Mangrove carbon assessment tool: Model development and sensitivity analysis

It is important to have the capability to assess carbon (C) dynamics in mangrove forests and estimate their role in mitigating climate change because of their high carbon density, the threats to their integrity from land-use change and sea-level rise, and functional linkages of the many goods and services. A process-based model for mangroves was developed by integrating new features with existing biogeochemical processes in Forest-DNDC for simulating C sequestration and turnover in mangrove ecosystems. The new model is used to assess (1) the dynamics of C, nitrogen and phosphorous in mangrove ecosystems, including above-and below-ground C in saline wetlands, (2) the impacts of ecological drivers, including climate, soil nitrogen and phosphorous deficit and salt stress, on mangrove production, (3) the production of methane, and aerobic and anaerobic oxidation of methane with sulfate, nitrate and nitrite reductions, (4) the contributions of dissolved inorganic C (DIC), dissolved organic C (DOC), particulate organic C (POC) and burial C (BC) to blue C, and (5) impacts of natural and anthropogenic disturbances on C sequestration in mangrove ecosystems. Model sensitivity analysis showed that C sequestration in mangrove ecosystems was highly sensitive to multiple ecological factors, including climate, soil phosphorus, salinity and sulfate, as well as latitude. The responses of different C components to these factors were distinct. The responses of gross and net primary productivity and aboveground biomass to alterations of mean daily temperature (MDT) were quadratic, or increasing or decreasing non-linearly with an increment or decrement in MDT, but leaf production was linear. Similarly, other mangrove C components, such as BC, DIC, DOC and POC, respond substantially to variations of the ecological drivers. The combined effects of the driving factors are complex due to their intricate interactions. For example, while mangrove productivity is sensitive to available phosphorous, phosphorous cannot mitigate the stress imposed by high salinity. These results highlight the value of a tool to assess C dynamics in mangroves, especially for regional or large mangrove forests.