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| Titel |
Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use |
| VerfasserIn |
E. Asmala, R. Autio, H. Kaartokallio, L. Pitkänen, C. A. Stedmon, D. N. Thomas |
| 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 ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-05), S.6969-6986 |
| Datensatznummer |
250085395
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| Publikation (Nr.) |
 copernicus.org/bg-10-6969-2013.pdf |
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| Zusammenfassung |
| The microbial degradation of dissolved organic carbon and nitrogen (DOC, DON)
was studied in three Finnish boreal estuaries with contrasting land use
patterns (Kiiminkijoki – natural forest and peatland; Kyrönjoki –
agricultural; Karjaanjoki – mixed/urban). Bioassays of 12–18 d long durations were
used in 3 seasons at in situ temperatures. Besides the bulk parameters, a
suite of dissolved organic matter (DOM) quality parameters were also
investigated, including colored DOM (CDOM), fluorescent DOM and the molecular
weight of DOM. Bioavailable DOC and DON pools varied significantly between
the estuaries, from 7.9 to 10.6% and from 5.5 to 21.9%,
respectively. DOM originating from the catchment dominated by natural forests and
peatlands (Kiiminkijoki) had the lowest DOC and DON degradation rates, as
well as the lowest proportions of biodegradable DOC and DON. A greater
proportion of agricultural land in the catchment increased the
bioavailability of DON, but not the bioavailability of DOC (Kyrönjoki).
Additionally, DOM quality varied significantly between the estuaries, and DOM
originating from the agricultural Kyrönjoki catchment sustained higher
DOC and DON degradation rates and higher bacterial growth efficiency (BGE)
compared to those of the natural forest and peat dominated Kiiminkijoki
catchment. The quality of DOM, indicated by differences in CDOM, fluorescent
DOM and molecular weight, varied between estuaries with differing land use
and was concluded to be major driver of BGE of these systems and thereafter
to the microbial CO2 fluxes from the estuaries. The differences in BGE
resulted in a 5-fold difference in the calculated daily bacterial
CO2 emissions between the study's estuaries due to bacterial activity,
ranging from 40 kg C d−1 in the Karjaanjoki estuary to
200 kg C d−1 in the Kyrönjoki estuary. Lower DOC:DON ratios, smaller
molecular weight and higher CDOM absorption spectral slope values of DOM
resulted in higher proportion of the initial DOC and DON being transferred to
microbial growth and therefore to the pelagic food web. The pristine,
peatland and forest-dominated Kiiminkijoki catchment had the lowest BGE, and
therefore proportionally highest CO2 fluxes. |
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