Spatial and temporal variability in summertime dissolved carbon dioxide and methane in temperate ponds and shallow lakes

Abstract

Small waterbodies have potentially high greenhouse gas emissions relative to their small footprint on the landscape, although there is high uncertainty in model estimates. Scaling their carbon dioxide (CO2) and methane (CH4) exchange with the atmosphere remains challenging due to an incomplete understanding and characterization of spatial and temporal variability in CO2 and CH4. Here, we measured partial pressures of CO2 (pCO2) and CH4 (pCH4) across 30 ponds and shallow lakes during summer in temperate regions of Europe and North America. We sampled each waterbody in three locations at three times during the growing season, and tested which physical, chemical, and biological characteristics related to the means and variability of pCO2 and pCH4 in space and time. Summer means of pCO2 and pCH4 were inversely related to waterbody size and positively related to floating vegetative cover; pCO2 was also positively related to dissolved phosphorus. Temporal variability in partial pressure in both gases weas greater than spatial variability. Although sampling on a single date was likely to misestimate mean seasonal pCO2 by up to 26%, mean seasonal pCH4 could be misestimated by up to 64.5%. Shallower systems displayed the most temporal variability in pCH4 and waterbodies with more vegetation cover had lower temporal variability. Inland waters remain one of the most uncertain components of the global carbon budget; understanding spatial and temporal variability will ultimately help us to constrain our estimates and inform research priorities.

Wetland productivity determines trade‐off between biodiversity support and greenhouse gas production

“…It is important to highlight that our headspace method only gives an indication of open water GHG dynamics and does not account for plant‐mediated fluxes, which can be an important pathway for CH 4 and N 2 O emissions (Jørgensen et al., 2011; Sebacher et al., 1985). However, our sampling approach is frequently used in studies of GHGs in small wetlands and ponds, especially when sampling a relatively large number of wetlands across regional scales (Jensen et al., 2023; Ray et al., 2023; Webb et al., 2019). Finally, we measured chlorophyll‐ a concentrations in triplicate as a proxy for aquatic primary production using a FluoroSense™ chlorophyll probe.…”

Submersed Macrophyte Density Regulates Aquatic Greenhouse Gas Emissions

“…Shallow inland waterbodies are globally abundant with an estimated 98.7% of all waterbodies having a mean depth of 4.1 m or shallower (Cael et al., 2017). These shallow waters play an outsized role in freshwater greenhouse gas (GHG) emissions, yet the magnitude of emissions is highly variable and uncertain across time and space (Bansal et al., 2023; Deemer & Holgerson, 2021; Ray et al., 2023; Rosentreter et al., 2021; Saunois et al., 2020). Aquatic vegetation is an underexplored driver of aquatic GHG emissions, especially in shallow systems where submersed plants can cover the entire footprint of the waterbody (Carmichael et al., 2014).…”

High Intra‐Seasonal Variability in Greenhouse Gas Emissions From Temperate Constructed Ponds

“…Yet, monthly measurements of GHG fluxes from lakes and reservoirs do not follow a smooth curve and can vary several orders of magnitude over the course of 2–3 months, particularly in the shoulder seasons when changes in the physical, chemical, and biological functions and properties of an ecosystem may yield high rates and possibly unexpected source‐sink behavior (e.g., Vachon et al., 2020; Waldo et al., 2021). Temporal variability in pond GHG concentrations is high relative to larger waterbodies and may relate to intermittent periods of water column mixing and stratification (Ray et al., 2023). Specifically, stratification can lead to the accumulation of GHGs and reduced oxygen availability in bottom waters, whereas mixing can release these gases and reintroduce oxygen to the sediment‐water interface (Bastviken et al., 2008; Søndergaard et al., 2023).…”