Abstract Freshwater urban wetlands are important ecosystems that can naturally filter and remove excess nitrogen (N) through the process of denitrification (DNF). However, anthropogenic inputs such as road salt application may affect the N removal capacity of urban wetlands by affecting the relative rates of DNF and another competing reductive process that retains N – dissimilatory nitrate reduction to ammonium (DNRA). Here, we assessed 13 roadside wetlands in urban/suburban areas of Delaware, USA to determine the effects of road salt sodium (Na + ) on soil physical, chemical, and biological properties and the rates of DNF and DNRA. Based on soil Na + concentrations, wetlands were grouped into three categories: low (Na + < 70 mg kg −1 ), medium (70 mg kg −1 < Na + < 150 mg kg −1 ) and high (Na + > 150 mg kg −1 ). Rates of DNF and DNRA ranged from 0.8 – 83 and 0.2 – 24 μg N L −1 slurry h −1 , respectively. DNF was significantly lower in high Na + category wetlands whereas DNRA did not show any significant differences. Similarly, macroaggregates and bioavailable Fe were lowest in the high Na + category, whereas concentrations of soil NH 4 + , NO 3 − , TOC, TN, and microbial metrics (biomass and nosZ and nrfA functional genes) did not reveal any consistent patterns. These findings imply that road salt Na + input exhibited mixed effects on soil properties in these wetlands. Overall, elevated Na + from road salt could undermine the N removal capacity of the roadside urban wetlands. Therefore, strategies should be implemented to reduce the application of road salt or identify effective alternatives.

Abstract With the accelerated urbanization of coastal areas, the demand for coastal land use has increased significantly, and the contradiction between resources and the environment has intensified. This has posed great challenges to the protection of mangrove wetlands, making the strengthening of mangrove conservation in relevant areas an urgent task. In this study, on the basis of assessing the land use data of the Qingmei Port Mangrove Wetland in Sanya, China, at three time points (2009, 2015 and 2022), the PLUS model was used to predict the land use changes in the region in 2035 under three development scenarios: natural development, urban construction and ecological protection. The results of the study show that the area of construction land in the region grew rapidly from 2009 to 2015 and stagnated after 2015; the area of mangrove land in the region maintained a stable growth trend between 2009 and 2022, and cultivated land, parkland and arbor forest land as a whole showed different degrees of decline. The results of the multi-scenario modelling of the land in the region show that under the urban development scenario, the artificial land types such as construction land, bare land, parkland and grasslands increase the most. Under the ecological conservation scenario, the area of ecological land such as arbor woodland and rivers increases significantly. However, there is no significant increase in the area of mangroves under any of the three development scenarios. Currently, the “ponds to wetlands” conversion project in this region has been substantially completed. For the long-term conservation and management of the Qingmei Port Mangrove Wetland, future efforts should focus on enhancing the quality and optimizing the ecological functions of the mangrove ecosystem, while continuing the phased restoration of mangrove habitats. To mitigate the shrinkage of mangrove areas induced by the unregulated expansion of urban construction land, the government should strengthen the delimitation and supervision of urban development boundaries and improve the regulatory framework for mangrove protection. This study provides a scientific reference for the conservation and restoration of mangrove wetlands in analogous urbanized coastal areas.