Gas advection in sediments of a South Carolina salt marsh

• Published in: Marine ecology. Progress series (Halstenbek) Vol. 27; no. 1/2; pp. 187 - 194
• Main Authors: Morris, James T., Whiting, Gary J.
• Format: Journal Article
• Language: English
• Published: Inter-Research 01-01-1985
• Subjects: Advection; Creeks; Marine; Marshes; Methane; RESEARCH PAPERS; Salt marshes; Sediments; Spartina alterniflora; Transpiration; Water depth; Water loss; Water tables; ANW, USA, South Carolina
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps027187

The volume of water removed from marsh sediments by evapotranspiration and drainage during low tide is replaced at least in part by air drawn into the sediment. The volume of gas advected into salt marsh sediments was measured in situ by recording the displacement of air in manometers connected to the sealed headspace of core tubes placed in the sediment. Measurements, made during June and July in short form Spartina alterniflora marshes in South Carolina, indicated that as much as 4.0 l m⁻² of gas was drawn into the sediment, depending on marsh location and climatic variables. Gas advection rates were equivalent to water losses of 1.5 to 4.0 % of the total sediment water above the water table and corresponded to water table depths that fell to as much as 34 cm during low tide. Transpiration rates of S. alterniflora accounted for about 22 % of the gas volume drawn into the sediment. Analyses of gas bubbles expelled from the sediment during tidal inundation showed that O₂ was consumed in excess of CO₂ advected. Excess O₂ consumption may result because of sulfide oxidation; this possibility is supported by decreasing pore-water pH during low tide exposure. Alternatively, some CO₂ produced in the sediment may remain in the pore water in dissolved form. Considering both advective and diffusive gas fluxes, a total of 56.3 mmol m⁻² of CO₂ (4.9 by advection, 51.4 by diffusion) was evolved from the sediment during low tide compared to a total O₂ consumption of 32.9 mmol m⁻². The mean O₂ consumption from gas drawn into the sediment during low tide was 10.9 mmol m⁻². This compares to a mean diffusive O₂ consumption by surface sediment of 22.0 mmol m⁻² during 10 h of low tide exposure.