Divergent dynamics of microbial components in two temperate shallow lakes with contrasting steady states in the Southern Hemisphere.

Factors that affect abundances of organisms in water bodies are influenced by extrinsic and intrinsic drivers that operate from outside and within a system. A high temporal coherence in the dynamics of abiotic parameters and biological communities among neighboring lakes evidences a strong extrinsic control operating similarly across lakes, and allows for prediction of ecosystems evolution in the context of global change and intensive land use. The Pampa region (Argentina) encompasses many shallow lakes submitted to different degrees of anthropic influence and showing contrasting alternative states.

The dynamics of picocyanobacteria from a hypereutrophic shallow lake is affected by light-climate and small-bodied zooplankton: a 10-year cytometric time-series analysis.

In aquatic systems, an interplay between bottom-up and top-down processes determines the dynamic of picocyanobacteria (Pcy) abundance and community structure. Here, we analyzed a 10-year time series (sampled fortnightly) from a hypereutrophic turbid shallow lake located within the Pampa Region of South America, generating the first long-term record of freshwater Pcy from the Southern Hemisphere. We used a cytometric approach to study Pcy community, and focused on its relations with nutrient and light conditions (bottom-up) and potential grazers (top-down).

Field evidence supports former experimental claims on the stimulatory effect of glyphosate on picocyanobacteria communities.

Glyphosate-based herbicides are the most commonly used herbicide worldwide. Although glyphosate is known to be toxic to aquatic organisms, it can also have stimulatory effects on small-size (ø <2 µm) cyanobacteria (Pcy) able to metabolize and degrade glyphosate and AMPA. Several previous experimental studies in micro- and mesocosms reported increases of Pcy abundance in response to glyphosate additions, but comparable field evidence is presently unavailable.

Species-specific phenological trends in shallow Pampean lakes' (Argentina) zooplankton driven by contemporary climate change in the Southern Hemisphere.

The relationship between the timing of recurrent biological events and seasonal climatic patterns (i.e., phenology) is a crucial ecological process.

Occurrence and levels of glyphosate and AMPA in shallow lakes from the Pampean and Patagonian regions of Argentina.

Glyphosate (N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide used to kill weeds that compete with commercial crops. In Argentina, the use of glyphosate-based herbicides increased dramatically (up to ∼200,000 tons on 2012) since the introduction of glyphosate-resistant crops, such as transgenic soy and resistant corn, and the adoption of non-till practices in the 1990's. Sallow lakes within the Pampa region may be potentially impacted by continuous herbicide usage.

Rotifer dynamics in three shallow lakes from the Salado river watershed (Argentina): the potential modulating role of incident solar radiation.

In turbid Pampean lakes, incident solar radiation is a major driver of plankton seasonal dynamics. Higher light availability in summer translates into higher primary production, and therefore more food for zooplankton grazers. However, experimental evidence suggests that food produced under the high irradiance conditions prevailing in summer are less suitable to sustain rotifer population growth than that produced under the lower irradiance conditions typical of winter.

Contrasting patterns of MAAs accumulation in two populations of the copepod Boeckella gracilipes.

The bio-accumulation of mycosporine-like amino acids (MAAs) is common in planktonic copepods that inhabit environments exposed to high levels of solar radiation. MAAs accumulation in copepods can be affected both by extrinsic (environmental) and intrinsic factors (local adaptation, genotype, etc.).

Alternative states drive the patterns in the bacterioplankton composition in shallow Pampean lakes (Argentina).

We assessed the influence of environmental factors in shaping the free-living bacterial community structure in a set of shallow lakes characterized by contrasting stable state patterns (clear-vegetated, inorganic-turbid and phytoplankton-turbid). Six temperate shallow lakes from the Pampa Plain (Argentina) were sampled over an annual cycle, and two fingerprinting techniques were applied: a 16S rDNA analysis was performed using denaturing gradient gel electrophoresis (DGGE) profiles, and a 16S-23S internally transcribed spacer region analysis was conducted by means of automated ribosomal intergenic spacer analysis (ARISA) profiles. Our results show that the steady state that characterized the different shallow lakes played a major role in structuring the community: the composition of free-living bacteria differed significantly between clear-vegetated, inorganic-turbid and phytoplankton-turbid shallow lakes.

Seasonal variability of optical properties in a highly turbid lake (Laguna Chascomús, Argentina).

We study the underwater light field seasonality in a turbid lake, Laguna Chascomús (Buenos Aires, Argentina). We report (1) relationships between optical properties (OPs) and optically active substances (OASs); (2) relationships between inherent (IOPs) and apparent (AOPs) optical properties; and (3) the seasonal variability in OASs and OPs. Light absorption was dominated by the particulate fraction.

Lakes as sentinels of climate change.

While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate.

New evidences of Roundup (glyphosate formulation) impact on the periphyton community and the water quality of freshwater ecosystems.

Argentina is the second largest world producer of soybeans (after the USA) and along with the increase in planted surface and production in the country, glyphosate consumption has grown in the same way. We investigated the effects of Roundup (glyphosate formulation) on the periphyton colonization. The experiment was carried out over 42 days in ten outdoor mesocosms of different typology: "clear" waters with aquatic macrophytes and/or metaphyton and "turbid" waters with great occurrence of phytoplankton or suspended inorganic matter.

Mycosporine-like amino acids in freshwater copepods: potential sources and some factors that affect their bioaccumulation.

Mycosporine-like amino acids (MAAs) are ubiquitous photoprotective compounds in aquatic environments. MAAs are synthesized by a wide variety of organisms (i.e.

Quality of UVR exposure for different biological systems along a latitudinal gradient.

The exposure of organisms to ultraviolet radiation (UVR) is characterized by the climatology (annual cycle) and the variance (anomalies) of biologically-weighted irradiances at eight geographical locations in austral South America, from 1995-2002. The net effect of UVR on biological systems is a result of the balance of damage and repair which depends on intensity and duration of irradiance and is modulated by its variability. The emphasis in this study is on day-to-day variability, a time scale of importance to adaptive strategies that counteract UVR damage.

Occurrence of photoprotective compounds in yeasts from freshwater ecosystems of northwestern Patagonia (Argentina).

In this paper we present the results of research on the occurrence, induction and role of photoprotective compounds (PPCs) present in native aquatic yeasts from freshwater Patagonian ecosystems. We focus on the effect of UV radiation (UVR) as a factor that controls the level of photoprotection of yeasts, and explore its potential significance in shaping yeast distributional patterns. The research presented here combines field surveys and laboratory work, including the isolation and culture of native yeasts strains, and laboratory assays under different radiation conditions.

Vertical mixing and ecological effects of ultraviolet radiation in planktonic communities.

We present a mathematical model for a phytoplankton-zooplankton system, based on a predator-prey scheme. The model considers the effects of sinking in the phytoplankton, vertical mixing and attenuation of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) in the water column. In a first approach, the model was studied under conditions of average PAR irradiance and shows fluctuations and stable equilibrium points.

UV radiation as a potential driving force for zooplankton community structure in Patagonian lakes.

This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity.

Mycosporines from freshwater yeasts: a trophic cul-de-sac?

Mycosporine-like amino-acids (MAAs) are found in aquatic bacteria, algae, and animals. A related compound, the mycosporine-glutaminol-glucoside (myc-glu-glu), has recently been reported in freshwater yeasts. Although animals depend on other organisms as their source of MAAs, they can efficiently accumulate them in their tissues.

Mycosporines in carotenogenic yeasts.

The ability to produce mycosporines (MYCs) in 157 pigmented yeast strains (eight genera, 25 species) isolated from natural environments of Patagonia (Argentina) was assessed. The strains belong to four taxonomic groups: the Sporidiobolales and Erythrobasidium clade of the class Urediniomycetes, and Cystofilobasidiales and Tremellales of the class Hymenomycetes. Induction of MYCs did not occur in all yeast strains tested and appeared to be an exclusive trait of members of the Erythrobasidium clade and Tremellales.

Multichannel radiometer calibration: a new approach.

The error in irradiance measured with Sun-calibrated multichannel radiometers may be large when the solar zenith angle (SZA) increases. This could be particularly detrimental in radiometers installed at mid and high latitudes, where SZAs at noon are larger than 50 degrees during part of the year. When a multiregressive methodology, including the total ozone column and SZA, was applied in the calculation of the calibration constant, an important improvement was observed.

Mycosporine-like amino acids in planktonic organisms living under different UV exposure conditions in Patagonian lakes.

Mycosporine-like amino acids (MAAs) were studied in zooplankton from 13 Argentinian lakes covering a broad range in altitude, maximum depth and physico-chemical properties of the water. Four to nine different MAAs (predominantly porphyra-334 and shinorine) were found in the copepods Boeckella gibbosa, B. gracilipes, B.

Constitutive and UV-inducible synthesis of photoprotective compounds (carotenoids and mycosporines) by freshwater yeasts.

Twelve yeasts isolated from lakes of Northwestern Patagonia, Argentina, belonging to eight genera (Sporobolomyces, Sporidiobolus, Rhodotorula, Rhodosporidium, Cystofilobasidium, Cryptococcus, Torulaspora, and Candida) were analysed for their ability to produce photoprotective compounds. For this purpose, three laboratory experiments were performed to study the effect of photosynthetically active radiation (PAR) and PAR in combination with UV radiation (PAR + UVR) on the production of carotenoids and mycosporines. The synthesis of carotenoid compounds was clearly stimulated in six out of nine red yeast strains tested upon exposure to PAR or PAR + UVR; however, the latter conditions produced a stronger response than PAR alone.

Assessing sublethal effects of ultraviolet radiation in juvenile rainbow trout (Oncorhynchus mykiss).

This paper presents a method for assessing sublethal effects of ultraviolet radiation in fish. The method is based on the assumption that UV-B exposure is stressful to fish. We measured oxygen consumption in UV-B-irradiated rainbow trout juveniles using a UV-transparent respirometer chamber.

Replicated mesocosm study on the role of natural ultraviolet radiation in high CDOM, shallow lakes.

The role of ultraviolet radiation on shallow, high CDOM (colored dissolved organic matter) lakes was investigated during two consecutive summers (1999 and 2000) in replicated mesocosms (rectangular fiberglass tanks). Each tank (volume: 300 L; depth: 40 cm) was covered with a layer (approximately 3 cm) of sediment from lake El Toro (40 degrees 14' S; 70 degrees 22' W) and filled with filtered water. The experimental design consisted of two treatments: full natural radiation (UV-exposed) and natural radiation without ultraviolet radiation (UV-shielded).

A field and laboratory study on factors affecting polymorphism in the rotifer Keratella tropica.

We present data on polymorphism of the rotifer Keratella tropica from an outdoor, mesoscale experiment and a series of laboratory induction assays. In the outdoor experiment the biomass of planktonic crustaceans was noticeably depressed by larval fish predation, and associated with this depression K. tropica underwent a striking reduction of caudal spines.