17 Mar, 2014 Author: administrator

Alex Hackman, Restoration Specialist at MA Fish and Game's Division of Ecological Restoration, serves as Project Manager for the Tidmarsh Farms Restoration effort. In this critical leadership role, Alex shapes the assessment and design phase, coordinates with our 22 partnering organizations and applies for necessary funding to make the project happen. Throughout design process, Alex's commitment to "process-based restoration" and his extensive on the ground experience, including on the Eel River project, allows him to set a high standard for assessment and decision making. Very simply, this project could not happen without him!

As we apply for permitting, Alex is increasingly called on to present to agencies, funders and researchers. On February 25th, Alex gave an informational presentation to Plymouth’s Conservation Commission. Three days later, on February 28th, he provided an overview of the project to researchers who had gathered for the 2014 Living Observatory Research Summit. In this post, I draw on these recent presentations to provide an overview of the near-final design and the expected schedule for implementation.

Alex begins most presentations by situating Tidmarsh Farms geographically and historically. Where does all the water come from? What do old maps tell us about how the water was manipulated first for light manufacturing and later for farming?

On this map, a blue outline indicates the limits of the small (5.4 square mile) coastal watershed; the pink shows the extent of Tidmarsh Farms (577 acres); and the green defines the 250 acre restoration area. The restoration site is a valley that collects water from Pine Hills and Long Island Pond to the West, from Fresh Pond to the East, and from two headwater areas with in the restoration envelop: the former Beaver Dam Pond and "The Arm". All this water flows northward through a red maple swamp before it crosses 3A, where it continues onwards through Bartlett Pond, to the ocean at White Horse Beach.

What is the restoration area like today? Two images tell the story. In 2011, we drained the 35 acre reservoir in the Southern portion of the restoration site. Despite its man-made origins, this water body carried the name Beaver Dam Pond. Today, this area supports a beautiful naturalized marsh. Just to the north, an earthen dam with concrete spillways still separates this naturalized marsh from the former cranberry bogs. Across this 130 acre expanse, water is channelized and stagnant, the bog surface flat and featureless.

This was not always the case. A map from 1830 shows that at that time much of the property was forested. When we were digging test pits, we discovered wood stumps under the bog surface. The 1830's map also provides the tell-tale evidence of a dam at 3A. This dam backed up water into what 70 years later would become the central area of the cranberry bog complex. Alex encourages us to remember the a distinctive kidney bean shape of the pond as seen in this map.

In 2012, a team from the GeoSciences Department at University of Massachusetts, Amherst, used Ground Penetrating Radar (GPR) to image the peat kettles below the surface of the bogs. The location of the peat corresponds to the lowest areas of the site. The most recent LIDAR survey clearly shows the lowest depressions across the landscape, and echoes the kidney bean shape of the left by the earlier pond as seen on the 1830 map.

Learning what the site looked like in the past is critical to thinking about how to design for the future. Here are our goals:

To encourage the development of a self-sustaining, complex, productive and dynamic (resilient) systems of high-quality streams and native wetlands.
To establish a refuge for diverse native plant and animal communities, including a restored herring run.
To increase the connection between people and the land by providing an evolving, beautiful naturalized area for public use and enjoyment, engaging people in discovery, and communicating our discoveries in meaningful ways.

With these goals and knowledge of the site, Alex lays out the 4 elements of our approach beginning with a guiding theory, "Process-based restoration". Process-based restoration focuses on the restoration of underlying ecological processes. In the case of Tidmarsh, we want to restore the natural movement of water across the landscape. The restoration of this physical process will have a cascading impact on other physical processes such as the movement of sediment, organic matter, nutrients and organisms. Theoretically, this generative network of processes will bring about the formation of an adaptive system of living and non-living elements, a complex eco-system that supports resilience or the ability of the landscape to adjust itself over time with changing underlying conditions.

In order to restore the natural movement of water across the site, we need to identify those conditions that limit how the water moves across the site today. In the assessment phase, we identified 3 main limiting factors or stressors: a sand layer that separates the vegetative surface from the ground water; a physical simplification of water passages; and the existence of dams and barriers.

Physical simplification; Physical barriers (Credit: A Hackman)

The straightened channels and dams were built when the cranberry bog was constructed; in farming, sand is incrementally added every three years. The sand buries leaf drop and allows new roots to grow from the cranberry vine. In the photo to the left, Nick Nelson stands in a test pit which clearly shows the 18” to 2 foot layer of alternating sand and leaf drop that exists across the surface of the cranberry cells today. This 18" to 2' layering of sand separates the ground water from the vegetative surface of the landscape causing it to become drier than it would naturally be.

In order to put the landscape on a healing trajectory, we need to plan coordinated actions that would remove the stress caused these limiting factors. In this effort, we were able to learn from Eel River, a smaller site in an adjacent watershed where a similar restoration design was completed in 2010.

Eel River 2009; Eel River 2013 (Credit: A Hackman)

The actions taken at Eel River (above in construction in 2009, and in 2014) will be repeated at Tidmarsh where large equipment will be on the ground beginning in 2015.

While it is not economically feasible to remove the sand from the entire site, the groundwater needs to be elevated to insure the wetlands are wet. This will be accomplished by filling the edge ditches and by building underground riffles in particular locations. We will address the physical simplification of water movement by removing or replacing all dams and culverts. At the northern end of the former cranberry bogs, just as the site transitions to the Red Maple Swamp, we will move the river channel back into the relic channel. A bridge will be built here to connect the Eastern and Western portions of the site. A sinuous channel will be constructed through much of the former cranberry bogs. In discussing this step, Alex points out that digging a new channel is not a preferred solution in a process-based restoration, however it is required in cases where the gradient is so minimal that it would take many decades for a natural channel to develop on its own. As the channel is built, the vegetative surface of the former bogs will be roughened and approximately 3,000 pieces of large wood will be added to the surface. The wood helps roughen the surface, provides some shade as well as complex habitat in the early stages of the restoration. These actions help to activate the native seed bank. We anticipate that this seed bank will rapidly vegetate the bog surfaces. In the final phase (2016), we will be adding some young plants including 8,000+ Atlantic White Cedar. These plants will help jumpstart the natural communities.

The final step in this restoration will be to walk away and leave natural processes to heal the land over time. After the construction equipment leaves and the plants have been put in the ground, we leave the future to "Mother Nature, Father Time".