| Abstract/Description or Keywords |
The health of the St Mary’s River was reviewed using the results of benthic inverterbate and water quality monitoring from 2010 to 2012. Monitoring was conducted at three sites on the mainstem: two sites were located upstream of St Mary Lake and one was downstream. The condition of the benthic invertebrate community was the best and near reference condition at the upstream sampling site. Benthic community indicators of stress increased with downstream distance in early sampling years. However, the health of the benthic community improved with time, and by 2012 the two downstream sites were only potentially stressed (or mildy divergent from reference conditions). NGSTM01, the upstream sampling site, was determined to be in a healthy condition between 2010 and 2012. This was evidenced by an unstressed assessment and similarity in species composition compared to reference conditions using the CABIN reference model. Benthic community metrics supported the CABIN model findings, showing a high diversity of species and a large number of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa present. At this site, non-metal water quality data was collected annually and there were no exceedances of water quality guidelines for the protection of aquatic life or drinking water. Although rated as stressed compared to CABIN reference conditions in 2010, Site NGSTM02, located downstream of Redding Creek, showed improvement with time and was potentially stressed in 2011 and 2012. The number of invertebrate taxa not present that were expected under reference conditions supported the CABIN rating and was initially high, but decreased with time. The overall diversity of species also increased with time indicating improving water quality conditions. Non-metal water quality data was collected annually and did not exceed any aquatic life or drinking water guidelines. Sediment quality data had not been collected. The benthic invertebrate community at the most downstream site (NGSTM03), located downstream of St Mary Lake, was stressed both in 2010 and 2011, but improved and was rated as potentially stressed in 2012. Water quality, which was typically collected monthly, was consistent throughout the study, was similar to upstream sites, and did not exceed any of the available guidelines. This site also had sediment quality monitored annually. Results found arsenic and manganese concentrations that exceeded guidelines for the protection of aquatic life. The likelihood of effect on the biological community was uncertain given the concentrations measured were low. This is because arsenic only exceeded the ISQG guideline, above which adverse biological effects are expected to only rarely occur (CCME 2001). In 2010 and 2012 manganese exceeded the high effect guideline; however, a benthic community response was only observed in 2010 when the site was rated as stressed. There were insufficient stream temperature records to conduct any analysis. Year-round stream temperature monitoring should continue as part of this project. |
