Relative importance of periphyton and phytoplankton in turbid and clear vegetated shallow lakes from the Pampa Plain (Argentina): a comparative experimental study

We analyzed experimentally the relative contribution of phytoplankton and periphyton in two shallow lakes from the Pampa Plain (Argentina) that represent opposite scenarios according to the alternative states hypothesis for shallow lakes: a clear lake with submerged macrophytes, and a turbid lake with high phytoplankton biomass. To study the temporal changes of both microalgal communities under such contrasting conditions, we placed enclosures in the littoral zone of each lake, including natural phytoplankton and artificial substrata, half previously colonized by periphyton until a mature stage and half clean to analyze periphyton colonization. In the clear vegetated shallow lake, periphyton chlorophyll a concentrations were 3–6 times higher than those of the phytoplankton community. In contrast, phytoplankton chlorophyll a concentrations were 76–1,325 times higher than those of periphyton in the turbid lake. Here, under light limitation conditions, the colonization of the periphyton was significantly lower than in the clear lake. Our results indicate that in turbid shallow lakes, the light limitation caused by phytoplankton determines a low periphyton biomass dominated by heterotrophic components. In clear vegetated shallow lakes, where nitrogen limitation probably occurs, periphyton may develop higher biomass, most likely due to their higher efficiency in nutrient recycling.