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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. ; This work was funded by the following organisations: The UK Natural Environment Research Council grants and studentships GR9/2913, NE/E003729/1, NE/E004539/1, NE/E004148/1, 20 NE/G523963/1, NER/S/A/2003/11192, and NE/L002574/1; the European Union Environment and Climate Programme Arctic and Alpine Stream Ecosystem Research (AASER) project (ENV-CT95-0164); EU-FP7 Assessing Climate impacts on the Quality and quantity of WAter (ACQWA) project (212250); Icelandic Research Council (954890095, 954890096); University of Iceland Research Fund (GMG96, GMG97, GMG98), Wyoming Center for Environmental Hydrology and Geophysics-National Science Foundation (1208909); USA-Wyoming NASA Space Grant Faculty Research Initiation (#NNX10A095H); USA-NSF Wyoming Epscor; Nationalpark Hohe Tauern, Austria; the Royal Society (International Outgoing Grant 2006/R4); the Leverhulme Trust; the Universities of Leeds, Birmingham, Iceland and Innsbruck; European Centre for Arctic Environmental Research (ARCFAC): a Research Infrastructures Action of the European Community FP6 (026129-2008- 72); the Stelvio National Park (2000-2001); the Autonomous Province of Trento (HIGHEST project, 2001-2004, del. PAT n. 1060/2001; VETTA project, 2003-2006, del. PAT n. 3402/2002); MUSE-Museo delle Scienze. We are grateful to Russell Taylor and Mike Winterbourn at the University of Canterbury, NZ, who helped to collect NZ invertebrate data and assisted with identification, and to Hakon Adalsteinsson who contributed to data collection in Iceland. Many other people, too numerous to mention, assisted with fieldwork at all of the study locations. The European Science Foundation sponsored an exploratory ┘ラヴニゲエラヮ WミデキデノWS さGノ;IキWヴ-fed rivers, hydroecology and climate change: current knowledge and future network of monitoring sites (GLAC-HYDROECO-NETぶざ デエ;デ ┘;ゲ エWノS キミ Birmingham, UK in September of 2013 where some of the ideas in this paper were first discussed ; Peer Reviewed

Although most field and modeling studies of river corridor exchange have been conducted at scales ranging from tens to hundreds of meters, results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchanges are expected to vary with hydrologic forcing and the local geomorphic setting. While we desire predictive power, we lack a complete spatiotemporal relationship relating discharge to the variation in geologic setting and hydrologic forcing that is expected across a river basin. Indeed, the conceptual model of Wondzell (2011) predicts systematic variation in river corridor exchange as a function of (1) variation in baseflow over time at a fixed location, (2) variation in discharge with location in the river network, and (3) local geomorphic setting. To test this conceptual model we conducted more than 60 solute tracer studies including a synoptic campaign in the 5th-order river network of the H. J. Andrews Experimental Forest (Oregon, USA) and replicate-intime experiments in four watersheds. We interpret the data using a series of metrics describing river corridor exchange and solute transport, testing for consistent direction and magnitude of relationships relating these metrics to discharge and local geomorphic setting. We confirmed systematic decrease in river corridor exchange space through the river networks, from headwaters to the larger main stem. However, we did not find systematic variation with changes in discharge through time or with local geomorphic setting. While interpretation of our results is complicated by problems with the analytical methods, the results are sufficiently robust for us to conclude that space-for-time and time-for-space substitutions are not appropriate in our study system. Finally, we suggest two strategies that will improve the interpretability of tracer test results and help the hyporheic community develop robust datasets that will enable comparisons across multiple sites and/or discharge conditions. ; Leverhulme Trust (Where rivers, groundwater and disciplines meet: a hyporheic research network); UK Natural Environment Research CouncilNERC Natural Environment Research Council [NE/L003872/1]; European Commission, H2020 Marie Sklodowska-Curie Actions (HiFreq) [734317]; U.S. Department of Energy (Pacific Northwest National Lab); National Science FoundationNational Science Foundation (NSF) [DEB-1440409, EAR-1652293, EAR-1417603, EAR-1446328]; University of Birmingham (Institute of Advanced Studies); U.S. Department of EnergyUnited States Department of Energy (DOE) [DE-SC0019377] ; This research has been supported by the Leverhulme Trust (Where rivers, groundwater and disciplines meet: a hyporheic research network), the UK Natural Environment Research Council (grant no. NE/L003872/1), the European Commission, H2020 Marie Sklodowska-Curie Actions (HiFreq (grant no. 734317)), the U.S. Department of Energy (Pacific Northwest National Lab and DE-SC0019377), the National Science Foundation (grant nos. DEB-1440409, EAR-1652293, EAR-1417603, and EAR-1446328), and the University of Birmingham (Institute of Advanced Studies). ; Public domain authored by a U.S. government employee