Carbon Dynamics in Artificial Aquatic Ecosystems: Comparing Greenhouse Gases and DOM in Stormwater and Natural Ponds

Urban stormwater ponds (SWPs) are increasingly recognized as critical hotspots for carbon (C) and nitrogen (N) cycling, driven by high external inputs and elevated internal productivity. In developed watersheds, SWPs often replace natural aquatic ecosystems at equal or greater densities, but direct comparisons of the C and N dynamics between these engineered and natural ecosystems remain scarce. During distinct wet and dry seasons (Florida, USA), we compared the diffusive air‐water flux and hypolimnetic saturation of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O), as well as the composition of dissolved organic matter (DOM) between SWPs ( n = 15) and naturally occurring clear ( n = 3) and dark colored ( n = 3) ponds in undisturbed watersheds. SWPs had similar CO 2 and lower CH 4 fluxes compared with natural‐dark ponds, and higher fluxes than natural‐clear ponds. Both natural pond types (clear and dark) were more stratified than SWPs, resulting in a greater CH 4 buildup in the natural ponds. N 2 O fluxes were negligible across all pond types, with dark ponds being N 2 O sinks. SWPs contained unique humic DOM not found in natural ponds, as well as microbially derived DOM that was similar to, and humic DOM that was identical to, that of natural ponds. Our study underscores that SWPs differ from natural ponds in greenhouse gas production and DOM composition, providing evidence that these rapidly emerging ecosystems alter C forms and greenhouse gas fluxes in developed landscapes.