Answer:
Wetlands have come under natural and human threats (from
subsiding or sinking land to draining or filling for new
development). Scientists estimate that the lower 48 United
States have lost more than half of their wetlands since
colonial times.
Coastal wetlands especially have been seriously
threatened. For example, Louisiana alone has 40 percent of
the coastal wetlands in the lower 48 States and is still
losing from 25 to 35 square miles a year of wetlands to
open water because of erosion and subsidence.
In addition to coastal wetlands, seagrasses in the
estuaries along the coast of the Gulf of Mexico and
worldwide have been depleted. Serious problems also
include the tremendous loss of forested wetlands in the
South; while they account for more than a third of all
wetlands in the lower 48 States, they also account for two
thirds of the annual loss of all wetlands in the
continental United States. Wildlife, especially migratory
birds like waterfowl and Neotropical birds have
experienced population declines and distributional shifts,
partly because of habitat alteration.
Rivers and other aquatic habitats have also undergone huge
changes. They suffer impacts from various causes, ranging
from dredging to both point and nonpoint source pollutants
to contaminants. Estuaries have also seen enormous changes
in water quality and structure from dredging, fringing
urban development, industries, and shipping. All of these,
in turn, change the ecological structure and functions of
these habitats and their ability to support fish,
shellfish, and wildlife.
Restoring these wetlands and improving aquatic habitats
have become imperative to maintaining an ecological
balance. To restore and manage these valuable wetlands and
deepwater habitats, however, requires scientific research
because much remains unknown about which restoration and
management techniques work best and how restored
ecosystems work compared to natural ones.
