COMPARISONS OF PHYTOPLANKTON BIOMASS IN TEMPERATE AND TROPICAL LAKES

Phytoplankton biomass is compared for 16 temperate and 5 tropical lakes that are sufficiently deep to develop seasonal stratification. The ratio of annual mean to maximum biomass averages 0.45 for tropical lakes and is significantly lower for temperature lakes (0.36). Seasonal (3-month peak) ratios of mean to maximum biomass (approximately 0.7) do not differ for oligotrophic tropical and temperature lakes, but the ratios for temperate lakes fall below those of tropical lakes at higher trophic states. Tropical lakes of given trophic state have a higher minimum biomass than temperate lakes of the same trophic state; both temperate and tropical lakes show a strong increase in minimum biomass with increasing maximum biomass. The relative range of annual variation for temperate lakes is approximately 40% greater than for tropical lakes. Differences in the stability of layering and in the duration of seasonal mixing probably explain much of the difference in variability of biomass for tropical and temperate lakes that stratify.