DOI: 10.5061/dryad.pnvx0k6r9
title: Global biological condition of rivers

description: Rivers suffer from multiple stressors acting simultaneously on
 their biota, but the consequences are poorly quantified at the global
 scale. We evaluated the biological condition of rivers globally, including
 the largest proportion of countries from the Global South published to
 date. We gathered macroinvertebrate- and fish-based assessments from
 72,275 and 37,676 sites, respectively, from 64 study regions across six
 continents and 45 nations. Because assessments were based on differing
 methods, different systems were consolidated into a 3-class system: Good,
 Impaired, or Severely Impaired, following common guidelines. The
 proportion of sites in each class by study area was calculated and each
 region was assigned a Köppen-Geiger climate type, Human Footprint score
 (addressing landscape alterations), Human Development score (addressing
 social welfare), % rivers with good ambient water quality, %
 protected freshwater key biodiversity areas; and % of forest area net
 change rate. We found that 50% of macroinvertebrate sites and 42%
 of fish sites were in Good condition, whereas 21% and 29% were Severely
 Impaired, respectively. Poorest biological conditions
 occurred in Arid and Equatorial climates and the best conditions
 occurred in Snow climates. Severely Impaired conditions were
 associated (Pearson correlation coefficient) with higher
 Human Development Index scores, poorer physico-chemical water quality, and
 lower proportions of protected freshwater areas. Good biological
 conditions were associated with good water quality and increased forested
 areas. It is essential to implement statutory bioassessment programs in
 Asian, African and South American countries, and continue them in Oceania,
 Europe and North America. There is a need to invest in assessments based
 on fish, as there is less information globally and fish were strong
 indicators of degradation. Our study highlights a need to increase the
 extent and number of protected river catchments, preserve and restore
 natural forested areas in the catchments, treat wastewater discharges, and
 improve river connectivity.
description: Benthic macroinvertebrate and fish assessment data from
 national/continental validated databases, from peer reviewed publications,
 or from research projects with validated and/or published biological
 classification methods were collected by the authors from each country. We
 targeted the most recent bioassessment data available for each site. Data
 sources are indicated in the csv file. The biological quality indices used
 were those previously validated for the study regions and were based on
 the reference condition approach (RCA, Hughes et al. 1986, Reynoldson et
 al. 1997, Stoddard et al. 2006). This means that the index scores were
 adjusted to the reference values of the most appropriate river
 type/ecoregion. For multimetric indices and predictive models the index
 score produced is on a 0-1 scale. The use of the RCA and normalized scales
 contribute to reducing the importance of differing sampling methods and
 indices.To homogenize site assessments globally and reduce the importance
 of differences in study designs and sampling and assessment methods, we
 converted all the site quality classification systems into a simple
 3-class system: Good (no rehabilitation measures needed, assemblages
 similar to reference conditions); Impaired (scores clearly lower than in
 reference conditions); and Severely Impaired (many fewer taxa than
 expected; substantial alteration in assemblage composition compared to
 reference conditions). In practical terms, this means that the High and
 Good classes from European indices, the Equivalent to Reference of BEAST
 predictive models, the A band of AUSRIVAS and RIVPACS models, or classes A
 (Pristine) and B (largely natural) of the South African system were
 considered as Good in our classification system. The remaining degradation
 gradient was divided into two classes. An intermediate degradation class
 (Impaired) corresponds with classes C (moderately modified) and D (largely
 modified) in the South African system, and to the Moderate and Poor
 classes of the WFD system. A substantial degradation level (Severely
 Impaired) integrated classes E (seriously modified) and F (Critically
 modified) from South Africa, and Bad from the WFD. Those results were
 reported as % of sites in Good, Impaired and Severely Impaired for each
 study region.
description: Excel or similar.