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.