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| Koolstof en stikstof cycli in de Westerschelde | |
| www.onderzoekinformatie.nl/nl/oi/nod/onderzoek/OND1290734 | |
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Engelstalige titel: Carbon and Nitrogen cycling in the Westerschelde Identifier financieringsorganisatie: OND1290734 (Other contract id) Periode: Januari 2002 tot December 2005 Status: Afgelopen Thesaurustermen Koolstofcyclus; Stikstofcyclus |
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| Abstract |
| OBJECTIVES:
Estuaries are heterotrophic systems, with overall respiration, mainly bacterial, exceeding primary production. This heterotrophy of estuarine systems is sustained by the import of organic matter from the river, the sea, lateral ecosystems and sewage. In heterotrophic systems, organic carbon cycling controls nitrogen cycling rather than the other way round. Heterotrophic systems are characterised by extensive denitrification and bacterial assimilation of dissolved nitrogen substrates. Our research will be performed in the Scheldt Estuary, a well-mixed tidal system with a long water residence time (1-3 months) that allows significant biogeochemical transformation to occur as reflected in oxygen depletion and pCO2 supersaturation. The general objective of this project is to assess the balance between production and respiration processes at the scale of the estuary and at the level of isolated communities, considering the dynamics of Carbon and Nitrogen simultaneously. This project is financed the Dutch Organization for Scientific Research (NWO) and the Fund for Scientific Research-Flanders (FWO). The project will specifically investigate: (1) system and functional group specific primary production; (2) assimilation of carbon and nitrogen by algae and bacteria; (3) study the three major nitrogen cycling processes (denitrification, nitrification and ammonium regeneration). This project is a co-operation with the dept. of Ecosystem studies and Frank Dehairs from the Free University of Brussels (VUB). Emphasis of the work of the department of Marine Microbiology will be on the C-aspects of this project, which will be summarized below. APPROACH: Primary productivity will be established using a suite of methods: 1) total 14C-uptake; 2), production of 18O2 from H218O2; 3), photosynthetic electron flow (PAM). Specific growth rates of functional groups of algae will be determined by measuring the rate of incorporation of 13C into phospholipid derived fatty acids (PLFA's) using GC-C-IRMS. Estimates of respiration in the light vs. respiration in the dark will be made using 18O2 measurements with Membrane Inlet Mass Spectrometry. The capacity of algae to growth heterotrophically will be measured using uptake of 13C-labeled organic compounds with GC-c-IRMS. The growth rates will be compared with the d13C signature of the algae and the specific biomarkers, in order to test some ideas that the C-fractionation pattern is dependent upon the growth rate and the external CO2-availability. PLANNING 2003: In order to estimate the specific growth rate, it is necessary to know the (variation) in PLFA-content under different growth conditions. This will be investigated using simple light limited batch cultures with algae representative for the Westerschelde. A number of field campaigns in different seasons along the salinity gradient will be organized to measure primary production and functional group specific growth rates. A prototype of a specially designed submersible absorption meter will be tested and further improved. With the in situ light field, the absorption characteristics of the algae and the PAM-derived estimates of photosynthesis a bio-optical model to estimate primary production will be constructed. |
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