No abstract

The Bañado Carilauquen (BC) is part of the "Laguna Llancanelo" Watershed, an area of international relevance for biodiversity conservation that holds interest for oil production. Records on the biological attributes of the system's waters are scarce, particularly regarding benthic macroinvertebrate assemblages. The goal was to study the diversity of malacofauna in the BC and the relationship between its distribution patterns and water physicochemical parameters. Biological samplings and records of environmental parameters were carried out between summer of 2000 and spring of 2001 for fi ve reaches of the BC. Complete individuals and empty shells of each species were recorded for every sample, and height and width were measured for all shells. Conchological relationships were estimated and sizes compared. The relationship between presence and abundance of molluscs and environmental parameters was explored using CCA. Five gastropod species were identifi ed: Heleobia parchappii, H.hatcheri, Chilina mendozana, Lymnaea viator and Biomphalaria peregrina. A growing gradient of conductivity and hardness was detected between the headwaters (relatively soft waters) and the outlet-lake (very hard and saline waters). The distribution of molluscs is related to this gradient. Our results suggest that, except for the headwaters, the BC is hardly favourable for the development of gastropod populations. This was expressed in low species diversity, low densities, reduced sizes, fl uctuating populations and high proportion of empty shells (> 80 %).

Environmental variables and benthic macroinvertebrate assemblages were spatially and seasonally examined over two consecutive years (2000)(2001)(2002)

a b s t r a c tThe goal was to examine how macroinvertebrate taxonomic richness and density respond to spatialtemporal changes and to the influence of water physicochemical characteristics along the Bañ ado Carilauquen (BC). Benthic samplings were conducted seasonally and environmental parameters were recorded in five reaches of the BC. Cluster analysis was applied to compare taxonomic richness among sites. Community structure and spatial-temporal variation were explored using logarithmic regression. CCA was applied to explore the relationship between species and environmental variables. A total of 36 taxa were identified, predominantly insects. A growing gradient of conductivity and hardness was registered between headwaters (HD; relatively soft waters) and outlet (OL; very hard and saline waters). Total density of taxa showed significant differences among sampling sites and climate seasons. A decline in richness and density was observed from HD to OL. The spatial conductivity gradient is the major factor modulating macroinvertebrate distribution along this saline arid wetland. With the exception of the headwaters, hard, eutrophic, polysaprobic and contaminated waters such of those of the BC represent critical conditions for the development of macroinvertebrate assemblages.

Regionalization in biogeography allows division of the globe into areas according to different criteria, such as combination of biotic elements, physiognomy and climate. This regionalization constitutes a hierarchical system which comprises many categories of areas, from realms to biogeographic districts

Benthic invertebrate communities have been poorly studied in Andean streams apart from the Patagonian region. The primary objective of this work was to analyse the faunal composition at three different altitudes and to observe whether there were differences in aquatic insect community structure at spatial and temporal scales. Physicochemical variables were measured on a monthly basis. Sixteen families were found, the most frequent and abundant taxa being Massartellopsis (Ephemeroptera), Andesiops (Ephemeroptera), Metrichia neotropicalis (Trichoptera), Cailloma lucidula (Trichoptera), Austrelmis (Coleoptera), and the Chironomidae (Diptera). There was a change in benthic composition associated with land use and with the diminution of water quality from the headwaters to the mouth of the system. The middle reach was a transitional area where headwater species coexisted with species characteristic of the lower reach, with Austrelmis and the family Chironomidae being the most abundant elements.

Chironomidae are an abundant, diverse and ecologically important group common in mountain streams worldwide, but their patterns of distribution have been poorly described for the Andes region in western-central Argentina. Here we examine chironomid assemblages along an altitudinal gradient in the Mendoza River basin to study how spatial and seasonal variations affect the abundance patterns of genera across a gradient of elevation, assess the effects of environmental variables on the chironomid community and to describe its diversity using rarefaction and Shannon's indices. Three replicate samples and physicochemical parameters were measured seasonally at 11 sites in 2000 and 2001. Twelve genera of chironomid larvae were identified, which belonged to 5 subfamilies. Chironomid composition changed from the headwaters to the outlet and was associated with changes in altitude, water temperature, substrate size and conductivity. We found a pronounced seasonal and spatial variation in the macroinvertebrate community and in physicochemical parameters. Environmental conditions such as elevated conductivity levels and increased river discharge occurring during the summer produced low chironomid density values at the sampling sites. The rarefaction index revealed that the sampling sites with highest richness were LU (middle section of the river) and PO (lower section). However, Shannon's diversity index indicated that LU had the lowest diversity as a consequence of the dominance of Cricotopus over the other genera found. We attribute the low diversity found in our aquatic system to the aridity of the sampling area, as has been demonstrated in studies of other similar lotic systems in this mountain region.

Mountain wetlands provide unique information because their biota is highly specific and contributes significantly to regional diversity. The goals of this study were assessing altitudinal and temporal variation in the distribution of Heteropteran assemblages in mountain wetlands; and studying the phenology of the most abundant species. All stages of Heteroptera and data on environmental variables were collected monthly over one year from five mountain wetlands. A simple community structure, and also a low richness of aquatic true bugs, composed of four Heteropteran families (C o r i x i d a e , B e l o s t o m a t i d a e , N o t o n e c t i d a e a n d Gelastocoridae), characterized our ponds. Richness and abundance varied temporally and spatially (p < 0.0001); and increased at higher elevations. Additionally, the highest abundance of cold stenothermal species occurred at the highest altitudes where harsh conditions are prevalent. Ectemnostega (E.) quadrata and S. (T.) jensenhaarupi, both endemic to the Andes region, were the most abundant species. Both these species showed univoltine cycles and overwintered as adults. Biodiversity of the Heteroptera reached maximum values in summer when water temperature increased. Temporal and spatial monitoring studies provide key information on the distribution, diversity, and habitat requirements of Heteropteran species as well as on conservation and management of these vulnerable habitats and species which are faced with climate warming.