Nutrient uptake rates by the alien alga Undaria pinnatifida (Phaeophyta) (Nuevo Gulf, Patagonia, Argentina) when exposed to diluted sewage effluent

Abstract

In the early nineties, Undaria pinnatifida has been accidentally introduced to Nuevo Gulf (Patagonia, Argentina) where the environmental conditions would have favored its expansion. The effect of the secondary treated sewage discharge from Puerto Madryn city into Nueva Bay (located in the western extreme of Nuevo Gulf) is one of the probable factors to be taken into account. Laboratory cultures of this macroalgae were conducted in seawater enriched with the effluent. The nutrients (ammonium, nitrate and phosphate) uptake kinetics was studied at constant temperature and radiation (16 °C and 50 μE m−2 s−1 respectively). Uptake kinetics of both inorganic forms of nitrogen were described by the Michaelis?Menten model during the surge phase (ammonium: V max sur: 218.1 μmol h−1 g−1, K s sur: 476.5 μM and nitrate V max sur: 10.7 μmol h−1 g−1, K s sur: 6.1 μM) and during the assimilation phase (ammonium: V max ass: 135.6 μmol h−1 g−1, K s ass: 407.2 μM and nitrate V max ass: 1.9 μmol h−1 g−1, K s ass: 2.2 μM), with ammonium rates always higher than those of nitrate. Even though a net phosphate disappearance was observed in all treatments, uptake kinetics of this ion could not be properly estimated by the employed methodology.