Carbon dioxide supersaturation in Florida lakes

We examined data on CO2 and related limnological and geographic information from a sample of 948 Florida freshwater lakes. The objectives for this study were (1) to determine the partial pressures of carbon dioxide (ρCO2) in the surface waters of a large sample of Florida lakes, (2) to determine if several limnological or geographic factors are related to levels of ρCO2 in Florida lakes, and (3) to estimate the net annual rate of loss of CO2 to the atmosphere from the freshwater lakes of Florida. The calculated ρCO2 for the lakes in our sample range from 0 to 81,000 μatm, with a mean of 3,550 μatm, a median of 1,030 μatm, and a geometric mean of 1,270 μatm. About 87% of the Florida lakes were supersaturated with CO2. There were statistically significant correlations between values for ρCO2 and several water chemistry variables; however, the R2 values were small and accounted for only a small portion of the variance. In general the ρCO2 values were higher in the lakes with low alkalinities and low contents of dissolved salts. The best predictor of ρCO2 is pH, with an R2 of 0.82 for a polynomial relationship. The ρCO2 values tend to decrease from northwest to southeast across the state of Florida, which corresponds to the gradients we found for pH, alkalinity, and specific conductance. The average areal rate of carbon emission from the Florida lakes was 328 g C m−2 y−1, and the total carbon loss for the lakes and ponds of Florida was 2.0 Tg y−1. This amounts to about 2% of the total carbon emissions from all the lakes of the world as estimated by previous studies.