Haydée Pizarro

Water level as the main driver of the alternation between a free-floating plant and a phytoplankton dominated state: a long-term study in a floodplain lake

This 10-year field data study explores the relevance of water level fluctuations in driving the shift from a free-floating plant (FFP) to a phytoplankton dominated state in a shallow floodplain lake from the Lower Paraná River. The multi-year natural flood pulse pattern in the Lower Paraná River drove the ecosystem regime from a FFP-dominant state during very high waters (1998–1999) to absolute phytoplankton prevalence with blooms of nitrogen fixing Cyanobacteria during extreme low waters (2008–2009). Satellite images support the observed changes over the decade and show the decrease of the surface lake area covered by FFP as well as the modification of the spectral firm in open waters, which documents the significant increases in phytoplankton chlorophyll a concentrations. We discuss the possibility that, despite a slow eutrophication in these highly vegetated systems, water level changes and not nutrients account for the shift from a floating macrophyte community to phytoplankton dominance. Cyclic shifts may occur in response to the seasonal floodpulse, but more strongly, as indicated by our results, in association to the extreme drought and flood events related to the El Niño Southern Oscillation, which is linked to discharge anomalies in the Paraná River.

Periphyton flora of some lotic and lentic environments of Hope Bay (Antarctic Peninsula)

A taxonomic study was made of the periphytic algal flora of some freshwater environments at Hope Bay, Antarctic Peninsula (63°27′S; 56°59′W), during summer 1992–1993. Seven lakes and two pools that are characterized by different trophic levels were studied. The largest, Boeckella Lake, has an important outflow (Prasiola Stream) that was also analyzed. Ninety-seven algal taxa, including specific and infraspecific entities, are recorded. Thirty-one new records for the Antarctic continent are described and illustrated. The flora comprises 44.4% Cyanophyceae, 21.6% Bacillariophyceae, 18.5% Chlorophyceae, 9.3% Tribophyceae, 4.2% Chrysophyceae and 2% Zygophyceae. The epilithic flora of Hope Bay shows a high species richness. Phormidiumfragile and Lyngbya lagerheimii were the most abundant species among the Cyanophyceae. In the algal mats we also found Chrysophyceae (mainly Hydrurus foetidus and Chrysococcus rufescens) and the macroscopic chlorophycean Prasiola crispa. Tribonema australis sp. nov. (Tribonematales, Tribophyceae) is put forward as a new species. Hormidium fluitans (Gay) Heering is renamed Klebshormidium fluitans.

Epilithic algae from a freshwater stream at Hope Bay, Antarctica

Temporal and spatial variations of the epilithic phycoflora were studied in one of the largest streams at Hope Bay (Antarctic Peninsula) during the summer of 1992/93. A complete floristic inventory was made, and the relative frequencies of each algal taxon were estimated. Periphytic cumulative chlorophyll a was measured by means of artificial substrata. The stream was a typical maritime Antarctic lotic ecosystem, with evident signs of enrichment by sea-birds. Variability in discharge strongly affected the water chemistry, with the high water level periods characterized by the lowest conductivities and dissolved reactive phosphorus concentrations. Epilithic algal communities predominantly consisted of algal mats or filamentous and foliose forms of Prasiola crispa. Other dominant species were Leptolyngbya fragilis, Hydrurus foetidus, Chrysococcus cf. rufescens and Phaeogloea mucosa. Whereas P. crispa appeared more frequently near to the origin of the stream in Boeckella Lake, Chrysophyceae were better developed towards the mouth.

Epiphytic Algal Biodiversity in Humic Shallow Lakes from the Lower Paraná River Basin (Argentina)

We analyzed the algal composition (including Cyanobacteria) of epiphyton on macrophytes and the environmental data from five water bodies of a wetland from the Natural Reserve Otamendi (NRO) located in the Paraná River Basin, South America, during one year. Also, we described the diversity patterns (α, β, and γ diversity) of the epiphyton in the wetland. We selected two different macrophytes: the emergent rush Schoenoplectus californicus and the free-floating liverwort Ricciocarpus natans. We found 105 epiphytic taxa, of which 48% were represented by Bacillariophyceae, 22% were Cyanobacteria, 18% were Chlorophyta, and the rest (12%) belonged to Euglenophyta, Xanthophyceae, Synurophyceae and Cryptophyta. The structure of the epiphytic assemblage changed in relation to water level fluctuations, showing a major proportion of planktonic, metaphytic, and ticoplanktonic components during high water phases. The overall low algal richness may be related to the low light penetration in this humic wetland. The geographical pattern in taxa turnover was explained by the combination of metapopulation dynamics (dispersal distance) and continuum theories (infrequent connectivity followed by spatial differences associated in geographic habitat differences). Water level fluctuations affected the epiphytes on S. californicus, while temperature and light penetration influenced the epiphytes on R. natans.

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.

Littoral epilithon of lentic water bodies at Hope Bay, Antarctic Peninsula: biomass variables in relation to environmental conditions

We studied the structural characteristics of the littoral epilithon in nine lentic water bodies at Hope Bay, Antarctic Peninsula, during summer 2002. At each site we measured the main physical and chemical variables and took epilithic samples for the analysis of dry weigh, ash, ash-free dry weight and chlorophyll a concentration. Distance from the sea of each water body was also considered. One site was selected for sampling lakes and ponds, except for Boeckella lake, where two sampling sites (A and B) were selected due to the heterogeneity of its littoral zone. Three stones for chlorophyll a analysis and another three to estimate dry weight, ash and ash-free dry weight, were taken randomly about 1 m away from the shore-line of each sampling site. Measurements of physical and chemical characteristics were obtained similarly. Water samples for chemical analysis were taken sub-superficially. Lakatos’s system of classification and the Autotrophic Index were used to make functional inferences about the epilithic communities. Two PCA analyses were made to classify the water bodies according to environmental features and epilithic variables. In the latter, major patterns in data of epilithon were subsequently interpreted based on environmental data using external validation. Pingüi pond, located in the middle of the penguin rookery, was considered as a passive sample in both PCA analyses due to its extreme characteristics. Limnological features of the studied water bodies were similar to those of other Maritime Antarctic lakes. According to the Lakatos’s index, 60% of the sampled lakes had high epilithic mass and a same proportion showed an inorganic type of epilithon The fact that 40% of the water bodies were autotrophic confirmed the importance of benthos as primary producer. According to environmental features, the well-defined groups of lakes emerged from the PCA were mainly determined by distance from the sea, pH, conductivity and salinity, and corresponded to the principal hydrological basins found in the region. Based on the results of the second PCA, littoral epilithon was affected by nitrate concentration and conductivity. In this ordination, water bodies from the same hydrological basin were separated probably as a result of a very complex inter-play of factors with a site-specific response to particular microhabitat characteristics.

Primary production of phytoplankton and periphyton in two humic lakes of a South American wetland

Seasonal primary productivities of periphyton and phytoplankton were compared in Grande Lake (GL) and a relict oxbow lake (ROL) in winter 2006 and summer 2007. GL was free of floating plants on the sampling dates and covered over 80 and 100% of the ROL surface in winter and summer, respectively. The 14C assimilation technique was used to obtain the P–E curves of phytoplankton and periphyton on artificial substrata. The periphytic maximum photosynthetic rate (Pmax) was higher in the ROL in winter and summer, being better adapted to low irradiances than those in the GL. Phytoplankton and periphytic algae were light-limited in the ROL in summer due to complete coverage by floating macrophytes. In summer, Pmax and α values for periphyton in the ROL were higher than those for phytoplankton, and were even higher than in GL. In turn, Pmax and α values for phytoplankton in Grande Lake were higher than those for periphyton due to improved light conditions and the presence of algae that were adapted to movement through the water column. These results suggest that the complete coverage by floating macrophytes restricted phytoplankton productivity and allowed the development of a periphytic community that was better adapted to low-light conditions.

Ecology and taxonomy of the epilithic algal community from a stream in Cierva Point (Antarctic Peninsula)

Flowing waters in Antarctica comprise various types of rivers and streams of different origins. Some are fed by melting snow-banks, ice fields and glacier ice, while others are lake outflows (HAWES 1989, VINCENT et al. 1993). Most flow in summer only, often for only a few weeks. Several authors have described the microbial communities o f Antarctic streams. T ypically they form epilithic mats and films dominated by algae associated with bacteria, fungi and microherbivores (HowARD-WILLIAMS et al. 1986). According ro HAWES (1989), annual algal species tend to dominate in maritime streams, while perennial taxa prevail in continental Antarctic sites (HOWARD-WILLIAMS et ai. 1986). Despite these differences, in most Antarctic streams cyanobacteria constitute one of the dominant groups of the algal mats (e.g. BROADY 1982, HowARD-WILLIAMS et al. 1986, HAWEs & BRAZIER 1991, PIZARRO et al. 1996, IZAGUIRRE & PIZARRO 1998, PIZARRO & VINOCUR 1998). Filamentous chlorophytes are often also conspicuous components of the epilithic communities (HEYWOOD 1977, HAWEs 1989, HAWES & BRAZIER 1991). Recent studies also revealed the abundance of attached chrysophytes in streams of Hope Bay, Antarctic Peninsula (VINOCUR & PIZARRO 1995, lZAGUIRRE & PIZARRO 1998, PIZARRO & VINOCUR 1998). Studies on algal communities carried out at eierva Point have centered on the phytoplankton of the main lake (MATALONI et al. 1998) and on cryobiontic algae (MATALONI & TESOLfN 1997). This work constitutes the first report of the epilithic algal flora of the streams of this area. The survey was conducted at one of the main streams of eierva Point. We examined the floristic composition and its spatial variation along the stream during the summer of 1997. Algal biomass on natural substrata (measured as chlorophyll a) is reported for each sampling site. The main physical and chemical properties of the water course were also analyzed. Study site

The sudestadas : a hydro-meteorological phenomenon that affects river pollution (River Luján, South America)

Abstract The “sudestadas” are short-term hydro-meteorological phenomena that produce a “hydraulic plug”, preventing the normal drainage of the water courses in the Río de la Plata Estuary. The purpose of this study was to analyse the influence of the sudestadas on the water quality of the Lower River Luján, which discharges into the Río de la Plata Estuary (59°37′W; 34°43′S). Samplings were conducted from November 1998 to July 2001 at six sites on the lower stretch of river. Physical and chemical variables were measured and a nonparametric test was applied to each variable, grouping samples affected and non-affected by sudestadas, which further diminish the water quality of the river. The frequency and intensity of sudestadas are predicted to increase as a consequence of the Earths warming; thus, this research suggests that the environmental risk produced by the effects of global change, will be greater.

Phytoplankton and Periphyton Primary Production in Clear and Turbid Shallow Lakes: Influence of the Light Environment on the Interactions between these Communities

The ecological relevance of shallow lakes has been largely documented. The Pampean plain (Argentina) holds one of the main wetlands of South America, constituted by thousands of shallow lakes which provide valuable ecosystem services, and can be found in any of three regimes: clear-vegetated, inorganic-turbid or phytoplankton-turbid. Since these lakes play an important role in the global carbon balance, metabolism studies encompassing phytoplankton and periphyton under different regimes become relevant. Here, we analyzed the primary production (PP) of phytoplankton and periphyton in three Pampean shallow lakes representing the main types mentioned. The relative contribution of each algal community to the joint PP was different in each lake and related to their regime. The periphyton contribution was higher in the clear-vegetated lake than in the turbid lakes. The phytoplankton-turbid lake exhibited the highest PP for both communities. The inorganic-turbid lake presented the highest light limitation; nonetheless, the efficiency of periphyton in this lake showed an increasing trend with depth, suggesting light acclimation. Although phytoplankton dominated the PP in the three lakes, periphyton contribution was also important, particularly in the clear-vegetated lake. Our results emphasize that the PP of attached communities should be considered to estimate the PP of the whole lake.