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Patterns and trends in nutrients and phytoplankton in Dutch coastal waters: comparison of time-series analysis, ecological model simulation, and mesocosm experiments
de Vries, I.; Duin, R.N.M.; Peeters, J.C.H.; Los, F.J.; Bokhorst, M.; Laane, R.W.P.M. (1998). Patterns and trends in nutrients and phytoplankton in Dutch coastal waters: comparison of time-series analysis, ecological model simulation, and mesocosm experiments. ICES J. Mar. Sci./J. Cons. int. Explor. Mer 55(4): 620-634
In: ICES Journal of Marine Science. Academic Press: London. ISSN 1054-3139, more
Peer reviewed article  

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Keyword
    Marine
Author keywords
    coastal eutrophication, ecological eYciency, mesocosm experiments, model simulation, nutrients (phosphorus, nitrogen, N:P ratio), productivity, riverine inputs, trend analysis

Authors  Top 
  • de Vries, I., more
  • Duin, R.N.M.
  • Peeters, J.C.H.
  • Los, F.J., more
  • Bokhorst, M.
  • Laane, R.W.P.M., more

Abstract
    In the Dutch coastal zone, nutrient and chlorophyll concentrations show gradients of up to one order of magnitude perpendicular to the coast within the first 30–50 km offshore. Time-series analysis reveals significant decreasing trends for dissolved inorganic phosphorus (40%) and total phosphorus (35%) and an increase in the dissolved inorganic N:P ratio from 25–30 to 40–55 over the period 1988–1995. Trends in nitrogen (-15%), silicate (stable), and chlorophyll are smaller and generally not statistically significant. The trends in phosphorus reflect a proportional and immediate response to decreasing riverine inputs. The observed trends, spatial gradients, and long-term seasonal patterns are simulated quite well with a coupled physical–ecological model with high spatial resolution for the coastal zone. The model results indicate no effect of decreasing phosphorus, but an important role for both nitrogen and light climate in primary production and algal biomass. These results have been reproduced in mesocosm experiments. Moreover, these experiments indicate a strong response of primary production and chlorophyll to nitrogen load, whereas secondary production (macrobenthos) remains relatively stable. Ecological effciency of secondary production increases from 7% to >10%, with a decrease in nitrogen loading by 50% from the present level. In the absence of a significant nitrogen reduction in coastal waters, the mesocosm results cannot be related to field data as yet. However, the expectation is that reducing nitrogen inputs will not affect productivity at higher trophic levels to any great extent.

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