# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 2 Biological Assessment of Rivers
### Europe
In addition to taxonomic-based indices, the use of macroinvertebrate biological traits in the assessment of rivers has been investigated by several European authors as a way of assessing river ecological functioning (e.g., [180; 181; 182; 183; 184; 185; 186; 187; 188; 189; 190; 191; 192; 193; 194; 195; 196; 197; 198; 199; 190; 191; 192; 193; 194; 195; 196; 197; 198; 199; 199; 1  
and was based on the bioindicator performance of macrophytes along a degradation gradient from reference (oligotrophic) to highly impaired river systems [193]. However, many of these national efforts were unsuccessful because of the lack of correlation with pressures, lack of reference standards or failure in the harmonization procedure (e.g., sampling and taxonomic precision) [167]. Presently, only 15 official metrics are used after the WFD intercalibration exercise [17; 170]. Besides eutrophication, macrophytes also respond to general degradation, which includes multi-pressures such as organic matter, hydomorphological alterations or single nutrients. The fish national methods included in the IC [173; 194] ranged from MMIs (most countries), to predictive models, as is the case of the methods adopted by England-Wales, Ireland and Scotland. The French method is a guild-based metric, although also relying on predictive models of species occurrence [195]. The Portuguese index for fish, F-IBIP (Indice Piscicola de Integridade Biotica para Rios Vadeaveis de Portugal Continental, [196]), is a typical type-specific MMI for wadeable streams based on the reference condition approach. Metrics are either based on presence/absence or abundance data and are included in six main functional attributes: composition, general tolerance, trophic function, habitat preference, reproductive classification, potamodromy and age structure [173]. In the Intercalibration Exercise, a common pan-European fish index, the EFI+ index was developed (European Fish Index, [197]). This is a multimetric guild-based index that uses a predictive model to derive expected taxa under reference conditions from abiotic environmental characteristics of individual sites and quantifies the deviations between the observed and predicted fish assemblages [173]. The monitoring guidelines of the WFD do not explicitly take into account non-native species [198]. However, the presence of non-native invertebrates, particularly when invasive, has influenced the results of some indices for benthic macroinvertebrates, including those used for the WFD assessment [199]. Also, the detection of rare species is generally beyond the scope of WFD monitoring. In fact, the design of the monitoring procedures emphasizes time and cost efficiency to maximize the number of sites to be sampled, which often means the production of taxonomic lists at a coarser taxonomic resolution than species (e.g., families for macroinvertebrates). Some studies have assessed this trade-off as acceptable [200], but others have identified an impact on the assignment of EQS [199; 201]. The monitoring networks established in the EU aim to generate comprehensive and coherent information on the ecological status of all waterbodies, across all river basin districts, providing crucial data for elaborating River Basin Management Plans. There are three types of monitoring each with different objectives. (1) Surveillance monitoring assesses natural and anthropogenic long-term changes in river basins [202]. It includes biological, hydomorphological, and general physico-chemical quality parameters, as well as pollutants. (2) Operational monitoring assesses possible changes through time in the status of those water bodies for which a reasonable concern of not meeting environmental objectives exists. The quality elements to be assessed depending on the relevant pressures. (3) Investigative monitoring is conducted when a water body is not meeting environmental objectives because of an unknown cause or a pollution spill. The last two types of monitoring determine measures to achieve environmental objectives.