Mud on the move: predicting how marshes will change as sea levels rise

Healthy tidal marshes support the food webs that underpin our fisheries; they mitigate the impact of coastal storms, and they improve water quality. However, as sea levels rise, marshes are at risk from “drowning.” To survive, marshes must maintain their elevation relative to surrounding waters. They do this, in part, through accretion, a process by which sediment suspended in the water accumulates on the marsh’s surface. For marshes to survive, accretion must keep pace with sea level rise. Making decisions to support marsh sustainability depends on the ability to accurately measure suspended sediment concentrations, yet current monitoring programs lack well-tested, effective approaches to doing so. A San Francisco Bay reserve-led team addressed this gap by developing a protocol to assess suspended sediment in tidal marshes, improve understanding of sediment dynamics, increase accuracy of ecological models, and inform marsh conservation and restoration for the future.

Project Impact

This project developed a standardized, nationally applicable protocol to measure suspended sediment concentrations above tidal wetlands that is informing marsh monitoring, conservation, and restoration in the reserve system and beyond.

This user friendly protocol allows reserves to collect data that will enhance the reserves’ Sentinel Site Program, a national monitoring program that studies how marshes change and migrate as water levels and tidal dynamics shift. The protocol is the critical first step toward access to standardized data that will help decision-makers in their efforts to support sustainable tidal wetlands in the face of rising sea levels.

The team worked with the Chesapeake Bay Virginia, Narragansett Bay, and Wells reserves to test the sampling protocol and illustrate the importance of suspended sediment concentration data in improving models for wetland accretion. The team found that the data improved understanding of marsh sediment dynamics in tidal wetlands—including variations within a site and among different types of marshes—and helped to clarify how sediment moved from offshore shallows onto marsh surfaces.

This protocol will allow standardized comparison of suspended sediment inputs across a wide range of estuarine wetlands, and when coupled with other physical measurements, will enable more detailed research into how sediment moves between wetlands and adjacent areas.

How it worked

The San Francisco Bay reserve worked with coastal managers, monitoring programs, and scientists to develop and test a standardized sampling protocol to assess suspended sediment concentration (SSC) in tidal marshes, refine inputs to marsh accretion models, and support more effective marsh management in the context of sea level rise.

To develop the protocol, the team modified and refined a previously established sampling methodology through repeated SSC sampling in San Francisco Bay area marshes. Researchers partnered with the Grand Bay and North Inlet-Winyah Bay reserves to test and apply the protocol at each reserve and explore how differences in tidal regimes, marsh characteristics, and vegetation affects protocol implementation and the resulting data. Using the San Francisco Bay marsh data as inputs into three wetland accretion models commonly used by decision-makers, they compared model outputs and assessed how data from the refined protocol changed the models’ predictive outputs.

The team engaged regional and national scientific and tidal wetland management communities throughout the project to ensure that the protocol was widely distributed, implemented, and readily understood. Team members hosted workshops and conducted an online survey to solicit input on stakeholders’ interests, needs, and understanding of SSC sampling methods and wetland accretion models. They organized working groups of key stakeholders to advise the development and implementation of the sampling protocol and convened a collaboration steering committee, comprised of outreach and facilitation experts, to ensure they implemented effective stakeholder engagement approaches.

NERRA Collaboration Research Guide

Determining who will be responsible for making decisions is an important, yet easily overlooked, part of project management. Read how this team took steps to clarify the decision-making process in our Collaborative Project Toolkit.

NERRA Collaboration Research Guide

Resources

This project developed products that coastal managers and monitoring programs at local, regional, and national levels can use to assess tidal marsh sediment dynamics, model the future distribution of tidal wetlands under projections of sea level rise, and support effective marsh management. You can learn more on the project’s web site or browse the resources below: