Foreward DEPETRIS, P.J. Introduction TORRES, A.I., AND CAMPODONICO, V.A. 1 Effects of Multiple Stressors Associated with Land-use Practices in the Percy Corintos Basin (Northwest Chubut): An Ecological Assessment MISERENDINO, M.L., WILLIAMS-SUBIZA, E., MANZO, L.M., HORAK, C.N., BRAND, C., ASSEF, Y.A., AND EPELE, L.B. 1.1 Introduction 1.2 Study Area Description 1.2.1 Esquel Stream 1.2.2 Percy River 1.2.3 Corintos Lower Basin 1.3 Land Use Practices in the Catchment 1.3.1 Esquel Stream-Percy River System: Urbanization Effects 1.3.2 Lower Percy River: Sedimentation and Eutrophication Symptoms 1.3.3 Effects of Agricultural Practices on the Corintos Lower Basin 1.3.4 Environmental and Ecological Functions of Wetlands in the Basin 1.3.5 Water Quality and the Ecological Status of the Aquatic Systems in the Basin 1.4 Mitigation Action and Perspectives 2 The Manso River Drainage System in the Northern Patagonian Andes: Hydrological, Hydrochemical and Nutrient Dynamics LECOMTE, K.L., PASQUINI, A.I., SEPÚLVEDA, L.D., TEMPORETTI, P., PEDROZO, F., AND DEPETRIS, P.J. 2.1 Introduction 2.2 Geographical Framework 2.3 Hydroclimatic Overview 2.4 Hydrochemistry and Weathering Signature 2.5 Suspended Sediments and Nutrient Dynamic 2.6 Concluding Summary 3 Geothermal Influence on the Hydrochemistry of Surface Streams in Patagonia Neuquina VILLALBA, E., SANTUCCI, L., BORZI, G., PASQUINI, A.I., PÁEZ, G., AND CAROL, E. 3.1 Introduction 3.2 Field Methodology and Laboratory Analysis 3.3 Chemical Characteristics of Streams 3.4 Hydrogeochemical Processes and Geothermal Influence on Streams 3.5 Perspectives and Future Work 4 Hydrogeochemistry of an Acid River and Lake Related to an Active Volcano. The Case of Study: Agrio River - Copahue Volcano in Patagonia, Argentina LLANO, J., LAMBERTI, M.C., SIERRA, D., AND AGUSTO, M. 4.1 Introduction 4.2 Study Area 4.2.1 Geological Setting 4.2.2 The Hydrological System of the Caviahue-Copahue Volcanic Complex 4.3 Methodology 4.4 Results 4.5 Discussion 4.5.1 Major cations 4.5.2 Trace and Rare Earth Elements 4.5.3 Hydroxysulfates Precipitation 4.6 Conclusions 5 Negro River Environmental Assessment ARIAS, A.H., MACCHI, P., ABRAMETTO, M., SOLIMANO, P., MIGUELES, N., RIVAS, F.G., FUNES, A.I., CALABRESE, G., SORICETTI, M., BERNARDIS, A., BAGGIO, R.B., LABAUT, Y., AND MARCOVECCHIO, J.E. 5.1 Introduction 5.2 Persistent Organic Pollutants 5.3 Heavy Metal Pollution 5.3.1 Water 5.3.2 Sediments 5.3.3 Fish 5.4 Freshwater Macroinvertebrates Assemblages 5.5 Introduced species: Status and Potential Problems 5.5.1 Salmonids 5.5.2 Cyprinus carpio 5.5.3 Native species 5.5.3.1 Geotria macrostoma 5.5.3.2 Aplochiton spp. 5.5.3.3 Dyplomistes viedmensis 5.5.4 Environmental Threats for Fish Assemblages 6 Patagonia's Chubut River: Overview of the Main Hydrological and Geochemical Features DEPETRIS, P.J., AND PASQUINI, A.I. 6.1 Introduction 6.1.1 Physiographic and Climatic Features 6.1.2 Geological Setting 6.1.3 Methodology 6.2 Hydrological Aspects 6.3 Geochemical Perspective 6.3.1 Main Characteristics 6.3.2 Provenance of Inorganic Dissolved Phases 6.3.3 The Organic Load 6.4 Sediments 6.4.1 TSS Yield and Transport 6.4.2 The Geochemical Signature of Sediments 6.5 Summary and Final Comments 7 Hydrochemical Characteristics of Mid-Low Sections of North Patagonia Rivers, Argentina VÉLEZ-AGUDELO, C., MARTÍNEZ, D.E., QUIROZ LONDOÑO, O.M., AND ESPINOSA, M.A. 7.1 Introduction 7.2 Regional Setting and Previous Studies 7.3 Materials and Methods 7.3.1 Sample Collection and Chemical Analysis 7.3.2 Preprocessing Data and Numerical Methods 7.4 Results 7.4.1 General and Seasonal Variability 7.4.2 Rivers Hydrogeochemistry 7.5 Discussion 7.6 Conclusions 8 Hydrochemistry of Patagonian Wet Meadows (mallines) Under Different Geological Frames ALVAREZ, M.P., CAROL, E., PASQUALE PÉREZ, M.P., MELENDI, E., AND VILLALBA, E. 8.1 Introduction 8.2 Wet Meadows