Drains vs Natural Streams: A comparison of fish communities in the South Nation Watershed
Alicia Howse (1), Frances Pick (2), Mary Ann Perron (2), Naomi Langlois-Anderson (3)
(1) Department of Earth and Environmental Sciences, University of Ottawa
(2) Department of Biology, University of Ottawa
(3) South Nation Conservation Authority
Alicia Howse (1), Frances Pick (2), Mary Ann Perron (2), Naomi Langlois-Anderson (3)
(1) Department of Earth and Environmental Sciences, University of Ottawa
(2) Department of Biology, University of Ottawa
(3) South Nation Conservation Authority
The impacts of agriculture on aquatic environments are extensively documented and include negative effects on water quality and biodiversity. Drainage solutions in the form of man-made channels are often implemented to maximize flow off agricultural fields and increase crop yields. Drains are then managed through periodic dredging. Despite these disturbances, drains can provide habitat for fish. In this study we compared fish communities in drains with those in natural streams in a large agricultural watershed (South Nation River, Eastern Ontario); given the difference in disturbance, we predicted lower fish species richness and abundance in drains when compared to natural streams, while accounting for the effect of discharge (typically a strong predictor of fish diversity in lotic ecosystems). The watershed examined extends from the St. Lawrence River at Prescott to the Ottawa River at Plantagenet and counts over 1,200 municipal drains. Fish communities have been consistently surveyed by the South Nation Conservation Authority since 2002 via electrofishing and seine netting in 79 natural streams and 276 municipal drains. Overall, fish species richness and Shannon diversity index were not significantly different between natural watercourses and municipal drains. In both watercourse types, the dominant species were creek chub (Semotilus atromaculatus), central mudminnow (Umbra limi), and brook stickleback (Culaea inconstans), accounting for 44% of total abundance across the drainage network. While drains and natural watercourses share 37 species in common, natural watercourses count 9 additional unique species and 13 in drains. Species of particular conservation status, unique to a watercourse type were only documented in natural watercourses (cutlip minnow, Exoglossum maxillingua and greater redhorse, Moxostoma valenciennesi). The species-discharge relation was also tested via Strahler stream order and showed, as anticipated, a significant relationship between stream order and measures of diversity. As there was no indication that drains host different fish communities than natural streams, it is likely that both types of watercourses are experiencing pressures from the changing land-use, which may reflect a homogenization of fish communities across the South Nation drainage network.