by John Sollows
People in Forest Glen, Carleton, and Raynardton remember it well: In the summer of 2007, all the lakes on the main Carleton River, from Ogden down to the upper end of Vaughan turned green. The following year, the problem returned with a vengeance. Some of those folks contacted TREPA, and thus began our biggest single job over the past decade.
Thanks to the efforts of many concerned citizens, the province began a series of water quality investigations in 2008. With the support of many actors, these investigations have continued in one form or another, ever since.
So, what’s going on out there?
Like all plant life, those troublesome little green things fundamentally need two things to develop: sufficient nutrients and sufficient light. In our infertile part of the world, nutrient levels are usually too low for their populations to explode. Also, the darker the water in a lake, the less the light penetration, so clear water lakes are more vulnerable.
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This complicated figure explains a lot. The nutrient which limits growth in our fresh water systems is usually phosphorus. Rivers run downhill, dissolving stuff as they go. Unless something strange is going on, then, concentrations of dissolved solids (including phosphorus) should go up from upstream to down.
The reverse has been happening along the Carleton, so something unusual has been going on in the upper Carleton catchment. Nutrients come from any sources, but various results, including this figure, have pointed convincingly to the crucial role of uncontrolled effluent from mink farms in enriching the Carleton. To deal with such problems, the Fur Industry Regulations were drafted in 2011, and after some changes, went into effect in January, 2013.
On the ground, summer surface phosphorus levels peaked in Placides in 2011, and after 2014, dropped in the affected Yarmouth County lakes. It is too soon to conclude why, and the drop is probably due to a combination of things. Are the regulations working? Maybe, but the hot, dry summers of 2015 and 2016 would also have had some effect. Other factors, such as industry downsizing, may apply, as well.
We can expect to see the blooms again this June, probably as bad as ever. Based on the last two years, however, there is a good chance that they will be of shorter duration than in the bad old days. In the long run, though, it is too soon to predict if and when they will vanish completely. There’s still plenty of phosphorus to get washed out of the system.
This saga has told us that our lakes are vulnerable to pollution. Mink farms are not the only problem, and we are concerned that green water could show up elsewhere. Trends in lakes on the lower Annis and Kegeshook Lake, near Quinan have us concerned.
Lawns, gardens, livestock and farm operations, and faulty septic systems can all contribute to the problem. Leave as wide as possible a shoreline zone as wild as possible. Don’t use fertilizer near water bodies and watercourses. Locate gardens well away from the water. Check provincial regulations and municipal by-laws before you develop your land. In Yarmouth Municipality, for instance, only minimum development is allowed within forty feet of the shoreline. That sets a good example both for other municipalities, and for property-owners.