Lunau, M., Erickson, M., Voß, M., Ducklow, H. and Engel, Anja (2010) Impact of unbalanced nitrate inputs on the microbial transformation of Nitrogen: a stable isotope and sorting flow cytometric study. [Talk] In: ASLO Summer Meeting. , 06.-11.06.2010, Santa Fe, USA .

Abstract

The anthropogenic perturbation of the global nitrogen cycle profoundly affects the ecology of coastal environments. Increasing riverine inputs of nitrate into coastal areas due to intensified use of fertilizers can lead to eutrophication, to changes in the community composition and to anoxia in stream beds and coastal sediments. However, mechanistic (short-term) studies on the impact of unbalanced nitrate supply on the transformation of inorganic nitrogen by both autotrophic and heterotrophic microplankton are still rare. Here we used a 15N stable isotope tracer approach in combination with cell sorting by flow cytometry to study the cycling of reactive nitrogen within the lower food web (phytoplankton and bacteria) in a coastal ecosystem (Waquoit Bay, MA, USA). Our data indicate that excess nitrate supply with respect to Redfield ratios of C:N:P:Si induced preferential uptake of ammonium over nitrate by microplankton. This findings point to a potential decrease in buffer capacity of coastal environments for increasing nitrate concentrations. Our finding has implications for the extension of eutrophication from coastal areas towards the more open ocean.

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