CONSTANCY AND VARIABILITY OF STOICHIOMETRIC RATIOS IN PELAGIC ECOSYSTEMS

A.C. Redfield decades ago used information on constancy and variability of C:N:P ratios to infer biological control of chemical concentrations in the world’s oceans. Redfield found that oceanic particulate matter had a relatively constant chemical content of C:N:P=106:16:1 (molar). These ratios matched the relative differences in dissolved nutrient content in high- vs. low-nutrient sites. In contrast, the stoichiometry of lakes exhibits much greater variability in particulate C:N:P ratios. In lakes, particulate C:P ratios range tenfold and may exceed values of 1000. Such high ratios have implications for nutrient recycling and biomass production dynamics. In this paper, I will utilize newly collected stoichiometric data on >100 upper Midwest lakes and ponds to explore the controls of C:N:P composition of freshwater seston. Lake seston nutrient composition shows great regional variability. In addition, there are consistent shifts in C:N and C:P ratios with lake productivity. Higher ratios are associated with lower productivity. For these reasons, lake C:N:P are not characterized by a single “Redfield-like” ratio, but rather they are better described by nonlinear functions of C vs. N and C vs. P.