Short- and Long-Term Mechanisms for Increasing Inputs of Phosphorus in Mountain Waterbodies of Northeastern Utah, USA

Phosphorus is an essential nutrient that allows life in water to flourish, but changes in phosphorus supplies are not well understood in remote watersheds. In mountain environments, remote watersheds contain critical high-quality water supplies and unique ecosystems, but excess phosphorus can diminish water quality by producing unfavorable aquatic species. Therefore, observed trends of increasing phosphorus concentrations in remote lakes and rivers in the US over the last two decades are a significant concern. Using the Uinta Mountains as a case study, we evaluated three different direct and indirect pathways for phosphorus increases in remote mountain watersheds that may explain observed increases over the last two decades. These mechanisms include atmospheric deposition of dust enriched in phosphorus and changing soil conditions (i.e., increasing soil temperatures and increasing soil pH), leading to greater land exports of phosphorus from runoff or erosion. In the Uinta Mountains, dust had concentrations of phosphorus considered biologically available and could be contributing 4.9 to 17.7 mg P m-2 yr-1, This likely represents an important source of phosphorus to this area. Also, greater release of SRP from soils incubated at the higher temperatures suggests climate change may further increase phosphorus concentrations in the future. Given the lack of historical acidification in the Uinta mountains, changing pH conditions are not likely to be a factor driving phosphorus increases in this system, but could potentially be in other alpine systems. This study highlights the importance of identifying local variables in discerning significant sources of phosphorus and disparages a single explanation for national increases in phosphorus in remote systems