Phytoplankton and Epipelon Responses to Clear and Turbid Phases in a Seepage Lake (Buenos Aires, Argentina)

Abstract

Annual changes in the algal density and concentrations of chlorophyll a, total phosphorus, and organic matter were analyzed in water and sediments at four sites characterized by the presence or absence of submerged and emergent macrophytes, during turbid-and clear-water conditions to determine the contribution of the algal components of the plankton and the epipelon and to identify the most typical species in each community. Three states were recognized: one turbid and two clear, with different submerged macrophyte cover. The peaks of phytoplankton and epipelon occurred in the turbid phase, whereas the highest proportion of true epipelic algae in sediments was reached in the second clear phase. The Oscillatoriaceae dominated during the turbid phase in the water and throughout the entire year within the sediments. IntroductionIn shallow lakes where alternative equilibrium states can occur, the importance of the relationships between epipelic and pelagic algae has recently been highlighted (VADEBON-COEUR et al., 2002). In such lakes the structure and biomass of epipelon varies in relation to spatial heterogeneity created by the presence or absence of emergent and submerged macrophytes. According to CYR (1998), the biomass of benthic algae varies among sites and according to depth in small oligotrophic and mesotrophic lakes.The benthic assemblages are made up of autochthonous species plus others incorporated from the plankton and periphyton. Thus, changes in environmental conditions can promote an increase in the density of those algae that can develop in both the sediment and the water column, giving them a competitive advantage over the algae that can live in only one of those lake habitats. The seasonal distribution of algal productivity observed by HANSSON (1996) in North American lakes, and by BARKO et al. (1977) andFLÖDER et al. (2006) in small ponds, suggests an exchange of algal organisms between the planktonic and epipelic populations.The phosphorus in shallow lakes tends to accumulate in the sediments and in the macrophytes (SØNDERGAARD et al., 2003;ROONEY and KALFF, 2003). Thus, the nonplanktonic algae 154 M. A. CASCO et al.

Effect of environmental variables on epiphyton in a pampean lake with stable turbid- and clear-water states

“…Thus, the periphyton presented a dual-period variation pattern (i.e. turbid to clear) in contrast to the 3-period dynamic observed by Casco et al (2009) for the phytoplankton.…”

“…With respect to time, our analysis of the environmental variables at both of the sampling sites resulted in a discrimination of 3 periods that coincided with the equilibrium states previously identified by Casco et al (2009) on the basis of data gathered at 4 sampling points plus a consideration of the biological variables that were necessary for the establishment of equilibrium.…”

“…During the sampling period, from July 2001 through June 2002, the maximum and minimum depths were 2.5 and 1.7 m, respectively (the mean depth from the 12 monthly depth measurements was 2.2 m). More information has been detailed by Cano et al (2008) and Casco et al (2009). Most of the lake area is colonized by dense stands of emergent bulrush Schoenoplectus californicus and the submerged macrophytes Stuckenia striata (Ruiz & Pavon) Holub and Myriophyllum quitense Kunth ).…”

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

“…Nevertheless, as our two experiments were conducted in different seasons, further studies are needed to analyze possible seasonal changes in periphyton composition. In a recent study, Casco et al (2009) characterized the epipelon community in the Pampean shallow Lake Lacombe and found that the algal groups change when the lake shifts from a clear to a turbid state.…”

Influence of underwater light climate on periphyton and phytoplankton communities in shallow lakes from the Pampa plain (Argentina) with contrasting steady states

“…However, the information about the periphyton community of this region is still scarce (e.g., Cano et al, 2008;Casco et al, 2009). In a recent study, we compared the periphyton community with phytoplankton under contrasting optical scenarios, and found that in a clear-vegetated lake the algal fraction of periphyton was dominant (Sánchez et al, 2010).…”