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| Titel |
The influence of biogeochemical processes on the pH dynamics in the seasonally hypoxic saline Lake Grevelingen, The Netherlands |
| VerfasserIn |
Mathilde Hagens, Caroline Slomp, Filip Meysman, Alberto Borges, Jack Middelburg |
| 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 |
250078265
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| Zusammenfassung |
| Coastal areas experience more pronounced short-term fluctuations in pH than the open ocean
due to higher rates of biogeochemical processes such as primary production, respiration and
nitrification. These processes and changes therein can mask or amplify the ocean acidification
signal induced by increasing atmospheric pCO2. Coastal acidification can be enhanced when
eutrophication-induced hypoxia develops. This is because the carbon dioxide produced
during respiration leads to a decrease in the buffering capacity of the hypoxic bottom water.
Saline Lake Grevelingen (SW Netherlands) has limited water exchange with the North Sea
and experiences seasonal bottom water hypoxia, which differs in severity interannually.
Hence this lake provides an ideal site to study how coastal acidification is affected by
seasonal hypoxia.
We examined the annual cycle of the carbonate system in Lake Grevelingen in 2012 and
how biogeochemical processes in the water column impact it. Monthly measurements of all
carbonate system parameters (DIC, pH, fCO2 and TA), suspended matter, oxygen and
nutrients were accompanied by measurements of primary production and respiration using
O2 light-dark incubations. Primary production was also estimated every season using
14C-incubations and monthly via 13C-labeling of phospholipid-derived fatty acids (PLFA).
Finally, incubations to estimate nitrification and NH4 uptake using 15N-enriched ammonium
were carried out seasonally.
Preliminary results show that the hypoxic period was rather short in 2012. During
stratification and hypoxia, pH varied by up to 0.75 units between the oxic surface water and
the hypoxic bottom water. Consistency calculations of the carbonate system reveal that pH is
best computed using DIC and TA and that there is no significant difference between TA
measured on filtered (0.45 μm) and unfiltered samples. Primary production rates were highest
in summer and range up to 800 mmol C/m2/d. Nitrification rates varied between 73-2702
nmol/L/h and did not vary much with depth in winter (March) but increased with depth in
spring (May) due to a lack of NH4 in the surface water. Further calculations are necessary
to estimate a proton budget for Lake Grevelingen and will reveal whether on an
annual scale this saline lake is currently a source or sink for atmospheric CO2. |
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