# Compounded effects on wetland greenhouse gas fluxes from climate change and water management along a saline to freshwater gradient

## TL;DR

This study examines how wetlands in Florida manage carbon and methane under climate and water changes, showing how management can enhance their role in climate solutions.

## Contribution

The paper introduces a data-driven method to upscale greenhouse gas fluxes across saline to freshwater wetlands using satellite data and ground measurements.

## Key findings

- Restoring hydrologic flows can increase carbon dioxide uptake and reduce methane emissions in wetlands.
- Mangroves show higher carbon uptake despite disturbances, while freshwater marshes emit more methane.
- Regional CO2eq uptake increased by 18% from 2003 to 2020 due to improved wetland management.

## Abstract

To manage a large wetland landscape like the Everglades as a net carbon sink, carbon uptake and emissions must be balanced along a gradient of coastal saline mangroves and marshes to nontidal freshwater marshes and forests. Pairing ground and airborne measurements with long-term satellite imagery helps monitor how greenhouse gas exchange changes with wetland vegetation, salt and freshwater levels, disturbances, and management of these compounding factors. Our dataset revealed the importance of restoring hydrologic flows to potentially increase aerobic conditions that minimize freshwater marshes as methane sources and to maximize carbon dioxide uptake in healthy and recovering mangroves. Data upscaling enabled a landscape perspective of carbon exchange needed to improve carbon inventories and manage diverse wetlands as nature-based climate solutions.

Saline and freshwater wetlands store large amounts of carbon, which has driven interest in their role as nature-based climate solutions. Because these ecosystems can be both sinks and sources of carbon to the atmosphere as environmental conditions and human influence change, the net climate mitigation potential of wetlands at regional to global scales remains uncertain. We used a data-driven approach to measure ground-based and airborne fluxes to upscale carbon dioxide (CO2) and methane (CH4) fluxes using satellite-based surface reflectances at 500-m resolution across a gradient of saline to freshwater wetlands in Southern Florida, USA. Daily time series of CO2 and CH4 fluxes from 2000 to 2024 integrated surface properties related to vegetation productivity, flooding, and disturbance, and captured 80% and 91% of the variability in annual fluxes of CO2 and CH4, respectively. Long-term (23-y) patterns in the fluxes of CH4, CO2, and their CO2-equivalent (CO2eq) are represented as Global Warming Potential 100 (GWP100) and were shown to vary spatially with wetland management, revealing higher carbon uptake in mangroves susceptible to hurricane damage and coastal hydrology, and greater carbon emissions in freshwater sawgrass marshes where freshwater hydrology is managed for restoration. Regional net annual CO2eq uptake in coastal and freshwater wetlands increased by 18% from −7.0 ± 3.3 MMT CO2eq y−1 in ~2003 to −8.4 ± 3.8 MMT CO2eq y−1 in ~2020 at an uptake rate of −0.06 ± 0.01 MMT CO2eq y−2. Annually, roughly 43% of CO2 uptake was offset by CH4 emissions from all wetlands in the region (from 16% in mangroves to 82% in freshwater marshes).