Julie Shahan

All Publications

• Methane fluxes in tidal marshes of the conterminous United States. Global change biology Arias-Ortiz, A., Wolfe, J., Bridgham, S. D., Knox, S., McNicol, G., Needelman, B. A., Shahan, J., Stuart-Haëntjens, E. J., Windham-Myers, L., Oikawa, P. Y., Baldocchi, D. D., Caplan, J. S., Capooci, M., Czapla, K. M., Derby, R. K., Diefenderfer, H. L., Forbrich, I., Groseclose, G., Keller, J. K., Kelley, C., Keshta, A. E., Kleiner, H. S., Krauss, K. W., Lane, R. R., Mack, S., Moseman-Valtierra, S., Mozdzer, T. J., Mueller, P., Neubauer, S. C., Noyce, G., Schäfer, K. V., Sanders-DeMott, R., Schutte, C. A., Vargas, R., Weston, N. B., Wilson, B., Megonigal, J. P., Holmquist, J. R. 2024; 30 (9): e17462

  Abstract

  Methane (CH4) is a potent greenhouse gas (GHG) with atmospheric concentrations that have nearly tripled since pre-industrial times. Wetlands account for a large share of global CH4 emissions, yet the magnitude and factors controlling CH4 fluxes in tidal wetlands remain uncertain. We synthesized CH4 flux data from 100 chamber and 9 eddy covariance (EC) sites across tidal marshes in the conterminous United States to assess controlling factors and improve predictions of CH4 emissions. This effort included creating an open-source database of chamber-based GHG fluxes (https://doi.org/10.25573/serc.14227085). Annual fluxes across chamber and EC sites averaged 26 ± 53 g CH4 m-2 year-1, with a median of 3.9 g CH4 m-2 year-1, and only 25% of sites exceeding 18 g CH4 m-2 year-1. The highest fluxes were observed at fresh-oligohaline sites with daily maximum temperature normals (MATmax) above 25.6°C. These were followed by frequently inundated low and mid-fresh-oligohaline marshes with MATmax ≤25.6°C, and mesohaline sites with MATmax >19°C. Quantile regressions of paired chamber CH4 flux and porewater biogeochemistry revealed that the 90th percentile of fluxes fell below 5 ± 3 nmol m-2 s-1 at sulfate concentrations >4.7 ± 0.6 mM, porewater salinity >21 ± 2 psu, or surface water salinity >15 ± 3 psu. Across sites, salinity was the dominant predictor of annual CH4 fluxes, while within sites, temperature, gross primary productivity (GPP), and tidal height controlled variability at diel and seasonal scales. At the diel scale, GPP preceded temperature in importance for predicting CH4 flux changes, while the opposite was observed at the seasonal scale. Water levels influenced the timing and pathway of diel CH4 fluxes, with pulsed releases of stored CH4 at low to rising tide. This study provides data and methods to improve tidal marsh CH4 emission estimates, support blue carbon assessments, and refine national and global GHG inventories.

  View details for DOI 10.1111/gcb.17462

  View details for PubMedID 39234688

• On the Relationship Between Aquatic CO₂ Concentration and Ecosystem Fluxes in Some of the World's Key Wetland Types WETLANDS Richardson, J. L., Desai, A. R., Thom, J., Lindgren, K., Laudon, H., Peichl, M., Nilsson, M., Campeau, A., Jarveoja, J., Hawman, P., Mishra, D. R., Smith, D., D'Acunha, B., Knox, S. H., Ng, D., Johnson, M. S., Blackstock, J., Malone, S. L., Oberbauer, S. F., Detto, M., Wickland, K. P., Forbrich, I., Weston, N., Hung, J. Y., Edgar, C., Euskirchen, E. S., Bret-Harte, S., Dobkowski, J., Kling, G., Kane, E. S., Badiou, P., Bogard, M., Bohrer, G., O'Halloran, T., Ritson, J., Arias-Ortiz, A., Baldocchi, D., Oikawa, P., Shahan, J., Matsumura, M. 2024; 44 (1)

  View details for DOI 10.1007/s13157-023-01751-x

  View details for Web of Science ID 001118749200001

• Combining Eddy Covariance and Chamber Methods to Better Constrain CO₂ and CH₄ Fluxes Across a Heterogeneous Restored Tidal Wetland JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Shahan, J., Chu, H., Windham-Myers, L., Matsumura, M., Carlin, J., Eichelmann, E., Stuart-Haentjens, E., Bergamaschi, B., Nakatsuka, K., Sturtevant, C., Oikawa, P. 2022; 127 (9)

  View details for DOI 10.1029/2022JG007112

  View details for Web of Science ID 000859015400001

• Tidal and Nontidal Marsh Restoration: A Trade-Off Between Carbon Sequestration, Methane Emissions, and Soil Accretion JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Arias-Ortiz, A., Oikawa, P. Y., Carlin, J., Masque, P., Shahan, J., Kanneg, S., Paytan, A., Baldocchi, D. D. 2021; 126 (12)

  View details for DOI 10.1029/2021JG006573

  View details for Web of Science ID 000734472100017

• The Potential of Satellite Remote Sensing Time Series to Uncover Wetland Phenology under Unique Challenges of Tidal Setting REMOTE SENSING Miller, G., Dronova, I., Oikawa, P. Y., Knox, S., Windham-Myers, L., Shahan, J., Stuart-Haentjens, E. 2021; 13 (18)

  View details for DOI 10.3390/rs13183589

  View details for Web of Science ID 000701274300001