Variable photosynthetic characteristics in waste stabilisation ponds

Algae play several key roles in waste stabilisation ponds. A model has been developed to predict algal concentration in waste stabilisation ponds, in which the relationship between photosynthesis and underwater light availability is central. One equation was selected from several alternative expressions that describe this relationship. The selected equation consisted of four photosynthetic parameters. A field sampling programme was designed to investigate the relationships between the photosynthetic parameters and the pond environment. Although initial regression analyses were unsuccessful, distinct diurnal variations were revealed in two key photosynthetic parameters, related to an inverse variation in chlorophyll a concentration. This led to the derivation of a dynamic feedback hypothesis which challenges the classic assumption in algal modelling of constant photosynthetic parameters.