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| Titel |
Hypoxia and cyanobacteria blooms - are they really natural features of the late Holocene history of the Baltic Sea? |
| VerfasserIn |
L. Zillén, D. J. Conley |
| 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 ; 7, no. 8 ; Nr. 7, no. 8 (2010-08-31), S.2567-2580 |
| Datensatznummer |
250004940
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| Publikation (Nr.) |
 copernicus.org/bg-7-2567-2010.pdf |
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| Zusammenfassung |
| During the last century (1900s) industrialized forms of agriculture and human
activities have caused eutrophication of Baltic Sea waters. As a consequence, the hypoxic
zone in the Baltic Sea has increased, especially during the last 50 years, and has caused severe
ecosystem disturbance. Climate forcing has been proposed to be responsible for the reported
trends in hypoxia (< 2 mg/l O2) both during the last c. 100 years (since c. 1900 AD) and the
Medieval Period. By contrast, investigations of the degree of anthropogenic forcing on the
ecosystem on long time-scales (millennial and greater) have not been thoroughly addressed.
This paper examines evidence for anthropogenic disturbance of the marine environment
beyond the last century through the analysis of the human population growth, technological
development and land-use changes in the drainage area. Natural environmental changes, i.e.
changes in the morphology and depths of the Baltic basin and the sills, were probably the
main driver for large-scale hypoxia during the early Holocene (8000–4000 cal yr BP). We
show that hypoxia during the last two millennia has followed the general expansion and
contraction trends in Europe and that human perturbation has been an important driver for
hypoxia during that time. Hypoxia occurring during the Medieval Period coincides with a
doubling of the population (from c. 4.6 to 9.5 million) in the Baltic Sea watershed, a massive
reclamation of land in both established and marginal cultivated areas and significant increases
in soil nutrient release. The role of climate forcing on hypoxia in the Baltic Sea has yet to be
demonstrated convincingly, although it could have helped to sustain hypoxia through
enhanced salt water inflows or through changes in hydrological inputs. In addition,
cyanobacteria blooms are not natural features of the Baltic Sea as previously deduced, but are
a consequence of enhanced phosphorus release from the seabed that occurs during hypoxia. |
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