Study Teases Out What Makes a Tidal Marsh “Happy” or “Unhappy”

The Takeaway: Research reserve scientists and others explain marsh persistence with a twist on novelist Leo Tolstoy’s famous “happy families” opening line.

A study’s major discovery—which the authors dub the “Anna Karenina principle”—is summed up, “Happy marshes are all alike; every unhappy marsh is unhappy in its own way.” The findings behind that playful twist on the novel’s “happy families” opening line can help coastal managers make wiser conservation decisions that consider which tidal marshes are likely to stay in place and which are likely to degrade. Published in Environmental Research Letters, the study ground-truthed previous resilience findings from the National Estuarine Research Reserve System and U.S. Geological Survey. Many partners contributed, and the authors included scientists from the Elkhorn Slough and Narragansett Bay Research Reserves.

According to the study, “happy,” or persistent, marshes all shared common traits. What healthy marshes shared most of all was vegetation distributed on the higher end across low-to-high landscape elevations. The single most important measurement in assessing a “happy” tidal marsh is whether a sizeable proportion of its vegetation is at a high elevation in relation to current water levels. Another feature of “happy” marshes is a low percentage of unvegetated versus vegetated area in the marsh landscape.

Characterizing an “unhappy,” deteriorating tidal marsh is more complex because marshes can fall apart in many different ways. One finding contradicted a previous assumption: namely, that gains in marsh elevation and sediment indicate greater resilience. The authors say marshes with these characteristics performed inconsistently and often signaled the muddy mess that degrading marshes can become, not marsh health. (2019)

More Information: Understanding Tidal Marsh Trajectories

Partners: Louisiana State University’s Department of Oceanography and Coastal Sciences, NOAA’s Elkhorn Slough and Narragansett Bay Research Reserves, University of Michigan Water Center, Woods Hole Coastal and Marine Science Center, and U.S. Geological Survey’s Pacific Coastal and Marine Science Center, Patuxent Wildlife Research Center, and Western Ecological Research Center