Phosphorus kinetics of planktonic and benthic assemblages in a shallow subtropical lake

Abstract

Summary1. Phosphate uptake kinetics and uptake rates were calculated for planktonic (phytoplankton and bacterioplankton) and benthic (epiphyton and epipelon) assemblages in a large, shallow, subtropical lake. Samples were taken bimonthly over the period of 1 year at three different sites to examine spatial and temporal variability in these processes.2. Two of the sites, located at the edge of the littoral zone next to the open water (ecotone sites), had low irradiance at the sediment surface and high total phosphorus (TP) concentration (annual mean TP = 112 μg L–1). The third site, located in the littoral marsh zone, had high irradiance at the sediment surface and low TP concentration (annual mean TP = 7 μg L–1).3. Based on 32P‐PO4 turnover time, P availability varied temporally and spatially. At the two high TP ecotone sites, P concentration was lowest in July and August. At the low TP marsh site, P limited algal production throughout the year.4. The quotient of maximum uptake rate to half saturation constant (Vm/Ks) in the plankton increased by over two orders of magnitude during the P‐limited (summer) period at the two ecotone sites, suggesting that plankton used the scarce phosphorus more efficiently. The specific uptake rate of plankton was significantly greater than that of periphyton at all sites, suggesting that the plankton were more efficient than periphyton at taking up phosphate.5. Periphyton biomass, as well as absolute and percentage P uptake rate, was greater at the marsh site than at the ecotone sites, despite the lower P concentrations in the marsh. This was probably a result of rapid nutrient cycling, combined with high light availability in the marsh.