Natural controls on phosphorus concentrations in small Lakes in Central Alberta, Canada

Small lakes can act as environmental sensors for understanding regional hydrogeological conditions and elemental cycles. Because of their small size, they react quickly to changes in nutrient runoff, groundwater exchange and climate. In the post-glacial landscape of Alberta, the Carvel Pitted Delta harbours a variety of small lakes, which, despite being close together, can have markedly different chemistries and nutrient characteristics. Here, we focused on nine lakes with surface areas <10 ha and maximal depths ranging from 5 to 18 m. We hypothesised that differences in their trophic states are caused by variations in Ca concentrations, controlled by groundwater inputs. All lakes tended toward permanent stratification due to small mixing depths (1.6–2.4 m). The deeper lakes were oligotrophic with high concentrations of Ca and a high fraction of phosphorus (Ca-bound P) in the sediments (HCl extractable fraction). A correlation was found between Ca-bound P and aqueous Ca concentrations at 0.5 m depth, suggesting that P stability could be estimated based on surface water chemistry. Calcium was shown to be concentrated in groundwater located above the bedrock, suggesting that groundwater inputs controlled Ca concentrations in the lakes. We conclude that the hydrogeological conditions and Ca inputs act as natural regulators for P availability and, by extension, water quality in these lakes.

小型湖泊可作为环境传感器，助力解析区域水文地质条件与元素循环过程。由于体量小巧，它们对营养盐径流、地下水交换及气候变化的响应极为迅速。在阿尔伯塔省（Alberta）的冰后地貌景观中，卡尔韦尔坑洼三角洲（Carvel Pitted Delta）分布着众多小型湖泊；尽管彼此邻近，这些湖泊的化学特征与营养盐特性却存在显著差异。本研究聚焦于9座表面积小于10公顷、最大水深介于5至18米的湖泊。我们提出研究假设：湖泊营养状态的差异由钙（Ca）浓度变化所驱动，而钙浓度受地下水补给量调控。由于混合深度仅为1.6至2.4米，所有湖泊均呈现永久性分层特征。水深较深的湖泊为贫营养型，其水体钙浓度较高，且沉积物中钙结合态磷（Ca-bound P，即盐酸可提取组分）占比更高。研究发现，0.5米水深处的水体钙浓度与钙结合态磷之间存在相关性，这表明可通过地表水化学特征估算磷的稳定性。研究表明，基岩上方的地下水中钙元素富集，由此证明地下水补给量调控了湖泊内的钙浓度。综上，本研究认为水文地质条件与钙补给量是调控这些湖泊磷生物有效性乃至整体水质的天然因素。