Algal growth response to particle‐bound orthophosphate and zinc

Abstract

Dissolved nutrient concentrations in natural waters may at times be controlled by interactions between particulate and solution phases. Effects of Zn [0–1 µM total Zn(II)] and orthophosphate (8–12 µM total P) additions on growth indices for the chlorophyte Selenastrum capricornutum Printz were examined in a synthetic growth medium containing 50 mg liter−1 colloidal titania. Over the Zn(II) concentration range used, detrimental growth and yield effects were observed. Addition of P to a synthetic growth medium (S‐3) increased stationary phase cell density, but had minimal effect on growth rate and duration of lag phase. Presence of TiO2 particles in culture media significantly reduced Zn and P dissolved fractions. Although adsorbed Zn and P were less available to Selenastrum, desorption of both solutes increased their availability. Rapid desorption of Zn(II) from TiO2 particles served in effect to buffer Zn2+ free ion concentration, until Zn became partitioned primarily with the algal fraction as cell concentration approached stationary phase density. Although phosphate desorption from TiO2 in nonbiological systems was negligible, Selenastrum was able to scavenge some P initially adsorbed onto TiO2. Accurate primary productivity predictions in nature may therefore require an understanding of equilibrium and reaction rates involved in the partitioning of nutrients and toxic substances between dissolved and particulate phases.