Calcium in the envionment: the highs and the lows

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Calcium (Ca) is an essential element required in large amounts by terrestrial and aquatic biota. Recent observations have shown that Ca concentrations are falling in many Canadian lakes, often approaching or exceeding reported critical biological thresholds for aquatic biota. Perplexingly, current biogeochemical models suggest that lakes are currently returning to their pre-industrial state whereas paleo-models suggest current Ca concentrations in lakes are lower than ever before. Decreasing Ca concentrations in forest soils may also lead to decreased forest productivity and forest health. Yet, in other regions, such as the Athabasca Oil Sands (AOSR) in Alberta, industrial activities have resulted in an enormous increase in atmospheric Ca deposition, which can effectively change the chemical composition of naturally acidic forest soils with potentially damaging ecological consequences. This research will use state-of-the-art techniques and novel experimental studies to fill knowledge gaps that are required to evaluate the impacts of changing Ca concentrations in Canada's environment. Specifically, this research program will investigate Ca biogeochemistry in both the (a) low-Ca Precambrian Shield region of Ontario, where improved understanding of mineral weathering rates is necessary to predict future Ca levels in soils and waters, and (b) the equally low-Ca AOSR, where the opposite problem of Ca enrichment requires further study. To evaluate whether changes in weathering have or will occur, soil measurements combined with isotopic analyses will be used to quantify the importance of Ca-rich minerals such as apatite to lake and soil Ca levels. Lake sediment cores and tree ring cores will be evaluated to determine whether isotopic changes consistent with decreases in minerals such as apatite are evident over the past 100-200 years. This information will be used to refine weathering rates that are used in biogeochemical models to predict future Ca levels under various management and atmospheric deposition scenarios. In Ca-poor environments litter fall is the single largest annual contributor to soil Ca levels. To evaluate whether land use change has contributed to the observed Ca decline comparisons of Ca cycling under sugar maple stands (current) will be compared with Ca cycling under pine stands (historic) in field and laboratory studies to evaluate the impact of changing forest composition from species with low Ca requirements (and low Ca litter inputs to soil) to one with high Ca requirements. To address concerns over elevated Ca deposition originating from Oil sands emissions a field survey will be used to evaluate the impact of increased a deposition on soil chemistry and plant/tree health. Combined this research will result in a greater understanding of Ca biogeochemistry, which is necessary to protect vast regions of Canada's Boreal Eco zone.