Nonlinear water clarity trends and impacts on littoral area in Minnesota lakes

Lake water clarity is an indicator of water quality, trophic status, and habitat condition. Changes in clarity impact lake ecosystems and may reflect land use changes or presence of invasive species. Quantifying temporal changes in water clarity can be challenging because clarity varies seasonally, annually, and spatially within and among lakes. We developed a hierarchical generalized additive model to quantify trends in water clarity (Secchi depth) from 1979 to 2018 for 909 Minnesota lakes, accounting for seasonal and spatial variability. Water clarity increased by 0.41 m across lakes from 1984 to 1988 and 2014 to 2018. Lake-specific clarity trends varied: clarity did not change significantly in 59.0% of lakes, increased in 34.5% of lakes, and decreased in 6.5% of lakes. Water clarity dynamics caused considerable variability in littoral area between seasons and years. Our results have wide applications in aquatic ecology, including understanding changes to food webs, assessing fish habitat, and evaluating impacts of invasive species.

Automated summary

Lake water clarity is an important indicator of water quality, trophic status, and habitat condition. A study conducted on 909 Minnesota lakes from 1979 to 2018 showed that water clarity increased across lakes from 1984 to 1988 and 2014 to 2018. However, there was significant variation in clarity trends among lakes, with some lakes showing no change and others experiencing increases or decreases in clarity. The study highlights the importance of understanding water clarity dynamics in aquatic ecology for various purposes such as assessing fish habitat and evaluating the impacts of invasive species.