WHAT ARE THE GEOCHEMICAL CONTROLS ON PHOSPHORUS AVAILABILITY IN ALPINE LAKES OF THE CANADIAN ROCKIES?

Primary productivity of many alpine lakes in the Canadian Rockies is limited by bioavailable phosphorus, which differs from many other alpine regions that are limited by nitrogen. The changing climate has led to a recent increase in wildfires that may increase atmospheric P deposition and could alter lake nutrient availability. We hypothesize that associations of P with calcium from carbonate bedrock limits bioavailable P. We collected water and sediment samples from nine alpine and subalpine lakes in the Canadian Rockies in 2024 to evaluate the associations of P in these samples and water chemistry. To our knowledge, lake sediment P associations in this region have not previously been reported. We evaluated nutrient limitation using the ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) as a surrogate for bioassay experiments. Preliminary data show that of these lakes, only one is co-limited while the other eight are P-limited. Photic zone water samples of each lake show that seven of nine lakes have a mean TP ≤ 10µg-P/L and DIN ≥ 85µg-N/L. To contextualize our data, we compare our samples with nutrient data of seven lakes from 2007. These initial data indicate a potentially large increase in DIN in two of the lakes, while TP has remained approximately constant. Five of the lakes show that there have been little change in nutrient concentrations. We will analyze surface sediment samples by sequential extraction to empirically evaluate the percentage of Ca, Fe, or organic C associated P. In this presentation, we will discuss the differences in P associations and what this indicates for storage of P and the sensitivities of these lakes to climatic and nutrient changes.