The problem won’t fix itself in the near term, even though the era of acid rain is largely behind us. Our soils lost a lot of calcium (Ca) during the half century of acid rain. Today the rain is indeed much less acidic, but it is not a large Ca source. In fact, calcium input from rain and snow in Muskoka has actually fallen quite a bit as we have cleaned up pollution of the atmosphere. We need a source of Ca to replace that half tonne of Ca that was lost to acid rain, especially, compounding the problem, as we wish to continue harvesting trees in the region, removing their stored Ca from watersheds. The needed Ca must come either from us, or from nature, via long-term weathering of soil minerals. However, calcium-rich minerals were in low supply in Muskoka to start with, and they were the first to go during the acid rain era. What’s left will supply Ca very slowly as Muskoka rocks weather very slowly and produce little Ca when they do break down. Further, calcium-levels are now so low in our soils it will take a long time for these slow natural processes to rebuild soil Ca levels. If we want to fix the problem over the next few decades, we can’t rely on nature to do it for us. We created the problem, and we can fix it.
At roughly 4%, calcium (Ca) is the 5th most common element in the earth’s crust. Some regions, however, suffer from a calcium decline problem, both because crustal calcium is unevenly distributed on the earth’s surface, and because it has been depleted by human activities in some regions that didn’t have much Ca in the first place.
Muskoka is one of those regions.
We didn’t have much calcium in our soil historically, because our soil was “built” by the weathering of granitic rocks – a slow process that produces very little calcium – and then much of the soil we had was pushed south by glaciers only a few millennia ago.
Acid rain compounded the problem, leaching much of the Ca in the soil away. Muskoka soils lost roughly half a tonne  of Ca per ha  to acid rain, leaving so little Ca in the soils that the growth (and carbon capture) of Muskoka forests is now commonly limited by calcium supply, and Ca input to lakes has been reduced. These factors have led to a calcium decline problem in Muskoka. Ca is currently limiting the growth of trees, especially sugar maple, in Muskoka forests, and Ca levels have fallen to levels at or below 1.5 mg/L in many Muskoka lakes, levels that are too low for calcium-rich animals such as crayfish and Daphnia to survive, let alone thrive. It is this Ca decline problem that scientists have called “ecological osteoporosis”, by analogy to the syndrome in humans caused by long-term intake of too little Ca.
- one metric tonne (1000 kg) is equal to 2,204 pounds
- one hectare (ha) is equal to 2.47 acres
The element calcium (Ca) supports all animals in two main ways; it builds their skeletons and supports their muscle and nerve function. Ca is the basic mineral in vertebrate teeth and bones and invertebrate (think clams and lobsters) shells and carapaces. It is also the crucial trigger for contraction in muscles, and it initiates impulses in nerves.
Without an adequate supply of calcium over the long-term your teeth, vision and brains are damaged, and your bones become brittle. You suffer from osteoporosis. Given all these roles it is no surprise that humans and other animals need a lot of Ca.
Calcium forms about 6% of our body weight, ignoring our water content. The Ca needs of aquatic animals range from lows of 0.1% or less in some non-crusty plankton to 10 to more than 20% in turtles, snails, crayfish, and crusty animal plankton such as Daphnia. Given this range in need, it is no surprise that calcium decline in lakes first affects calcium-rich animals such as crayfish and Daphnia.
Calcium is as important to plants as it is to animals. Although they don’t need quite as much as animals, needs do vary among plant species. For example, sugar maple need about 5 times more Ca than conifers, and are thus more sensitive to Ca decline in the soil. In plants, as in animals, Ca plays both structural and physiological roles. Calcium forms an essential mineral that holds cells of plants together in proper alignment. Too little Ca and root tips and young leaves don’t grow properly. Ca also serves as a messenger in plant signalling. With inadequate Ca, plants can’t properly defend themselves against invaders, as they can’t properly signal the attack.
Dr. Norman Yan, PhD, FRSC
Chairman, Friends of the Muskoka Watershed
Friends of the Muskoka Watershed takes on the most widespread threats to our lakes that aren’t being adequately resolved, pointing the path forward to solutions. That is the basis of our ASHMuskoka project. We selected it because “ecological osteoporosis” (environmental calcium decline) was damaging almost half of our lakes.
Where did all the calcium go?
A century of acid rain and historically poor logging practices have flushed calcium from the soil and from the lakes and rivers. Most of Muskoka’s lakes have lost 25% to 50% of the calcium they need. Even though acid rain has largely stopped, and forestry practices have improved, without intervention it will take centuries for calcium levels to rebound.