María Adela Casco

Hydrological complexity supports high phytoplankton richness in the Doñana marshland (SW Spain)

Two hundred and twenty-four phytoplanktonic taxa were recorded in a riverine floodplain on the NE side of the Doñana marshland from September 2002 to 2004. This collection of 11 samples included 80 Bacillariophyceae (Diatoms), 71 Chlorophyta, 39 Cyanophyta, 19 Euglenophyta, 6 Chrysophyceae, 5 Cryptophyta, and 4 Dinophyceae. Fifty-five percent of the total taxa had a very low frequency of appearance (<5%), while only three species appeared with a frequency >90% (Monoraphidium contortum Komárková-Legnevorá, Cyclotella atomus Hustedt, and Nitzschia palea W. Smith). According to multivariate analyses, both temporal and spatial factors produced a pattern in the phytoplankton assemblages dominated by freshwater inputs during winter flooding, tidal inputs in summer, and transitional stages during the rest of the year. Spatial segregation of phytoplankton was likely due to differences in retention time and distance to water input. The main taxa involved in this segregation were Chrysidalis sp. 1 (June 2003 and 2004), Chlamydomonas sp. 4 (September 2003), C. atomus (December 2003), and Tetradesmus aff. crocini (February 2004). The hydrologic complexity of the study area could account for this high taxa richness by promoting replacement and colonization episodes following seasonal changes in water source (freshwater versus tidal inputs).

Phytoplankton chlorophyte structure as related to ENSO events in a saline lowland river (Salado River, Buenos Aires, Argentina)

We analyzed the phytoplankton present in the lower sector of the Salado River (Buenos Aires, Argentina) for 10 years (1995–2005) and detected significant changes occurring in chlorophyte abundance and species richness during La Niña event (1998–1999), which period was analyzed throughout the entire basin (main stream and tributaries). We compared the physicochemical and biologic variables between two El Niño–La Niña–Southern Oscillation (ENSO) periods – El Niño (March 1997–January 1998) and La Niña (May 1998–May 1999) – to identify possible indicators of a relationship between climatic anomalies and chlorophyte performance. Chlorophyte density increased during the La Niña. Under normal or extreme hydrologic conditions, mobile (Chlamydomonas spp.) and nonmobile (Monoraphidium spp.) chlorophytes codominated. These species belonged to Reynoldss functional groups X1 and X2, those typical of nutrient-enriched environments. Comparative analyses between El Niño and La Niña periods indicated significant differences in physicochemical (K+, dissolved polyphenols, particulate reactive phosphorus, alkalinity, pH) and biologic (species diversity and richness, phytoplankton and chlorophyte total densities) variables between the two periods at all basin sites. During the La Niña condition, species richness was greater owing to interconnected shallow lakes and drainage-channel inputs, while the Shannon diversity index was lower because of the high abundance values of Monoraphidium minutum. A detailed analysis of the chlorophytes in the entire basin, indicated that changes in density and species dominance occurred on a regional scale although diverse chlorophyte assemblages were identified in the different sectors of the Salado River basin. After La Niña event, the entire basin had the potential to revert to the previous density values, showing the resilience to global environmental changes and the ability to reestablish the general conditions of stability.

Long-term study of plankton in Río Tercero Reservoir (Argentina) in relation to a nuclear power plant operation

The Río Tercero Reservoir was built for hydroelectric purposes in Córdoba Province, Argentina in 1936. Since 1983 the reservoir has been regulated by the requirements of a nuclear power plant of 600 MW; which uses the water for cooling, resulting in large water-level fluctuations. The warmer water (about + 7 •q is restricted to a sector in a bay. The aim of this study was to examine the plankton structure related to the functioning of the nuclear plant, based on data collected during 1977-2000, in the form o f Technical Reports (BoLTOVSKOY et al. 1979, 1981, MARIAzzi et al. 1994), papers (MA!uAzzi & CONZONNO 1980, MAiuAzZI et al. 1983, BOLTOVSKOY & FoGETIA 1985, EsCALANTE 1988, GOMEZ 1988, CoNZONNO & MARIAzzi 1991) and results of previous investigations by the current aurhors (MAluNELARENA et al. 1996, 1998, 1999, 2000).

Phytoplankton of the reservoirs of Central and North Patagonia

The basins of the Limay, Neuquén, and Negro rivers comprise the greatest hydrographic system developed in its entirety in Argentina. The reservoirs constructed in this basin are distinguished by their numbers, dimensions and unitary system of management. Within the framework of environmental-monitoring programs carried out from 1977 to the present, 394 species were identifi ed in these systems. Only 30 taxa were common to all the reservoirs. Some of the dominant taxa were: Anabaena spp. (toxic complex), Ceratium hirundinella, Gymnodinium sp., Asterionella formosa, Aulacoseira ambigua var. ambigua f. spiralis, Aulacoseira pseudogranulata, Aulacoseira subarctica, and Stephanodiscus niagarae. Chlorophyta and Chrysophyta were the algal groups with the highest species richness. The Cyanobacteria played a signifi cant role, and so, two agendas for monitoring algal blooms were developed in the basin: (a) at one sampling station on the Limay River (near Arroyito Reservoir), (b) in the Mari Menuco reservoirs of the Neuquén River. Anabaena spp. (toxic complex) was seen to exhibit the greatest abundance between the spring, the summer, and the beginning of the autumn. Another reservoir that has been the object of limnological investigations since 1990 is the Florentino Ameghino, situated within the eastern-central region on the Chubut River. The centric diatoms – principally Aulacoseira granulata, Stephanodiscus sp., and Cyclotella sp. were the best represented in this reservoir. The phytoplankton was composed of species characteristic of mesotrophic to eutrophic lakes.

Periphyton responses to non-point pollution in naturally eutrophic conditions in Pampean streams

Abstract: The aim of this study was to examine the effects of different intensities of non-point pollution on water quality and the periphyton community in natural eutrophic environments such as the Pampean streams. Non-point pollution caused by agricultural and farming activities is an important contributor to water quality deterioration. Our hypothesis was that, in spite of the natural water eutrophication in Pampean streams, pollution generated by rural activities promotes changes in water quality modifying nutrient concentrations and promoting or inhibiting the periphyton developed depending on the kind and intensity of land use. The most important periphyton param-eters to assess the non-point pollution effect due to rural activities estimated in this study were chlorophyll- a , net production and alkaline phosphatase activity. Water quality parameters which proved useful in differentiating rural activities were soluble reactive phosphorus and conductivity. Agriculture caused an increase in autotrophic bio-mass and hence an increase in net production whereas cattle farming caused an increase in heterotrophic biomass. Chlorophytes were abundant in agricultural zones whereas cyanophytes or euglenophytes were more abundant in cattle farming areas. Thus, periphyton could be used as an indicator of non-point pollution, differentiating not only the types of activity but also the persistence and intensity of rural practices.

Reservoirs of the Peri-Pampean region

In this article we analyze the reservoirs of the Peri-Pampean region comprised in the arid western corridor, taking into account their biogeographic areas and the characteristics of their basins. Since many of these reservoirs are impacted by agriculture, tourism and effl uents from industries and urban areas, they are typically meso-eutrophic and with low levels of dissolved oxygen in the hypolimnion during summer. The Río Tercero Reservoir receives an additional impact from the change in operation prescribed for the functioning of a nuclear power plant. This water body, located in the “El Espinal” region, is oligo-mesotrophic, and its plankton has varied in composition and biomass during the preand post-operational periods of the plant. In all the reservoirs here studied, blooms have been registered, most frequently and recurrently produced by Cyanobacteria (e.g., species of Dolichospermum and Microcystis), and have been associated with the presence of toxins in the reservoirs of San Luis and in the San Roque Reservoir of Córdoba. Ceratium hirundinella (Pyrrophyta), a species widely colonizing the Peri-Pampean region, was also associated with blooms. In many reservoirs of the area no studies have been performed at all, while in others the investigations have been scarce and motivated by specifi c objectives with the results usually being published in either private or classifi ed reports.