High-elevation mountain lakes are sensitive to environmental change, making them ideal ecosystems for studying the effects of global change. Over the past several decades, lakes in the Southern Rocky Mountains have experienced major environmental changes, including warming air temperatures, increasing droughts, and decreasing air pollutants. Air pollutants like nitrogen and sulfate can travel long distances and deposit in mountain lakes, potentially altering lake chemistry. Warming and drought can also change lake chemistry by altering internal processes, concentrating pollutants and nutrients, and accelerating glacial melt. We investigated whether these changes have affected water chemistry in lakes across the Southern Rocky Mountains. Across 40 years, we found that most lakes have experienced changes in their chemistry. However, despite similar trends in climate and air pollutants regionally, not all lakes respond similarly. For example, while sulfate pollution has declined, some lakes have experienced increasing sulfate levels.

Overall, we found that a combination of climate, air pollution, and landscape all interact to shape unique trends in chemistry at each lake, sometimes in ways that differ from what we might expect based on broader regional patterns. Regional monitoring is essential for understanding what drives long-term changes in these sensitive ecosystems and informing effective management strategies.