갯벌 제거로 인한 수질 오염의 사례 (샌프란시스코만 사례)

[Estuarine Wetland Loss]

Destruction of most of the tidal wetlands in San Francisco Bay
is a major factor contributing to the diminished water quality in this large estuary.

Source: Nichols, F. H., 2007. The San Francisco Bay and Delta–An Estuary Undergoing Change. U.S. Geological Survey. http://sfbay.wr.usgs.gov/general_factsheets/change.html

출처 : The Environment and You by Norman Christensen (2012) Pearson - 359page

Sacramento and San Joaquin rivers. Prior to 1930, water

flowing into San Francisco Bay from these two rivers

averaged about 34 km 3 (8.2 mi 3 ) per year. Between 1930

and 1970, a number of dams and canals were installed

to divert water to agricultural fields and urban centers.

The California Aqueduct alone transports as much as 8

km 3 (1.9 mi 3 ) of water to the San Joaquin Valley and the

city of Los Angeles. By 1980, the annual flow into the

bay was less than 13 km 3 (3.1 mi 3 ), and today it is less

than 10 km 3 (2.4 mi 3 ). Over that same time, springtime

salinity in the northern portion of the bay has increased

by three- to fivefold. These changes have altered the

composition of species in the pelagic, benthic, and

wetland communities in the northern portion of the bay

and in the lower stretches of the rivers that feed it.

Many estuaries have been modified by dredging to

facilitate boat traffic and by levee construction to allow

the development of former wetlands. San Francisco Bay

again provides a striking case study. Nearly 95% of the

bay’s tidal marshes have been lost to dredging and levee

construction (위의 그림). The loss of these marshes has

greatly diminished the ability of the estuary to filter out

the municipal, industrial, and agricultural pollutants that

rivers now carry to the bay.

Over the past few decades, communities have come

to recognize the value of estuaries and the services they

provide. As a result, they have begun to implement

programs to restore and maintain these ecosystems. For

example, the U.S. Environmental Protection Agency’s

(EPA’s) National Estuary Program works with states and

communities to restore shorelines and wetlands and

to reduce the inputs of pollutants. The EPA also sets

standards for salinity and regulates the minimum flow of

rivers into many estuaries.

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