Investigating the effects of forestry road crossings on stream habitat health and benthic macroinvertebrate communities in Napu’saqnuk (the St. Mary’s River watershed) in Mi’kma’ki (Nova Scotia)

Abstract

Napu’saqnuk (the St. Mary’s River) is a culturally, economically, and recreationally significant watershed in Mi’kma’ki (Nova Scotia). Napu’saqnuk provides habitat got the endangered Southern Upland Designatable Unit of Atlantic salmon (Salmo salar) and other species protected under the Endangered Species Act and Species at Risk Act. Historical and current forestry activities (harvesting and roads) are expected to be degrading stream habitat health and contributing to the decline of the Atlantic salmon population in Napu’saqnuk. Under the Fisheries Act, fish and fish habitat are protected, emphasizing the importance of understanding how forestry affects stream health. Benthic macroinvertebrates (BMI) are biological indicators of freshwater ecosystem health. BMI community structures are compared between disturbed and undisturbed habitats to assess whether disturbance has reduced habitat quality. BMI Orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) are sensitive to disturbance and tend to decline in degraded habitats. To assess stream health, BMIs and stream habitats were sampled upstream and downstream of road crossings in 12 streams. BMIs were subsampled and identified at the family level. Community structure was analyzed using community metrics, diversity indices, and multiple linear regression (MLR). T-tests were used to compare stream habitats and community structures between upstream and downstream of crossings, and between streams with culverts and bridges. Findings showed road crossings steepened stream gradient downstream, possibly due to improper road crossing design. However, this did not negatively impact stream health. Community structures and other habitat characteristics were similar between upstream and downstream of crossings. Streams with culverts and bridges reflected two distinct stream types, likely due to their location in the watershed- culverted streams were closer to headwaters and bridge streams were near the West River (main river in West Branch). Differences in habitat and community structures reflect natural habitat variation across a watershed, not differences in stream health. Most streams met habitat requirements for juvenile Atlantic salmon, suggesting the presence of healthy habitat in the West Branch. Ongoing monitoring and a greater focus on harvesting impacts are recommended. Findings can inform forestry management and Atlantic salmon habitat conservation in Mi’kma’ki. Keywords: Stream health; benthic macroinvertebrates; Atlantic salmon habitat; St. Mary’s River watershed; road crossings; culverts