Effects of climate warming are apparent in lake ecosystems evidenced by rising water temperatures and shorter duration in ice cover. Modeling exercises, studies of anomalous weather years, and examination of lakes across latitudinal gradients suggest that changes in temperature will result in changes in the physical structure of lakes, nutrient cycling, phenology, water quality and habitat availability. Yet, few studies can empirically document the effects of warming trends on physical, chemical and biological aspects of the system. Here we present a long-term record from Lake Mendota of changes in ice cover, physical characteristics, phosphorus dynamics and water quality metrics that provides evidence of the link between changes in chemical and biological variables and changes in the physical characteristics of the lake. We also examine the effects of changes in physical and chemical variables on the general water quality characteristics of the lake.
Results/Conclusions
Temporal trends show a decline in ice cover and concurrent increases in strength and duration of stratification. At the same time, we observed significant increases in phosphorus concentrations and anoxic conditions in the hypolimnion. The trends in phosphorus and oxygen conditions were likely due to a common relationship with increasing stability and length of stratification over time. Changes in the physical and chemical features of the lake were tied to changes in water quality. We observed a significant improvement in water clarity over time, and a significant relationship between Secchi depth readings and stability of the water column. Thus, our study provides empirical evidence of changing physical conditions in a deep dimictic lake and demonstrates that these physical changes have implications for the distribution of solutes and the trajectory of water quality in lakes.
