Is trophic state or regional location the strongest determinant for Chl-a/TP relationships in lakes?

Based on data from the four Nordic countries: Denmark, Sweden, Norway and F inland, regressions have been developed relating phytoplankton abundance as chlorophyll-a, chi-a, to nutrient concentrations las total phosphorus, TP, and total nitrogen, TN). Regressions were developed for the full data set from each country and for three ranges of trophy (expressed as TP < 20 mg . m(-3), 20 mg . m(-3) > TP > 200 mg . m(-3), and TP > 200 mg . m(-3)). Our results suggest that trophic level is a stronger determinant for characteri sing the chl-a = f(TP) and Chi-a = g(TN) relationships than the regional lo calisation of the lakes. Thus, in contrast to many other pollution criteria , (e.g., acidification) equal guideline- or criteria values for phosphorus- or nitrogen- loads across regions will give equal end-point effects in lak es. Total phosphorus seems to limit phytoplankton growth when TP < 20 mg . m(-3). There is no clear indication which of the nutrients, TP or TN, that limit phytoplankton growth for 20 mg . m(-3) > TP > 200 mg . m(-3). There a re signs that neither TP nor TN are limiting factors for phytoplankton grow th at TP > 200 mg . m(-3)