OCEANS AND ESTUARIES - Water Quality Engineering in Natural Systems - page 328

TABLE 9.9. Sample of Major Estuaries in the United States

Area Watershed Size

Estuary (km 2 ) (mi 2 ) (km 2 ) (mi 2 ) Features Major Threats

San Francisco
Bay

4140 16.0 155,400 600 Two major inflow rivers: Sacramento

and San Joaquin. Depth of Central
Bay averages 13.1 m (43 ft),
southern and northern areas
4.6-5.2 m (15-17 ft), deepest point
110 m (360 ft) below sea level,
under golden gate Bridge.

Variety of contaminants
originating from sewage
discharges, agricultural and
urban runoff.

long Island
Sound

3420 13.2 43,560 168 Average depth is 19.2 m (63 ft). low dissolved oxygen, toxics,

pathogens, floatable debris, living
resources and habitat. Domestic
and industrial wastewater are
significant sources.

galveston Bay 1550 6.0 10,980 42 Average depth is 2.1 m (6.9 ft). Variety of contaminants

originating from sewage
discharges and urban runoff.

Tampa Bay 1040 4.0 5700 22 Four major inflow rivers:

Hillsborough, Alafia, Manatee, and
little Manatee. On average, only
3.7 m (12 ft) deep.

Excess nitrogen from stormwater
and wastewater discharges,
habitat loss.

from urban and agricultural areas are the major con-
tributors to water-quality degradation in estuaries.

Bar-built estuaries or lagoons were formed by breach-
ing of ancient sandbars (barrier islands) and flood-
ing of the region behind them due to rising sea
levels. They are typically well mixed and are found
off the gulf coast or South Atlantic regions of the
United States. Examples include Pamlico Sound in
North Carolina and Biscayne Bay in south Florida.
Other estuaries that do not fit into the preceding
three categories include San Francisco Bay, which
was formed by tectonic forces.

9.3.1 Classification of Estuaries

Analysis of estuaries can be simplified by using a clas-
sification system to compare similar types of estuaries.
The most common classifications are based on geomor-
phology and stratification. geomorphological classifica-
tion of estuaries is as follows: (1) coastal plain estuaries,
(2) fjords, (3) bar-built estuaries, and (4) other estuaries
produced by tectonic activity, faulting, landslides, and
volcanic eruptions. These types of estuaries are described
below.

Shallow partially mixed estuaries tend to be very pro-
ductive and sensitive to the input of nutrients, while
elongated deep estuaries tend to be migration routes for
anadromous and catadromous fish and are less sensitive
to nutrient inputs. Anadromous fish live most of their
lives in saltwater and return to freshwater to spawn (e.g.,
herring and salmon), while catadromous fish live most
of their lives in freshwater and return to saltwater to
spawn (e.g., eels).

Coastal plain estuaries are gently sloping toward the
mouth of the estuary (i.e., where the estuary meets
the sea) and are sometimes stratified. Examples
include Chesapeake Bay, Delaware River estuary,
and New York Bight. Coastal plain estuaries were
formed by the drowning of an ancient river mouth
due to the rising sea levels at the end of the last
ice age.
Fjords are formed by glaciation and are typically
strongly stratified, deep, and in the shape of narrow
gorges. Fjords are usually found a higher latitudes,
with many occuring in Norway and Alaska. Puget
Sound is an example of an estuary formed by
glacial scouring.

9.3.2 Water-Quality Issues

The most critical water-quality indicators regarding the
health of an estuary are usually dissolved oxygen (DO),
chlorophyll a , nutrients, toxicants, and pathogens. DO is
an important water-quality indicator for all fisheries
uses. Chlorophyll a is the most popular indicator of algal