Water Quality - Jan 2022 (Prepared by Reginald Genge)
After a brief hiatus in 2020, an intensive water quality survey was completed on Charleston Lake during the summer of 2021. During the summer, forty-two phosphorus samples and water clarity recordings were collected over the period May 17th to October 20th inclusive; six samples from each of seven basins in the lake. This work is a continuation of the yearly monitoring effort for water clarity and phosphorus concentrations conducted since the year 2000. The sample sites are located in Big Water, Deep Water (Runnings Bay), Donaldson Bay, Webster Bay, north of Goose Island, Eastern Waters and Southern Waters. In addition, surface to bottom dissolved oxygen and temperature profiles were recorded at all sites for the September 3rd, September 25th and October 20th survey dates; the last time this work was completed was the year 2015.

As of the writing of this newsletter the analysis for total phosphorus was not yet available from the MOECP Lake Partner
Program. These results will be reported upon, inclusive of all the temperature and oxygen recordings, in the final report to the Charleston Lake Association in the spring of 2022.
During the spring, summer and fall of 2021, Charleston Lake once again experienced excellent water clarity (Average Secchi depth 6.873 m); this value is within the year-to-year natural variability for water clarity. When the first five years (2000 to 2004 inclusive) of clarity data is compared against the last five years (2015 to 2021 inclusive) of data, the improvement is remarkable. The mean water clarity value for the first five years is 4.305 m while for the most recent five-years of survey it is 6.377 m; an improvement of 2.072 m. The great improvement in clarity is the result of the zebra mussel colonization of the lake.

Water clarity has improved so much in recent years that the mean value for the 21-year period of record (6.097 m) places Charleston Lake in the oligotrophic category for the entire time frame, despite the fact that for the first five years of that period (2000 to 2004 inclusive) the water clarity averaged only 4.305 m. Oligotrophic lakes have a water clarity > 5.0 metres.

Surface to bottom oxygen and temperature profiles are conducted to document, among other things, the amount of water column suitable as lake trout habitat. The concern for this relates to nutrient loadings. The more phosphorus, the poorer the water clarity and the greater the rate of oxygen depletion from the cold deep waters and hence the loss of lake trout habitat. The in situ profiles show that there has been an improvement in deep water oxygen concentrations in recent years (2007, 2009, 2012, 2015 and 2021) when compared with data from the years 2000 and 2002.

The 2021 sampling shows that optimal conditions for lake trout exist at all the sites for each of the survey dates with the exception of Southern Waters. Southern Waters is too shallow to support lake trout and the oxygen conditions below the thermocline become depleted by mid-summer.

I must express my thanks to CLA members Gary Nielsen and John Willson for assisting in the 2021survey. They are now trained and will carry on with this survey work in the future. I am confident the continued monitoring effort is in good hands.

Water Quality - Jan 2020

(see full report)

 

Water clarity is recorded at each of the seven sample sites on the lake on six dates between May 1st and the end of October each year. There is an extensive database on Charleston Lake for this parameter extending back into the mid-1970s; since the year 2000 the seven basins of Charleston have been monitored for water clarity, phosphorus and calcium concentrations and periodically surface to bottom water column oxygen and temperature values. These are reported on annually. As of the writing of this article, the phosphorus and calcium analytical data for the summer of 2019 is not yet available from the Ministry of Environment, Conservation and Parks.

 

The 20 years of findings are summarized in the graph.

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The mean water clarity value (Secchi disc depth) for the lake as a whole in 2019 is 6.415 metres (42 recordings). Since and including the year 2014, Charleston Lake has experienced a decline in water clarity when compared with values for the period 2009 to 2013 inclusive.  The whole lake average water clarity for the period 2009 to 2013 inclusive was 7.56m; for the period 2014 to 2019 inclusive, the average water clarity value was 6.32m. The mean whole-lake average water clarity value for all twenty years combined (years 2000 to 2019) is 6.058 metres.

 

For the 20-year period of record, the poorest whole lake average water clarity (3.873 m) was recorded in 2002, the same year that the highest whole-lake mean total phosphorus value (16.857 ug/L) was recorded. More phosphorus produces more algae and results in higher turbidity and therefore poorer water clarity.

 

The distribution of zebra mussels (Dreissena polymorpha) is lake-wide in Charleston Lake and zebra mussel densities are highest in the littoral zone areas where the rocky shoreline provides the most and best substrate for the organisms to become attached. Zebra mussels filter particulates, algae and zooplankton out of the water and therefore increase water transparency. In the matter of little more than a decade (2002-2013 inclusive) the mean whole-lake Secchi disc depth value increased by 4.26 metres.

 

The year-2019 mean value of 6.567m is lower than the clearer values in the range of 8 metres recorded in the years 2010, 2012 and 2013; the mean value for the period of record 2010 to 2013 inclusive is 7.753m. The apparent decline in water clarity since 2013 may be due to a decline in the zebra mussel population; invasive zebra mussel populations are known to increase to a climax population density and then decline to a background new equilibrium level. Once established at that lower population level, a ‘new’ norm becomes established for water clarity. Zebra mussel densities have likely reached a steady state equilibrium; their influence on improved water clarity is undeniable. As a result, water clarity values will likely continue at the present level into the future.

 

Prior to the year 2005, Charleston Lake was classified as mesotrophic on the basis of water clarity; lakes with mean Secchi disc depths > 2.0 m and < 5.0 m are considered to be mesotrophic. However, for all years since and including the year 2005, Charleston Lake would be classified as oligotrophic on the basis of water clarity; the whole-lake mean water clarity for the years 2005 to 2019 inclusive is 6.643 m.

 

When the first five years (2000 to 2004 inclusive) of clarity data is compared against the last five years (2015 to 2019 inclusive) of data, the improvement is quite remarkable. The mean water clarity value for the first five years is 4.31 m (mesotrophic) while for the most recent five-year period it is 6.28 m (oligotrophic); an improvement of 1.97m.