Hydrobiologia 516: 1–20, 2004. D. Hering, P.F.M.Verdonschot, O. Moog & L. Sandin (eds), Integrated Assessment of Running Waters in Europe. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 1 Overview and application of the AQEM assessment system Daniel Hering 1 , Otto Moog 2 , Leonard Sandin 3 & Piet F. M. Verdonschot 4 1 Department of Ecology, Faculty of Hydrobiology, University of Duisburg-Essen, D-45117 Essen, Germany E-mail: daniel.hering@uni-essen.de 2 BOKU-University of Agricultural Sciences, Institute for Water Provision, Stream Ecology & Waste Management, Department of Hydrobiology, Fisheries and Aquaculture, Max Emanuel Straße 17, A-1180 Vienna, Austria 3 Swedish University of Agricultural Sciences, Department of Environmental Assessment, P.O. Box 7050, S-750 07 Uppsala, Sweden 4 Alterra Green World Research, Freshwater Ecology, Droevendaalsesteeg 3a, NL-6700 AA Wageningen, The Netherlands Key words: stream assessment, macroinvertebrates, Europe, AQEM, multimetric index, standardisation Abstract The main objective of the European Union (EU) funded project AQEM 1 was to develop a framework of an as- sessment system for streams in Europe based on benthic macroinvertebrates that fulfils the requirements of the EU Water Framework Directive. Initial assessment methods for 28 European stream types and more generally applicable tools for stream biomonitoring in Europe were generated. The development of the system was based on a newly collected data set covering stream types in Austria, the Czech Republic, Germany, Greece, Italy, The Netherlands, Portugal and Sweden. Altogether, 901 benthic invertebrate samples were taken using a standardised multi-habitat sampling procedure and a large number of parameters describing the streams and their catchments was recorded for all sampling sites. From the stream and catchment characteristics measures of stress were derived. A large number of metrics was tested independently for each of the stream types, to identify the response of each metric to degradation of a site. This process resulted in up to 18 core metrics for the individual stream types, which were combined into a different multimetric index in each country. The multimetric AQEM assessment system is used to classify a stream stretch into an Ecological Quality Class ranging from 5 (high quality) to 1 (bad quality) and often provides information on the possible causes of degradation. AQEM provides a taxa list of 9557 European macroinvertebrate taxa with associated autecological information, a software package for performing all the calculations necessary for applying the multimetric AQEM assessment system and a manual describing all aspects of the application of the system from site selection to data interpretation. Introduction The EU Water Framework Directive (WFD; Directive 2000/60/EC – Establishing a Framework for Community Action in the Field of Water Policy) outlines a legal structure for the as- sessment of all types of water bodies in Europe. A main focus of the WFD is the use of biotic indicators 1 The Development and Testing of an Integrated Assessment System for the Ecological Quality of Streams and Rivers throughout Europe using Benthic Macroinvertebrates. (macrobenthic fauna, fish fauna and aquatic flora) in stream assessment, which is a concept new to many European countries. Furthermore, the ecological status of a water body is defined by comparing the biological community composition present with the near-natural reference conditions. These new WFD guidelines on ecological water quality assessment have generated a strong demand for either ‘new’ assessment systems fulfilling the criteria or to adapt existing systems to meet the criteria of the WFD. Benthic macroinverteb- rates, together with algae, serve as the most common