Mangroves are known to sequester carbon at rates exceeding even those of other tropical forests; however, to understand carbon cycling in these systems, soil-atmosphere fluxes and gas exchanges in mangrove-adjacent shallow waters need to be quantified. Further, despite the ever-increasing impact of development on mangrove systems, there is even less data on how subtropical, greenhouse gas (GHG) fluxes are affected by urbanization. We quantified carbon dioxide (CO₂) and methane (CH₄) fluxes from mangrove soils and adjacent, coastal waters along a gradient of urbanization in the densely-populated, subtropical San Juan Bay Estuary (PR). Edaphic (salinity, pH, surface temperature) factors among sites significantly covaried with GHG fluxes. We found that mangrove systems in more highly-urbanized reaches of the estuary were characterized by relatively lower porewater salinities and substantially larger GHG emissions, particularly CH₄, which has a high global warming potential. The magnitude of the CO₂ emissions was similar in the mangrove soils and adjacent waters, but the CH₄ emissions in the adjacent waters were an order of magnitude higher than in the soils and showed a marked response to urbanization. This study underscores the importance of considering GHG emissions of adjacent waters in carbon cycling dynamics in urbanized, tropical mangrove systems.

众所周知，红树林的固碳速度甚至超过了其他热带森林。然而，要了解这些系统中的碳循环，需要量化红树林附近浅水区的土壤-大气通量和气体交换。此外，尽管发展对红树林系统的影响越来越大，但关于亚热带温室气体 (GHG) 通量如何受到城市化影响的数据就更少了。我们量化了二氧化碳 (CO ₂ ) 和甲烷 (CH ₄) 在人口稠密的亚热带圣胡安湾河口 (PR) 的城市化梯度中，来自红树林土壤和邻近沿海水域的通量。地点之间的土壤（盐度、pH、地表温度）因素与温室气体通量显着相关。我们发现，河口城市化程度更高的红树林系统的特点是孔隙水盐度相对较低，温室气体排放量显着增加，尤其是具有较高全球变暖潜力的CH _{4 。}红树林土壤和邻近水域的 CO ₂排放量相似，但 CH ₄邻近水域的排放量比土壤中的排放量高一个数量级，并显示出对城市化的显着反应。这项研究强调了在城市化热带红树林系统的碳循环动态中考虑邻近水域的温室气体排放的重要性。