Biological recovery in an urban industrial stream: using the reference condition approach to assess the current state of Junction Creek, Sudbury, Ontario

Benthic macroinvertebrate communities in Junction Creek, Sudbury, have recovered remarkably since the 1970s, following government initiatives to lower atmospheric pollution, the implementation of mine wastewater treatment, and Greater Sudbury’s Regreening Program. To understand contemporary temporal and spatial patterns of biological condition in this stream system, I employed a number of benthic community metrics and the Reference Condition Approach. There was little evidence of temporal trends in the benthic macroinvertebrate communities across the 2003-2015 study period, however there was strong evidence of community composition, water and sediment quality differences among study sites. This urban industrial stream is affected by multiple stressors (straightening, culverts, urban and mining pollutants, overflow from sewer outfalls, etc.), which accumulate as the water flows downstream. Lime-treated metal mining effluent forms the headwaters, which receive cold groundwater from the upper reaches and is further diluted by the Maley tributary before reaching the heavily urbanized city. In these upper reaches, community metrics that are indicative of sensitive organisms and higher diversity are elevated and metal levels are lowest within the study area. Biological and chemical conditions decrease slightly heading downstream, but are much better following the millions of dollars spent in 2001 on diverting acid mine drainage underground to be treated kilometers away before being discharged into the creek below the study area. Treated surface runoff from a historic mine site, and a portion of each the Clarabelle Mill property and slag storage area from one of the world’s largest metal mining and smelting complexes in the world feed Nolin Creek, which then enters the stream through concrete box culverts that run beneath the city’s downtown core before re-surfacing and flowing South of the city. Despite the recent appearance of fish within Nolin Creek, it is still a major source of contaminants to Junction Creek, with elevated water and sediment metal levels and low benthic macroinvertebrate community diversity and abundance. This research showed that use of select benthic macroinvertebrate community metrics served as a better tool to assess biological conditions within the stream than comparison to near-pristine reference sites, but that local reference sites would serve as a best practise since they take account for naturally high regional metal levels, and the effects from decades of atmospheric pollution have had on Sudbury soil, lakes and streams. Additionally, test site benthic macroinvertebrate metric scores were surprisingly similar to those of pristine reference sites, but abundance was much higher at all reference sites. The apparent similarities between test and reference biotic conditions may be due to high nutrients and ions found in urban environments, inappropriate matching of reference and test sites or numerous cumulative effects. It was therefore recommended that ecosystem processes and functioning be studied in order to obtain a more accurate view of the current biological condition of Junction Creek. Finally, aqueous metal levels have decreased substantially and benthic macroinvertebrate community abundance and richness have increased substantially in the last 50 years, but appear to be at a relatively stable point currently, although the variation in both metrics is generally higher than those of reference sites. Biological and chemical conditions will likely not improve until the major current stressors (residual contamination of sediments and soils, and addition of mining effluent) are removed and habitat is improved.

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