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Journal of Environmental Quality Abstract - Special Sections: Environmental Standards for Agricultural Watersheds

Physical and Ecological Thresholds for Deposited Sediments in Streams in Agricultural Landscapes


This article in JEQ

  1. Vol. 41 No. 1, p. 31-40
    Received: June 2, 2010
    Accepted: Aug 26, 2011

    * Corresponding author(s): glenn.benoy@ec.gc.ca
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  1. Glenn A. Benoy *a,
  2. Andrew B. Sutherlandb,
  3. Joseph M. Culpb and
  4. Robert B. Bruac
  1. a Environment Canada and Agriculture and Agri-Food Canada, Potato Research Centre, 850 Lincoln Rd., P.O. Box 20280, Fredericton, NB, E3B 4Z7, Canada
    b Environment Canada at the Canadian Rivers Institute and the Dep. of Biology, Univ. of New Brunswick, 10 Bailey Dr., P.O. Box 4400, Fredericton, NB, E3B 5A3, Canada
    c Environment Canada, National Hydrology Research Centre, 11 Innovation Blvd., Saskatoon, SK, S7N 3H5, Canada. Assigned to Associate Editor Patricia Chambers


Excessive sedimentation in streams and rivers remains a pervasive problem for the protection of aquatic habitat and the sustainability of aquatic communities. Whereas water quality criteria have been determined for suspended sediments in many jurisdictions across North America, comparably little has been done for deposited (also known as bedded) sediments. Through Canada's National Agri-Environmental Standards Initiative, assessment techniques and analytical tools were developed for estimating environmental thresholds for deposited sediments in agricultural watersheds in New Brunswick (NB) and Prince Edward Island (PEI) in the Atlantic Maritimes of Canada. Physical thresholds were developed through assessment of geomorphic metrics, which were then analyzed using y-intercept and 25th percentile approaches. For NB, there was strong agreement in physical thresholds for both analytical approaches (e.g., percent fines <2 mm were 7.5 for y-intercept and 6.9 for 25th percentile approaches). In contrast, physical thresholds for PEI differed considerably between approaches (e.g., percent fines <2 mm were 6.1 for y-intercept and 19.6 for 25th percentile approaches), likely due to a narrower range in agricultural land cover. Cross-calibration of our provisional physical thresholds for NB with ecological (i.e., benthic macroinvertebrate) assessments show that ecological thresholds, calculated as change-points in relationships between Ephemeroptera-Plecoptera-Trichoptera relative abundance or Modified Family Biotic Index and geomorphic criteria, were more liberal than physical thresholds. These results suggest that provisional thresholds developed using geomorphic criteria should demarcate change from the least disturbed condition and reduce the risk of sedimentation degrading benthic ecosystems.

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