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Constructed wetlands are environmental solutions that mitigate the impacts of urban effluents. It is unclear how the performance of these wastewater treatment plants (WWTP) is affected by climatic conditions. The dissipation of nutrients, suspended solids, and changes in dissolved oxygen were investigated on a monthly basis over two years (2018/2019) at six sampling points across a WWTP located in Esquel, Patagonia. It was predicted that climatic variables (rain pattern and air temperature) would affect the functioning and efficiency of the WWTP (i.e., via nutrient load mitigation and sediment retention). Rainfall and temporal patterns differed markedly between and throughout the two years, leading to a clear seasonality in the transformation of pollutants. Nitrate loads were significantly higher in 2018 than in 2019 suggesting some degree of operational failure, whereas ammonia levels in treated effluents were extremely high during both years, with marked peaks occurring during autumn 2018 and summer 2019. The WWTP was moderately successful (~36%) in reducing TSS contents during 2018 but was inefficient in 2019. Ammonia levels in receiving waters underwent dilution due to rains rather than due to adequate WWTP nutrient retention. In terms of nutrients, effluent values exceeded those established by governmental regulation during most months, but worsened during summer coinciding with low flows. This lack of predictability for the values of the treated effluent strongly jeopardizes the ecological integrity and biodiversity of the receiving stream.

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The effects of volcanic disturbance on aquatic communities and their recovery are poorly studied. To fill this gap, we explored the effects on fish communities in rivers in Argentina of the 2008 eruption of Chaitén Volcano in southern Chile (42.8° lat. S). The eruption produced volcanic plumes of ash that persisted in the atmosphere for several months. Borne on westerly winds, deposits of tephra crossed the Andes Mountains, reaching the Atlantic coast (Argentina). We compared the pre- and post-eruption abundances of a native catfish Hatcheria macraei, and two introduced trout from rivers covered by the volcanic plumes (Argentina) using Before-After-Control-Impact analysis to explore fish recovery. Total suspended solids from volcanic ashfall, macroinvertebrate abundance and richness, and species ecological attributes influenced the spatial arrangement of fish in rivers. Twenty-one months after the eruption, Rainbow Trout, Oncorhynchus mykiss, had not returned to pre-eruption abundances in the sampled rivers, and only four rivers had regained pre-eruption species composition, suggesting that disturbance is still ongoing. The abundance of introduced fishes was strongly, negatively correlated with TSS, suggesting that ashfall affected these fish probably by clogging and abrasion of the gills. Fish recolonized previously occupied habitats 4 days to 9 months after the disturbance. Hatcheria macraei was the slowest to recolonize, whereas O. mykiss were the pioneer fish in 4 rivers following the eruption and recolonized all 5 rivers where they were present prior to the eruption. In one river, the catfish and the Brown Trout, Salmo trutta, were still absent 21 months post-eruption, potentially owing to the lack of riparian cover that would have deflected the entry of ash. Rainbow Trout suffered significant declines in abundance, whereas Brown Trout and catfish generally did not, owing to their ecological attributes. Total fish abundance was negatively correlated with ash thickness, but positively related to prey availability.

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Freshwater biodiversity is showing a global decline in relation to environmental change and there is an urgent need to quantify different facets of biodiversity to assess the conservation value of freshwater ecosystems. Identifying the ecological drivers of arid and semiarid Patagonian waterbodies is a critical requirement for planning action to conserve these still poorly understood habitats. We tested the responses of alpha and beta diversity of invertebrates (presence-absence, abundance, and biomass) to local, landscape, and climatic features, in 45 Patagonian freshwater bodies classified in three groups: isolated ponds, connected ponds, and lotic systems. We first compared the invertebrate community compositions of the different waterbodies. Secondly, using a co-inertia analysis we assessed the relative roles of local, landscape and climatic factors in driving variation in assemblage composition. Finally, we compared different facets of beta diversity and modelled their responses to environmental variables (predictors), by generalized dissimilarity modelling (GDM). Unexpectedly, lotic systems with a total of 109 taxa, were richer than lentic ones, but isolated ponds contributed most to beta diversity and supported more unique and proportionally more endemic species. Alpha and beta diversity were mainly driven by local features and secondly by climatic descriptors. However, these patterns shifted according to different community composition measures. Collectively, our results suggest that isolated ponds have a higher biodiversity value and would be more vulnerable than connected ponds and lotic systems to environmental changes. However, all waterbody types contributed to gamma biodiversity, reinforcing the importance of conserving a diversity of freshwater ecosystems in any landscape and particularly in arid and semiarid Patagonia. Our findings are a first step to resolving and quantifying the amount of changes occurring in Patagonian waterbodies, and are a prerequisite for predicting changes in species distributions in the face of global change.

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Patagonia is by far the largest glacierized area in South America. However, little is known about ecology, functioning and biodiversity of glacier-fed streams facing global warming. We investigated changes in environmental features and macroinvertebrate communities along a longitudinal gradient of glacier influence of two Patagonian systems that differ in glacier cover magnitude and the spatial sequence of lotic and lentic phases. Both glaciers, Torrecillas (~5.5km2, Torrecillas system) and Cónico (~0.44km2, Baggilt system), are retreating. Longitudinal distribution of benthic invertebrates partially fitted to predictions for glacierized temperate systems, with Diamesinae spp. dominating at closest sites to the Cónico, and Orthocladiinae increasing downstream, but patterns were unclear at Torrecillas. Generalized Linear Model identified chlorophyll a and conductivity as having significant effect on richness and density respectively at Torrecillas; detritus biomass and gravel influenced species richness, and boulder percentage and water temperature affected density, at Baggilt. Canonical Correspondence Analyses integrating benthic biota and environmental variables revealed that a higher environmental heterogeneity at Baggilt, related with spatial dimension (unshaded/shaded reaches, wetland reaches), local resources (detritus, bryophytes) and temperature, probably explained the unexpected high richness in benthic assemblages (67 taxa). Environmental conditions imposed by the lake outlet (proglacial) at Torrecillas resulted in a less diverse community (31 taxa). Finally our results suggest that these isolated, small glacier-fed streams typical of the Patagonian landscape appear highly vulnerable to global warming. Endemic elements could disappear at upper segments being replaced by other species common at rhithral environments, which might increase local diversity (alfa diversity) but decrease regional diversity (gamma diversity). From an ecosystem perspective stream functioning can result altered. Glacier retreating or disappearing threatens major ecosystem services for Patagonian inhabitants such as water supply, hydrological regulation, recreation and tourism.

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Livestock grazing can compromise the biotic integrity and health of wetlands, especially in remotes areas like Patagonia, which provide habitat for several endemic terrestrial and aquatic species. Understanding the effects of these land use practices on invertebrate communities can help prevent the deterioration of wetlands and provide insights for restoration. In this contribution, we assessed the responses of 36 metrics based on the structural and functional attributes of invertebrates (130 taxa) at 30 Patagonian wetlands that were subject to different levels of livestock grazing intensity. These levels were categorized as low, medium and high based on eight features (livestock stock densities plus seven wetland measurements). Significant changes in environmental features were detected across the gradient of wetlands, mainly related to pH, conductivity, and nutrient values. Regardless of rainfall gradient, symptoms of eutrophication were remarkable at some highly disturbed sites. Seven invertebrate metrics consistently and accurately responded to livestock grazing on wetlands. All of them were negatively related to increased levels of grazing disturbance, with the number of insect families appearing as the most robust measure. A multivariate approach (RDA) revealed that invertebrate metrics were significantly affected by environmental variables related to water quality: in particular, pH, conductivity, dissolved oxygen, nutrient concentrations, and the richness and coverage of aquatic plants. Our results suggest that the seven aforementioned metrics could be used to assess ecological quality in the arid and semi-arid wetlands of Patagonia, helping to ensure the creation of protected areas and their associated ecological services.

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BACKGROUND: It is well known that fish predation alters ecosystem processes by top-down effects. Salmonids are described as aggressive, visually and size-selective predators. Thus, prey selection by the non-native rainbow trout was examined on a seasonal basis at two streams: Nant y Fall (NyF) and Cabeza de Vaca (CVA) at Patagonia, a region where this kind of information is lacking. RESULTS: The benthos density at NyF was higher than that at CVA, and at both streams, riffles supported higher macroinvertebrate densities than pools. The diet of trouts from both streams was dominated by aquatic macroinvertebrates, was diverse, and was varied seasonally. The individuals represented in the stomachcontents were among the largest available at the streams. Diet diversity peaked during spring at NyF and during summer at CVA, whereas at both streams, the niche width peaked during spring. Preyselectivity varied seasonally. The selected preys included both aquatic (Gasteropoda, Crustacea, Plecoptera, Trichoptera, Ephemeroptera, Coleoptera, Diptera, and Odonata) and terrestrial organisms (adult dipterans, Oligochaeta, Araneae, Homoptera, Hymenoptera, Orthoptera, and Hemiptera). Some infaunal invertebrates like oligochaetes and some small Coleoptera and Diptera larvae (mainly Chironomidae) were not selected by trouts. CONCLUSIONS: Despite of the overall dominance of trichopteran species, the composition of the diet of the rainbow trout varied seasonally. This fish positively selected both aquatic and terrestrial organisms. We observed that in both streams, trouts consumed the larger individuals available in those environments.

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Chironomid substrate-specific associations regarding the nature (organic-inorganic) and stability (stable-unstable) of different habitats were investigated at two low order Patagonian streams, during high and low water periods. Nant y Fall and Glyn rivers were visited twice (October 2007 and March 2008) and seven different habitat types were identified. A total of 60 samples were collected using a Surber sampler (0.09 m(-2) and 250 µm) and a set of 23 environmental descriptors including physicochemical parameters and different fractions of particulate organic matter were assessed. 35 Chironomidae taxa were recorded with Orthocladiinae (20), Chironominae (7), and Podonominae (4) being the most well-represented subfamilies. Paratrichocladius sp. 1, Parapsectrocladius sp. 2, Parametriocnemus sp. 1, Pseudochironomus sp., and Rheotanytarsus sp. were the most abundant taxa. According to the relative preference index, at least 14 taxa showed strong affinity for a particular substrate. The structurally complex macrophyte Myriophyllum quitense supported 11 taxa compared with only five taxa found on the less complex Isoetes savatieri. Generally, stable substrates (boulders, cobbles, and rooted plants) supported significantly higher chironomids richness, abundance, and diversity than unstable ones (gravel-sand). Canonical correspondence analysis revealed that detritus (leaves, seeds, and biomass), macrophyte biomass, and secondarily hydraulic variables had high explanatory power on chironomids species composition and structure. This work suggests that more complex substrates showing persistence in the temporal dimension supported a diverse array of chironomids, meaning that the maintenance of natural habitat heterogeneity is essential for the community. Land-use practices having significant effects on ecological stream attributes such as increased turbidity, sediment deposition, and runoff patterns will alter assemblages. Understanding environmental associations of the Chironomidae assemblage at the habitat scale is significant for conservation purposes and for the management of low order streams in Patagonia.

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On May 2nd of 2008 the Chaitén Volcano (Chile, 42°50'S and 72°39'W) erupted explosively producing a strong emission of volcanic ash. As a result of this eruption wide areas on the Argentinean side became covered by ashes. In order to investigate the effects of ashfall on environmental features, water quality and macroinvertebrate communities we conducted a study on 10 rivers affected by ash deposition in their hydrographic basins. Sites were visited seasonally (June 2008-March 2010) and results were compared with data obtained from previous research projects. Measures of pH, conductivity, oxygen content, main nutrients, and total suspended solids (TSS) were taken. Macroinvertebrate samples were obtained from riffles and pools. Community attributes were measured and metrics were calculated. A strong and significant increase in TSS values at most sites was recorded and although the peak diminished rapidly during the following months, resuspension and remobilization of ash continue even 20 months after. No significant changes in pH, conductivity and nutrients, comparing with data previous to the ashfall, were detected. Most rivers showed a strong diminution on macroinvertebrate density and richness, being small rivers more severely affected than the big ones. Correspondence analysis based on abundance data allows distinguishing preeruption from posteruption dates at five rivers. Density data and species richness showed low values in March of 2010, indicating that the community was not completely recovered at some sites. At least 25 taxa resulted significantly and negatively affected. Increased mortality could be related to several factors such as habitat deterioration, food quality diminution, interference with breathing mechanisms and with other physiological and morphological characteristics. Specific-taxa responses on the recolonization process were related to dispersal mechanisms and specific strategies.

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Changes in land-use practices have affected the integrity and quality of water resources worldwide. In Patagonia there is a strong concern about the ecological status of surface waters because these changes are rapidly occurring in the region. To test the hypothesis that greater intensity of land-use will have negative effects on water quality, stream habitat and biodiversity we assessed benthic macroinvertebrates, riparian/littoral invertebrates, fish and birds from the riparian corridor and environmental variables of 15 rivers (Patagonia) subjected to a gradient of land-use practices (non-managed native forest, managed native forest, pine plantations, pasture, urbanization). A total of 158 macroinvertebrate taxa, 105 riparian/littoral invertebrate taxa, 5 fish species, 34 bird species, and 15 aquatic plant species, were recorded considering all sites. Urban land-use produced the most significant changes in streams including physical features, conductivity, nutrients, habitat condition, riparian quality and invertebrate metrics. Pasture and managed native forest sites appeared in an intermediate situation. The highest values of fish and bird abundance and diversity were observed at disturbed sites; this might be explained by the opportunistic behavior displayed by these communities which let them take advantage of increased trophic resources in these environments. As expected, non-managed native forest sites showed the highest integrity of ecological conditions and also great biodiversity of benthic communities. Macroinvertebrate metrics that reflected good water quality were positively related to forest land cover and negatively related to urban and pasture land cover. However, by offering stream edge areas, pasture sites still supported rich communities of riparian/littoral invertebrates, increasing overall biodiversity. Macroinvertebrates were good indicators of land-use impact and water quality conditions and resulted useful tools to early alert of disturbances in streams. Fish and birds having a greater ability of dispersion and capacity to move quickly from disturbances would reflect changes at a higher scale.

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