This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10-15 years . The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen . Sampling methods are briefly reviewed .The composition of drift in streams and rivers is assessed, especially with respect to temporal variation, drift densities and drift distances . This body of descriptive literature is subsequently analysed in relation to both abiotic and biotic variables, such as current/discharge, photoperiod, temperature, benthic densities, predators and life cycle stage .The ecosystem significance of drift in terms of colonization and distribution, population dynamics and its importance as a food resource are then reviewed and discussed . Drift enables organisms to escape unfavourable conditions and gives them the potential to colonize new habitats . However, mortality poses a constant threat . The drift community is composed of components whose presence in the drift may be due to widely differing reasons . This renders unsuccessful most attempts to explain drift in terms of one or even a few factors, except in extreme cases, such as floods or pollution . The question whether drifting organisms are alive, dead, or "ecologically dead" is seldom addressed, as is variation at the level of the individual .The drift literature is dominated by large numbers of descriptive papers and there is a need for laboratory and field studies aimed at testing specific hypotheses .

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models. 2. Using this information, and data from other recent studies of glacier-fed rivers, a modi®ed conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate families and subfamilies as determined by maximum water temperature (Tmax) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure. 3. Where maximum water temperature is below 2 °C, Diamesinae chironomids are typically the sole inhabitants, but where Tmax >2 °C but <4 °C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 °C Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe. 4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period. 5. Dispersal constraints in¯uence macroinvertebrate assemblages of many glacier-fed rivers located on islands and in some alpine areas

Glaciers cover ∼10% of the Earth's land surface, but they are shrinking rapidly across most parts of the world, leading to cascading impacts on downstream systems. Glaciers impart unique footprints on river flow at times when other water sources are low. Changes in river hydrology and morphology caused by climate-induced glacier loss are projected to be the greatest of any hydrological system, with major implications for riverine and near-shore marine environments. Here, we synthesize current evidence of how glacier shrinkage will alter hydrological regimes, sediment transport, and biogeochemical and contaminant fluxes from rivers to oceans. This will profoundly influence the natural environment, including many facets of biodiversity, and the ecosystem services that glacier-fed rivers provide to humans, particularly provision of water for agriculture, hydropower, and consumption. We conclude that human society must plan adaptation and mitigation measures for the full breadth of impacts in all affected regions caused by glacier shrinkage.

The insect order Ephemeroptera, or mayflies as they are usually called, have attracted man's attention for centuries. As early as 1675, Swammerdam wrote Ephemeri vita (212), which contains an amazingly detailed study the biology and anatomy of the mayfly Palingenia. Mayflies date from Carboniferous and Permian times and represent the oldest of the existing winged insects. They are unique among the insects in having two winged adult stages, the subimago and imago. Adult mayflies do not feed; they rely on reserves built up during their nymphal life. They live from 1-2 hours to a few days and even up to 14 days in some ovoviviparous species. Thus mayflies spend most of their life in the aquatic environment, either as eggs or as nymphs, and the major part of this review concerns itself with their aquatic life. The nymphal life span in mayflies varies from 3-4 weeks to about 21/2 years. The length of egg development varies from ovoviviparity, in which the eggs hatch immediately after oviposition, to a period of up to 10-11 months in some arctic/alpine species. Because of their winged adult stage and a propensity for drift as nymphs, mayflies are often among the first macroinvertebrates to colonize virgin habitats (89, 128, 241). However, over longer distances their dispersal capacity is limited, owing to the fragile nature and short life of the adults. Mayfly faunas on oceanic islands and isolated mountain areas are poor in species andusually restricted to the Baetidae and/or Caenidae (62). Their conservative dispersal makes them useful subjects for biogeographical analysis (62). The mayflies are a small insect order containing somewhat over 2000 valid species, which are grouped into approximately 200 genera and 19 families (102, 152). Despite their poor fossil record, the conservative dispersal, together with the wide range of morphological, anatomical and

1. A study on glacial stream ecosystems was carried out in six regions across Europe, from Svalbard to the French Pyrenees. The main aim was to test the validity of the conceptual model of Milner & Petts (1994) with regard to the zonation of chironomids of glacier-fed rivers along altitudinal and latitudinal gradient. 2. Channel stability varied considerably, both on the latitudinal and altitudinal scale, being lowest in the northern regions (Svalbard, Iceland and Norway) and the Swiss Alps. Water temperature at the upstream sites was always <2 °C. 3. There was a prominent difference in taxonomic richness between the Alpine and the northern European regions, with a higher number of taxa in the south. In all regions, the chironomid community was characterized by the genus Diamesa and the subfamily Orthocladiinae. Of a total of 63 taxa recorded, two (Diamesa bertrami and Orthocladius frigidus) were common in all the regions except Svalbard. 4. On the basis of cluster analysis, seven distinct groups of sites were evident amongst glacial-fed systems of the ®ve regions (Pyrenees excluded). This classi®cation separated the glacier-fed streams on geographical, latitudinal and downstream gradients. 5. Canonical Correspondence Analysis (CCA) of environmental variables was carried out using 41 taxa at 105 sites. Slope, water depth, distance from source, water temperature and the Pfankuch channel stability index were found to be the major explanatory environmental variables. The analysis separated Diamesinae and typical upstream orthoclads from the other chironomids by low temperature and high channel instability. 6. In all six regions, Diamesa was present closest to the glacier. Within 200 m of the glacier snout, other genera of Diamesinae were found together with Orthocladiinae. Pioneer taxa like Diamesa species coexisted with later colonizers like Eukiefferiella minor/®ttkaui in relatively unstable channels. 7. The longitudinal succession of chironomid assemblages across altitudinal and latitudinal gradients in glacial streams followed the same pattern, with similar genera and groups of species. The general aspects of the conceptual model of Milner & Petts (1994) were supported. However, Diamesa species have wider temperature limits than predicted and other Diamesinae as well as Orthocladiinae colonize metakryal habitats. Correspondence: Brigitt

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier‐fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near‐pristine reaches were studied on each stream in 1996–97. 2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non‐insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa). 3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell‐shaped with an optimum at an intermediate level of stability. 4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross‐validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated. 5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier‐fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier‐fed streams under climate or hydrological change scenarios.

Global change threatens invertebrate biodiversity and its central role in numerous ecosystem functions and services. Functional trait analyses have been advocated to uncover global mechanisms behind biodiversity responses to environmental change, but the application of this approach for invertebrates is underdeveloped relative to other organism groups. From an evaluation of 363 records comprising >1.23 million invertebrates collected from rivers across nine biogeographic regions on three continents, consistent responses of community trait composition and diversity to replicated gradients of reduced glacier cover are demonstrated. After accounting for a systematic regional effect of latitude, the processes shaping river invertebrate functional diversity are globally consistent. Analyses nested within individual regions identified an increase in functional diversity as glacier cover decreases. Community assembly models demonstrated that dispersal limitation was the dominant process underlying these patterns, although environmental filtering was also evident in highly glacierized basins. These findings indicate that predictable mechanisms govern river invertebrate community responses to decreasing glacier cover globally.

No abstract