactory water temperature and to meet the needs of aquatic fauna.”

Fewer muskrats

The other MRNF study (Influence de la composition de la bande riveraine sur l'abondance du rat musqué dans les petits cours d'eau agricoles) was conducted in the drainage basins of the Fouquette and Kamouraska rivers, an area in the Lower St. Lawrence which is primarily given over to farming.

Muskrats Photo: Pierre Bernier

The researchers demonstrated that to build their burrows, muskrats clearly prefer herbaceous riparian buffers to forested buffers. Underwater cages installed in several segments of the farm streams captured three times more muskrats in segments where the riparian buffer was herbaceous than where the buffer was forested.

Watercourse with herbaceous buffers including cattails, the preferred food of muskrats Photo: Geneviève Bourget

The greater abundance of the rodent in the former habitat is, according to the Department’s scientists, the result of more abundant food resources (more numerous aquatic plants because of the added sunshine), the fact that it is easier to dig burrows and the smaller number of mink, one of the main predators of the species.

Over one third of muskrats in Quebec are found in drainage ditches and streams that run through farms. They shelter in burrows dug into the banks along watercourses. Their presence causes significant erosion, and sometimes even the collapse of banks when farm machinery travels over them (because of the networks of tunnels), in addition to an increase in water turbidity. According to some farmers, they also block farm drains and cause damage to the wrapper on bales of hay stored near the banks.

Watercourse with arbustive buffers Photo: Ministère des Ressources naturelles et de la Faune du Québec

The authors of the study noted that the conservation standard requiring a 3-m wide riparian buffer along small streams running through agricultural land is often not observed, and the existing buffers mainly consist of herbaceous plants. The development of riparian buffers that consist primarily of ligneous plants would limit muskrat abundance and the damage that they cause, according to the researchers.

For more information:

Bert Klein
Ministère des Ressources naturelles et de la Faune du Québec (MRNF)
Telephone : 418-627-8694, ext. 7439
E-mail: Bert.Klein@mrnf.gouv.qc.ca.