Balance of assimilative and dissimilative nitrogen processes in a diatom-rich tidal flat sediment

[摘要] Tidal flat sediments are subject to repetitive mixing and resuspensionevents. In a short-term (24 h) ¹⁵N-labelling experiment, we investigatedreactive nitrogen cycling in a tidal flat sediment following anexperimentally induced resuspension event. We focused on (a) the relativeimportance of assimilatory versus dissimilatory processes and (b) the roleof benthic microalgae therein. ¹⁵N-labelled substrate was added tohomogenized sediment, and ¹⁵N was subsequently traced into sediment anddissolved inorganic nitrogen (DIN) pools. Integration of results in aN-cycle model allowed us to quantify the proportion of major assimilatoryand dissimilatory processes in the sediment.

Upon sediment disturbance, rates of dissimilatory processes likenitrification and denitrification were very high, but declined rapidlytowards a steady state. Once this was reached, the balance betweenassimilation and dissimilation in this tidal mudflat was mainly dependent onthe nitrogen source: nitrate was utilized almost exclusively dissimilatoryvia denitrification, whereas ammonium was rapidly assimilated, with about aquarter of this assimilation due to benthic microalgae (BMA). Benthicmicroalgae significantly affected the nitrogen recycling balance insediments, because in the absence of BMA activity the recovering sedimentturned from a net ammonium sink to a net source.

The driving mechanisms for assimilation or dissimilation accordingly appearto be ruled to a large extent by external physical forcing, with the entiresystem being capable of rapid shifts following environmental changes.Assimilatory pathways gain importance under stable conditions, with asubstantial contribution of BMA to total assimilation.

[学科分类] 地球化学与岩石