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.

Storm events can drive highly variable behavior in catchment nutrient and water fluxes, yet short‐term event dynamics are frequently missed by low‐resolution sampling regimes. In addition, nutrient source zone contributions can vary significantly within and between storm events. Our inability to identify and characterize time‐dynamic source zone contributions severely hampers the adequate design of land use management practices in order to control nutrient exports from agricultural landscapes. Here we utilize an 8 month high‐frequency (hourly) time series of streamflow, nitrate (NO3‐N), dissolved organic carbon (DOC), and hydroclimatic variables for a headwater agricultural catchment. We identified 29 distinct storm events across the monitoring period. These events represented 31% of the time series and contributed disproportionately to nutrient loads (42% of NO3‐N and 43% of DOC) relative to their duration. Regression analysis identified a small subset of hydroclimatological variables (notably precipitation intensity and antecedent conditions) as key drivers of nutrient dynamics during storm events. Hysteresis analysis of nutrient concentration‐discharge relationships highlighted the dynamic activation of discrete NO3‐N and DOC source zones, which varied on an event‐specific basis. Our results highlight the benefits of high‐frequency in situ monitoring for characterizing short‐term nutrient fluxes and unraveling connections between hydroclimatological variability and river nutrient export and source zone activation under extreme flow conditions. These new process‐based insights, which we summarize in a conceptual model, are fundamental to underpinning targeted management measures to reduce nutrient loading of surface waters.

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Despite the high sensitivity of polar regions to climate change, and the strong influence of temperature upon ecosystem processes, contemporary understanding of water temperature dynamics in Arctic river systems is limited. This research gap was addressed by exploring high-resolution water column thermal regimes for glacier-fed and non-glacial rivers at eight sites across Svalbard during the 2010 melt season. Mean water column temperatures in glacier-fed rivers (0.3 -3.2 ºC) were lowest and least variable near the glacier terminus, but increased downstream (0.7 -2.3 ºC km -1 ). Non-glacial rivers, where discharge was sourced primarily from snowmelt runoff, were warmer (mean 2.9 -5.7 ºC) and more variable, indicating increased water residence times in shallow alluvial zones and increased potential for atmospheric influence. Mean summer water temperature and the magnitude of daily thermal variation were similar to those of some Alaskan Arctic rivers but low at all sites when compared to alpine glacierized environments at lower latitudes. Thermal regimes were correlated strongly (p<0.01) with incoming shortwave radiation, air temperature, and river discharge. Principal drivers of thermal variability were inferred to be: (1) water source (i.e. glacier melt, snowmelt, groundwater); (2) exposure time to the atmosphere; (3) prevailing meteorological conditions; (4) river discharge; (5) runoff interaction with permafrost and buried ice and (6) basin-specific geomorphological features (e.g. channel morphology). These results provide insight into the potential changes in high-latitude river systems in the context of projected warming in polar regions. We hypothesise warmer and more variable temperature regimes may prevail in future as the proportion of bulk discharge sourced from glacial meltwater declines and rivers undergo a progressive shift towards snow-and groundwater sources. Importantly, such changes could have implications for aquatic species diversity and abundance and influence rates of ecosystem functioning in high-latitude river systems.