Environmental Engineering Reference
In-Depth Information
ECOLOGICAL CONSEQUENCES OF ANOXIC
EVENTS AT THE NORTH-WESTERN BLACK SEA
SHELF
Yu. P. Zaitsev
Odessa Branch, Institute of Biology of the Southern Seas (OB IBSS) 37, Pushkinskaya Street,
65011 Odessa, Ukraine
Abstract
The Black Sea, due to its geographical position and large drainage basin, mor-
phometry and effective isolation, is one of the most characteristic examples of
impacted marine areas. The main kind of man-made influence on the Black Sea
ecosystem is the anthropogenic eutrophication. The main consequences of this
impact during the period 1950-2000: excessive blooms of algae, decline in water
transparency, depletion of oxygen in near-bottom layers of water on the North-
western Black Sea shelf and cases of mass mortalities of benthic organisms are
discussed.
Keywords:
Black Sea, North-western shelf, eutrophication, hypoxia, anoxia, mass mortality.
1. INTRODUCTION
As a rule, development of hypoxic zones on the shelf is among the ecological
consequences of man-made eutrophication. System-specific factors appear to
modulate the response to the changes in nutrient load with some systems
such as the Black Sea, Baltic Sea, northern Gulf of Mexico (Rabalais and
Turner, present volume) to be very sensitive, while others such as San Francisco
Bay, a number of estuarine systems around Europe are more 'robust' towards
nutrient enrichment. Density stratification usually accelerates eutrophication
effects. Among direct and indirect ecosystem responses are water transparency
loss, vascular plants and macroalgae biomass changes, changes in nutrient
regeneration, frequency of toxic/harmful algae blooms, habitat worsening for
metazoans and pelagic and benthic invertebrates [4].
Up to the 1950s, phytoplankton blooms in the Black Sea were sporadic and
unusual events, restricted to narrow coastal zones in the river mouth areas [19]
and were described at first as exceptional natural phenomena. Titles of related
articles of that time are enough indicative: “An interesting case of Black Sea
surface water coloration” [12] or “A special case of Black Sea water blooming in
spring 1959” [2]. Thanks to these and other relevant publications of specialists,
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