Interrelations among Plankton, Attached Algae, and the Phosphorus Cycle in Artificial Open Systems

The circulation of phosphorus in 200—liter aquaria, continuously supplied with tap water, was analyzed by means of analytical and tracer methods. This open—system design ultimately resulted in a steady—state system whereby the influx of phosphorus to various biological compartments was equaled by a corresponding outflow. This model of phosphorus circulation is believed to apply to small lakes with extensive littoral vegetation during summer stratification, but contrasts with models proposed from other tracer studies on such lakes. The other models are considered to be feasible, but unlikely and based on incorrect analyses of data. Previous estimates of the rate of phosphorus circulation based on tracer analyses are reanalyzed and appear to be of the correct magnitude. The 200—liter system developed two communities of attached and planktonic organisms, with the former rapidly removing a large percentage of the phosphorus from the latter. With this removal any direct relationship between the phosphorus concentration of the open water and the influx concentration was obscured. A major means by which phosphorus was removed from the open water was shown to be trapping of particles by the community associated with the sides of the aquaria. The rate of such removal varied widely, depending on the extent of "littoral" growth and the nature of the particle. These results suggest that a multicompartment analysis of nutrient circulation is significantly more realistic than a simplistic assumption of homogeneity. Considering succession to be the total change in physical and biological conditions over prolonged time, this open—system design developed from a one—community, few—species system into a two—community, several—species system. The rate of nutrient circulation greatly increased with time and developed into a steady state, not an equilibrium system which depended on a continual phosphorus influx to maintain the concentrations and circulation rates.