Geoscience Reference
In-Depth Information
Mangroves, in particular, are extremely vulner-
able to oil spills and are quite slow to recover
following oil pollution; whereas grass marshes
recover relatively quickly (Whigham et al.
2010). Barrier islands suffered especially. The
Chandeleur and Breton islands are nearly gone,
as noted above (see Figs. 15-17 and 19). These
islands, neighboring islands and shoals, and
adjacent shallow waters, comprise the Breton
National Wildlife Refuge, which was established
in 1904 and is the second oldest national wild-
life refuge in the United States. The brown
pelican population suffered especially during
the 2005 storm season (U.S. Fish and Wildlife
Service Breton 2011). The refuge was closed
beginning in May 2010 because of the BP oil
spill, but was reopened in 2011 for routine
visitation.
Dauphin Island, Alabama is another barrier
island on the Mississippi Sound near Mobile Bay
(see Color Plate 8-13). The western spit of the
island is 18 km long,
addition to their environmental and ecological
importance, Padre Island and Laguna Madre are
extremely popular for recreational purposes
(Fig. 15-24).
Padre Island is constructed primarily of
sand deposited along the beach and in wind-
blown dunes behind the beach. The island
formed during the past several thousand years,
as the last great ice sheets melted, sea level
rose, and the shoreline retreated inland. Based
on various lines of evidence, sea level stood in
the range 3-10 m below present from 8000 to
4000 calendar years ago along the northern
Gulf coast (Milliken, Anderson and Rodriguez
2008), at which time the South Texas shoreline
stabilized with drowned river valleys, such as
Bafi n Bay, and submerged bars offshore
(Weise and White 1980). For the past four mil-
lennia, sea level rose gradually at roughly 5 cm
per century, until it began accelerating rapidly
in the past century. As sea level approached
modern, submerged bars built up initially as
short, segmented barrier islands, which were
situated mainly in the divides between drowned
river valleys. Long-shore sediment drift caused
the barriers to extend parallel to the coast,
and eventually they grew together into Padre
Island.
The modern island contains several distinct
environmental zones passing from the Gulf side
to the lagoon side (Fig. 15-25). Erosion, trans-
portation and the deposition of sand by wind
and waves determine the morphology of the
island and may lead to changes in its size or
position. In general, the northern portion of
Padre Island is in stable equilibrium today;
whereas, the southern section is undergoing
loss, as erosion is predominant (Weise and
White 1980; Brown and Huey 1991). Long-shore
drift moves sand generally southward or north-
ward along the upper shoreface and beach envi-
ronments, and beach sand is blown inland by
prevailing onshore wind (Fig. 15-26). The fore-
island dune ridge is a fragile feature that pro-
tects the island from storm waves and surges
(Weise and White 1980); the dunes are stabilized
by marshhay cordgrass (
Spartina patens
),
morning-glory (
Ipomoea
sp.), sea purslane
(
Sesuvium portulacastrum
), bitter panicum
2 m above sea level, and
only 200-300 m wide. This portion of the island
has been developed for recreational properties.
Hurricane Katrina completely destroyed
<
∼
300
houses and severely damaged another
150
(Crozier 2009). This part of the island has been
damaged repeatedly during many previous
storms. However, infrastructure is repaired and
new houses are erected following each storm
with federal funding from the National Flood
Insurance Program (1968) and Stafford Act
(1988), which provide i nancial support to
rebuild. According to Crozier (2009), this failed
public policy contributes to irresponsible i scal
commitment to constant redevelopment of high-
risk coastal locales.
∼
15.5.3 Padre Island and Laguna Madre
Padre Island is among the most famous barrier
islands in the world. Stretching 185 km (115
miles) from Port Isabella to Corpus Christi, it is
the longest barrier island in the United States
(Weise and White 1980). A segment some 80
miles (129 km) long is designated as Padre
Island National Seashore, which was established
in 1962. Padre Island is separated from the
mainland by Laguna Madre (Fig. 15-23). In
