Macrophyte and periphyton dynamics in a UK Cretaceous Chalk stream: the river Kennet, a tributary of the Thames.

An initial study to observe the seasonal trends and to determine the factors influencing macrophyte and periphyton growth patterns was undertaken on a representative reach of the River Kennet (UK) over a 2-year period (1998-2000). Maximum average macrophyte and average periphyton dry matter biomass recorded during the growing season were 200 and 21 g m(-2), respectively. The relationships between macrophyte and periphyton percentage cover and biomass data with physico-chemical variables were investigated. Regression analysis indicated that of the parameters measured, flow, and in the case of the dominant Ranunculus spp., solar radiation, were best able to predict macrophyte biomass and cover. The periphytic biomass within the reach was low, possibly as a result of relatively high flows and low phosphorus concentrations following the introduction of effluent treatment at the sewage works immediately upstream of the reach. Periphytic biomass was poorly correlated with the physical variables measured. This indicates that biomass is regulated by complex interactions between the physical and chemical factors, such as flow, solar radiation and phosphorus concentration. These interrelationships require further investigation.