Long‐Term Trends in Productivity Across Intermountain West Lakes Provide No Evidence of Widespread Eutrophication

Abstract

Eutrophication represents a major threat to freshwater systems and climate change is expected to drive further increases in freshwater primary productivity. However, long‐term in situ data is available for very few lakes and makes identifying trends and drivers of eutrophication challenging. Using remote sensing data, we conducted a retrospective analysis of long‐term trends in trophic status among lakes greater than 10 ha across the Intermountain West, a region with understudied water quality trends and limited long‐term data sets. We found that most lakes (55%) were not exhibiting shifts in trophic status from 1984 to 2019. Our results also show that increases in eutrophication were rare (3% of lakes) during this period, and that lakes becoming increasingly oligotrophic were more common (17% of lakes). Lakes that were not trending occupied a wide range of lake and landscape characteristics, whereas lakes that were becoming more oligotrophic tended to have larger residence times and were located in catchments with greater clay content and more development. Our results highlight that while there are well‐established narratives that climate change can lead to more eutrophication of lakes, this is not broadly observed in our data set, where we found more lakes in the Intermountain West becoming more oligotrophic than lakes becoming eutrophic.