Greenhouse gas emissions from urban ponds are driven by nutrient status and hydrology

Abstract

Inland waters emit significant quantities of greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2) to the atmosphere. On a global scale, these emissions are large enough that their contribution to climate change is now recognized by the Intergovernmental Panel on Climate Change. Much of the past focus on GHG emissions from inland waters has focused on lakes, reservoirs, and rivers, and the role of small, artificial waterbodies such as ponds has been overlooked. To investigate the spatial variation in GHG fluxes from artificial ponds, we conducted a synoptic survey of forty urban ponds in a Swedish city. We measured dissolved concentrations of CH4 and CO2, and made complementary measurements of water chemistry. We found that CH4 concentrations were greatest in high‐nutrient ponds (measured as total phosphorus and total organic carbon). For CO2, higher concentrations were associated with silicon and calcium, suggesting that groundwater inputs lead to elevated CO2. When converted to diffusive GHG fluxes, mean emissions were 30.3 mg CH4·m−2·d−1 and 752 mg CO2·m−2·d−1. Although these fluxes are moderately high on an areal basis, upscaling them to all Swedish urban ponds gives an emission of 8336 t CO2eq/yr (±1689) equivalent to 0.1% of Swedish agricultural GHG emissions. Artificial ponds could be important GHG sources in countries with larger proportions of urban land.

Regulation of carbon dioxide and methane in small agricultural reservoirs: Optimizing potential for greenhouse gas uptake

“…The positive association between NOx and CO2 found in our reservoirs is consistent with similar patterns seen with dissolved inorganic N species in other artificial waterbodies (Ollivier et al, 2019;Peacock et al, 2019) and regional prairie lakes (Wiik et al, 2018). In some lakes, high N loading favoured elevated heterotrophy, despite simultaneous boosts in primary production which draws down free CO2 (Huttunen et al, 2003;Cole et al, 2000).…”

Regulation of carbon dioxide and methane in small agricultural reservoirs: optimizing potential for greenhouse gas uptake

“…In particular, CH 4 concentrations were lowest when WRT was long (> 1 year) and water was derived mainly from snow or groundwater sources (δ 18 O depleted). This may be due to a combination of reasons, including the prevalence of sulfate delivered from groundwater (Pennock et al, 2010), dilution of waterbody from snowmelt inflow, and sediments depleted in labile carbon due to longer biogeochemical processing times in the dams. The potential effect of sulfate limiting methanogenesis is in agreement with the strong negative relationship found between CH 4 and conductivity in our model (Fig.…”

“…This study builds on from our previous farm reservoir GHG research which found an unexpected nitrous oxide (N 2 O) sink in 67 % of reservoirs . The hydroclimate, lithology and edaphic features are vastly different compared to previous studies of agricultural areas (Australia, India, USA), with factors that favour CO 2 uptake by alkaline surface waters (Finlay et al, 2009(Finlay et al, , 2015 and lead to high variability in CH 4 fluxes from regional wetlands (Pennock et al, 2010;Badiou et al, 2019). Our aim was to identify the key environmental conditions regulating CO 2 and CH 4 fluxes, as well as to evaluate these baseline data in the context of emission mitigation strategies.…”

“…Understanding the controls and rates of carbon fluxes from small artificial waterbodies is the first step required to understand their landscape and eventually global importance. Further, estimates of CO 2 and CH 4 flux are complicated by high variation among reservoirs and regions in the importance of groundwater, littoral macrophytes, and local land use practises (Pennock et al, 2010;Badiou et al, 2019). Artificial reservoirs have the potential to be potent sources of CO 2 and CH 4 (Downing et al, 2008;Holgerson and Raymond, 2016).…”

Magnitudes and Drivers of Greenhouse Gas Fluxes in Floodplain Ponds During Drawdown and Inundation by the Three Gorges Reservoir

“…Holgerson and Raymond () estimate that natural ponds contribute 40% of diffusive CH 4 emissions from lentic inland waters worldwide. Ponds created on the terrestrial landscape for a variety of purposes including stock watering, irrigation, and aquaculture have been also found to emit CH 4 (Ollivier et al, ; Peacock et al, ). In some cases, these ponds emit CH 4 at higher rates than natural ponds through diffusive and ebullition flux pathways (Grinham et al, ), though more comparative data are needed.…”