Ted O’Callahan helps his wife, Kim Hubbard, through one of the preserve’s wetter areas.

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Mid-afternoon on the day after Thanksgiving, I went with friends to Mass Audubon’s Daniel Webster Wildlife Sanctuary in Marshfield. This formerly agricultural property, known to some locals as Dwyer Farm, is one of my favorite places to walk. Among other things, it’s expansive, picturesque, and relatively close to home, so it’s the place I most often bring guests from out of town. It was a chilly day, but sunny, and so we chose the sanctuary’s wide open fields over other, more woodsy options.
“Favorite place” aside, it had been a few years since I’d walked at Daniel Webster. At first it didn’t seem like much had changed. We made our way around the perimeter of the 600+ acres, strolling past the pond and an observation blind, and into the woods where a series of boardwalks led us over wetlands and among ice-encrusted trees. As usual, there was plenty of beauty to observe: the blue sky reflected on the water’s surface; the rich orange and reds of bittersweet vines; bright green tufts of meadow grass poking up through the snow.
My companions were unfamiliar with the property, so while I led them around, I told them what I knew of its history and geography. How it had been spared from development decades earlier through a sustained grassroots effort; how it once belonged to nineteenth-century Senator Daniel Webster; how a portion of the parcel was indeed “sanctuary” for wildlife and thus closed to the public.
As we neared Fox Hill, a rise from which – looking toward the ocean — one can see far down into the Green Harbor River Valley, I had a vague recollection of an article I’d read in the local paper a while back . . . something about adjusting the tide gates in the dike between the harbor and the river – an effort to improve water flow and reduce flooding. I wondered if there would be a discernible difference upstream.
We continued our circuit, traversing another boardwalk through what I remembered – a few years back – as being mostly-dry marsh grass. Looking down, I was surprised to see how flooded the marsh was! High tide was still an hour away, but indeed, there was a lot more water under the walkway than there used to be. So much that I wondered, when high tide came, whether the boardwalk would be submerged.
At the end of the boardwalk, there is a grassy path that leads to a short O-shaped trail. If you go right, you can follow the trail along the water’s edge. If you go left, you climb up onto a wooden bridge that crosses – and offers a great view of — the river. Well, those are the options at low tide, at least! We found the trail pretty-well swamped; even the few steps to the bridge required careful footing.
Beyond that bridge, another boardwalk leads through a red maple swamp, to a second bridge and river crossing. My memories were of at least a foot of clearance between the boardwalk planks and the water, but again, it seemed that the distance had shortened dramatically. An inch or two more of incoming tide would have put the walkway under water.
We completed our excursion with dry feet and – for me at least – a lot of questions. Was this a fluke occurrence, or are the water levels in the river and its wetlands this high all the time now? Has there always been such a tidal influence within the wildlife sanctuary, or is this new? Is the water saltier now, due to greater tidal influence, or is it just higher? What does this mean for the vegetation along the banks of the river, and the wildlife?
I directed my inquiries to Sue MacCallum, Director of Mass Audubon’s South Shore Sanctuaries, and Jay Wennemer, the Town of Marshfield’s Conservation Agent. Here’s what I learned: Yes, indeed, the tide gates at the Brant Rock Dike are now routinely adjusted to control the flow of water into and out of the Green Harbor River. In the past, there were issues with sedimentation, flooding, and especially in summer, stench. Now the town can – for example — open the gates to allow more water to flow in, or close them to protect the river valley from a coastal storm. Thanks to this joint effort by the town and several state agencies, the marsh and river are healthier now. Similar projects have taken place with great success at Straits Pond in Hull and Cohasset, and Musquashcut Pond in Scituate.
According to Samantha Woods, Executive Director of the North and South Rivers Watershed Association, “Managing tide gates to work in concert with nature allows us to reduce the impacts these structures have on the ecology of the river. Like the removal of dams on rivers, the restoration of tidal flows changes the landscape that we have come to know in our lifetimes but ultimately the system is much healthier when we try to mimic what nature intended.”
Sara Grady, Regional Coordinator of the Massachusetts Bays National Estuary Program, is part of the team that has been monitoring changes in vegetation, fish and invertebrates associated with this project. She explains, “the changes that have been seen are primarily that there are estuarine species of plants and animals (including some salt marsh habitat) upstream of the tide gate now, and the Phragmites near the tide gate and in the upper tributaries has started to disappear. In addition, there are places on the MassAudubon property that were meadow that are transitioning to wetland, particularly the area near the osprey pole, where there is a (formerly dry) creek that now experiences tides.”
It’s important to note that none of these are negatives. In fact, according to Wennemer, they are quite positive, as they vastly improve the ability of a large inland portion of Marshfield to tolerate storm-related flooding. The landscape will change over time, but we won’t know for sure in which ways or to what degree until more time has passed. For me, that’s an intriguing proposition. As the years pass, there will be fascinating to see what happens at the Daniel Webster Sanctuary.
 by Kezia Bacon
 January 2015 
Kezia Bacon’s articles appear courtesy of the North and South Rivers Watershed Association, a local non-profit organization devoted to the preservation, restoration, maintenance and conservation of the North and South Rivers and their watershed. For membership information and a copy of their latest newsletter, contact NSRWA at (781) 659-8168 or visit www.nsrwa.org. To browse 15 years of Nature (Human and Otherwise) columns, visit http://keziabaconbernstein.blogspot.com