Carbon fluxes and potential soil accumulation within Greater Everglades cypress and pine forested wetlands

Abstract

In forested wetlands, accumulation of organic matter in soil is partly governed by carbon fluxes where photosynthesis, respiration, lateral advection of waterborne carbon, fire-derived carbon emissions, and methanogenesis are balanced by changes in stored carbon. Stored carbon can eventually accumulate as soil over time if net primary productivity exceeds biomass decomposition. For this study, potential soil accumulation was estimated based on four years of continuous daily carbon cycling data and a one-dimensional mass-balance model of landscape-atmospheric exchange for cypress and pine forested wetlands in the Greater Everglades of south Florida. The mass-balance model was driven by eddy-covariance estimates of vertical net ecosystem exchange of carbon dioxide and methane. Key findings include confirmation of a basic premise of the historic Everglades restoration project; specifically, more water either from rainfall or water management encourages soil carbon accumulation and thus conservation of soils that support biologic activity and ecosystem services. For example, an anomalous wet season for south Florida that flooded the forested wetlands through the traditional dry season was followed by the most productive year for photosynthetic carbon uptake and potential soil accumulation. On the other hand, methane emissions were enhanced by the anomalous wet season and extended flooding – which confirmed a complex tradeoff to consider if wetlands are managed for both soil conservation and reduction of greenhouse gas emissions. Potential soil accumulation rates were about 1.7, 2.8, and 18 millimeters per year at the Dwarf Cypress, Cypress Swamp, and Pine Upland ecosystems, assuming soil C density values of 0.07, 0.09, and 0.02 grams of carbon per cubic centimeter, respectively. For these values of soil C density, the accumulation rates are considered a “best-case” upper limit because the lateral export of carbon in the canals and creeks that drain the study area were assumed negligible.