Academic Journals Database
Disseminating quality controlled scientific knowledge

Nitrogen turnover in a tidal flat sediment: assimilation and dissimilation by bacteria and benthic microalgae

Author(s): K. Dähnke | A. Moneta | B. Veuger | K. Soetaert | J. J. Middelburg

Journal: Biogeosciences Discussions
ISSN 1810-6277

Volume: 9;
Issue: 6;
Start page: 6987;
Date: 2012;
VIEW PDF   PDF DOWNLOAD PDF   Download PDF Original page

In a short-term (24 h) 15N-labeling experiment, we investigated reactive nitrogen cycling in a tidal flat sediment, focusing on the relative importance of assimilatory versus dissimilatory processes and the role of benthic microalgae therein. 15N-labeled ammonium and nitrate were added separately to homogenized sediment, and 15N was subsequently traced into sediment and dissolved inorganic nitrogen (DIN) pools. Integration of results in a N-cycle model allowed us to quantify rates for the major assimilatory and dissimilatory processes in the sediment. Overall, results indicate that the balance between assimilation and dissimilation in this tidal mudflat was mainly dependent on the nitrogen source. Nitrate was utilized almost exclusively dissimilatory via denitrification, whereas ammonium was rapidly assimilated, with about a quarter of this assimilation due to benthic microalgae (BMA). Benthic microalgae significantly affect assimilation of ammonium, because in the absence of BMA activity the sediments turns from a net ammonium sink to a net source. Nitrification rates were initially very high, but declined rapidly suggesting that nitrification rates are low in undisturbed sediments, and that in a dynamic environment like tidal flats, intense and fast nitrification/denitrification of ammonium is common. The driving mechanisms for assimilation or dissimilation accordingly appear to be ruled to a large extent by external physical forcing, with the entire system being capable of rapid shifts following environmental changes.
Save time & money - Smart Internet Solutions      Why do you need a reservation system?