Sentinel Monitoring of Salt Marshes in the Wells National Estuarine Research Reserve

Rachel M. Gregg
Posted on: 3/30/2010 - Updated on: 10/28/2021

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Rachel Gregg

Project Summary

The Wells National Estuarine Research Reserve (Wells Reserve), along with several other National Estuarine Research Reserves, acts as a sentinel site to monitor climate change impacts. The reserve is engaged in several long-term ecological monitoring programs to determine the effects of sea level rise, saltwater intrusion, warmer temperatures, shoreline erosion, and coastal storms on species and habitats.


The Wells Reserve in southern Maine protects over 2,000 acres of coastal habitats, including salt marshes, wetlands, dunes, and forests. The reserve’s salt marshes provide valuable habitat for fish, crabs, and other wildlife, and important ecosystem services by filtering water and protecting shorelines during strong coastal storms. Salt marshes in the reserve area have been altered by humans through dams, dredging, ditches, culverts, tide gates, filling, and development; these activities have resulted in restricted flow, reducing access for marine wildlife and causing continual habitat degradation. This habitat is also threatened by climate change; impacts of concern include sea level rise, warmer temperatures, and coastal storms.

The Wells Reserve was part of a national effort to establish salt marshes as long-term reference sites at five reserves (Narragansett; Wells, Maine; Chesapeake Bay, Virginia; North Carolina; South Slough, Oregon) to compare marsh restoration success. Additionally, the reserve, along with other NERRs, participates in the System Wide Monitoring Program (SWMP), tracking changes in water quality, plants, animals, and habitats within the reserve over time. SWMP provides real-time NERR data and allows users to compare variables between reserves over different time periods. In addition, the Wells NERR monitors for indicators of salt marsh health such as population densities of birds and larval, juvenile, and adult utilization.


The NERR System and NOAA Restoration Center partnered on a project—created in 2007—to establish salt marshes as long-term reference sites at five reserves (Narragansett; Wells, Maine; Chesapeake Bay, Virginia; North Carolina; South Slough, Oregon). The project was funded through the National Oceanic and Atmospheric Association to 1) use natural marshes as references to understand what is happening at restored marshes, and 2) use these natural reference sites to understand how marshes across the United States are responding to the impacts of climate change. The project required the reserves to conduct effectiveness monitoring of 17 Estuary Restoration Act-funded projects at paired restoration and reference sites. The study used a restoration performance index (RPI) to compare different salt marsh characteristics (e.g., salinity, vegetation cover, flow patterns, peat soils) at natural marsh reference sites and recently restored marsh sites over a two-year period (2008­–2010) to track water levels and marsh height in order to determine if and how salt marshes can respond to environmental changes, including sea level rise. The Wells Reserve compared results between one reference site (Webhannet Marsh) and four restoration sites (Cascade Brook, Drakes Island, Spruce Creek, Wheeler Marsh). The study determined that the restoration of hydrologic processes across the five NERRs were quite high while biological processes (e.g., species density, vegetation composition) varied as coastal marsh plant community development may lag in recovery (see Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index).

Through monitoring over the years, the Wells Reserve has provided valuable additions to the growing database of knowledge surrounding marshes and climate change. One of the ways marshes respond to climate change is by moving inland in a process known as marsh migration. Coastal infrastructure often blocks this movement resulting in “coastal squeeze.” Staff at the Wells Reserve partnered with the University of New England to research the effects of coastal squeeze in a neighboring estuary, further contributing to the national effort to increase knowledge about how tidal marshes respond to climate change. Through LiDAR mapping and sea level rise data, researchers were able to map marsh areas that would likely be lost to coastal squeeze. Other ways the reserve contributes to research is through innovating its monitoring systems with unique studies and projects such as:

  1. Creating an Unmanned Aerial Systems Roadmap as a pilot project to explore the opportunities for applying drone technology to monitoring;
  2. Tracking the spread of invasive marine species through citizen science using the Marine Invader Monitoring and Information Collaborative (MIMIC); and
  3. Becoming the first non-profit in Maine to have all of its electricity supplied by solar energy.

All of the reserve’s projects are guided by five core goals. One of their core goals is to reach a broader audience to expands people’s understanding of the effects of climate and to develop tools to adapt to those changes.

Outcomes and Conclusions

In general, NERRs can be particularly useful as long-term reference sites in a changing climate as they are protected areas that undergo regular long-term monitoring of environmental changes. The data collected may be used to inform other restoration efforts and coastal management.

Wells National Estuarine Research Reserve Management Plan 2013 – 2018
Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index (RPI)
National Estuarine Research Reserve System-Wide Monitoring Program Data


Gregg, R. M. and J. Sheldon. (2021). Sentinel Monitoring of Salt Marshes in the Wells National Estuarine Research Reserve [Case study on a project of the Wells National Estuarine Research Reserve]. Version 2.0. Product of EcoAdapt’s State of Adaptation Program. (Last updated June 2021)

Affiliated Organizations

The Wells Reserve is one of 27 reserves in the National Estuarine Research Reserve System (NERRS). Currently, NERRS protects over one million acres of estuarine waters and adjacent upland habitats. The Wells Reserve focuses on research, education, and stewardship, and operates programs in coastal research and monitoring, environmental learning and decision-maker training, and land and water resource management.

NOAA is an agency that enriches life through science. Our reach goes from the surface of the sun to the depths of the ocean floor as we work to keep citizens informed of the changing environment around them. From daily weather forecasts, severe storm warnings and climate monitoring to fisheries management, coastal restoration and supporting marine commerce, NOAA’s products and services support economic vitality and affect more than one-third of America’s gross domestic product.

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