Environmental Engineering Reference
In-Depth Information
Shrimp, blue crabs, gobies, blennies, and many other animals
live on oyster reefs. Oyster reefs also serve to reduce wave and
storm surge impacts in coastal areas and support fishing, since
some commercially important fish are more abundant in oys-
ter reefs than in nearby mudflats.
Coastal wetlands can also absorb a lot of the nutrients in
runoff. There are many projects restoring salt marshes for the
numerous services they provide, of which absorbing nutri-
ents is only one. (But as the Deegan study discussed earlier
showed, marshes have their limits before they, too, are dam-
aged by excess nutrients.) Marshes also protect the coastline
from storm surges, and provide habitat and food for many
marine animals and terrestrial ones like shore birds.
What is the prognosis for eutrophication in the future?
While coastal ecosystems may recover when nutrient inputs
are reduced, it is a very slow process. Currently, hypoxia is
among the most harmful human influences in the marine envi-
ronment. Although there has been legislation in Europe, lev-
els have not been improving, except in Danish waters. Where
eutrophication has been reduced it has generally been from
improvements in point sources (sewage treatment) rather than
reducing nonpoint runoff or atmospheric deposition, which
are much more difficult to control. There has been little prog-
ress in reducing nonpoint sources. Global river nutrient export
has increased steadily since 1970, with South Asia accounting
for at least half of the increase. Under various future scenar-
ios, nutrient exports could change significantly over the next
30 years. Eutrophication is likely to continue to impact fresh-
water and coastal ecosystems into the foreseeable future.
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