Mechanisms of Coastal Marsh Elevation Regulation

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Sediment deposition serves an important role in the long-term maintenance of coastal marshes. USGS investigates the mechanisms of coastal marsh elevation regulation to help predict marsh sediment requirements under various sea level rise scenarios. 

Field observations of extreme sedimentation events
Field observations of extreme sedimentation events

The Science Issue and Relevance: Episodic sediment deposition plays a vital role in the long-term maintenance of coastal marshes. Effects include promotion of above-ground plant production (and feedbacks with geomorphology) and a variety of below-surface processes. Our recent scientific findings show, however, that marsh elevation responses to sedimentation are nonlinear and we believe this is in part due to complex biological system responses. Initial evidence indicates that there is a strong negative relationship between the depths of surface deposits and the subsurface biogenic contributions (i.e., root-zone expansion) that are vital to certain marsh types. Such findings are mirrored in field studies exposed to natural levels of sediment inputs. Understanding the individual and collective effects of these mechanisms is important if we are to predict marsh sediment requirements under various sea level rise scenarios and settings.

Methodology for Addressing the Issue: We address this issue using field sediment addition experiments. Central to this effort is a response-surface type, multi-year field experiment that involves a continuous range of sediment depths. This study focuses on brackish marshes, which are generally the most vulnerable coastal marsh type and also where periodic sediments are thought to be most critical. Our study is investigating five non-exclusive hypotheses about possible biogenic and physical responses of the sediment-plant system to sedimentation events.

Elevation change and vegetative response to hurricane events
Elevation change and vegetative response to hurricane events

Future Steps: This work is ongoing. Complementary efforts involving microcosms is underway at the University of Alabama through our collaboration with Dr. Julia Cherry’s lab.

Related Projects: This project is part of a collaboration with the USGS Patuxent Wildlife Research Center, specifically Drs. Glenn Guntenspergen and Don Cahoon.

Diagram of physical responses of the sediment-plant system to sedimentation events
Diagram of physical responses of the sediment-plant system to sedimentation events