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 n eighboring lakes indicates the relative influence of regional climate varia bility. Furthermore, by determining which lakes tend to be most synchronous in their response to climate we can deduce the primary ways that climate i nfluences the dynamics of the variable in question. In this study, we look for evidence of synchrony in the temperature, calcium, and chlorophyll dyna mics of seven neighboring northern Wisconsin lakes. Our goals were to asses s 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 r(2) value from a regression relating observations of a var iable in one lake against simultaneous observations of the same variable in another. Temperature was the most synchronous variable, with all pairs dis playing significant synchrony, Calcium was also highly synchronous, with 15 of the 21 lake pairs exhibiting significant synchrony. Chlorophyll was sig nificantly synchronous for 11 of the 21 lake pairs, but only three pairs ex hibited r(2) > 0.50. Lakes that were most similar in water clarity and aver age epilimnetic depth were most synchronous in temperature. Calcium was mos t synchronous among lakes occupying similar positions in the: groundwater h ow system, as expected from the control of calcium by groundwater flow path s. Synchrony of chlorophyll was highest for lakes with similar degrees of t hermal stratification, suggesting that internal supplies of nutrients are a n important determinant of interannual variability. The importance of groun d- or bogwater flow to interannual chlorophyll dynamics is also suggested b y the systematic asynchrony of chlorophyll for the clear-water lake that re ceives the least groundwater discharge. Our results show that climate impos es a strong synchrony on the behavior of three very different properties of the study lakes. Furthermore, the lakes differed predictably in their resp onse to the same regional climate trends. Surprisingly, the differences bet ween average synchrony observed for the three variables we considered were largely due to the diversity of the study lakes, rather than the disproport ionate sensitivity of chlorophyll to local stochastic effects.