Calcium in the envionment: the highs and the lows

钙（Ca）是陆地和水生生物群大量需要的基本元素。最近的观察表明，加拿大许多湖泊的钙浓度正在下降，经常接近或超过水生生物群的临界生物阈值。令人困惑的是，目前的生物地球化学模型表明，湖泊目前正在恢复到工业化前的状态，而古模型表明，目前湖泊中的钙浓度比以往任何时候都低。森林土壤中钙浓度的降低也可能导致森林生产力和森林健康的下降。然而，在其他地区，如阿尔伯塔省的阿萨巴斯卡油砂（AOSR），工业活动导致大气中钙沉积的急剧增加，这可以有效地改变自然酸性森林土壤的化学成分，并可能造成破坏性的生态后果。这项研究将使用最先进的技术和新颖的实验研究来填补评估加拿大环境中钙浓度变化的影响所需的知识空白。具体来说，本研究项目将研究安大略省低钙前寒武纪盾区(a)的钙生物地球化学，在那里，提高对矿物风化速率的了解是预测未来土壤和水中钙水平的必要条件；(b)同样低钙的AOSR，在那里，钙富集的相反问题需要进一步研究。为了评估风化变化是否已经或将会发生，将使用土壤测量和同位素分析相结合来量化富钙矿物（如磷灰石）对湖泊和土壤钙水平的重要性。将评估湖泊沉积物岩心和树木年轮岩心，以确定同位素变化是否与过去100-200年间磷灰石等矿物的减少相一致。这些信息将用于改进生物地球化学模型中使用的风化速率，以预测未来在各种管理和大气沉积情景下的Ca水平。在缺钙环境中，凋落物是土壤钙水平的最大年度贡献者。为了评估土地利用变化是否对观测到的钙下降有所贡献，将在野外和实验室研究中将糖枫林下（当前）的钙循环与松林林下（历史）的钙循环进行比较，以评估从低钙需求物种（以及低钙凋落物对土壤的输入）到高钙需求物种的森林组成变化的影响。为了解决油砂排放引起的钙沉积升高的问题，将进行实地调查，以评估钙沉积增加对土壤化学和植物/树木健康的影响。这两项研究的结合将使人们对钙的生物地球化学有更深入的了解，这对保护加拿大北方生态区的广大地区是必要的。

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.