Dust mediated transfer of phosphorus to alpine lake ecosystems of the Wind River Range, Wyoming, USA

Abstract

Alpine lakes receive a large fraction of their nutrients from atmospheric sources and are consequently sensitive to variations in both the amount and chemistry of atmospheric deposition. In this study we explored the spatial changes in lake water chemistry and biology along a gradient of dust deposition in the Wind River Range, Wyoming. Regional differences were explored using the variation in bulk deposition, lake water, sediment, and bedrock geochemistry and catchment characteristics. Dust deposition rates in the Southwestern region averaged 3.34 g m⁻² year⁻¹, approximately three times higher than deposition rates in the Northwestern region (average 1.06 g m⁻² year⁻¹). Dust-P deposition rates ranged from 87 µg P m² day⁻¹ in the Northwestern region to 276 µg P m² day⁻¹ in the Southwestern region. Subalpine and alpine lakes in the Southwestern region had greater total phosphorus (TP) concentrations (5–13 µg L⁻¹) and greater sediment phosphorus (SP) concentrations (2–5 mg g⁻¹) than similar lakes elsewhere in the region (1–8 µg L⁻¹ TP, 0.5–2 mg g⁻¹ SP). Lake phosphorus concentrations were related to dissolved organic carbon (DOC) across vegetation gradients, but related to the percent of bare rock, catchment area to lake area, and catchment steepness across dust deposition gradients. Modern phytoplankton and zooplankton biomasses were two orders of magnitude greater in the Southwest than in the Northwest, and alpine lakes in the Southwest had a unique diatom species assemblage with relatively higher concentrations of Asterionella formosa, Pseudostaurosira pseudoconstruens, and Pseudostaurosira brevistriata. These results suggests that catchment controls on P export to lakes (i.e. DOC) are overridden in dominantly bare rock basins where poor soils cannot effectively retain dust deposited P.