Igneous rock, isformed as molten rock that rises from the earth’s core cools, If this solidification occurs below the earth’s surface it is call plutonic, and is only exposed when uplifting or erosion or glaciers exposes it. The Loon Lake Pluton, which underlies part of Chandos lake, is mostly granitic with little calcium. The low level of calcium in the Loon Lake Pluton may be a moderating factor in the inability of Zebra mussels to have gained a foothold in Chandos Lake. Calcium enters the lake through leachate runoff mainly from the catchment area soils, and from the weathering of area rocks; as well, there is an atmospheric source component.
Recently these molluscs have been found in Wollaston Lake. (see: zebra mussels in Wollaston Lake) The calcium levels in Wollaston are in the order of 28 mg/L, where as in Chandos the level is around 21 mg/L. Part of the geology influencing Wollaston Lake is metasedimentary marble (marble being a metamorphosed limestone, which is high in calcium).
Other factors, besides calcium levels, also influence the ability of Zebra Mussels to become established, such as magnesium, pH, and lake environment (littoral zone, rocks, depth, etc). So it is difficult to state an absolute calcium threshold for Zebra Mussels; however, few lakes below 25mg/L have these creatures in the full adult form.
See the map at EDDS Zebra Mussel mapping distribution for an idea of where Zebra mussels have been found. As of 2016, Zebra veligers have been noted at Catchacoma, Paudash and Jack Lake, but no adults, likely because the calcium levels are insufficient for them to advance to maturation.
The level of calcium in Chandos hopefully is just low enough to withstand an invasion, but one doesn’t want it too low, as the calcium carbonates act as a buffer towards acidification from acid rain. We seem to be right on the edge of having them or not, but given the experience of similar lakes, zebra mussels may still be in our future.
An intriguing fact is that the calcium levels in the Canadian Shield lakes have been in decline over the last several years. Fortunately, the levels in Chandos are sufficiently high to support various other organisms such as water fleas, snails, and crayfish, which have a fairly low threshold of about 1.5mg/L. click here: calcium-in-ontarios-inland-lakes-information-sheet , and here: calcium-decline-threat-dr-norman-yan
It is interesting to see how much calcium concentrations differ from lake to lake. See: calcium-2008-12