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Content archived on 2024-05-27

Nutrient dynamics mediated through turbulence and plankton interactions (NTAP)


In European coastal waters, affecting industries, fisheries, tourism, ecosystem health, and overall quality of life. Nutrient and organic matter load and dynamics play a key role in those processes. However, we lack an integral understanding of the influence of critical variables such as small-scale turbulence on the interaction between plankton and nutrient dynamics.
To achieve this understanding we will
1) summarise existing data into searchable databases,
2) experimentally determine the effects of turbulence on carbon and nutrient utilisation by planktonic organisms,
3) develop a miniaturised sensor to measure flow, and
4) build a dynamic model that includes turbulence effects on nutrient and carbon transfer for exploratory and predictive purposes.
The project has shown that nutrient affinity constants for bacteria, autotrophic flagellates and dinoflagellates can be reasonably well predicted using a simple model based on the assumption of diffusion-limited phosphate uptake. This work puts the experimental foundation for model parameterisation on a much more solid ground. Diatoms appear to be an exception from the idealised theory, having a higher affinity than predicted. We suspect this deviation to be caused by the simplifying assumption of spherical cells, an assumption not well suited for many diatoms. Experiments with the ciliate Strombidium sulcatum confirm a direct negative effect of turbulence on growth and feeding. In contrast, our results show little direct influence of turbulence on ciliate growth in natural communities. For the purposes of incorporating turbulence into models of the interactions of planktonic webs, direct effects of turbulence on the ciliate component can safely be omitted. Experiments of the growth of phototrophic and mixotrophic dinoflagellates subjected to turbulence show further complexities owing to changes in the pH of water and aggregate formation besides the response to nutrient/prey concentrations. This group of organisms shows a high species-specific response to turbulence making experiments with different organisms very valuable.

The response of the planktonic community to nutrient additions shows clear differences between the Mediterranean and Norwegian coastal systems and for different initial conditions, subjected to a range of time-scale variability, within a particular system. While in the Norwegian system the relationship between particulate organic carbon (POC) or chlorophyll a increase and nutrient dose was linear, in the Mediterranean system the response to nutrients levelled off at 8 µM nitrate. When data on coastal systems are pooled together, the production of POC shows a two-dimensional dome-shape relationship with respect to turbulence and nutrient load. This indicates the need to consider turbulence as a variable when assessing nutrient load thresholds in coastal systems. A model that incorporates turbulence effects to the fluxes within a food web shows that the organisms with the largest response are diatoms and mesozooplankton in accordance with theory which states that the bigger planktonic organisms show the largest potential for turbulence to affect nutrient fluxes and prey encounter rate. The development of a new sensor to measure turbulence in the laboratory enhances our research capabilities and improves the competitive edge of the European company NORTEK AS.

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S/N,Paseo Juan de Borbo S/N

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