Abstract

Wetlands are hotspots of CH4 emissions to the atmosphere, mainly sustained by microbial decomposition of organic matter in anoxic sediments. Several knowledge gaps exist on how environmental drivers shape CH4 emissions from these ecosystems, posing challenges in upscaling efforts to estimate global emissions from waterbodies. In this work, CH4 and CO2 diffusive fluxes, along with chemical and isotopic composition of dissolved ionic and gaseous species, were determined from two wetlands of Tuscany (Italy): (i) Porta Lake, a small wetland largely invaded by Phragmites australis reeds experiencing reed die-back syndrome, and (ii) Massaciuccoli Lake, a wide marsh area including open-water basins and channels affected by seawater intrusion and eutrophication. Both wetlands were recognized as net sources of CH4 to the atmosphere. Our data show that the magnitude of CH4 diffusive emission was controlled by CH4 production and consumption rates, being mostly governed by (i) water temperature and availability of labile carbon substrates and (ii) water column depth, wind exposure and dissolved O2 contents, respectively. This evidence suggests that the highest CH4 diffusive fluxes were sustained by reed beds, providing a large availability of organic matter supporting acetoclastic methanogenesis, with relevant implications for global carbon budget and future climate models.

Highlights

  • Surface aquatic systems only cover a small fraction of global land surface [1,2]

  • Degraded ecosystems may rapidly turn from carbon sinks to major sources of greenhouse gases (GHGs), releasing high amounts of CH4 and CO2 produced by microbial decomposition of organic matter, e.g., [7]

  • We present data on CH4 diffusive fluxes from two wetlands located in the Versilian Plain, i.e., Porta and Massaciuccoli Lakes

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Summary

Introduction

Surface aquatic systems only cover a small fraction of global land surface [1,2] They play a crucial role in the global carbon cycle, as they regulate the transport of terrestrial carbon between lands and seas. Wetlands are highly productive ecosystems capable of sequestering large amounts of carbon from the atmosphere through photosynthetic activity, which is stored in biomass and sediments. Its concentration in air is nearly three times higher than that recorded in 1750, with a stepwise increasing trend characterized by a relatively stable period from 2000 to and a renewed and rapid growth since 2007 [11,12,13].

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