The Relative Importance of Road Density and Physical Watershed Features in Determining Coastal Marsh Water Quality in Georgian Bay |
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Authors: | Rachel DeCatanzaro Maja Cvetkovic Patricia Chow-Fraser |
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Institution: | (1) Department of Biology, McMaster University, 1280 Main Street, West Hamilton, ON, L8S 4K1, Canada |
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Abstract: | We used a GIS-based approach to examine the influence of road density and physical watershed features (watershed size, wetland
cover, and bedrock type) on water quality in coastal marshes of Georgian Bay, Ontario. We created a GIS that included landscape
information and water-quality data from a 9-year synoptic survey of 105 coastal marshes covering 28 quaternary watersheds.
Multiple regressions and partial correlations were used to discern confounding effects of human-induced (road density) versus
natural physical watershed determinants of water quality. Road density was the dominant factor influencing many water quality
variables, showing positive correlations with specific conductivity (COND), total suspended solids (TSS), and inorganic suspended
solids (ISS) and a negative correlation with overall Water Quality Index scores. Road density also showed positive correlations
with total nitrate nitrogen (TNN) and total phosphorus (TP). By comparison, larger watershed area was the main factor leading
to elevated TP concentrations. The proportion of the watershed occupied by wetlands explained the largest amount of variation
in TNN concentrations (negative correlation) and was also negatively correlated with COND and positively correlated with TSS
and ISS when we controlled for road density. Bedrock type did not have a significant effect in any of the models. Our findings
suggest that road density is currently the overriding factor governing water quality of coastal marshes in Georgian Bay during
the summer low-flow period. We recommend that natural variation in physical watershed characteristics be considered when developing
water quality standards and management practices for freshwater coastal areas. |
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Keywords: | Wetland Watershed Water quality Anthropogenic stress Geographic information system Road density |
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