Evapotranspiration rates (ET) from contrasting Wisconsin bogs (one forested bog, one open bog)were compared over 4 years by analyzing diel oscillations of their water tables. Daily rates of ET from peatlands were also compared to rates of evaporation (E) from encircled bog ponds. We hypothesized that ET would be higher in the forested bog due to the greater leaf area index of forest canopy relative to moss and ericaceous shrubs. We also hypothesized that ET in peatlands would exceed the physical process of E from encircled ponds. Field data supported the first hypothesis, but the second only proved true for the forested peatland. Daily estimates of peatland ET varied widely, ranging from~1 to >10 mm/d; but average ET was higher in the forested peatland (4.04 vs. 3.09 mm/d; p < .01). Average ET in the forested peatland was also higher than E during summer (4.04 vs. 3.31 mm/d; p < .05); whereas in the open peatland, average ET was slightly lower than E for all measured seasons (p < .01). Methodologically, the performance of three equations used to estimate ET from daily water table fluctuations was similar. The specific yield of peat (S*y), which is a critical variable in all three equations, was found to be an exponential function of water table depth; and absent an empirically derived S*y, errors in estimates of peatland ET can be large. Given landscape composition across this northern temperate region (13% lakes, 20% peatland, and 54% upland forest) and estimates of forest ET gleaned from the literature, our findings suggest that the regional feedback of water to the atmosphere increases from open waters to peatlands to upland forest, consistent with prior observations that the biological process of transpiration dominates continental ET.

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The in vivo fluorescence (IVF) of photosynthetic pigments is used widely as a proxy for phytoplankton biomass in fresh and marine waters. Although fluorescence intensity is known to decrease with rising temperature for many fluorophores, temperature quench is rarely accounted for in field studies of plankton IVF. Here, we quantified the effect of temperature on in vivo chlorophyll and phycocyanin fluorescence in the laboratory (∼ 5°C to 30°C), and we derived temperature compensation equations for IVF sensors commonly used in freshwaters. The equations reference measured fluorescence to a standard temperature, and they have the same linear form as the equation derived in an earlier study of chromophoric dissolved organic matter fluorescence: Fr = Fm/(1 + ρ(Tm – Tr)), where F is fluorescence intensity (RFU, relative fluorescence units), T is temperature (°C), ρ is the temperature coefficient at a given reference temperature (°C−1), and the subscripts r and m stand for the reference and measured values. At a reference temperature of 20°C, the temperature coefficients (ρ) for chlorophyll and phycocyanin in Wisconsin lake waters ranged from −0.008°C−1 to −0.012°C−1 and −0.006°C−1 to −0.012°C−1, respectively. For chlorophyll in a pure culture of the green alga Scenedesmus dimorphus, the value for ρ was similar to the value in natural assemblages, averaging −0.018 ± 0.003°C−1; but for phycocyanin in the blue‐green alga Synechococcus leopoliensis it was lower (more negative), averaging −0.034 ± 0.003°C−1. This disparity notwithstanding, we conclude that temperature compensation is an important component of IVF monitoring.