Tidal Triggers and Hot Spot Switches in Coastal Marsh
Authors
Zoe Cardon1* (zcardon@mbl.edu), Inke Forbrich2, Joaquim Oller1, Suzanne Thomas1, Anne Giblin1, Jennifer Bowen3, Benjamin Sulman4, Theresa O’Meara4
Institutions
1Marine Biological Laboratory, Woods Hole, MA; 2University of Toledo, Toledo, OH; 3Northeastern University–Nahant, MA; 4Oak Ridge National Laboratory, Oak Ridge, TN
Abstract
Plum Island Estuary is the largest remaining tidal wetland complex in the northeastern United States. During drought in July 2022, eddy covariance revealed a surprisingly rapid switch in ecosystem-scale biogeochemistry of methane in the estuarine oligohaline zone. Methane (CH4) flux from Typha angustifolia marsh to the atmosphere plummeted from ~200 nmol m-2 s-1 to near zero within hours of inundation by an unusually saline tide (Forbrich DE- SC0022108). Reduced CH4 flux to the atmosphere was sustained for months despite persistent CH4 pools in sediment porewater. Researchers are testing four hypotheses related to CH4 production and consumption:
- Hypothesis 1. Salinity stress induces increased catalase activity in Typha roots, leading to enhanced root O2 release from the H2O2 produced during stress. Aerobic methanotrophy may therefore increase in rhizosphere hot spots of enhanced O2
- Hypothesis 2. Anaerobic methane (ANME) oxidation in the upper 10 cm (hot layer) of sediment is stimulated by saline inundation. ANME archaea in consortia with sulfate reducing bacteria are potential actors.
- Hypothesis 3: Methylotrophic methanogens produce methane despite high porewater sulfate concentration.
- Hypothesis 4. Typha angustifolia roots produce glycine betaine as a compatible osmolyte, which, once fermented to trimethylamine, could make roots hot spots for support of methylotrophic methanogenesis.
Results of hypothesis testing will guide developments within the E3SM-PFLOTRAN marsh modeling framework. Field-robust planar optode systems were developed and deployed Oct. 2023, revealing remarkably dynamic O2 concentrations to 15 cm depth with tidal forcing.
Potential impact: Incorporation of microbial and plant mechanisms into process-based models has tremendous potential for improving understanding and prediction of CH4 emissions as coastal terrestrial-aquatic interfaces experience sea level rise and more frequent saline inundation. Evidence is accumulating from diverse ecosystems that methylotrophic methanogenesis can proceed at high salinity. H2O2 production and the induction of catalase during stress is widely shared across plant species, suggesting catalase-dependent oxygenation of the rhizosphere could be generalizable.