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| Titel |
Are coastal North Sea sediments an efficient filter for anthropogenic nitrogen? |
| VerfasserIn |
Kirstin Dähnke, Astrid Deek, Andreas Neumann, Michael Newham, Kay Emeis |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076172
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| Zusammenfassung |
| Coastal oceans like the North Sea and German Bight nowadays receive very high amounts of
surplus nitrogen from anthropogenic sources such as rivers or atmospheric deposition. The
subsequent removal of these excess nutrient loads hence is a critical feature of coastal and
marine sediments, with the strong potential to alleviate negative eutrophication
phenomena.
However, massive dredging of riverine and estuarine sediments and a long history of
diverse anthropogenic pressures can potentially alter this natural filter function of
marine/coastal sediments, and we accordingly aimed to quantify denitrification along a
gradient from the Elbe River estuary to the German Bight and North Sea.
In a joint approach, we measured natural and potential denitrification rates along a
gradient from the Elbe estuary to the Wadden Sea and further off-shore sediments. We used
both in situ and incubation techniques, aiming to quantify natural and potential rates of
denitrification. Based on our data, we also tried to unravel the influence of different factors
that limit denitrification. A statistical data analysis suggests that TOC and water column
nitrate are main controlling factors, with surprisingly little influence of oxygen penetration
depth.
We find that bulk N2 production is largely fuelled by coupled nitrification-denitrification,
with an equivalent of 19-43% of the Elbe River nitrate load being removed via this process in
spring and summer. In contrast, the direct removal of nitrate from the water column is of
subordinate role. Overall, our results show that the sedimentary filter function is only able to
remove small portions of anthropogenic nitrogen entrained to the coastal North Sea along the
coastal strip. An extrapolation of rates to different natural sediment types and their respective
areas suggests that ~ 2-3 kt, representing 5% of the spring/summer nitrate load of the Elbe
River, are removed in the near-shore region. This accordingly leaves a vast amount of surplus
nitrogen in the water column available for processes that further fuel eutrophication of the
coastal zone. |
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