The concept of limiting nutrients

Abstract

The very rapid turnover of the soluble nutrient pools in surface waters has meant that for many years the term ‘limiting nutrient’ has been used too loosely in the literature on phytoplankton. There is often considerable confusion as to whether the nutrient limits the rate of growth or the phytoplankton biomass. It has often been stated, for instance, that phosphorus limits phytoplankton growth in lakes because the concentration of dissolved inorganic phosphorus (DIP) is very low. The same has been said to be true of dissolved inorganic nitrogen (DIN) in the oceans. This, wrongly, assumes a relationship between the concentration of the nutrient and the rate of algal growth. Such ideas grew out of culture work, particularly batch cultures, where the initial concentration of the nutrient represents the entire available supply. Large scale correlations between the spatial distribution of nutrients and production also impressed early oceanographers (Hentschel and Wattenberg, 1931) as did the temporal inverse correlation in the temperate spring. At smaller scales recycling mechanisms are in operation which restock the pools of DIP and DIN continuously and thus we are concerned with both the pool size and the rates of uptake and resupply.