Saltwater reduces potential COsub2/sub and CHsub4/sub production in peat soils from a coastal freshwater forested wetland

摘要

A major concern for coastal freshwater wetland functionand health is the effects of saltwater intrusion on greenhouse gasproduction from peat soils. Coastal freshwater forested wetlands are likelyto experience increased hydroperiod with rising sea level, as well assaltwater intrusion. These potential changes to wetland hydrology may alsoalter forested wetland structure and lead to a transition from forest toshrub/marsh wetland ecosystems. Loss of forested wetlands is already evidentby dying trees and dead standing trees (“ghost” forests) along theAtlantic coast of the US, which will result in significant alterations toplant carbon (C) inputs, particularly that of coarse woody debris, to soils.We investigated the effects of salinity and wood C inputs on soils collectedfrom a coastal freshwater forested wetland in North Carolina, USA, andincubated in the laboratory with either freshwater or saltwater (2.5 or 5.0 ppt) and with or without the additions of wood. Saltwater additions at 2.5 and 5.0 ppt reduced CO2 production by 41 % and 37 %, respectively,compared to freshwater. Methane production was reduced by 98 % (wood-freeincubations) and by 75 %–87 % (wood-amended incubations) in saltwatertreatments compared to the freshwater plus wood treatment. Additions of woodalso resulted in lower CH4 production from the freshwater treatment andhigher CH4 production from saltwater treatments compared to wood-freeincubations. The δ13CH4-C isotopic signature suggestedthat, in wood-free incubations, CH4 produced from the freshwatertreatment originated primarily from the acetoclastic pathway, while CH4produced from the saltwater treatments originated primarily from thehydrogenotrophic pathway. These results suggest that saltwater intrusioninto coastal freshwater forested wetlands will reduce CH4 production,but long-term changes in C dynamics will likely depend on how changes inwetland vegetation and microbial function influence C cycling in peat soils.