Synchronous behavior of temperature, calcium, and chlorophyll in lakes of northern Wisconsin

The degree to which a variable's dynamics are synchronized among a set of neighboring lakes indicates the relative influence of regional climate variability. Furthermore, by determining which lakes tend to be most synchronous in their response to climate we can deduce the primary ways that climate influences the dynamics of the variable in question. In this study, we look for evidence of synchrony in the temperature, calcium, and chlorophyll dynamics of seven neighboring northern Wisconsin lakes. Our goals were to assess the influence of climate on dynamics of these variables and the effect of lake basin properties on their response to climate signals. Synchrony was measured as the r² value from a regression relating observations of a variable in one lake against simultaneous observations of the same variable in another. Temperature was the most synchronous variable, with all pairs displaying significant synchrony. Calcium was also highly synchronous, with 15 of the 21 lake pairs exhibiting significant synchrony. Chlorophyll was significantly synchronous for 11 of the 21 lake pairs, but only three pairs exhibited r² > 0.50. Lakes that were most similar in water clarity and average epilimnetic depth were most synchronous in temperature. Calcium was most synchronous among lakes occupying similar positions in the groundwater flow system, as expected from the control of calcium by groundwater flow paths. Synchrony of chlorophyll was highest for lakes with similar degrees of thermal stratification, suggesting that internal supplies of nutrients are an important determinant of interannual variability. The importance of ground- or bogwater flow to interannual chlorophyll dynamics is also suggested by the systematic asynchrony of chlorophyll for the clear-water lake that receives the least groundwater discharge. Our results show that climate imposes a strong synchrony on the behavior of three very different properties of the study lakes. Furthermore, the lakes differed predictably in their response to the same regional climate trends. Surprisingly, the differences between average synchrony observed for the three variables we considered were largely due to the diversity of the study lakes, rather than the disproportionate sensitivity of chlorophyll to local stochastic effects.