Freshwater wetlands are important components of the global carbon cycle and are generally considered carbon sinks. However, shoreline erosion of freshwater coastal wetlands can transition these landscapes from carbon sinks to carbon sources due to export of stored carbon and the reduction of wetland area. No previous studies have explored the impacts of coastal geomorphic processes on freshwater wetland carbon budgets, and to do so, we modified a saltmarsh carbon budget model for application in freshwater coastal wetlands. We validated the model with data collected from a wetland along southwestern Lake Michigan of the Laurentian Great Lakes. The model generates the carbon budget by differencing carbon export and carbon storage across three types of coastal environments: lacustrine sand plains, swale wetland, and overwash-buried wetland. The inputs for carbon storage are the carbon inventory (average inventory: 126 ± 43 kg C m-2), which was quantified through elemental analysis on samples from nine sediment cores, and wetland age. Ages were determined from AMS assay of seeds, needles, and wood fragments picked from core bottoms; modal ages ranged from 540 to 2,105 cal yrs BP. Inputs for carbon export include erosion rates and overwash extent, which were measured through analysis of aerial photographs and topographic survey data. The output from the carbon budget model indicates that the wetland examined in this study transitioned to a source of carbon during periods of erosion and overwash. In fact, the wetland exported over 10% of its original carbon reservoir between 2015 and 2018. This study indicates that geomorphic change can determine whether and how freshwater coastal wetlands serve as sources or sinks for terrestrial carbon, and that freshwater coastal wetlands can switch between the two on a geologically rapid timescale. We recommend that such geomorphic processes be considered when developing carbon budgets for these marginal environments. Furthermore, the carbon budget transect model refined in this study can be used to hone recommendations and prioritize wetlands in land management and conservation efforts.
|Original language||English (US)|
|Title of host publication||AGU Fall Meeting Abstracts|
|State||Published - 2018|