Vice-Chairman, Friends of the Muskoka Watershed
Vice-Chairman, Friends of the Muskoka Watershed
Wood ash is not particularly soluble in water, but it’s not quite that simple.
Solubility in water is simply a measure of how much of a solid can be dissolved in water under specified conditions. It’s complicated for wood ashes because ash isn’t a simple solid. It has a quite course charcoal-like component – the product of incomplete combustion of the wood, and this component isn’t very soluble at all. It just floats on water. The grey powdery component of the ashes is also a mixture of minerals. It’s about 9% potassium (K) minerals, for example, and these are very soluble in water. There is also a small component of phosphorus (P), and it is quite insoluble, likely a good thing as excess supply of P to watersheds could have unintended consequences. But what we care most about is the roughly 30% of the ash formed of minerals of calcium (Ca), mainly calcium carbonate. Calcium carbonate is somewhat soluble in water, much less than the potassium component and much more than the phosphorus competent, again likely a good thing. With every rain, a little more of the Ca in the ash will dissolve and percolate into the soil. Because of this modest water solubility, wood ashes should provide a long-term source of the missing Ca in soils, the long-term goal of ASHMuskoka.
Wood ashes are very alkaline, with pH levels of around 9 to 11. But what is pH and what pH is too acid or too alkaline to safely handle or for ecosystem health? The “p” in pH stand for “power”, as in “raised to the power of” in mathematical notation, and the “H” stands for hydrogen. Technically pH is a measure of the strength of an acid solution, i.e. a solution of H ions. It is calculated as -log10H. Complicated, but here’s what it means. It has a negative sign, implying the lower the number the stronger the acidity, so water with a pH of 4 is much more acidic that water with a pH of 5. It’s also a log-scale, meaning a unit change represents a ten-fold change. So pH 4 is actually 10 times more acid than pH 5, and 100 times more acidic than pH 6. A pH of 7 is deemed “neutral”, neither acidic nor alkaline.
pH is a log scale. So pH 4 is actually 10 times more acid than pH 5, and 100 times more acidic than pH 6.
We are exposed to solutions of many different pH levels in our every day lives. Battery acid has a pH of 1 – take care! In the kitchen, vinegar, soda drinks, and lemon juice are quite acidic with pH levels of 2 to 3. Milk is almost neutral with a pH just under 7. Meat has a pH of 5 to 7. Baking soda in solution is alkaline with a pH of about 8.5. Among the most alkaline products in our home are cleaning agents such as Javex (pH 11), and TSP (pH of 12-14), and we know to take care when using them. Wood ashes are almost as alkaline when dissolved in water, with a pH varying from about 9 to 11. Thus adding wood ash to our soils has two distinct benefits. It is alkaline so it can neutralize soil acidity, and the source of the alkalinity is calcium minerals, so it can replenish the Ca lost to decades of acid rain.
If you are interested, here is an interesting interactive demonstration on pH values from the University of Colorado Boulder. Click or tap on the Macro view and select various liquids from the drop-down menu at the top. More can be added by pushing the red button on the dropper. Dragging the green ‘sensor’ to the liquid will give you the pH reading on the scale. Try adding water via the tap to see how it affects the pH value.
Our lakes get calcium (Ca) naturally from the air and from surrounding lands, and on occasion, from us. Ca enters lakes directly from the atmosphere, in the form of windblown dust and precipitation, but as measured by MECP  scientists, these inputs have actually fallen by about 50% in Muskoka over the last few decades as we have reduced air pollution levels.
Secondly, Ca enters our lakes in overland flow in streams in the watershed. The rate of this calcium supply is controlled by both rates of stream flow and the Ca concentrations in stream waters, the product of which is the total Ca supply. This overland supply has fallen because both stream flow and Ca concentrations have fallen, the former likely linked to climate change, and the latter, a legacy of acid rain. This leaves us. We add Ca to our watersheds and the lakes they support in many ways, mainly inadvertently. We bring soil and fertilizer to our gardens and lawns. We clear the land, potentially mobilizing stored Ca. We add calcium chloride as a dust suppressant to our gravel roads. One such dust-controlling trip a year for several years reversed the Ca decline trend in Dickie Lake, east of Baysville.
Finally, we can add ashes from our fireplaces to our forests. If the wood came from our property we are recycling Ca from our land. If we brought the fire wood in from elsewhere, then spreading the ashes on our property can start the process of reversing decades of Ca loss. This is one of the goals of our ASHMuskoka project.
 Ontario Ministry of the Environment, Conservation and Parks
We are beginning our restoration work in three sugar bushes. These are perfect “test sites” for us as they are privately owned, controlled-access properties with large areas of accessible forest plots that we can manipulate in a controlled way. Our manipulation is the addition of specific quantities of ashes to staked-out plots to compare with control plots that don’t receive the treatments.
Independently of Friends of the Muskoka Watershed, local sugar bush operators recently documented levels of calcium (Ca) in their sugar bush soils that were so low that the health, growth and recruitment of their trees were at risk, and they were seeking solutions.
Thus, three local members of the Ontario Maple Syrup Producers Association (the Rileys, the Luptons and the Creasors) were pleased to give us permission to use their sugar bushes to determine how much ash would be needed to solve the problem of Ca limitation of maples in their sugar bushes. They hope we will both provide additional, definitive evidence of the Ca limitation problem of trees on their properties, but, more importantly, evidence for how much ash, and thus Ca, is needed to correct this problem.
ASHMuskoka is a three-year project of the Friends of the Muskoka Watershed funded by the Ontario Trillium Foundation. Its three main objectives are:
To conduct this work we are working in partnership with the District Municipality of Muskoka, the MECP’s Dorset Environmental Science Centre, the Muskoka Steamship and Discovery Centre, and researchers and their students from Laurentian and Trent universities and the University of Victoria. The ash is being collected from hundreds of local wood burners, and will be added in two stages. In the fall of 2019 we spread ash on forest soils in three Muskoka sugar bushes, to learn how much ash is needed to restore an entire block of forest. This larger demonstration is our plan for 2021.
In Muskoka, we generate 100s of tonnes of ashes in our wood stoves and fireplaces every heating season. The ashes left over are a waste product, but they could be a local solution to the calcium decline problem, because they are roughly 30% calcium (Ca) by weight. Given that we lost half a tonne of Ca per hectare (ha) of soil over the last century, roughly 1.7 tonnes of wood ash per ha should provide all the Ca that was typically lost to acid rain, assuming it all becomes available where we spread it. (We might need more as it likely won’t all become available and won’t all stay put.) This “waste” ash can be re-purposed to solve the Ca decline problem, closing a recycling loop, i.e. the calcium in our fire wood came from the soil in the first place, and we would be returning it to the soil in the form of ash, hopefully restoring normal growth of the forest, and leaving enough Ca left over to restore levels in ground water.