Salinity in the Sound is less than that of the open ocean. The water
with the highest salinity can be found at the Race. This is the area
where Long Island Sound Lake met the ocean. This is the main area
where saltwater flows into the Sound. The channel at the Race is 350
feet deep and very strong currents flow here.
It is estimated that 470 cubic meters (120,000) gallons of fresh water
enter the Sound every second. The Connecticut River accounts for 70%
of this. (DEP, 1989)
A good portion of LIS is made up of the tidal wetlands along which are
salt marshes, where summer salinity averages about 20 to 30 ppt. Such
an environment is termed polyhaline. This high and variable salinity
is an important factor contributing to the relatively low species
diversity. In contrast, brackish marshes occur where salinities range
from 0.5 to 18 ppt, and freshwater tidal wetlands are located where
there is no detectable salt in the water (less than 0.5 ppt). An
important concept is that all coastal marshes are tidal, but not all
tidal marshes are salty.
Moving up an estuary, away from the Sound, salinity starts to drop
while species diversity begins to increase. Tidal action is still
operative, and typical salt marsh plants and animals still dominate,
but some characteristics of salt marshes are lost, while less salt
tolerant plants and animals appear. This transition is gradual, but by
the time salinity averages 15 ppt there is a distinctive brackish
marsh community. The technical term for such relatively salty brackish
environments is mesohaline. Farther up the estuary, where salinities
average just 5 ppt - 8 ppt, typical salt marsh plants and animals have
largely disappeared; these low salinity brackish wetlands are termed
oligohaline. Continuing upstream on the Sound's two major tidal
rivers, the Connecticut and Housatonic, tides remain important but
salinity essentially disappears. Distinctive fresh tidal marsh
communities border the rivers in these areas. Freshwater tidal marshes
are limited in Connecticut, but they are highly productive and support
an extremely diverse assemblage of plants and animals.
The salinity of the surface waters of the Atlantic, where the Bahamas
and thus Paradise Island are located, and in the open ocean ranges
from 33 to 37 parts per thousand by mass and varies with latitude and
season. Although the minimum salinity values are found just north of
the equator, in general the lowest values are in the high latitudes
and along coasts where large rivers flow into the ocean. Maximum
salinity values occur at about 25° north latitude. Surface salinity
values are influenced by evaporation, precipitation, river inflow, and
melting of sea ice. |
