In situ measurements of sediment-water oxygen fluxes conducted in a riverine lake during different seasons were analyzed with the aim of quantifying the combined effects of hydrodynamic forcing and seasonal changes in temperature on sediment oxygen uptake rate. Oxygen fluxes measured using the eddy correlation (EC) technique varied widely between -6.4 and -84 mmol m -2 day -1 , while variations observed on hourly time scales were of comparable magnitude to seasonal variations. Oxygen fluxes were most strongly correlated to current speed in the benthic boundary layer and water depth, which both co-varied with discharge, temperature, and oxygen concentration. A direct correlation of measured fluxes with temperature and corresponding seasonal flux variations could not be observed. To explore the potential effect of temperature on oxygen fluxes, we applied a simplified analytical model, which couples the effect of hydrodynamic forcing with a temperature-dependent oxygen consumption rate within the sediment. The results suggest that the flux is a non-linear function of both variables and both can have comparable effects on the magnitude of the oxygen fluxes. The model confirms our observation that short-term variations of oxygen fluxes in response to hydrodynamic forcing can mask longer-term seasonal variations driven by temperature. The model further indicates that the magnitude and form of the temperature dependence of oxygen uptake and mineralization rates in freshwater sediments obtained from laboratory incubations can be strongly affected by flow conditions during incubations. We conclude that predictions of oxygen uptake and mineralization rates under changing climatic conditions should also take potential changes of flow conditions into account.

science projects, but also data providers, relatively early on. However, at the core and perhaps the most important factor contributing to the successful continuity of this project, is the dedication and engagement of the CLIC community scientists. We are incredibly fortunate that our community scientists are passionate and supportive of this work.To date, this project has collected over 52,500 lake ice phenology observations for 1008 lakes, and involved 935 monitors over the years (Fig. 3). As we work toward organizing these vast datasets, we look forward to exploring important questions on how climate change is affecting lake ice phenology across small and large lakes in the United States and identifying which lakes are most vulnerable to rapid ice loss. AUTHOR CONTRIBUTIONSS conceived the idea and led the project. SS and LSL wrote the first draft. KB created figure 3. LSL, AB, KB, KS, DB, GB, and SS helped conceptualize the survey questions for the community scientists, contextualize the historical aspects of the project, and edited the manuscript. ACKNOWLEDGMENTSFirst and foremost, the authors are indebted to the participants and citizen scientists from the Community Lake Ice Collaboration for their dedication and enthusiastic efforts to collect lake ice phenology data from their local lakes over the past 30 years.