Control of dissolved oxygen in northern temperate lakes over scales ranging from minutes to days

Dissolved oxygen (DO) observations from in situ sensors show complex temporal pat- terns, suggesting that the balance of control by underlying processes changes across scales. At scales ranging from minutes to days, a number of physical and biological processes, such as internal waves, mixing, and ecosystem metabolism, may impart pattern on observed DO. In discriminating the con- trol over DO variability by scale, this helps us to reduce uncertainty in estimates of important eco- system rates, such as gross primary production and respiration. In this study, we examined DO vari- ability over scales ranging from minutes to days and assessed the relative contributions from several physical and biotic drivers. High frequency measurements of DO, wind, temperature, and photosyn- thetically available radiation (PAR) were obtained over periods of approximately 4 d from 25 lakes in northern Wisconsin. Patterns in data were isolated by time scale through wavelet transforms. A suite of predictors were related to DO across time scales using artificial neural networks. At the diel scale, PAR explained most of the variability in DO signals. At sub-diel scales, temperature and wind largely explained variability in DO. However, the nature, strength, and time scale of the relationships between drivers and DO may be a function of lake size.