A comprehensive study of historical wetland losses between the 1880's and 2000's in the Long Island Sound, a 1,300 square mile estuary spanning the breadth of Long Island, New York City and up through Connecticut to Fishers Island was published this March by the Fish and Wildlife Service. The study is available here
The 31% loss of tidal wetland measured by the study mirror a common pattern of significant wetlands losses nationwide. Separately, Connecticut lost 27% of its coastal wetlands second to New York's 48% loss. Prior to 1970, wetland losses were largely a result of dredge and fill activities, which was sharply curtailed in 1970's with the passage of coastal wetlands laws protecting these valuable resources. The Connecticut Tidal Wetlands Act was passed in 1969.
The study was completed by scanning and georectifying old NOAA navigational charts dating back to the 1880's and comparing them against wetlands maps created during the last two decades. As expected, in some cases the margin of error is quite large. For many years wetland areas were only recorded as a byproduct of creating navigational charts, places to avoid running aground; they certainly were not mapped with the intention of measuring an important resource. Despite this, these maps still serve as an important, if not completely accurate, baseline depiction of wetlands.
Wetland losses can be broken into two groups, pre and post 1970. Prior to 1970, losses were largely conversion related. Losses after 1970 are less easily identifiable as being a result of a single practice, and appear to be a combination of multiple subtle stressors acting synergistically. These stressors include excessive nitrogen runoff, invasive species, sediment deprivation, changes in waterflow, pollution and climate change.
To illustrate this change, an average, healthy, unditched New England marsh is estimated to have 10% permanent open water. A recent Connecticut open water assessment determined that in the average wetland studied, 47% of it was considered permanent open water.
Ditching, a practice of digging a grid of ditches throughout a wetland to reduce its water level was a widespread practice throughout the East Coast and has hastened the conversion to open water. Networks of crisscrossing ditches were made in the early 20th century, frequently by hand, to combat mosquito borne diseases. Many of these ditches are still clearly visible and maintained throughout coastal Connecticut and Long Island. Since then, the efficacy of ditching to disrupt mosquito borne diseases has largely been discredited, and water levels are better managed through the use of tidal gates.
Today, the largest unditched tidal wetland in Connecticut measures 220 acres, is located in the Stratford Great Meadows part of the Stewart B. McKinney National Wildlife Refuge in Stratford, Connecticut.
To combat additional wetland losses a combined approach of addressing site-specific threats, and reaching out to the public to support large-scale conservation an d restoration projects could reduces wetland losses further in Long Island Sound.
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Long Island Sound Wetland Losses 1800's - Present
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- Written by charlie
- Category: Wetland Mapping
Wetlands in the News
25 April 2024
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