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Description
Mangrove forests are ecologically important ecosystems that have been identified as one of the most threatened ecosystems on earth. Given predicted range expansion, anthropogenic inputs, and destruction due to shrimp aquaculture, mangrove ecosystems will play a changing role in trace gas budgets. While various studies have measured CO2emissions from mangrove forests, few studies have measured CO2in conjunction with other radiatively important trace gases or quantified spatial patterns in emissions. This study quantifies the fluxes of CO2, CH4, and N2O and also identifies whether there were tidal and zonal, referring to low, mid, and high intertidal zones, patterns in trace gas fluxes. The study took place within the Bahia Magdalena Lagoon Complex in Baja California Sur, Mexico where samples were collected along land to sea transects. Gas samples were analyzed using gas chromatography. Sediment core and pore water samples were used to determine concentrations of dissolved gases, nutrients, and electron acceptors.Greenhouse gas fluxes averaged 94 kg km-2yr-1of C,2501 kg km-2yr-1of CH4, and 308 kg km-2yr-1of N2O. Multiple linear regression revealed nitrate and leaf litter were significant drivers of N2O flux (p<0.01) with significant interactions between nitrate and tidal zones, whereby NO3 was a significant driver of N2O flux in mid and high intertidal zones (p=0.01 and p<0.01, respectively). Negative N2O fluxes were observed and a logistic regression showed N2O consumption had an odds ratio 5.6 higher during high tide than low tide (p=0.01). Methane fluxes did not vary zonally or tidally but were driven by total iron concentrations, though the linear relationship was weak (p=0.04, R2=0.25). In low intertidal zones, methane emissions were regulated by salinity (r2=0.87), with higher salinities limiting CH4 fluxes. CO2 fluxes increased with increasing tide distance and redox (p=0.004). CO2 consumption was observed during high tide, with redox potentials, and SO4 concentrations (p=0.06) shown to be nearly significant predictors of consumption. CO2 consumption appears to be a result of physical and biological processes, with increased sulfate reduction creating more alkaline conditions, and increasing CO2 solubility into tidal waters, presumably resulting in negative CO2 fluxes. Twelve hour runs at a single station showed greater CO2 fluxes during an outgoing tide than an incoming tide and with greater tide distance (R2=0.24), and increasing CO2 flux with more acidic pH (R2=0.72). Nitrous oxide showed a positive relationship with decreasing daylight (R2=0.83) This study showed an interplay of both physical and biological factors control trace gas emissions.
