Water Quality Survey of Ten Lakes Located in the Carleton River Watershed Area
of Digby and Yarmouth Counties, Nova Scotia
SUMMARY
In 2008, as a result of concerns that water quality was becoming seriously degraded within a number of lakes located within the Carleton, Meteghan, and Sissaboo River watersheds, the Nova Scotia Department of Environment initiated a program designed to evaluate the water quality status of nine lakes located within these watersheds. The results of this initial evaluation indicated that water quality was impaired in a number of the lakes surveyed, particularly with respect to high nutrient concentrations resulting in the development of high algal concentrations. In some instances the high algal concentrations contained species of blue-green alga known to produce microcystins, a toxin that, under certain conditions, may be harmful to humans, livestock and wildlife. As a result, further studies were carried out in 2009 and 2010 to better document the extent of the degradation in water quality and to determine its potential causes. This report summarizes the results obtained during the three survey years with a focus on water quality parameters that, when impaired, are potentially harmful to humans or can lead to the deterioration of conditions necessary to support aquatic life.
A total of ten lakes were surveyed over the three year survey period. Of the ten, seven were found to be severely impacted by nutrient over-enrichment in at least one of the three survey years, two were moderately impacted and only one was found not to be impacted in any of the three years. The lakes exhibiting the most serious symptoms of nutrient over-enrichment were located within the upper region of the study area and in close proximity to a high concentration of mink farming operations, the activities of which are most likely to be the major source of nutrients leading to nutrient over-enrichment of the lakes. There was considerable yearly variation in the extent to which an individual lake exhibited excessive algal growth which was found to be closely related to yearly variations in lake color. Despite the poor water quality, most of the surveyed lakes met the available established water quality guidelines for recreational use related to health issues, but many often failed the recreational aesthetic guidelines related to water transparency. All of the lakes surveyed were found to contain microcystin producing algal species in at least one of the survey years, but microcystin concentrations never exceeded established guidelines for recreational water use.
To more specifically define the magnitude and location of nutrient inputs to the lakes, rudimentary estimates of nutrient loading to each lake were carried out in 2009 and 2010. In addition, as an aid to categorize which lakes are most in need of remediation activities to decrease nutrient input, an assessment procedure was developed to estimate the relative assimilation capacity of each lake and its susceptibility to nutrient over-enrichment. Of the ten lakes surveyed, three were found to be highly susceptible to nutrient over-enrichment, four were moderately susceptible, two had low susceptibility and one lacked the necessary data for assessment.
Recommendations are made for future studies to elucidate the sources of nutrient inputs and to monitor the effect of any remediation actions that may be carried out.