Phosphorus–Limited Growth Dynamics of Lotic Periphytic Diatom Communities: Areal Biomass and Cellular Growth Rate Responses

Abstract

Three long-term phosphate enrichment experiments were conducted at the Experimental Troughs Apparatus (EXTRA), South Thompson River British Columbia to determine the relationship between external orthophosphate (PO₄³⁻) concentration and peak areal biomass (PB) of periphytic diatom communities. Levels of PO₄³⁻which saturated PB were two orders of magnitude greater than those required to saturate specific growth rates in thin film periphyton communities of similar taxonomic composition. With PO₄³⁻additions between 0.1 to 1.0 μg P∙L⁻¹, PB responded in a hyperbolic fashion, initially increasing rapidly, then showing signs of saturation PB continued to increase in a slow, linear manner above 1.0 μg P∙L⁻¹. Maximum PB (PB_max) was calculated to occur at ca. 28 μg P∙L⁻¹. At higher PO₄³⁻concentrations (> 30–50 μg P∙L⁻¹) PB was no longer P limited. Below the saturation point, PB was approximated by a log–linear function of PO₄³⁻.