Measuring Sediment Flux in Blackwater National Wildlife Refuge

Science Center Objects

The Blackwater National Wildlife Refuge (NWR), Maryland, is a tidal wetland complex that has rapidly lost vegetated marsh to open water due to invasive species, sea level rise, and landscape change. The stability of this wetland complex and others nationally has consequences for habitat availability, retention of carbon stores in soils, and coastal flood protection.

Model of  sediment fluxes in the blackwater river complex

Sediment fluxes in the Blackwater River (BWR) complex (at Blackwater National Wildlife Refuge). Red colors correspond to strong winds from the northwest that export sediment from the wetland complex. 

(Public domain.)

Most assessments of wetland stability rely on measurements of suspended sediment concentration, as well as accretion and/or elevation change to the wetland, metrics that can be misleading. In fact, disintegrating wetlands release large amounts of sediment that can increase accretion and elevation but result in an overall loss of vegetated area. In order to protect our vital wetlands, we need to understand the mechanisms controlling sediment transport to and from wetland complexes.

To this end, a 2011 CMHRP study used acoustic and optical instrumentation to measure how much the atmosphere and tides influence sediment transport to Blackwater NWR and an adjacent stable marsh in Chesapeake Bay. Results showed that high accretion rates at Blackwater NWR were a result of disintegration of wetland elsewhere in the complex due to wind and wave action. With the measurements collected, CMHRP scientists were able to calculate sediment export from the unstable system, providing needed information for further sediment-replenishment investigations.

 

 

USGS scientists on a bridge measuring sediment fluxes in wetlands

USGS scientists Neil Ganju and Sandra Brosnahan measuring sediment fluxes out of the Blackwater National Wildlife Refuge wetland complex.

(Public domain.)