Calcium is an essential nutrient, particularly for tiny creatures called daphnia. They filter the water in our lakes, and without daphnia we would have serious algae problems. Calcium is also vital for trees, particularly sugar maples. Without enough calcium, it’s like the trees are half-asleep even in summer.
In Muskoka, years of acid rain has washed a lot of the calcium out of the soil and the lakes. We’re already seeing the results of this.
One way to get calcium back into the system is to add it directly to the soil. Trees can absorb some of it, and some of it will get filtered through into the lakes.
Wood ash is a fantastic source of calcium. Spreading it in the forest is a great way to get it into the soil and the lakes.
Most wood ash currently goes into the landfill. This project aims to set up a collection system that will get ash into the forests, where it can do the most good.
How low are calcium (Ca) levels?
Calcium levels in lakes are determined by the calcium level in the surrounding soils. Levels in Muskoka have always been low, and creatures here have adapted to that. But in the last 40 years, calcium levels in Muskoka lakes have dropped by an average of 30%. Over half our lakes are now below 2 mg/L, likely below the threshold that many creatures can survive.
Where did the calcium go?
During the worst years of acid rain, calcium levels in our lakes increased slightly, as the calcium was washed from the soil into the lakes. Poor logging practice and soil erosion also helped remove calcium from land. Eventually it was flushed downstream. Even though acid rain has been largely halted, it will take centuries for calcium levels to recover on their own.
Why animals need Ca
Calcium provides skeletal support and allows nerves and muscles to function. Anything with a hard shell (snails, crayfish, turtles, mussels) needs a lot of calcium. Some crayfish, for example, are 30% calcium by dry weight. We have lost a quarter of the crayfish species from our lakes in Muskoka, and calcium is the most likely cause.
What about daphnia?
Daphnia are tiny filter feeders. There are millions of them in every lake, and they eat algae by filtering lake water. The entire body of Lake Muskoka is filtered through daphnia every ten days. As calcium levels drop, daphnia begin to vanish. They’re replaced by a different kind of creature called Holopedium. They don’t need as much calcium. They eat less algae, and they are less nutritious food for fish. As a result, falling calcium levels have been shown to increase algal biomass in a lake.
Why plants need calcium
Calcium helps trees grow, breathe and store water, and makes their limbs strong. Sugar maples have particularly high calcium needs. Without enough calcium, they grow much more slowly, are more vulnerable to wind damage, don’t capture as much carbon, and don’t draw as much water from the soil (which is important for flood prevention).
How fast can things get better?
Studies have shown that calcium shortage is the main factor limiting growth of some species, such as sugar maple. When calcium is added to the soil, the rate of growth and seedling survival increases by 50% in just a few years. It takes a few more years for the calcium to filter through to the lakes.
Is this just a problem in Muskoka?
No. Anywhere that has thin soil and granitic bedrock tends to be low in calcium. If those areas were also hit with acid rain, they will have suffered calcium loss. This is a problem from central Ontario to Atlantic Canada, from Michigan through to New England, as well as in Scandinavia. Solutions we develop in Muskoka are being shared with researchers worldwide.