Carbon Dynamic Studies in the San Juan Bay Estuary
Hanson, Alana AND C. Wigand. Carbon Dynamic Studies in the San Juan Bay Estuary. San Juan Bay Estuary Program S.T.A.C. Summit Meeting 2022, San Juan, Puerto Rico, PUERTO RICO, November 15 - 17, 2022.
Tropical urban estuaries are understudied in the field of environmental research. In San Juan, Puerto Rico lies the San Juan Bay Estuary which has been heavily impacted from urban development. It is also heavily impacted by human driven inputs that lead to dangerous water quality conditions to the detriment of the estuary and nearby communities. The carbon dynamics in subtropical wetlands greatly differ from temperate ones. This project measuring carbon dioxide and methane fluxes as well as examining carbon burial and accretion in San Juan Bay mangroves adds important data for those studying these unique estuaries.
Mangroves sequester significant quantities of organic carbon (C) because of high rates of burial in the soil and storage in biomass. We estimated mangrove forest C storage and accumulation rates in aboveground and belowground components among five sites along an urbanization gradient in the San Juan Bay Estuary, Puerto Rico. Sites included the highly urbanized and clogged Caño Martin Peña in the western half of the estuary, a series of lagoons in the center of the estuary, and a tropical forest reserve (Piñones) in the easternmost part. Radiometrically dated cores were used to determine sediment accretion and soil C storage and burial rates. Measurements of tree dendrometers coupled with allometric equations were used to estimate aboveground biomass. Estuary-wide mangrove forest C storage and accumulation rates were estimated using interpolation methods and coastal vegetation cover data. In recent decades (1970–2016), the highly urbanized Martin Peña East (MPE) site with low flushing had the highest C storage and burial rates among sites. The MPE soil carbon burial rate was over twice as great as global estimates. Mangrove forest C burial rates in recent decades were significantly greater than historic decades (1930–1970) at Caño Martin Peña and Piñones. Although MPE and Piñones had similarly low flushing, the landscape settings (clogged canal vs forest reserve) and urbanization (high vs low) were different. Apparently, not only urbanization, but site-specific flushing patterns, landscape setting, and soil fertility affected soil C storage and burial rates. There was no difference in C burial rates between historic and recent decades at the San José and La Torrecilla lagoons. Watershed anthropogenic far exceeded the annual mangrove forest C storage rates. A combination of maintaining healthy mangrove forests and reducing anthropogenic emissions might be necessary to mitigate greenhouse gas emissions in urban, tropical areas.