Results
of the Narragansett Bay
Coastal Wetland and Buffer Zone Trend Analysis
Trends
in Narragansett Bay Coastal Wetlands from the 1950s to 1990s
From the 1950s to the 1990s, the Narragansett Bay estuary experienced
a net loss of 548 acres (1% loss) of tidal habitat including coastal
wetlands and waters. The losses concentrated on intertidal habitats
with a net loss of 306 acres (10% loss) of estuarine marshes (excluding
oligohaline marshes) and a net loss of 205 acres (11% loss) of
intertidal nonvegetated wetlands (unconsolidated shores). Almost
110 acres (0.1% loss) of coastal waters were lost. The details
of acreage losses are provided in Table
6.
The nature
and causes of coastal wetland changes such as coastal processes,
plant succession, tidal restriction, and residential development,
are summarized in Table
7. The loss of a given wetland may be attributed to more than
one cause so the acreage totals from Table 7 may be greater than
the net acreage figures reported in Table 6. Over 50% of the loss
of estuarine marsh was due to filling that created upland (dryland),
and nearly 40% of the loss was attributed to conversion to open
water (15%), fresh water wetland (12%), and tidal flats (11%).
Nine percent of the loss was represented by acreage that changed
to estuarine scrub-shrub wetland. While estuarine marshes experienced
net losses, there were some gains in estuarine wetland acreage
in places. Gains largely came from tidal flats and estuarine water
which accounted for over 70% of the estuarine marsh acreage gained.
Of the changes to estuarine scrub-shrub wetlands, nearly 60% was
due to a gain from estuarine emergent wetland.
Forty percent of the changes in these shrub swamps were losses
to estuarine marshes (33%) and to upland (7%). Most of the change
in estuarine nonvegetated flats and shores were losses. More acreage
was converted to open water than came from open water. This may
be a sign of the impact of rising sea level associated with global
warming. About 106 acres of nonvegetated coastal wetlands were
converted to upland.
Trends
in Land Use/Land Cover within the 500-Ft. Buffer of Narragansett
Bay Coastal Wetlands from the 1950s to 1990s
Significant
changes in the buffer occurred during the 40-year study interval.
A 40% (2,505 acres) increase in residential land occurred largely
at the expense of rangeland and agricultural land which decreased
by 31% (1,729 acres) and 55% (1,630 acres), respectively (Table
8). This increase was mostly (94%) attributed to a rise in
single-family homes along the coastal wetlands, whereas 92% of
the loss of agricultural land was from pasture and haylands.
Trends
in Coastal Wetlands at Six Demonstration Sites in Narragansett
Bay from 1930s to 1950s and 1950s to 1990s
Wetland trends
from the 1930s to the 1950s and the 1950s to the 1990s were examined
for six study areas in the Narragansett Bay Estuary: 1) Allins
Cove (including West Shore of Barrington), 2) Calf Pasture Point
(North Kingstown), 3) Jacobs Point (Warren and Bristol), 4) Palmer
River (Warren and Swansea), 5) Sachuest Point (Middletown), and
6) Wesquage Pond (Narragansett). All sites experienced net losses
of coastal wetlands (Table
9). With a net loss of 104.0 acres (53% loss), Calf Pasture
Point lost the most coastal wetland acreage between the 1930s
and the 1990s. Wesquage Pond was next ranked with a net loss of
52.6 acres (50% loss), followed by Sachuest Point (net loss of
27.9 acres or 16% loss). The other areas experienced only minor
net losses (Allins Cove - 7.4 acres or 7% loss; Jacobs Point -
4.4 acres or 8% loss; Palmer River - 0.7 acre or 0.3% loss). The
nature and causes of changes in wetlands and deepwater habitats
are presented for each study area in Tables 10 through 15.
Calf Pasture
Point lost more acreage of coastal marsh prior to the 1950s, while
it lost more unconsolidated shore (e.g., flats) since then
(Table
11). In the earlier period, roughly 70 acres of marsh were
lost, with 83% converted to upland; 17 acres of tidal flats were
lost with about 14 acres filled (10 acres - commercial/services).
Most of this new land was undeveloped in the 1950s (e.g., barren
land and rangeland). The rest of the lost marsh was classified
as irregularly flooded nonvegetated wetland (spoil deposits in
the high marsh) which likely were converted to upland thereafter.
From the 50s to the 90s, Calf Pasture Point lost 86 acres of tidal
flat and 17 acres of coastal marsh. About 60% of the former losses
resulted in an increase in estuarine open water possibly due to
a combination of coastal processes (erosion) before the shoreline
was stabilized. Filling at Calf Pasture Point created nonvegetated
wetlands from open water during the earlier period (this operation
was ongoing in the 1950s) and as more fill was deposited these
areas were converted to upland. Most of the marsh loss in this
area took place during the early stages of this filling operation.
By the 1990s, much of the lost coastal marsh between the 1950s
and 1990s had become palustrine Phragmites marsh.
Wesquage Pond
lost most of its tidal flats prior to the 1950s, accounting for
87% of the losses between the 1930s and 1990s (Table
15). Nearly all of these losses were attributed to tidal restriction
which converted intertidal flats mostly to estuarine open water
(oligohaline). This action also affected tidal marshes contributing
to about a one-acre gain and a five-acre change in tidal marsh
type (i.e., some irregularly flooded wetland to regularly flooded
marsh and creating oligohaline conditions). About five acres of
tidal marshes were filled in Wesquage Pond between the 1950s and
the 1990s, with most being undeveloped (rangeland) in the 1990s.
About four acres of marsh became open water due to tidal restriction.
Sachuest Point lost most of its coastal wetlands from the 1950s
to the 1990s (Table
14). Thirty-eight acres of emergent wetlands were filled during
this time. Filling most likely took place prior to passage of
the tidal wetland protection act. Spoil deposition was a major
factor impacting wetlands from the 1930s into the 1950s. In the
1990s, much of this acreage remained undeveloped in shrub or herbaceous
cover. Some filling also took place at Sachuest Point between
the 1930s and 1950s with about 6 acres of tidal flat (estuarine
unconsolidated shore) impacted.
