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| Titel |
Temporal responses of coastal hypoxia to nutrient loading and physical controls |
| VerfasserIn |
W. M. Kemp, J. M. Testa, D. J. Conley, D. Gilbert, J. D. Hagy |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 12 ; Nr. 6, no. 12 (2009-12-15), S.2985-3008 |
| Datensatznummer |
250004226
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| Publikation (Nr.) |
 copernicus.org/bg-6-2985-2009.pdf |
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| Zusammenfassung |
| The incidence and intensity of hypoxic waters in coastal aquatic ecosystems
has been expanding in recent decades coincident with eutrophication of the
coastal zone. Worldwide, there is strong interest in reducing the size and
duration of hypoxia in coastal waters, because hypoxia causes negative
effects for many organisms and ecosystem processes. Although strategies to
reduce hypoxia by decreasing nutrient loading are predicated on the
assumption that this action would reverse eutrophication, recent analyses of
historical data from European and North American coastal systems suggest
little evidence for simple linear response trajectories. We review published
parallel time-series data on hypoxia and loading rates for inorganic
nutrients and labile organic matter to analyze trajectories of oxygen
(O2) response to nutrient loading. We also assess existing knowledge of
physical and ecological factors regulating O2 in coastal marine waters
to facilitate analysis of hypoxia responses to reductions in nutrient
(and/or organic matter) inputs. Of the 24 systems identified where
concurrent time series of loading and O2 were available, half displayed
relatively clear and direct recoveries following remediation. We explored in
detail 5 well-studied systems that have exhibited complex, non-linear
responses to variations in loading, including apparent "regime shifts". A
summary of these analyses suggests that O2 conditions improved rapidly
and linearly in systems where remediation focused on organic inputs from
sewage treatment plants, which were the primary drivers of hypoxia. In
larger more open systems where diffuse nutrient loads are more important in
fueling O2 depletion and where climatic influences are pronounced,
responses to remediation tended to follow non-linear trends that may include
hysteresis and time-lags. Improved understanding of hypoxia remediation
requires that future studies use comparative approaches and consider
multiple regulating factors. These analyses should consider: (1) the
dominant temporal scales of the hypoxia, (2) the relative contributions of
inorganic and organic nutrients, (3) the influence of shifts in climatic and
oceanographic processes, and (4) the roles of feedback interactions whereby
O2-sensitive biogeochemistry, trophic interactions, and habitat
conditions influence the nutrient and algal dynamics that regulate O2
levels. |
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