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Effect of salinity-altering pulsing events on soil organic carbon loss along an intertidal wetland gradient: a laboratory experiment

Chambers, Lisa G., Osborne, Todd Z., Reddy, K. Ramesh
Biogeochemistry 2013 v.115 no.1-3 pp. 363-383
carbon dioxide, correlation, freshwater, hydraulic conductivity, laboratory experimentation, methane, microbial biomass, salinity, salt marshes, sea level, soil microorganisms, soil organic carbon, soil respiration, soil water, storms, stormwater, tides, United States
Salinity changes resulting from storm surge, tides, precipitation, and stormwater run-off are common in coastal wetlands. Soil microbial communities respond quickly to salinity changes, altering the rate of soil organic carbon (SOC) loss and associated biogeochemical processes. This study quantified the impact of salinity-altering pulses on SOC loss, defined as microbial respiration (CO₂flux) at high and low tide, CH₄flux, and dissolved OC (DOC) release, in 3 intertidal wetlands (Jacksonville, FL, USA). Intact soil cores from a freshwater tidal, brackish, and salt marsh were exposed to simulated tides and 3 salinity pulsing events during a 53-day laboratory experiment. Soil and water physio-chemical properties, nutrient release, and microbial indicators were measured. Microbial respiration was the dominate pathway of SOC loss (>97 %). Soil hydraulic conductivity was greater in brackish and salt marshes and was critical to overall soil respiration. High tide CO₂flux was greatest in the freshwater marsh (58 % of SOC loss) and positively correlated with DOC concentration; low tide CO₂flux was greatest in brackish and salt marshes (62 and 70 % of SOC loss, respectively) and correlated with NH₄⁺and microbial biomass. The freshwater marsh was sensitive to brackish pulses, causing a 112 % increase in respiration, presumably from accelerated sulfate reduction and N-cycling. SOC loss increased in the salt marsh pulsed with freshwater, suggesting freshwater run-off may reduce a salt marsh’s ability to keep-pace with sea level rise. Increased inundation from storm surges could accelerate SOC loss in freshwater marshes, while decreasing SOC loss in brackish and salt marshes.