Relationships among Typha Biomass, Pore Water Methane, and Reflectance in a Delaware (U.S.A.) Brackish Marsh

Abstract

Methane is a "greenhouse effect" gas produced in wetland soils, yet factors controlling its production and emission are not well understood. Often, methane pore water concentration and atmospheric flux are positively correlated. If correlations can be found among wetland plant biomass, reflectance, and methane concentrations or flux, it may be possible to study the global methane cycle using remote sensing. Our study had two objectives: (1) to determine if remote sensing could be used to estimate biomass of Typha angustifolia plants in a Delaware (U.S.A.) brackish marsh, and (2) to determine if Typha plants influence dissolved pore water methane concentrations throughout a year. Canopy reflectance was correlated (r = 0.887) with live aerial biomass, which was correlated with live belowground biomass (r = 0.809). Dissolved pore water methane concentrations were generally lower in vegetated than in unvegetated areas. In vegetated areas only, concentrations were much lower in the top 10 cm of sediments than at greater depths. Since over 60% of the live root/rhizome biomass is in the top 10 cm, it is likely that an oxygenated rhizosphere and methane transport through roots kept the methane concentration low near the soil surface. Substantial growing season increases in methane at depths of 10-20 cm, where the remaining live tissue is, suggest the release of enough methanogenic substrates to cause methane production to exceed methane emission/oxidation. Overall, methane concentrations diminished in winter and increased in late spring, but lagged changes in soil temperature and in live aerial biomass by two months, and were not significantly correlated with substrate salinity. Since remote sensing can be used to estimate Typha biomass, and since live root biomass influences the sedimentary methane reservoir, it might be possible to estimate methane concentrations indirectly based on remote sensing measurements.