Are elevation and open-water conversion of salt marshes connected?

Abstract

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(3), (2020): e2019GL086703, doi:10.1029/2019GL086703.Salt marsh assessments focus on vertical metrics such as accretion or lateral metrics such as open‐water conversion, without exploration of how the dimensions are related. We exploited a novel geospatial data set to explore how elevation is related to the unvegetated‐vegetated marsh ratio (UVVR), a lateral metric, across individual marsh “units” within four estuarine‐marsh systems. We find that elevation scales consistently with the UVVR across systems, with lower elevation units demonstrating more open‐water conversion and higher UVVRs. A normalized elevation‐UVVR relationship converges across systems near the system‐mean elevation and a UVVR of 0.1, a critical threshold identified by prior studies. This indicates that open‐water conversion becomes a dominant lateral instability process at a relatively conservative elevation threshold. We then integrate the UVVR and elevation to yield lifespan estimates, which demonstrate that higher elevation marshes are more resilient to internal deterioration, with an order‐of‐magnitude longer lifespan than predicted for lower elevation marshes.This study was supported by the USGS through the Coastal Marine Hazards/Resources Program, the National Park Service through the Natural Resource Preservation Program, and the U.S. Fish and Wildlife Service through the Science Support Partnership. Erika Lentz, Elizabeth Pendleton, Meagan Gonneea, Joel Carr, and two anonymous reviewers provided constructive advice on the study. S.F. was partly supported by US National Science Foundation award 1637630 (PIE LTER), 1832221 (VCR LTER). The geospatial data used in this study are published in the Coastal Wetlands Synthesis Products catalog on ScienceBase (https://www.sciencebase.gov/catalog/item/5b73325ee4b0f5d5787c5ff3)