Food webs from oligotrophic Andean lakes of Bariloche region (41°S) are described. Their peculiarities in comparison with Northern Hemisphere studies are noted. The endemic species composition, the extended euphotic zone, and the oxygenated bottom allow a particular structure of the pelagic and benthic food webs. Experimental work with pelagic communities indicates that models based only on zooplankton body size are questionable and that nutrient enrichment does not necessarily lead to a positive effect on herbivorous populations. Invertebrate predation effects depend on the lake and type of predator, while vertebrate predation does control crustacean populations. The characteristic low species richness of top predators is likely to change following the introduction of exotic salmonids. The benthic food web is quite distinctive with a slow rate of decaying organic matter and easily altered by the introduction of exotic tree species.

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. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.

Chironomid communities were studied in a sediment core collected from Lake Moreno Oeste, located in Nahuel Huapi National Park. A major change in midge assemblages occurred at ∼AD 1760, which was characterized by a decrease of “cold taxa” including Polypedilum sp.2 and Dicrotendipes, and an increase of “warm taxa” including Apsectrotanypus and Polypedilum sp.1. These taxa are likely related to climatic conditions concurrent with the end of a cold period at ∼AD 1500-1700 and the beginning of a drying climate at ∼AD 1740-1900 in northern Patagonia. Coarse tephra layers had low midge diversity; however they did not disrupt the climatic trend as the community recovered rapidly after the event. Since AD 1910, after the increase in suburban housing, fish introduction, and the construction of a road, there was an increase in the relative abundances of taxa typically associated with the littoral zone, such as Parapsectrocladius, Riethia, Apsectrotanypus, and some Tanytarsini morphotypes. The main change in the chironomid community appears to be associated with long-term climate change. At the beginning of the 20th century, other site-specific environmental factors (catchment change and fish introduction) altered the chironomid assemblages, making it more difficult to understand the relative importance of each driver of assemblage change.

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Through the last millennium, Patagonia has been affected by changing climate conditions and successive volcanic eruptions. Lake Tonček is a high-altitude lake in the Southern Volcanic Zone in the northern Patagonian Andes. We documented the responses of the subfossil chironomid community to the effects of successive volcanic and different conditions in a sedimentary sequence from this lake comprising the last 900 years. The community composition and structure (abundance, diversity, and richness) and the development of morphological anomalies in the chironomid mouthparts were evaluated throughout the core. Both climatic conditions and volcanism affected the chironomid community differentially. The chironomid community changed following short-term climate change patterns, being affecting not only by temperature changes but also by variations in the regional precipitation regime. Decreases in abundance and diversity were only observed in coarse volcanic layers. In these samples, we recorded a high percentage of damaged chironomid mouthparts caused by mechanical wear, breakage or abrasion, possibly due to the increase of mineral particles. Our results represent important baseline data about the responses of chironomid communities to environmental disturbances in high-altitude lakes over long time frames.

Dissolved organic matter (DOM) is a complex mixture of carbon compounds from autochthonous and allochthonous sources. Dissolved organic carbon (DOC) concentrations and optical metrics of DOM provide clues as to the sources and processes affecting the DOM pool. Herein we provide the first broad-scale characterisation of DOM from Patagonian lakes across a strong west–east precipitation gradient. Fifty-eight lakes from Northern Patagonia (Argentina and Chile) plus six lakes from the Antarctic Peninsula were sampled during summer 2000–01. Six DOM metrics were evaluated: DOC absorbance at 254nm (a254) and 350nm (a350), DOC-specific absorbance at 254nm (a254/DOC) and 350nm (a350/DOC) and spectral slope between 275 and 295nm (S275–295). The DOM of Chilean maritime lakes and shallow (<15m) Andean lakes exhibited terrestrial signatures and a pattern of variation consistent with their occurrence across the longitudinal precipitation gradient (i.e. S275–295 increased, whereas a350/DOC decreased from west to east). The contribution of allochthonous DOM was smaller in deep (>15m) Andean lakes, which is consistent with their longer water retention time. Steppe lakes, mostly from endorheic basins, made up the most heterogeneous group with regard to DOM characteristics.

A new chironomid genus Wuelkerella is described. Pupae collected from the ultraoligotrophic Lakes Tonĉek and Jujuy, inRío Negro Province, Argentina were individually reared to adults. Pupa and adult male and female of Wuelkerella toncekensis sp. n. show intermediate features of Alotanypus Roback, Brundiniella Roback and Radotanypus Fittkau et Murray.

Silver (Ag) is a pollutant of high concern in aquatic ecosystems, considered among the most toxic metallic ions. In lacustrine environments, contaminated sediments are a source of Ag for the food web. Chironomidae (Insecta: Diptera) are the most abundant, diverse, and representative insect groups in aquatic ecosystems. Chironomid larvae are closely associated to benthic substrates and link primary producers and secondary consumers. Given their trophic position and their life habits, these larvae can be considered the entry point for the transference of Ag, from the benthic deposit to the higher trophic levels of the food web. Previous studies in lakes from Nahuel Huapi National Park (Northern Patagonia) showed Ag enrichment over background levels (0.04-0.1 μg g dry weight) both in biota (bivalves and fish liver) and sediments from sites near human settlements. The aim of this study was to analyze the role of chironomids in the transference of Ag from the benthic reservoir of Lake Moreno Oeste to the food web. The concentration of Ag in chironomid larvae tissue ranged from 0.1 to 1.5 μg g dry weight, reaching a bioaccumulation factor up to 17 over substrates and depending on the associated substrate type, feeding habitats, larval stage, and season. The main Ag transfer to higher trophic levels by chironomids occurs in the littoral zone, mostly from larvae inhabiting submerged vegetation (Myriophyllum quitense) and sediment from vegetated zones. This study presents novel evidence of the doorway role played by chironomid larvae in Ag pathways from the sediments into food webs of freshwater ecosystems.