Global primary production of lakes: 19th Baldi Memorial Lecture

Global primary production of lakes is controlled by factors that are mainly deterministic (incident irradiance, temperature, ice cover) or mainly stochastic (nonalgal light attenuation, mixing depth, nutrient supply) with respect to latitude. The combined effect of these factors on the global lake population was estimated by Monte Carlo simulation based on lakes sampled randomly from the global lake size and latitudinal abundance density functions. Incident irradiance and temperature have strong and approximately equal effects globally on potential production. Ice cover has an additional effect that is approximately half as great as temperature or irradiance at latitudes where ice cover occurs. Together these 3 variables explain about half of the total constraint on global primary production. Among the stochastic factors, mixed layer thickness has a substantially stronger effect than nonalgal light attenuation. When nutrients and relative light availability in the water column (mixing depth, transparency) are considered together, nutrient limitation is the dominant control on algal biomass and production for about 80% of lake area. Estimated global net primary production per unit area for lakes averages 160 gC/m2/y (gross, 200 gC/m2/y; algal respiration 40 gC/m2/y) under background nutrient conditions, but under current conditions it is 260 gC/m2/y (gross, 360 gC/m2/y; algal respiration 100 gC/m2/y) because of eutrophication. Global totals of net primary production for current conditions are 1.3 PgC/y gross, 1.0 PgC/y net, 0.3 PgC/y algal respiration.