A multi-level concept for fish-based, river-type-specific assessment of ecological integrity

We propose a multi-level concept for fish-based assessment (MuLFA) of the ecological integrity of running waters. This concept is designed for large-scale monitoring programmes such as required for the proposed Water Framework Directive of the EU. Out of five different biological organisation levels (fauna, community, guild, population and individual), we propose seven criteria: River-type-specific species, species with self-sustaining populations, fish region, number of guilds, guild composition, population size and population age structure. The principle of the MuLFA is based on assessing the deviation from undisturbed reference conditions. Reference conditions have to be compiled for every distinct river type using historical fish and abiotic data, present river-type-specific reference sites and reference models. The final assessment procedure is done by comparing the assessment reach with the reference conditions using a 5-tiered normative scheme and assigning that reach to the level of highest coincidence. The benefit of the MuLFA is its potential for consistent sensitivity to low- and high-dose human alterations, and due to its general character, its adaptability to all river types.