Investigating greenhouse gases in small prairie ponds: do season and water chemistry matter?
There are millions of small ponds in the Prairie region. One valuable feature of these ponds is that they store carbon in their sediments and vegetation. But ponds also release greenhouse gases which could offset some of this carbon storage. Our goal was to understand the conditions that are favourable for greenhouse gas release in ponds across the Prairie region of Canada.
We visited nearly 150 small ponds in the Prairie region of Canada, once in spring and once in summer of 2019. We quantified greenhouse gases (methane, carbon dioxide, and nitrous oxide) dissolved in the surface water of these ponds, and corresponding rates of greenhouse gas release or uptake. We also measured a variety of water chemistry parameters that could explain the behaviour of these greenhouse gases.
Read this open access paper on the FACETS website.
We found that all ponds release methane and these rates were higher in summer than in spring. Methane concentrations, however, were related to the amount of sulfate in the water, and there was a clear threshold above which methane concentrations were consistently low. Ponds with sulphate below this threshold demonstrated stronger increase of methane in response to water temperature increase.
Over half of the ponds (57%) were observed to release carbon dioxide from the water to the atmosphere, while fewer were taking up carbon dioxide. Like methane, carbon dioxide release rates increased from spring to summer, but only for ponds with a pH below 9. Few ponds were found to release nitrous oxide, with very low concentrations overall, and it proved difficult to find relationships that could predict the behaviour of this gas.
We showed the potential of greenhouse gas release from small ponds across the Canadian prairies. Season and water chemistry (sulfate and pH) can tell us when and which ponds may offset some carbon storage by releasing greenhouse gases. These findings can be used in ongoing efforts to estimate carbon balances and regional greenhouse gas release from ponds in this agriculture-dominated region.
Read the paper — Seasonal patterns and key chemical predictors of dissolved greenhouse gases in small prairie pothole ponds by Lauren T. Miranda and Colin J. Whitfield.
