Human Impacts on Tidal
Wetlands: History and
Regulations (Part 1)
(Part 2)
Human Impacts on Tidal
Wetlands: History and
Regulations (Part 1)
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Ron Rozsa, Ecologist,
Office of Long Island Sound Programs
Connecticut Department of Environmental Protection
THE PREHISTORIC PERIOD
Human use of tidal wetlands could not have been important until about 1,500 to 2,000 years ago, when sea level rise slowed
and tidal wetlands became a more permanent aspect of the landscape. There is recent archeological evidence that Native
Americans living in Southern New England had established seasonal settlements near these productive wetlands, particularly
after the gradual adoption of horticulture circa 1000 AD. Digs along the lower sections of the Connecticut River indicate that
during the next 600 years there was a shift toward larger, year-round settlements. It is believed that the ecological diversity
and richness of these tidal wetlands were keys to sustaining multi-season occupation by larger groups of people.
THE COLONIAL PERIOD
The first European colonists in southern New England arrived in the early decades of the 17th Century, and immediately
recognized the value of these vast, flat expanses of tidal grasslands. Salt Meadow Cord-grass (Spartina patens), Spikegrass
(Distichlis spicata) and especially Blackgrass (Juncus gerardii) where all preferred species for livestock fodder and
bedding. Connecticut salt marshes were both hayed and, to a lesser extent, pastured continuously into the beginning of the
twentieth century (Fig. 1).
The Continental Marsh in Stonington, owned by the Davis family, was named as a reminder that hay from this marsh supplied General Washington's Continental Armies during the American Revolution. It is one of the few marshes which is still part of a working farm in which the marshes are periodically mowed.
Very early on farmers began digging shallow ditches into the marsh peat to drain standing water. This tended to increase yields of Salt Meadow Cord-grass and made access with equipment easier. Today, salt marsh hay is only harvested on a few marshes, and is sold at a premium as a weed-free garden mulch. By 1900, nearly 50% of the marshes between Southport and the Connecticut River had been ditched. Ditches were also used as boundary markers between properties. In some marshes such as Leetes Island and Sluice Creek in Guilford, complete drainage was achieved through the installation of tidal gates (doors hinged at the top which are suspended across a bridge or culvert to eliminate the inflow of salt water, Fig. 2).
Fig. 2 A pair of tidal gates on Sybil Creek, Branford (R. Rozsa) (111K)
The conversion of tidal coves and embayments into millponds began in the 1700's, primarily in central and western Long Island Sound where the greater tidal range provided more tidal energy for the mill operation. Sherwood Mill Pond, Holly Pond, and Sluice Creek are each examples of former millponds. The inlets to these coves were modified through the installation of tide gates which allowed tidal flow into the cove but closed at high tide. Water was returned to the Sound through a narrow channel called a sluiceway, which contained the waterwheel for the mill. In many places the gates caused prolonged flooding of areas of salt marsh, contracting the once extensive vegetation to a narrow fringe along the elevated borders of the millpond. This pattern can still be observed today at Gorham Pond in Darien. Although tidal mills no longer exist along the coast, many of the original water control structures have been retained in order to create permanent ponds. The reduced tidal flows to these sites often cause water quality problems and increased sedimentation.
POST-COLONIAL PERIOD
Since colonial times, transportation facilities have caused notable direct losses of wetlands. Among the earlier projects were
the construction of the shoreline railroad in the mid 1800s and the shoreline trolley in the late 1800s. However, major impacts
came in the mid 1900s with the large east-west roads such as Interstate 95. Fill was placed in tidal wetlands to create an
elevated base for the various projects. The last major loss of marsh in highway construction was on I-95 when a portion of the
Sherwood Island State Park salt marsh was filled for a parking lot, as documented in Arboretum Bulletin No. 12 (1961).
Some of the largest wetland areas filled for transportation facilities include what are now the Quinnipiac River railroad yard
and Bridgeport Airport. The latter is entirely constructed on fill placed over tidal wetlands.
In recent years, concerns have been expressed regarding secondary impacts of modern, narrow bridge spans. Most of the wetland or water is now crossed via filled causeways and the actual new bridges span a much smaller distance than did the older, trestle bridges they replaced. It was thought that the newer causeway/bridges restricted tidal flow, which in turn reduced the amplitude of the tide and promoted increased sedimentation. Recent investigations in eastern Connecticut found no significant changes in tidal hydrology or increased sedimentation behind at least two of these narrow span bridges.
Boats were a primary means of travel and commerce until the early part of this century. Extensive areas of wetland were filled and bulkheaded, creating upland to support shipping facilities, or were dredged providing deep water for navigation. The sediments dredged from harbors were often dumped on nearby wetlands. Many examples exist: Morris Creek in East Haven; West River in West Haven; Great Meadows in Stratford; East River in Guilford; and Mumford Cove in Groton. As the need for waterborne commerce diminished, the recreational boating industry blossomed and numerous wetlands were dredged and filled to create sheltered water bodies for marinas.
Mosquito Control
Virtually all salt marshes adjacent to the Sound were altered by a variety of mosquito control activities. Mosquito control
practices began after the Civil War as homeward bound soldiers brought malaria to Connecticut. The disease soon reached
epidemic proportions, and wetlands of all types were filled or drained to prevent malaria transmission by Anopheles
mosquitoes. With the elimination of malaria as a health threat, control efforts targeted the large broods of nuisance mosquitoes
that originated on tidal wetlands, especially salt marshes. Hundreds of kilometers of mosquito ditches were hand dug to drain
marsh surface waters, especially the intermittent pools or pannes which are the preferred breeding habitat for salt marsh
mosquitoes (Fig. 3). While ditching did not destroy the salt marshes, it did change the abundance of certain plants and animals.
In some wetter high marshes where the pannes were dominated by Stunted Smooth Cord-grass(Spartina alterniflora - short
form), they were replaced by Salt Meadow Cord-grass. The loss of pannes also probably contributed to reduced populations
of the Seaside Sparrow (Ammodramus maritimus) which today is an increasingly rare species. Use of the salt marsh by
waterfowl, shorebirds and wading birds also declined as their preferred shallow water habitats disappeared. In other cases,
the levees along the edge of the ditches actually improved wildlife habitat, since tidal water could not readily drain off.
Fig. 3 Many miles of mosquito ditches were hand-dug during the Great Depression. (DEP) (125K)
By the 1940's nearly all of Connecticut's salt marshes were ditched, with much of the labor supplied by government programs to put unemployed men to work during the Great Depression. In some towns the original ditches were not maintained after their initial construction, but are still very much in evidence. A good example is Great Meadows, Stratford, where sixty years after being dug, all ditches are still visible on aerial photographs and some are still functioning to remove surface water. Clearly salt marshes recover very slowly from such physical alterations (Fig. 4).
Fig. 4 The extent of mosquito ditching is best seen in aerial photographs. (DEP OLISP) (109K)
SUGGESTED READING
Tedone, D., editor. 1982. A History of Connecticut's Coast: 400 Years of Coastal Industry and Development. Coastal Area Management, Hartford, Connecticut. 75 pgs.
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