Selection and validation of reference sites in small river basins

Abstract

Type-specific reference conditions that describe sites with no or only very minor anthropogenic disturbances are a basic requirement of the European Water Framework Directive. The reference condition approach implies a previous determination of criteria acceptable for the definition of near-natural stretches. In this paper, a methodology based on selection and validation procedures is applied to a Portuguese watershed to guide the identification of reference sites. The methodology consisted of three phases: (1) a preliminary site inspection through the use of maps, available data and an extensive screening field campaign that resulted in the selection of 52 potentially undisturbed small-and medium-sized rivers stretches, ranging from 43 to 1069 m in altitude, with catchment areas between 4 and 641 km 2 and representing siliceous and calcareous riverbeds; (2) a detailed site selection based on ten pre-defined criteria involving physical/social/biological attributes that indicated catchment land use changes and alien vegetal riparian species as major human impacts; (3) a site validation procedure involving detailed investigation of benthic macroinvertebrate communities, riparian vegetation, in-stream habitat quality and chemical parameters that showed riparian wood-related problems as a major restriction to validate a stretch as a near-natural site. Only about 12% of all investigated river sites, accounting for 600 m of all 5200 m studied, could be considered as near-reference stretches or sites retaining essential natural functions. Selection and validation procedures can identify different sites as reference, which reinforces the need for applying both procedures. The results presented can help to accomplish the requirements of the EU -Water Framework Directive by selecting reference sites as the first step to establish biological reference conditions and, simultaneously, to form a basis for nature conservation strategies.

Using multiple approaches to develop nutrient criteria for lakes in the conterminous USA

“…For example, in southeastern Arkansas, Justus (2010) considered all lakes with available water-quality data and used field reconnaissance and intensive sampling to identify a reference lake as the one with the least impairment in each of their 4 lake classes. In Portugal, Chaves et al (2006) identified candidate lakes from maps and used field visits and validation with biological data to identify reference sites in the 6700-km 2 Mondego River basin. However, as the scale of study increases and becomes continent-wide, this level of intensive effort is not practical, and less-intensive screening is required.…”

Fish-based groups for ecological assessment in rivers: the importance of environmental drivers on taxonomic and functional traits of fish assemblages

“…Overall, river-types with higher human density tend to present higher degradation conditions and therefore reference sites can be quite rare (Matono, 2012). The least disturbed river-types are usually located in high altitude regions (and small drainage basins), frequently in isolated areas with difficult human access, far from the main human pathways (Chaves et al, 2006;Schinegger et al, 2011). The WFD defined abiotic descriptors for classifying streams and rivers into types (Annex II, Section 1 of the WFD) according to two alternative systems: (i) "system A", the fixed typology, is defined by ecoregions (according to Illies, 1978), based on the catchment area, catchment geology and altitude; (ii) "system B" uses five obligatory factors (latitude, longitude, altitude, geology and drainage area of the basin), and an additional group of optional factors.…”

Are Water Framework Directive stream types biologically relevant? The case of the Mondego river, Portugal

“…According to Chaves et al (2006), natural and seminatural areas cover 43% of the catchment area, but the natural hydrology of the basin has been heavily changed by the construction of several major dams and hundreds of small weirs. These factors were taken into consideration during site selection, which was initially based on maps, literature review and a preliminary field campaign performed during early spring 2002.…”

“…1) are near-natural systems since they exclude streams in the vicinity of urban, industrial or intensely cultivated areas, or influenced by dams, water withdrawals, high density of roads or other structures or known to have fish stocking and fishing activity. All sites exhibit no or only minor evidence of human disturbance and have the expected riparian vegetation and good apparent in-stream habitat quality (for details see Chaves et al, 2006). For the present study, a site was considered as near-natural only if it had high ecological water quality, i.e.…”

“…For the present study, a site was considered as near-natural only if it had high ecological water quality, i.e. a value of the Iberian BioMonitoring Working Party index (IBMWP) higher than 100 during all three sampling events (Ja´imez-Cue´llar et al, 2002) (for further information about the use of the IBMWP, see Chaves et al, 2006).…”