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Stormwater ponds (SWPs) are an increasingly common management tool for flood control and water quality protection in urban areas. They are designed to buffer the impacts to downstream environments caused by altered hydrologic, chemical, biological, and ecological processes in developed watersheds. While small in size, they can have disproportionately large impacts on watersheds because they store, transform, and release inputs of carbon (C) and nutrients, mainly nitrogen (N) and phosphorus (P). In this review, we discuss how SWPs are not passive conveyances of nutrients and C, where minimal internal processing occurs. Rather, they are active hotspots of biogeochemical processing, with implications for downstream water quality protection. We highlight how processes of assimilation, sedimentation, erosion, filtration, remineralization and remobilization, gaseous transformations, and the activities of living organisms all transform nutrients and C in SWPs, sometimes making ponds net exporters of nutrients, rather than net sinks or removers, as is often believed. There are numerous unaccounted challenges in SWP management, such as in-pond processes that decouple pond effluent and influent quality; that sedimentation often fails as a proxy indicator for nutrient removal; how optimizing for removal of one nutrient (nitrogen or phosphorus) may reduce removal efficiencies of the other; or how nutrient removal strategies may be at odds with strategies to mitigate greenhouse gas emissions from SWPs. Our goal is to show that SWPs play large roles in constraining and mediating the fluxes of materials and energy in urban ecosystems and that their effluent water quality is driven not only by inflowing water quality but largely also by in-pond processes that warrant increased future research., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Alexander Reisinger reports financial support was provided by National Science Foundation. Basil Iannone reports financial support was provided by Florida Department of Environmental Protection. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Designed ecosystems are built as part of ongoing urban expansion, providing a suite of valued ecosystem services. However, these new ecosystems could also promote disservices by facilitating the colonization and spread of invasive species. We conduct the first assessment of the quantity and invasion of an overlooked designed ecosystem: stormwater ponds. These ponds are commonly recommended for managing urban hydrology, but little is known about their ecology or extent of proliferation. Using a broad-scale survey of pond coverage in Florida, USA, we found that over 76,000 stormwater ponds have been built just in this state, forming 2.7% of total urban land cover. This extensive pondscape of manufactured habitats could facilitate species spread throughout urban areas and into nearby natural waterbodies. We also conducted a survey of the severity of plant invasion in 30 ponds in Gainesville, FL, US across two pond types (dry vs. wet), and a gradient of management intensities (low, medium, high) and pond ages. We unexpectedly found a high number of invasive plant species (28 in just 30 ponds). Ninety-six percent of surveyed ponds contained from one to ten of these species, with ponds exhibiting high turnover in invader composition (i.e., high beta diversity). The bank sections of dry unmanaged ponds exhibited the highest mean invasive species richness (5.8 ± 1.3) and the inundated centers of wet medium managed ponds exhibited the highest mean invasive species cover (34 ± 12%). Invasive plant richness and cover also tended to be greater in dry ponds with higher soil nutrient levels, and in older wet ponds. Therefore, we found that highly maintained and younger wet ponds were the least invaded. Nevertheless, common management practices that limit plant invasions may also limit native species establishment and invasion may increase in the decades following pond construction., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier B.V. All rights reserved.)