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On the transformation from healthy
to degraded aquatic ecosystems
David J. Rapport
College Faculty of Environmental Design and
Rural Development, University of Guelph, Guelph, Ontario,
Canada
Faculty of Medicine and Dentistry, The University of Western
Ontario, London, Ontario, Canada
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Abstract
Aquatic ecosystems that have become degraded under stress
show similarities both in the signs of pathology and in the mechanisms
that promote degradation. A review of the transformations in several
aquatic systems, including the Laurentian Great Lakes (Canada/US),
the Baltic Sea (Finland) and Lake Chapala (Mexico) reveals signs
of 'ecosystem distress, including alterations in primary and secondary
productivity, nutrient cycling, species diversity and biotic composition.
A shift from a predominantly vertical to horizontal nutrient spiraling
characterizes all three aquatic ecosystems, as does a reduction
in the abundance of the larger (high-valued) fish stocks. Once the
health of robust systems begins to decline, mechanisms are called
into play that tend to perpetuate the ecosystem breakdown. The process
may be difficult to reverse, even when sources of initial stress
are removed. © 1999 Elsevier Science Ltd and AEHMS. All rights
reserved.
Keywords: Ecosystem distress; Nutrient spiraling; Ecosystem
breakdown
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