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The interplay between nutrient load, N partitioning and turbulence: three key factors in the dynamics of coastal plankton

AuthorsRomero, Estela ; Peters, Francesc ; Marrasé, Cèlia ; Guadayol, Òscar
Issue Date17-May-2013
Citation45th International Liège Colloquium (2013)
AbstractTwo intensive surveys were conducted in the coastal waters of Barcelona (NW Mediterranean) to assess short term variations of biological parameters in relation to environmental conditions. Surveys lasted 1 week, with 3 to 4 samplings per day, and were carried out in autumn and spring. We focused on two attributes: wave height, as a proxy for mechanical energy entering the system, and nutrient inputs, whose variability in total load and relative composition is a central characteristic of coastal areas. The effects of the temporal coupling or uncoupling of both factors were examined. The interplay between nutrients and turbulence was also studied by means of 2 experimental simulations with natural planktonic communities. Experimental nutrient additions varied both in terms of total nutrient load and in the balance of elements, with a particular focus on N sources, since the various forms of N are closely related to different human activities and specific land uses. In the experiments, shifts in community composition appeared to be mostly related to the interaction between turbulence and N partitioning: under still conditions, ammonium rich waters favoured small organisms and reinforced the microbial loop, whereas nitrate mostly favoured diatom growth. Turbulence added complexity to the final outcome, because mixing tended to favour large over small osmotrophs. Therefore, the results suggested that the rapid growth of small autotrophs and heterotrophic bacteria in ammonium rich waters could be partly counteracted by diatom increases if nutrient pulses were coupled with turbulent mixing, and diatom bursts after nitrate enrichments could be largely enhanced by concomitant turbulence. This was consistent with the observations in the field, where a fine balance between moderate turbulent mixing and nutrient availability pushed our system toward diverse trophic pathways: sudden nutrient fluxes uncoupled from water motion tended to favour bacteria and heterotrophic nanoflagellates, while their concurrence with some water column mixing shaped a favourable scenario for large autotrophs. Ultimately, these two distinct biological responses pointed toward two main disturbance scenarios: Episodes of nutrient enrichment uncoupled from mixing, mostly related to episodic water spills from the nearby city that contributed to high relative loads of ammonium and organic compounds; episodes of increased wind caused by passing weather fronts that promoted some water column mixing and the entrainment of nutrients from bottom sediments or from adjacent water masses
DescriptionThe 45th International Liège Colloquium: Primary production in the ocean: from the synoptic to the global scale, 13-17 May 2013, Liège, Belgium
Publisher version (URL)http://modb.oce.ulg.ac.be/colloquium/2013/#col_abstracts
Appears in Collections:(ICM) Comunicaciones congresos
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