Environmental Engineering Reference
In-Depth Information
5. BLACK SEA MARGINAL HABITATS IN
EUTROPHICATION CONDITIONS
The distribution of normoxic, oligoxic and anoxic [8] habitats on the NWS
is the main determining environmental factor in eutrophication conditions.
Usually, oligoxic (having reduced levels of oxygen) and anoxic (devoid of
oxygen) areas on the NWS occurs at depths from 7-10 to 35-40 m. Normoxic
habitats (having normal level of oxygen) remain in the narrow coastal zone
from the shore to 7-10m and in the deeper shelf zone from 40m to the upper
level of the permanent anoxic zone at 130-130m depth.
The first zone (from the shore to the 7-10m depth) in spring, summer and au-
tumn seasons is the most important in terms of numbers, biomass, productivity
and diversity of plant and animal species. The appearance of hydrogen sul-
phide in this habitat is an exceptional and short-term event during wind-driven
coastal upwelling. This is the reason that near-coastal biotopes are inhabited by
a large variety of algae, mollusks crustaceans, worms and other invertebrates
and coastal fish. There has even been a considerable increase in the populations
of some invertebrates such as the amphipod,
Pontogammarus maeoticus
and
the small pelagic coastal fish such as the silverside,
Atherina mochon pontica
,
sand lance,
Gymnammodites cicerellus
, gobies such as the round goby,
Neogob-
ius melanostomus
, Blenniidae species. Schools of young and adult silversides,
migrating just near the shoreline, are very dense numbering up to one-two
thousand of fish per one cubic meter of water. Such rich food attracts pelagic
predators to the shore and during recent years there has been a successful hook
fishery of the garfish,
Belone belone euxini
, bluefish,
Pomatomus saltator
, and
even the rare Black Sea salmon,
Salmo trutta labrax
. This is a new kind of
recreational fishery in the Odessa Gulf and other coastal areas, and one of very
few positive consequences of its man-made eutrophication.
6. THE CRITICAL 1970s
The major recurrent phytoplankton blooms, events of hypoxia and anoxia in
the 1970s were not limited to the Black Sea. Similar events from the late 1960s
to early 1980s were noted in the Baltic Sea, Southern North Sea, Northern
Adriatic Sea, the Persian Gulf, the Inland Sea of Japan, the Gulf of Mexico,
New York Bight [5], Elands Bay in South Africa [14], the Bay of Fundy in
Canada [15] and other coastal areas.
Such a coincidence in time of similar ecological events in different coastal
marine areas suggests that there may be a common causative factor influencing
eutrophication on a global scale. There are reasons to believe that this factor
was the sudden global increase in economic activity in the 1960s. One of
ecologically important manifestations of this activity was the Indicative World
Plan (IWP) for agricultural development, which has been named the “Green
