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Title: Phytoplankton patchiness and their role in the modelled productivity of a large, seasonally stratified lake Authored by: Hillmer, I.A., van Reenen, P., Imberger, J., Zohary, T. Abstract:
Field data from Lake Kinneret (Israel) have shown that phytoplankton concentration varies up to10-fold in space and time, with horizontal patches ranging from a couple of kilometres to a basin scale; yet previous studies have used a 1D model to reproduce temporal evolution. The question that arises is how appropriate a 1D approach is to represent the dynamic of a spatially heterogeneous system, where there are non-linear dependencies between variables. Extensive set of field data, numerical models and analytical method are used to understand the role of spatial variability, expressed ultimately as phytoplankton patchiness. A N-P-Z model is coupled to both a 1D and a 3D model and their results are used to investigate the effect of incorporating horizontal spatial variability in forcing data and in phytoplankton patches formation in the modeling of primary production. A 1D diffusion-reaction equation allowed identifying horizontal diffusion as a main mechanism that moulds the growth of the patterns in the field and in the model; and establishes that scales of patterns predicted by the 3D numerical model compare well with field data. L=(k/μ)0.5 yields a length scale to characterise the patterns in this confined system and that may be used as a criteria for the one-dimensionality condition. The total chlorophyll from both models shows similar behavior when the variability, expressed as Chlamax/Chlamin, is low. When Chlamax/Chlamin is high, the difference between the two models reaches up to 30% due to the generation of localised patches. Comparison of results from the 1D and 3D models highlights the need of using models that are able to resolve the spatial complexity to some extent, as the use of averaged properties may produce misleading results. This is especially important in the presence of patches with differential physiological and biogeochemical characteristics, and non-linear processes, in which case biomass average is not necessarily linearly related to the averaged environment.
Reference: Hillmer, I.A., van Reenen, P., Imberger, J., Zohary, T., 2008, Phytoplankton patchiness and their role in the modelled productivity of a large, seasonally stratified lake, 218:49-59 Keywords: ELCOM, ELCOM-CAEDYM, CAEDYM, DYRESM, Lake Kinneret |
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