TREAM: Time series of freshwater macroinvertebrate abundances and site characteristics of European streams and rivers

Freshwater macroinvertebrates are a diverse group that play many key ecological roles, including accelerating nutrient cycling, filtering water, controlling aquatic primary producers, and providing food for predators. Since they rapidly respond to environmental changes, macroinvertebrate community composition is a commonly used indicator of water quality. In Europe, efforts to improve water quality following environmental legislation, primarily starting in the 1980s, may have driven a recovery of macroinvertebrate communities. Towards understanding temporal changes of these organisms, we compiled the TREAM database (Time seRies of European freshwAter Macroinvertebrates). The TREAM database consists of whole macroinvertebrate community time series from 1,816 river and stream sites (mean length of 19.2 years with 14.9 sampling years) of 22 European countries sampled between 1968 and 2020. In total, the data include >93 million sampled individuals of 2,648 taxa from 959 genera and 212 families. These data can be used to ask a wide range of questions from identifying drivers of the population dynamics of specific taxa to assessing the success of legislative and management restoration efforts.Usage Notes:Several key characteristics about these data should be noted by future data users. First, and most importantly, sampling methods and effort, and seasonality are standardised within individual time series but can vary across time series. This means that raw data are not directly comparable across the 41 independent projects included in the TREAM dataset.Second, while we use the taxonomic backbone of freshwaterecology.info as it is a common tool used by European freshwater ecologists, we are aware that it does not capture all recent changes to taxonomic names.Third, two pairs of time series overlap in sampling locations: 1) Site ID = 100000001 (SVD) & 100000309 (Bugey_SVD) refer to the same location; 2) Site ID = 100000002 (SVG) & 100000308 (Bugey_SVG) refer to the same location. The data from these sites were collected by the Institut national de la recherche agronomique (referent: Maxence Forcellini) between 1980 and 2014, and by Électricité de France (Referent: Anthony Maire) between 2000 and 2019.Fourth, although standardised taxonomic resolution within time series was a criterion for data inclusion, some datasets switch taxonomic resolution (e.g. from genus to species level) for a given taxon part-way through the time series. This is particularly the case for data from Denmark within the Baetidae, Brachycentridae, Chironomidae, Gammaridae, Oligochaeta and Simuliidae. We did not alter these names because they represent the original information provided for and published in Haase et al. (2023), and standardisation methods may vary depending on intended future use. In the time series provided, these issues could affect analyses of shifts in community composition, which could reflect a shift in identification level rather than compositional change. These issues do not affect analyses of total abundance and have little influence taxa richness or diversity, including their temporal trends, as they are typically substitutions of one unique taxon for another. As with all large datasets of ecological time series, data users should carefully check the data in light of their intended use and when questions arise, contact data providers (listed in TREAM_siteLevel.csv).Finally, since each record was assigned the Hydrography90m stream network subcatchment, users can directly interact with the hydrographr R-package which facilitates subsequent network and distance analyses using the data records.