Phosphorus uptake by plankton and periphyton in relation to irradiance and phosphate availability in a subtropical lake (Lake Okeechobee, Florida, USA)

Abstract

Phosphorus (P) uptake by plankton and periphyton was studied at the wholecommunity level, and a conceptual model was developed relating community P dynamics to irradiance and phosphate (PO 4 ) availability. Studies were done in the littoral wetland and pelagic-littoral ecotone regions of a shallow subtropical lake using 32 P-labelled inorganic (DIP) and organic (DOP) phosphorus as tracers, under laboratory conditions simulating ambient temperature, In the pelagic-littoral ecotone, where light attenuation and P availability are highly variable, P dynamics displayed a strong temporal pattern. During a turbid period when underwater irradiance was low, water column PO 4 was high, and community P uptake was very low. During a clear water period when underwater irradiance was higher, water column PO 4 was lower, and there was rapid uptake of both PO 4 and DOP by plankton. In the littoral region underwater irradiance always was high, PO 4 always was low, and there was active yearround uptake of PO 4 and DOP both by plankton and periphyton. We also observed adaptations to P deficiency at the community level, in terms of greater use of DOP as a P source when PO 4 availability declined.