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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.)

Urban stormwater ponds (SWPs) are engineered ecosystems designed to prevent flooding and protect downstream ecosystems by retaining nutrients associated with stormwater runoff, including nitrogen (N). Despite these expectations, multiple studies have found that SWPs have low N removal efficiencies and can be sources of N to downstream ecosystems. To understand mechanisms controlling the fate of N in SWPs, we quantified dinitrogen (N2) gas saturation to characterize net N2 exchange as either net denitrification or net N-fixation. We assessed temporal and spatial patterns of N2 dynamics in fifteen SWPs and six naturally occurring ponds in undisturbed watersheds (Florida, USA) by sampling in two seasons (dry and wet) and from multiple depths of the water column. Samples from SWPs were equally likely to exhibit N2 supersaturation (net denitrification; 50%) or undersaturation (net N-fixation; 50%). In contrast, the majority (82%) of samples from natural ponds were supersaturated with N2, indicating net denitrification. The mean SWP air–water N2 flux was − 1.7 μg N2-N m−2 h−1 (range − 500 to 433 μg N2-N m−2 h−1), which was lower than clear (40 μg N2-N m−2 h−1; range − 68 to 74 μg N2-N m−2 h−1) and humic (202 μg N2-N m−2 h−1; range 41 to 407 μg N2-N m−2 h−1) natural ponds despite considerably higher variation in SWPs. These results indicate that SWPs may have low N removal efficiencies in part due to N-fixation adding new N to the system. Overall, this study shows that SWPs are less effective than natural ponds at removing reactive N from the environment, potentially impacting downstream water quality. [ABSTRACT FROM AUTHOR]

Despite the assumption that residential fertilizer ordinances improve regional water quality, their impacts across space and time largely remain unknown. Here, we analyze changes in water quality of lakes throughout the State of Florida from 1987 to 2018, comparing trends in water quality parameters before and after implementation of county‐wide fertilizer ordinances. We used a large dataset of publicly collected water quality data and linear mixed models to analyze ordinance impacts on total nitrogen, total phosphorus, chlorophyll a, and Secchi depth across 160 lakes throughout Florida. We further analyze water quality impacts relative to the type of ordinance (winter fertilizer ban, summer ban, nonseasonal ban, no ban). We found fertilizer ordinances favorably impacted lacustrine water quality, and winter (dry season) fertilizer bans had the greatest effect across all water quality metrics. Results of this study can be used to support the effectiveness of fertilizer ordinances across humid tropical and subtropical climate regions. [ABSTRACT FROM AUTHOR]

The steadily rising global urban population has placed substantial strain on urban water quality, and this strain is projected to increase for the foreseeable future. Considerable attention has been given to the hydrological and physico‐chemical effects of urbanization on stream ecosystems. However, due to the relative infancy of the field of urban ecology, long‐term water quality analyses in urban streams are sparse. Using a 15‐yr stream chemistry monitoring record from Baltimore, Maryland, we quantified long‐term trends in nitrate, phosphate, total nitrogen, total phosphorus, chloride, and sulfate export at several sites along a rural–urban gradient. We found no significant change in solute export at most sites, although we did find specific patterns of interest for certain solutes. For example, nitrogen export declined at the most headwater urban site, while phosphorus export declined at the most downstream urban site. Coupling long‐term monitoring with data on gray and green infrastructure management throughout the landscape, we established relationships between solute export at the most downstream urban monitoring site and sanitary sewer overflows (SSOs), best management practice (BMP) implementation, and road salt application rates. Phosphorus export was correlated with BMP implementation in the watershed, whereas nitrogen export was related to SSOs. Despite highly urbanized watersheds, water quality does not appear to be declining at most of these sites, suggesting that current management may have limited further impairment. Results of our study suggest that both gray and green infrastructure are key for maintaining and improving water quality in this highly urbanized watershed. [ABSTRACT FROM AUTHOR]

Climate change, recurrent droughts, and increasing urban water demands have limited water availability in urban landscapes. Water quantity challenges have led to irrigation restrictions and turfgrass removal programs. An experiment was conducted at the University of Florida, West Florida Research and Education Center, Jay, FL, to evaluate the effect of turfgrass conversion to other landscape types on nutrient leaching and groundwater recharge. In April 2021, all surface vegetation was removed from existing turfgrass plots using a sod harvester. Thereafter, plots were planted or covered with three landscape types: a pollinator landscape with flowering forbs (Mimosa sp., Coreopsis sp., and Phyla sp.) + turfgrass (Eremochloa ophiuroides); a nitrogen (N)‐efficient lawn (Arachis glabrata + Paspalum notatum); and a low‐input landscape with unplanted woodchip mulch. Undisturbed turfgrass (E. ophiuroides) served as a control. For 2 years, leachate samples were collected weekly from previously installed 168‐L drainage lysimeters for NO3‐N and NH4‐N load determination. Temporal changes in landscape composition, groundwater recharge, water use, and soil bulk density were also quantified. While the mulch leached 44.7 kg ha−1 NO3‐N year−1, this landscape still offers positive attributes, including erosion protection and water conservation. Conversely, the pollinator landscape minimized nitrogen leaching (8.3 kg ha−1 NO3‐N year−1) due to their relatively greater water use rates (3.56 mm day−1). The turfgrass and nitrogen‐efficient lawn returned ∼35% of the water inputs as groundwater recharge while maintaining relatively low nitrogen leaching (3.6 and 2.7 kg ha−1 NO3‐N year−1, respectively), making these landscapes efficient for protecting both water quality and quantity. [ABSTRACT FROM AUTHOR]