Tidal Attenuation and Poor Drainage Make Interior Microtidal Marshes Vulnerable to Sea Level Rise

Empirical and simulation models often assume a uniform tidal range across marsh platforms to predict marsh vulnerability to sea level rise (SLR), overlooking the hydrological heterogeneity caused by tidal attenuation and drainage conditions. We measured water level fluctuations at two microtidal marshes in Chesapeake Bay to evaluate how this assumption misrepresents hydrological stress and marsh vulnerability. Tidal attenuation reduced water level fluctuations from 60 cm at tidal creeks to 20–30 cm in deteriorating interior marsh and caused increasing hydrological sensitivity to elevation loss. Poor drainage of interior marsh zones led to consistently higher water levels and slower recession at low tide. Consequently, hydroperiod and soil saturation in interior marshes were underestimated by 10%–62%, while plant performance was overestimated by 10%–25%. These biases suggest that future models must incorporate spatially decreasing tidal range and increasing baseline water levels from marsh edge to interior to improve predictions of marsh resilience under SLR.