Inland waters are one of the largest natural sources of methane (CH₄), a potent greenhouse gas, but emissions models and estimates were developed for solute-poor ecosystems and may not apply to salt-rich inland waters. Here we combine field surveys and eddy covariance measurements to show that salinity constrains microbial CH₄ cycling through complex mechanisms, restricting aquatic emissions from one of the largest global hardwater regions (the Canadian Prairies). Existing models overestimated CH₄ emissions from ponds and wetlands by up to several orders of magnitude, with discrepancies linked to salinity. While not significant for rivers and larger lakes, salinity interacted with organic matter availability to shape CH₄ patterns in small lentic habitats. We estimate that excluding salinity leads to overestimation of emissions from small Canadian Prairie waterbodies by at least 81% ( ~ 1 Tg yr⁻¹ CO₂ equivalent), a quantity comparable to other major national emissions sources. Our findings are consistent with patterns in other hardwater landscapes, likely leading to an overestimation of global lentic CH₄ emissions. Widespread salinization of inland waters may impact CH₄ cycling and should be considered in future projections of aquatic emissions.

Many peatlands have been drained and harvested for peat mining, agriculture, and other purposes, which has turned them from carbon (C) sinks into C emitters. Rewetting of disturbed peatlands facilitates their ecological recovery and may help them revert to carbon dioxide (CO₂) sinks. However, rewetting may also cause substantial emissions of the more potent greenhouse gas (GHG) methane (CH₄). Our knowledge of the exchange of CO₂ and CH₄ following rewetting during restoration of disturbed peatlands is currently limited. This study quantifies annual fluxes of CO₂ and CH₄ in a disturbed and rewetted area located in the Burns Bog Ecological Conservancy Area in Delta, BC, Canada. Burns Bog is recognized as the largest raised bog ecosystem on North America's west coast. Burns Bog was substantially reduced in size and degraded by peat mining and agriculture. Since 2005, the bog has been declared a conservancy area, with restoration efforts focusing on rewetting disturbed ecosystems to recover Sphagnum and suppress fires. Using the eddy covariance (EC) technique, we measured year-round (16 June 2015 to 15 June 2016) turbulent fluxes of CO₂ and CH₄ from a tower platform in an area rewetted for the last 8 years. The study area, dominated by sedges and Sphagnum, experienced a varying water table position that ranged between 7.7 (inundation) and −26.5 cm from the surface during the study year. The annual CO₂ budget of the rewetted area was −179 ± 26.2 g CO₂–C m⁻² yr⁻¹ (CO₂ sink) and the annual CH₄ budget was 17 ± 1.0 g CH₄–C m⁻² yr⁻¹ (CH₄ source). Gross ecosystem productivity (GEP) exceeded ecosystem respiration (R_e) during summer months (June–August), causing a net CO₂ uptake. In summer, high CH₄ emissions (121 mg CH₄–C m⁻² day⁻¹) were measured. In winter (December–February), while roughly equal magnitudes of GEP and R_e made the study area CO₂ neutral, very low CH₄ emissions (9 mg CH₄–C m⁻² day⁻¹) were observed. The key environmental factors controlling the seasonality of these exchanges were downwelling photosynthetically active radiation and 5 cm soil temperature. It appears that the high water table caused by ditch blocking suppressed R_e. With low temperatures in winter, CH₄ emissions were more suppressed than R_e. Annual net GHG flux from CO₂ and CH₄ expressed in terms of CO₂ equivalents (CO₂ eq.) during the study period totalled −22 ± 103.1 g CO₂ eq. m⁻² yr⁻¹ (net CO₂ eq. sink) and 1248 ± 147.6 g CO₂ eq. m⁻² yr⁻¹ (net CO₂ eq. source) by using 100- and 20-year global warming potential values, respectively. Consequently, the ecosystem was almost CO₂ eq. neutral during the study period expressed on a 100-year time horizon but was a significant CO₂ eq. source on a 20-year time horizon.

A short, but severe, wildfire smoke episode in July 2015, with an aerosol optical depth (AOD) approaching 9, is shown to strongly impact radiation budgets across four distinct land-use types (forest, field, urban and wetland). At three of the sites, impacts on the energy balance are also apparent, while the event also appears to elicit an ecosystem response with respect to carbon fluxes at the wetland and a forested site. Greatest impacts on radiation and energy budgets were observed at the forested site where the role of canopy architecture and the complex physiological responses to an increase in diffuse radiation were most important. At the forest site, the arrival of smoke reduced both sensible and latent heat flux substantially but also lowered sensible heat flux more than the latent heat flux. With widespread standing water, and little physiological control on evapotranspiration, the impacts on the partitioning of turbulent fluxes were modest at the wetland compared to the physiologically dominated fluxes at the forested site. Despite the short duration and singular nature of the event, there was some evidence of a diffuse radiation fertilization effect when AOD was near or below 2. With lighter smoke, both the wetland and forested site appeared to show enhanced photosynthetic activity (a greater sink for carbon dioxide). However, with dense smoke, the forested site was a strong carbon source. Given the extensive forest cover in the Pacific Northwest and the growing importance of forest fires in the region, these results suggest that wildfire aerosol during the growing season potentially plays an important role in the regional ecosystem response to smoke and ultimately the carbon budget of the region.