Biomonitoring of nutrient limiation

The traditional growth potential algal bioassay with cultured algae is analysed using a kinetic model and compared to short-term assays with indigenous phytoplankton. The different types of information obtained with the two techniques is discussed along with the concepts kinetic limitation (growth rate reduction) and yield or Liebig's law limitation, respectively. From short-term tests with the indigenous phytoplankton it can be assessed which nutrient (e.g. N or P) is actually (kinetically) limiting at a given time, whereas growth potential tests can be used to determine which nutrient is limiting in a Liebig's law sense. Both types of information can be valuable in eutrophication studies. By analogy from batch culture algal assays to algal blooms in natural waters the model calculations performed indicate that in some situations available phosphorus may be depleted from the aqueous phase before available nitrogen, even if nitrogen provides the only significant nutrient limitation.