vi. Degradation of Benthos

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BUI vi Degradation of Benthos

Status: Impaired

What was the original problem? The benthic communities in 1964 and 1984 were dominated by pollution-tolerant worms, but with improvements in the abundance and community composition over those 20 years. Stress on the benthos was caused by toxic chemicals in the sediment and extended periods of low to no oxygen.
Listing Guideline: When the benthic macroinvertebrate community structure significantly diverges from unimpacted control sites of comparable physical and chemical characteristics. In addition, this use will be considered impaired when toxicity of sediment-associated contaminants at a site is significantly higher than controls.
Delisting Guideline: When the benthic macroinvertebrate community structure does not significantly diverge from unimpacted control sites of comparable physical and chemical characteristics. Further, in the absence of community structure data, this use will be considered restored when toxicity of sediment-associated contaminants is not significantly higher than controls.
What Has Been Done?
  • There have been no direct projects targeted at changing the sediment characteristics. Various projects have been undertaken to reduce toxic substances and phosphorus input to Hamilton Harbour
  • BEAST (BEnthic Assessment of SedimenT) assessments have been completed at different scales in Hamilton Harbour. A full survey was completed in 2000 and a partial survey in 2002. Surveys focused on the Randle Reef Remediation were completed in 2005, 2006, and 2007
How Are Things Today?
  • BEAST is recommended as part of biological sediment guidelines adopted by the Canada-Ontario Agreement (COA)
  • From a 2000 BEAST survey, there is strong evidence of benthic community impairment at 27 of 44 sites with strong evidence of toxicity at 21 sites and in general, there is a tendency towards lower taxon diversity. However, available Great Lakes reference sites are not well matched to Hamilton Harbour sites due to site-specific conditions (low-energy bay), multiple stressors (seasonal anoxia at depth >7m), and confounding factors (physical disturbance from ships). Therefore, reference conditions may need to be modelled
What Still Needs To Happen?
  • Level of Toxicity compared to Reference Sites
  • Complete ArcelorMittal Boat Slip Sediment Remediation Project (targeted for 2015)
  • Complete ongoing track down of the source of Polychlorinated biphenyls (PCBs) in Strathearne Slip and determine any necessary management
  • Continue exploring causes for the “severely toxic ”sites in Windermere Arm
  • Planned upgrades to the Woodward and Skyway Wastewater Treatment Plants will reduce nutrient and sediment loadings
  • Complete in-water work for the Randle Reef Sediment Remediation Project (targeted for 2019)
  • Re-do BEAST surveys after Randle Reef Remediation is completed (1 year and 5 years post remediation)
When Will The Status Change? 
  • A re-evaluation should be made when all scientifically feasible and economically reasonable actions have been implemented
  • Anticipate years of natural recovery after sediment projects are completed before the desired outcomes are reached

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Photo Credit: Dave Heidebrecht