2024 Abstracts

Responses to Flooding in a Coastal Forest: Insights from the TEMPEST Landscape-Scale Manipulation Experiment


Peter Regier1* (peter.regier@pnnl.gov), Nick Ward1, Moses Adebayo2, Donnie Day2, Kennedy Doro2, Efemena D. Emmanuel2, Anya Hopple3, Matt Kovach2, Pat Megonigal3, Allison Myers-Pigg1, Stephanie Pennington1, Evan Phillips3, Roy Rich3, Richard Smith4, Alice Stearns3, Stephanie Wilson3, Stella Woodard4, Vanessa Bailey1


1Pacific Northwest National Laboratory, Richland, WA; 2University of Toledo, Toledo, OH; 3Smithsonian Environmental Research Center, Edgewater, MD; 4Global Aquatic Research LLC, Sodus, NY



Flooding of coastal forests is predicted to increase with rising seas and higher frequency and intensity of extreme weather. Because flooding increases soil saturation and sometimes salinity, extreme precipitation or storm surge may impact forest health and soil biogeochemistry. However, it is difficult to quantify relationships between soil saturation, salinity exposure, and ecosystem function because flooding driven by sea-level rise is occurring across decadal scales and flooding driven by storms is difficult to predict and therefore difficult to measure. To address these challenges, the team subjected 50m x 40m experimental plots in a coastal forest in Maryland, U.S. to fresh and estuarine water inundation events equal to precipitation from a ~10 year return interval storm for a duration of 10 hours as part of the Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments (TEMPEST) experiment over multiple years. Researchers present a synthesis of ecosystem responses to flooding during the first flooding event, TEMPEST 1 (2022), where researchers found immediate and clear responses to flooding and salinity from the geosphere to the atmosphere with variable return times for biogeochemical, hydrologic, and vegetation variables. During TEMPEST 2 (2023), based on findings from TEMPEST 1, researchers installed in situ dissolved oxygen and redox sensors in the upper soil profile and applied two sequential flood treatments. Researchers found that saturation drives short-lived anoxia throughout the top 30 cm of the soil column in both treatment plots, which recovered to antecedent oxygen conditions within hours post-event near the surface but days at depth. Decreased redox potential persisted for more than a week following inundation, indicating that flooding has prolonged effects on ecological and soil biogeochemical processes. Together, these results provide quantitative, spatiotemporally resolved insights into the impacts that increasing inundation regimes will have on coastal forest health and function.