To evaluate boreal peatland C losses from warming, novel technologies were used to expose intact bog plots in northern Minnesota to a range of future temperatures (+0°C to +9°C) with and without elevated CO₂ (eCO₂). After 3 years, warming linearly increased net C loss at a rate of 31.3 g C·m⁻²·year⁻¹·°C⁻¹. Increasing losses were associated with increased decomposition and corroborated by measures of declining peat elevation. Effects of eCO₂ were minor. Results indicate a range of C losses from boreal peatlands 4.5 to 18 times faster than historical rates of accumulation, with substantial emissions of CO₂ and CH₄ to the atmosphere. A model of peatland C cycle captured the temperature response dominated by peat decomposition under ambient CO₂, but improvements will be needed to predict the lack of observable responses to elevated CO₂ concentrations thus far.

Emissions of CO₂ and CH₄ from freshwater reservoirs constitute a globally significant source of atmospheric greenhouse gases (GHGs), but knowledge gaps remain with regard to spatiotemporal drivers of emissions. We document the spatial and seasonal variation in surface diffusion of CO₂ and CH₄ from Douglas Lake, a hydropower reservoir in Tennessee, USA. Monthly estimates across 13 reservoir sites from January to November 2010 indicated that surface diffusions ranged from 236 to 18,806 mg·m⁻²·day⁻¹ for CO₂ and 0 to 0.95 mg·m⁻²·day⁻¹ for CH₄. Next, we developed statistical models using spatial and physicochemical variables to predict surface diffusions of CO₂ and CH₄. Models explained 22.7% and 20.9% of the variation in CO₂ and CH₄ diffusions respectively, and identified pH, temperature, dissolved oxygen, and Julian day as the most informative predictors. These findings provide baseline estimates of GHG emissions from a reservoir in eastern temperate North America, a region for which estimates of reservoir GHGs emissions are limited. Our statistical models effectively characterized non-linear and threshold relationships between physicochemical predictors and GHG emissions. Further refinement of such modeling approaches will aid in predicting current GHG emissions from unsampled reservoirs and forecasting future GHG emissions.

During August–September 2012, we sampled six hydropower reservoirs in southeastern United States for CO₂ and CH₄ emissions via three pathways: diffusive emissions from water surface; ebullition in the water column; and losses from dam tailwaters during power generation. Estimates of average areal emission rates of CO₂ attributable to the six reservoirs (i.e., reservoir plus tailwater emissions) ranged from 994 to 2760 mg·m⁻²·day⁻¹, which is low to moderate compared to CO₂ emissions rates reported for tropical hydropower reservoirs and boreal ponds and lakes, and similar to rates reported for other temperate reservoirs. Similar average rates for CH₄ were also relatively low, ranging from 6 to 187 mg·m⁻²·day⁻¹. On a whole-reservoir basis, estimates of total emissions of CO₂ ranged 10-fold, from 42,740 kg per day for Fontana to 501,151 kg per day for Guntersville, and total emissions of CH₄ ranged over 30-fold, from 251 kg per day for Fontana to 9153 kg per day for Allatoona. Emissions through the tailwater pathway varied among reservoirs, comprising from 19% to 65% of total CO₂ emissions and 0% to 84% of CH₄ emissions, depending on the reservoir. Emission rates were significantly correlated with several reservoir morphological and water quality characteristics, including metrics related to vertical stratification (e.g., minimum water column temperature and maximum dissolved oxygen) and reservoir productivity (e.g., water transparency and chlorophyll a concentration).