admin 管理员组文章数量: 1087135
2024年6月17日发(作者：论坛网站前端模板)
新托福TPO22阅读原文(一)：Spartina
TPO22-1：Spartina
Spartina alterniflora, known as cordgrass, is a deciduous, perennial flowering
plant native to the Atlantic coast and the Gulf Coast of the United States. It is the
dominant native species of the lower salt marshes along these coasts, where it grows
in the intertidal zone (the area covered by water some parts of the day and exposed
others).
These natural salt marshes are among the most productive habitats in the marine
environment. Nutrient-rich water is brought to the wetlands during each high tide,
making a high rate of food production possible. As the seaweed and marsh grass
leaves die, bacteria break down the plant material, and insects, small shrimplike
organisms, fiddler crabs, and marsh snails eat the decaying plant tissue, digest it, and
excrete wastes high in nutrients. Numerous insects occupy the marsh, feeding on
living or dead cordgrass tissue, and redwing blackbirds, sparrows, rodents, rabbits,
and deer feed directly on the cordgrass. Each tidal cycle carries plant material into the
offshore water to be used by the subtidal organisms.
Spartina is an exceedingly competitive plant. It spreads primarily by
underground stems; colonies form when pieces of the root system or whole plants
float into an area and take root or when seeds float into a suitable area and germinate.
Spartina establishes itself on substrates ranging from sand and silt to gravel and
cobble and is tolerant of salinities ranging from that of near freshwater (0.05 percent)
to that of salt water (3.5 percent). Because they lack oxygen, marsh sediments are
high in sulfides that are toxic to most plants. Spartina has the ability to take up
sulfides and convert them to sulfate, a form of sulfur that the plant can use; this ability
makes it easier for the grass to colonize marsh environments. Another adaptive
advantage is Spartina’s ability to use carbon dioxide more efficiently than most other
plants.
These characteristics make Spartina a valuable component of the estuaries where
it occurs naturally. The plant functions as a stabilizer and a sediment trap and as a
nursery area for estuarine fish and shellfish. Once established, a stand of Spartina
begins to trap sediment, changing the substrate elevation, and eventually the stand
evolves into a high marsh system where Spartina is gradually displaced by
higher-elevation, brackish-water species. As elevation increases, narrow, deep
channels of water form throughout the marsh. Along the east coast Spartina is
considered valuable for its ability to prevent erosion and marshland deterioration; it is
also used for coastal restoration projects and the creation of new wetland sites.
Spartina was transported to Washington State in packing materials for oysters
transplanted from the east coast in 1894. Leaving its insect predators behind, the
cordgrass has been spreading slowly and steadily along Washington’s tidal estuaries
on the west coast, crowding out the native plants and drastically altering the landscape
by trapping sediment. Spartina modifies tidal mudflats, turning them into high
marshes inhospitable to the many fish and waterfowl that depend on the mudflats. It is
already hampering the oyster harvest and the Dungeness crab fishery, and it interferes
with the recreational use of beaches and waterfronts. Spartina has been transplanted to
England and to New Zealand for land reclamation and shoreline stabilization. In New
Zealand the plant has spread rapidly, changing mudflats with marshy fringes to
extensive salt meadows and reducing the number and kinds of birds and animals that
use the marsh.
Efforts to control Spartina outside its natural environment have included burning,
flooding, shading plants with black canvas or plastic, smothering the plants with
dredged materials or clay, applying herbicide, and mowing repeatedly. Little success
has been reported in New Zealand and England; Washington State’s management
program has tried many of these methods and is presently using the herbicide
glyphosphate to control its spread. Work has begun to determine the feasibility of
using insects as biological controls, but effective biological controls are considered
years away. Even with a massive effort, it is doubtful that complete eradication of
Spartina from nonnative habitats is possible, for it has become an integral part of
these shorelines and estuaries during the last 100 to 200 years.
版权声明：本文标题：新托福TPO22阅读原文及译文(一):Spartina 内容由网友自发贡献，该文观点仅代表作者本人， 转载请联系作者并注明出处：http://roclinux.cn/p/1718623909a724737.html， 本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌抄袭侵权/违法违规的内容，一经查实，本站将立刻删除。
发表评论