Background/Question/Methods A diversity of nature-based climate solutions is needed in order to help achieve net zero carbon emissions. Some of the most appealing and scalable solutions concern the management of wetlands and agricultural land. We are focused on 2 land management practices: tidal wetland restoration and compost-amended rangelands. Tidal wetlands cover < 1% of the Earth’s surface however disproportionately remove carbon from the atmosphere relative to other ecosystems, with global burial rates of up to 87 Tg C yr-1. However tidal wetlands have been lost due to land development and are under threat from climate change, sea level rise, and eutrophication. Grasslands alternatively, can be small sinks of carbon however encompass a large proportion of the terrestrial land surface, nearly 30% globally. Therefore, even small carbon benefits resulting from the application of compost to grazed grasslands could have large climate benefits when scaled up. In both systems, we employ soil and ecosystem scale measurements of carbon dioxide and methane fluxes combined with soil sediment cores, soil and water chemistry measurements, and Phenocam images to constrain greenhouse gas budgets and estimate radiative forcing. This comprehensive measurement approach has also yielded information concerning ecosystem resilience and regional feed-backs.
Results/Conclusions One intensively studied restored tidal wetland in San Francisco Bay, California has shown to be a consistent sink of CO2 across multiple years of measurements (-407.4 g C-CO2 m-2 yr-1, SD= 47.1) and a small source of CH4 (0.6 g C-CH4 m-2 yr-1, SD= 0.3). However, soil sediment cores and measurements of dissolved inorganic carbon (DIC) suggest that a large amount of carbon is exported laterally during the growing season (238-316 g C m-2 yr-1) which amounts to 58-77% of the atmospherically removed carbon budget. We are investigating the significance of the laterally exported carbon with respect to radiative forcing and carbon markets as well as the regional impacts of exported DIC on other coastal ecosystems and ocean acidity.
We also report on an experimental rangeland site in California where compost amendment was applied before the growing season of 2020. Ecosystem flux data show that the amendment significantly increased gross primary productivity, however ecosystem respiration also increased. Additionally, the beginning of the growing season was 20 days earlier in the amended soils and methane uptake was significantly higher. These unexpected results have implications for the overall radiative forcing of compost-amended rangelands as well as the resilience of grasslands to drought.