228-4 Sediment Associations Limit Phosphorus Availability in Alpine Lakes of the Canadian Rockies National Parks

Session: Advances in Mountain Hydrology: Connecting Cryosphere, Surface, and Subsurface Processes (Posters)

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Abstract:

Primary productivity in many alpine lakes in Banff and Yoho National Parks (BYNP) of the Canadian Rockies is limited by bioavailable phosphorus, differing from nitrogen limitation in many other alpine regions. Phosphorus associates with particulate calcium, aluminum, and iron that can remove bioavailable phosphorus from the water column and sequester it in the sediment, reducing availability. We sampled eight small alpine lakes and ponds and one spring in BYNP during the summer of 2024 to evaluate water and sediment chemistry. These lakes have very low total phosphorus concentrations (most <10µg/L); seven are P-limited and one is co-N,P-limited as estimated by the ratio of dissolved inorganic nitrogen to total phosphorus. Carbonate bedrock dominates the catchments of four lakes and geochemical modeling of preliminary water column data suggests calcite saturation. The catchments of the others are dominantly siliciclastic rocks and geochemical modeling indicates they are unsaturated with respect to calcite. The spring flows from siliciclastic rocks and modeling indicates saturation with basaluminite, an aluminum sulfate mineral likely derived from sulfate oxidation. We hypothesize that calcite and basaluminite, or associated aluminum minerals, cause low total phosphorus by removing phosphorus from the water column and forming stable sediment associations that control nutrient limitation in the water column. Organic and inorganic Ca, Fe, and Al-bound P in the sediment were determined using a modified EDTA sequential extraction. Preliminary data show that three lakes have more Ca-bound P than Fe-bound; all were identified as calcite saturated. The three lakes with the most phosphate extracted (>600µg/g) had more Fe-bound P than the other lakes. Sediment extractions are ongoing and additional results, including for the Al-bound fraction, will be presented. Ca and Al-associated P are considered stable and require drastic changes to lake conditions for release. Sediments with Fe-P associations are sensitive to changes in redox conditions that can cause P release, making them less stable. This research will provide insight into the stability of phosphorus in these alpine lakes as they experience environmental changes and the likelihood of shifts in nutrient limitation. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9867

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