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Carbon sequestration of mangrove systems in the urban San Juan Bay Estuary, Puerto Rico
Citation:
Wigand, C., R. Martin, M. Gonneea, A. Oczkowski, Alana Hanson, S. Balogh, B. Branoff, E. Santos, AND E. Huertas. Carbon sequestration of mangrove systems in the urban San Juan Bay Estuary, Puerto Rico. Coastal and Research Federation (CERF) 25th Biennial Conference, Mobile, AL, November 03 - 07, 2019.
Impact/Purpose:
Mangrove forests provide many benefits including habitat for fish, shellfish, and wildlife, and water quality maintenance. Another benefit of mangrove forests is to capture carbon dioxide through photosynthesis. Mangrove forests store some of this captured carbon in the soil. Long-term storage of carbon in soils is one method to reduce the amount of carbon dioxide in the atmosphere. In this study we examine the effects of land development and population density on carbon storage in mangrove systems in the San Juan Bay Estuary in Puerto Rico. Carbon dioxide emissions associated with residential, commercial, and industrial electricity and vehicle operation were greatest at the sites with the highest land development and population density. In contrast, long-term carbon storage in mangrove soils was not apparently related to land development, but rather varied with the flushing of the system. The sites with lower flushing rates, one urban and the other a nature preserve, had the highest carbon burial rates.
Description:
The San Juan Bay Estuary (SJBE) in Puerto Rico is a tropical, urban system with varying land development, ranging from densely-populated along a clogged canal to mangrove reserve. Mangrove sediments usually provide high carbon sequestration because of long-term burial associated with high primary production and anoxic sediments. Carbon sources and emissions may vary with degree of urbanization; however, there is sparse data on how carbon sequestration in tropical regions are affected by urbanization. Land cover assessments and population density were used to develop urban indices in 500 m buffers around five mangrove sites in the SJBE. Clogged canal sites had the highest urban index (88–100), lagoon sites intermediate (25–45), and forested reserve the lowest (0). Carbon dioxide emissions associated with residential, commercial, and industrial electricity and vehicle operation were greatest at clogged canal sites (37–41 kg CO2 m-2 y-1), intermediate at lagoon sites (6–15 kg CO2 m-2 y-1), and least at the forest reserve (0.2 kg CO2 m-2 y-1). Similarly, methane emissions from the mangrove sediments and associated coastal waters were significantly greater at urban sites. The most urban sites had sediment CH4 effluxes of 140 µmol m-2 h-1 and the associated coastal waters had effluxes of 1890 µmol m-2 h-1. Highly urbanized areas emitted substantially greater CH4 from the mangrove sediments (24X) and nearby coastal waters (5X) relative to less urbanized sites. In contrast, long-term carbon storage was not related to urbanization, but rather appeared to vary with the flushing and hydraulic residence time of the system. The two sites with lower flushing rates, one urban and the other a mangrove reserve site, had the highest organic carbon burial rates (490 Mg ha-1 y-1 and 362 Mg ha-1 y-1, respectively). This study emphasizes the importance of assessing the contributions of mangrove systems to carbon storage, and how urbanization may contribute to carbon losses.