The Essential Link Between Lake Health, Calcium, Forests and Forest Floor Ecology

The amount of calcium (Ca) in our freshwater lakes is seeing a major reduction. This is due to the lack of calcium in our forest floor from acid rain and also from recent rises in deforestation for residential development. Calcium enters our watershed by the weathering of rocks and soil runoff. Weathering means the physical or chemical breakdown of rock; for example, when water collects in the crack of a rock and freezes it expands, so when it thaws again the rock has a bigger crack and can split apart revealing small particles that are now mobile. Weathering can also be from rain and water flowing over rocks and eroding the surface taking minute particles with the waters. The Canadian shield is made up of mostly hard igneous rock, which is a lot harder to break down, therefore the lakes in the northern half of The Land Between and Cottage Country mostly rely on runoff from forest-soils which receive calcium from trees and woody debris to get calcium. 

Due to many years of unsustainable forestry practices, and a current rise in unsustainable residential development, calcium in soil has depleted. When forests are undisturbed and a tree falls, the tree starts to decompose releasing important nutrients in the soil and creating a healthy environment for new flora to grow. These nutrients in both living and also dead trees include calcium.  Most of the calcium is stored in the bark and branches of trees. When the trees are cut down and removed, whether for development or for resource-use all their important nutrients go with them.  

Calcium in the soil has depleted significantly in the past 40 years, and has only been made worse by acid rain. In the 60’s and 70’s the amount of acid rain increased, and calcium was leaching into the lakes faster than it could be replenished by the soil. This increased the calcium in the lakes for only a brief period of time, and because the soil was leached of its calcium and the Precambrian doesn’t allow for calcium to come from the bedrock it continued to decline. Without the buffering capacity of lakes because of the levels of Calcium, lakes and also soils have become more acidic, leaving sub-optimal conditions for the surrounding flora and fauna. Calcium is an important mineral to a variety of species because it helps fortify bones and plant-cell walls and is the main component in exoskeletons for species like crayfish, but also for microscopic zooplankton such as Daphnia. 

Daphnia are important for overall lake health. They are small plankton that live in most freshwater environments and are commonly used as test species in toxicology reports. When the Calcium levels are below 2.5mg/L Daphnia can become stressed, but below 1.5mg/L they do not survive. Daphnia are essential to the aquatic food web because their abundance makes them an easy and nutritious food source for many different species. Moreover, Daphnia also consumes algae, keeping levels in check. When the base of the entire food web starts to disappear, it affects every aspect of the ecosystem. If Daphnia aren’t getting the proper nutrients to thrive, the entire lake and also the connected waters could be in serious trouble.

It’s not all grim; there are many ways to which we can help our forests keep their calcium. Leave forest “litter” alone; the decomposing matter at the base of the forest floor is providing important nutrients to our soil, and this layer of leaves and woody debris is also regulating the moisture that helps trees and other plants thrive; it also provides a really important habitat for creatures such as salamanders. small ways to the lake are better than lawns, and raised stairs are better than embedded stairs to maintain the integrity of the forest around you and the health of the lake. If you need firewood, leave the bark and branches and only take what you need. When “developing” a property, instead of removing trees to the shore, limb them by removing lower limbs if you are requiring a view to the lake. There have been studies showing that Non-Industrial Wood Ash (NIWA) can be helpful in replenishing calcium in the soil so if you live in an area with low calcium levels and use a wood burning stove, scatter the ashes back around the forest floor. It doesn’t take much to help restore an environment that’s had hundreds of years of abuse, any little bit that you do is helping create a healthier forest for generations to come. 

Written by Valerie Wiser

References 

Molot, L. A., & Dillon, P. J. (2008). Long-term trends in catchment export and lake concentrations of base cations in the Dorset study area, central Ontario. Canadian Journal of Fisheries and Aquatic Sciences, 65(5), 809-820. doi:10.1139/f08-035

Giardini, J., Yan, N. D., & Heyland, A. (2015). Consequences of calcium decline on the embryogenesis and life history of Daphnia magna. Journal of Experimental Biology. doi:10.1242/jeb.123513

Watmough, S. A., Aherne, J., & Dillon, P. J. (2003). Potential impact of forest harvesting on Lake Chemistry in south-central Ontario at current levels of acid deposition. Canadian Journal of Fisheries and Aquatic Sciences, 60(9), 1095–1103. https://doi.org/10.1139/f03-093 

Azan, S. S., Yan, N. D., Celis-Salgado, M. P., Arnott, S. E., Rusak, J. A., & Sutey, P. (2019). Could a residential wood ash recycling programme be part of the solution to calcium decline in lakes and forests in Muskoka (Ontario, Canada)? FACETS, 4(1), 69–90. https://doi.org/10.1139/facets-2018-0026