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Intermittent streams periodically cease to flow but still support diverse aquatic assemblages. Community dynamics within intermittent streams are likely driven by a wide range of factors, including drying regime, refuge availability, and connectivity with perennial systems. We compared fish community dynamics over the course of a drying and rewetting period to quantify differences in fish community composition and recovery trajectories across a gradient of drying. We predicted that shifts in fish community structure as streams dry and rewet would be similar across streams with similar drying regimes and streams with more severe drying would be less likely to recover when streams rewetted. Seasonal shifts in community composition were variable in streams that retained isolated pools, with similar patterns occurring in streams of similar size. Despite a lack of synchrony in shifts in community composition among sites, fish communities exhibited recovery post‐drying across all drying regimes. The quick recovery of stream fish communities after drying may suggest intermittent streams provide beneficial habitats or resources and highlight the importance of network connectivity to allow community recovery after drying. [ABSTRACT FROM AUTHOR]

Climate change is causing stream flow regimes to change in many regions globally, including southwestern Australia (SWA) where many perennial streams have switched to intermittent flow regimes. In drier landscapes, ecological refuges and evolutionary refugia will become critical for conserving freshwater biodiversity. This study aimed to determine the contribution of dry season refuges to species persistence and community recovery in a forested headwater catchment where perennial streams have been exposed to severe permanent drying, causing them to become intermittent. That is, in streams where formerly no drought refuges were present.Macroinvertebrate assemblages were sampled in dry season refuges within recently intermittent streams. Refuges included small spring‐fed pools, perched pools and subterranean refuges associated with granite inselbergs. Dry streambeds were searched for organisms aestivating in situ, and sediments were collected from each intermittent stream for rehydration.Mantel tests were used to compare the contribution of refuges to species assemblages in the early wet season when intermittent streams had begun to flow. Analysis of similarities was used to compare patterns between dry and wet season assemblages of intermittent streams and the single remaining perennial stream in the catchment, to infer the contribution of the perennial stream to community recovery in intermittent streams.Refuge types had very different assemblages: spring‐fed refuges supported several locally endemic species, but perched pools were dominated by opportunistic colonists. Several taxa were found aestivating in dry sediments, primarily adult Coleoptera and larval Chironomidae. Inselberg springs supported small populations of endemic Trichoptera and Ephemeroptera and provided subterranean refuge for an endemic amphipod. However, dry season refuges did not significantly contribute to community recovery. Rather, assemblages in early winter flows were similar to those inhabiting the perennial stream, showing that recolonisation from perennial streams is likely the primary process of community recovery in these recently intermittent streams.Newly formed dry season refuges supported some locally endemic species, but also colonising species that were formerly absent (or rare) when all streams were perennial. However, continued loss of perennial streams in SWA will result in landscape‐wide reductions in diversity (as colonisation sources are lost), because there are no known evolutionary refugia in this landscape for relictual species to retreat into. Granite inselbergs may become evolutionary refugia for a few species, as perennial streams are lost.Refuges will likely play a pivotal role in persistence of species able to use them; however, the existence of refuges is also under threat from prolonged climatic drying, including refuges newly formed by stream dry. Thus, identification and protection of future evolutionary refugia is a matter of urgency in regions facing drier climates, as it is ultimately evolutionary refugia that will become critical reservoirs of freshwater biodiversity as perennial streams and refuges are lost. [ABSTRACT FROM AUTHOR]

Intermittent streams exhibit regular patterns of drying and are widespread, but the patterns of drying among streams within geographic proximity are not fully understood. We compared annual patterns of flow and drying among 10 intermittent streams within a single drainage basin and assessed how traditional hydrologic metrics described variation between streams. We installed stream intermittency sensors and evaluated stage height using low‐cost methods and evaluated landscape factors as potential drivers of flow patterns. Intermittent streams varied based on both high‐ and low‐flow metrics, driven by a variety of landscape‐level factors, especially watershed size. Additionally, we compared the observed flow regimes within our system with predictions generated using an established Soil and Water Assessment Tool, finding that modeled streamflow patterns generally underrepresented observed drying within the system. [ABSTRACT FROM AUTHOR]

The purpose of this study is to analyze gully erosion processes and their management in the Trivale Forest Park. Although the inclusion of gullies in the category of risk phenomena is still debated, due to their spatial extent and evolution, both longitudinally and vertically, they can pose concern to woody vegetation by altering slope stability. This is the case of the Trivale Forest Park, situated in Pitești city, where gully erosion has been affecting tree growth and recreational activities, such as hiking or cycling, which has led to the implementation of erosion control measures and hydrotechnical structures. By carrying out field observations and cartographic analyses, the research has/proposes/seeks to support two objectives: firstly, to establish the impact of erosion processes on the valleys’ and slopes’ balance by evaluating the type of erosion processes and resulting features and secondly, to assess the exposure of the Trivale Forest area to erosional forms, by using GIS and the frequency ratio (FR) techniques. The results of the multicriteria analysis highlighted, in good agreement with the field observations, the areas most susceptible to slope erosion processes. [ABSTRACT FROM AUTHOR]

Despite rises in drought frequency and human water demands, streamflow regime shifts from perennial to non‐perennial have not been evaluated in many arid/semi‐arid regions. To document shifts, we created a methodology that classifies streams as naturally perennial or non‐perennial. Our classification used historical, minimally disturbed‐quality USGS streamflow gages (1950–2015) across California. The number of consecutive zero flow days (≥5 days) was used to classify 61% (96/158) and 39% (62/158) of gages as perennial and non‐perennial, respectively. We developed a random forest model to predict flow regime class based on climate and watershed characteristics. To identify regime shifts, we compared the observed class of contemporary (1980–2023) minimally disturbed and disturbed gages with their modeled, natural class. For most minimally disturbed gages, the observed and natural predicted classes were the same, but 13% (7/52) of gages had a modeled perennial regime with an observed non‐perennial class, indicating a drying trend. Among disturbed gages, 22% (64/290) shifted from perennial to non‐perennial and 7% (21/290) from non‐perennial to perennial. Trends in the minimum 7‐day moving average and number of zero‐flow days provided further evidence of drying at minimally disturbed streams, but no pattern at disturbed gages. Our results indicate that few minimally disturbed perennial streams have become non‐perennial to date, but many streams have experienced drying from climate. Streams impacted by human activities had greater drying rates, but regulation has caused some non‐perennial streams to become perennial. By quantifying expected natural streamflow regimes, this work can help monitor, manage, and conserve stream ecosystems. Key Points: Our approach classified 158 historical (1950–2015) minimally disturbed gages as perennial (61%) and non‐perennial (39%) in CaliforniaAmong 52 active minimally disturbed gages, 13% transitioned to non‐perennial (1980–2022), indicating a drying trend in response to climateFor 290 disturbed gages, 29% showed shifts in both directions, highlighting distinct anthropogenic effects on streamflow [ABSTRACT FROM AUTHOR]

Despite our deepening knowledge of non-perennial streams, they are still poorly recognized, and people still perceive them as less valuable and less worthy of conservation than perennial streams. Due to its power to shape attitudes and opinions, mass media plays a critical role, which can also contribute to improving perceptions regarding non-perennial streams. Here, we aim to analyse how non-perennial streams are depicted by mass media in the Balearic Islands and how a catastrophic flood influenced mass media communication about these ecosystems. We analysed all news reports related to streams, published in the most read online newspaper of the Balearic Islands, for 25 months (12 months before and after the catastrophic flood). A total of 407 news reports were analyzed to identify the topics covered (e.g. floods, ecology, stream uses, water quality). News reports related to non-perennial streams focused on past floods and their consequences; our analyses showed how the catastrophic flood event affected the news temporal agenda, as well as the territorial inequalities in media coverage. News reports rarely covered ecological aspects of non-perennial streams or their relevance for freshwater resources. We concluded that news reports contribute to generating a collective memory around flood events but also contribute to social misconception about non-perennial streams. [ABSTRACT FROM AUTHOR]

Even though more than half of the global river network does not have continuous flow, temporary (i.e., non-perennial) streams are poorly represented in traditional monitoring networks. Therefore, new approaches are needed to monitor these streams. Citizen science provides an interesting opportunity as people, equipped with smartphones, can observe the flow state of temporary streams. Such observations can go beyond a simple classification of flow vs. no flow and include ecologically important states, such as standing water, isolated pools, or wet streambeds. However, the quality of citizen science data for temporary streams has so far not been thoroughly assessed. Therefore, we asked more than 1,200 people during 23 field days to visually determine the flow state of eight temporary streams based on six classes ranging from a dry streambed to flowing water. Participants could most clearly distinguish a flowing stream from a non-flowing stream. The overall agreement between participants was 66%; 83% of the selected flow states were within one class of the most frequently selected flow state. The agreement with the expert was lower (56% chose the same class, and 79% chose a state within one class). Inconsistencies between the selected flow state and answers to specific yes-no statements about the temporary stream were largest for the dry streambed and damp/wet streambed states. These discrepancies were partly caused by participants looking at different parts of the stream (i.e., participants considered the flow state for a location further upstream or downstream). To ensure that all participants determine the flow state comparably, we recommend clear definitions of the flow state classes, detailed information on the exact location for which the flow state needs to be determined, as well as more training.

Abstract Aim To understand the distribution of fish species and their use of habitat, a range of environmental variables were evaluated as predictors of fish assemblage composition and richness in tropical semiarid aquatic systems. Methods We surveyed the species composition of fish assemblages in semiarid aquatic systems and established their degree of association with the structure of the aquatic habitat. Sites consisted of stream reaches with surface water flow, isolated temporary pools, and man-made reservoirs. Fish sampling was conducted on four occasions during the wet (April and June 2006) and dry seasons (September and December 2006). The correlation between richness and abundance with the habitat structure was evaluated using stepwise multiple regression. Patterns of variation in fish assemblage composition across sites were evaluated using Nonmetric Multidimensional Scaling, and the Indicator Species Analysis was used to determine which species were significant indicators of sites. To establish multivariate correlations and test the hypothesis of local fish composition being associated with the environmental variables we used a Canonical Correspondence Analysis. Results Morphometric variables, stream reach width, stream length and elevation explained 75.6% of the variation in fish richness. Macrophyte cover and overhanging vegetation added to the predictive power of the model equation, where the final model explained 86.9% of the variation in fish richness. Canonical Correspondence Analysis showed a significant relationship between fish composition data and site morphology (altitude, bank slope and littoral depth). Among the water quality, habitat composition and substrate variables, temperature, sand, and gravel showed higher correlation with the CCA axes. Conclusions These results indicated that fish communities assume different structures and compositions across different habitat types following the environmental heterogeneity in dryland aquatic systems.

ABSTRACTDespite our deepening knowledge of non-perennial streams, they are still poorly recognized, and people still perceive them as less valuable and less worthy of conservation than perennial streams. Due to its power to shape attitudes and opinions, mass media plays a critical role, which can also contribute to improving perceptions regarding non-perennial streams. Here, we aim to analyse how non-perennial streams are depicted by mass media in the Balearic Islands and how a catastrophic flood influenced mass media communication about these ecosystems. We analysed all news reports related to streams, published in the most read online newspaper of the Balearic Islands, for 25 months (12 months before and after the catastrophic flood). A total of 407 news reports were analyzed to identify the topics covered (e.g. floods, ecology, stream uses, water quality). News reports related to non-perennial streams focused on past floods and their consequences; our analyses showed how the catastrophic flood event affected the news temporal agenda, as well as the territorial inequalities in media coverage. News reports rarely covered ecological aspects of non-perennial streams or their relevance for freshwater resources. We concluded that news reports contribute to generating a collective memory around flood events but also contribute to social misconception about non-perennial streams.

The western U.S. is experiencing increasing rain to snow ratios due to climate change, and scientists are uncertain how changing recharge patterns will affect future groundwater‐surface water connection. We examined how watershed topography and streambed hydraulic conductivity impact groundwater age and stream discharge at eight sites along a headwater stream within the Manitou Experimental Forest, CO USA. To do so, we measured: (a) continuous stream and groundwater discharge/level and specific conductivity from April to November 2021; (b) biweekly stream and groundwater chemistry; (c) groundwater chlorofluorocarbons and tritium in spring and fall; (d) streambed hydraulic conductivity; and (e) local slope. We used the chemistry data to calculate fluorite saturation states that were used to inform end‐member mixing analysis of streamflow source. We then combined chlorofluorocarbon and tritium data to estimate the age composition of riparian groundwater. Our data suggest that future stream drying is more probable where local slope is steep and streambed hydraulic conductivity is high. In these areas, groundwater source shifted seasonally, as indicated by age increases, and we observed a high fraction of groundwater in streamflow, primarily interflow from adjacent hillslopes. In contrast, where local slope is flat and streambed hydraulic conductivity is low, streamflow is more likely to persist as groundwater age was seasonally constant and buffered by storage in alluvial sediments. Groundwater age and streamflow paired with characterization of watershed topography and subsurface characteristics enabled identification of likely controls on future stream drying patterns. Plain Language Summary: In the western U.S., climate change is causing more precipitation to fall as rain rather than snow and it is currently unclear how, where, and when this shift is going to impact groundwater contributions to streams, which is important for predicting streamflow and many ecosystem services, including stream contaminant processing or thermal refugia for fish habitat. In this study, we instrumented a small, high‐elevation stream in Colorado, USA to determine (a) how much groundwater is contributing to streamflow and (b) how long groundwater spends traveling through the subsurface before doing so. We found that groundwater age ranged from 10 to 55 years, with older groundwater located in areas with flat topography and where water could not move through streambed sediment quickly. We found the areas with steeper topography had more groundwater contributing to streamflow, but this groundwater was younger. We predict that under future climate scenarios, streams in areas with steep topography and young groundwater are more likely to dry. Key Points: Mean groundwater age is youngest in areas with high slope and streambed hydraulic conductivityMean groundwater age shifts older during low flow periodsFuture stream drying is more probable where local slope and streambed hydraulic conductivity are high [ABSTRACT FROM AUTHOR]

Geologic, geomorphic, and climatic factors have been hypothesized to influence where streams dry, but hydrologists struggle to explain the temporal drivers of drying. Few hydrologists have isolated the role that vegetation plays in controlling the timing and location of stream drying in headwater streams. We present a distributed, fine-scale water balance through the seasonal recession and onset of stream drying by combining spatiotemporal observations and modeling of flow presence/absence, evapotranspiration, and groundwater inputs. Surface flow presence/absence was collected at fine spatial (~80 m) and temporal (15-min) scales at 25 locations in a headwater stream in southwestern Idaho, USA. Evapotranspiration losses were modeled at the same locations using the Simultaneous Heat and Water (SHAW) model. Groundwater inputs were estimated at four of the locations using a mixing model approach. In addition, we compared high-frequency, fine-resolution riparian normalized vegetation difference index (NDVI) with stream flow status. We found that the stream wetted and dried on a daily basis before seasonally drying, and daily drying occurred when evapotranspiration outputs exceeded groundwater inputs, typically during the hours of peak evapotranspiration. Riparian NDVI decreased when the stream dried, with a ~2-week lag between stream drying and response. Stream diel drying cycles reflect the groundwater and evapotranspiration balance, and riparian NDVI may improve stream drying predictions for groundwater-supported headwater streams.

Many headwater wetlands are integrated into flowpath networks and can serve as sources of streamflow for downgradient waters. We demonstrate this with five years of data in vernal pool, swale, and headwater stream complexes in the Central Valley, California. Long-term United States Geological Survey data suggest that the mean flow duration from the smallest watersheds in this region, including those with vernal pool, swale, and headwater stream complexes, is ~ 85 days per year. Our data concur, indicating that the annual days of flow per year from our vernal pool, swale, and headwater stream complexes ranges from ~ 20–200, but is ~ 85 when annual precipitation is 100% of normal. Peak stages are evident first in vernal pools which then propagate sequentially downstream through swales, headwater streams, and to the Sacramento River at celerities of ~ 1-1.5 m/s, consistent with expected flood wave velocities. Geospatial analyses show that these vernal pool, swale, and headwater stream features cover > 4% of the study area. Our results suggest these systems can be significant sources of streamflow, and therefore play an important role in maintaining the chemical, physical, and biological integrity of downstream waters, which has important implications for the definition of waters of the United States subject to regulation under the Clean Water Act. [ABSTRACT FROM AUTHOR]

Vegetation plays an essential role in water partitioning, as it strongly influences evapotranspiration, infiltration and water retention. To analyse the influence of vegetation on water partitioning under innovative land management strategies, we used stable water isotopes as natural tracers to monitor precipitation, soil water and groundwater fluxes over the growing season of 2021 (March–October). We selected eight plot sites with four contrasting land covers and soil types in the drought‐sensitive Demnitzer Millcreek Catchment (DMC) in NE Germany. The land use types include forest, grassland, and arable with the latter being subdivided into conventional (e.g., crops) and innovative (e.g., agroforestry) sites. Two weather stations, a flux tower, and in situ soil moisture monitoring complemented our isotopic data with a hydroclimatic context. The year of 2021 had near‐normal precipitation totals compared to the prolonged drought of 2018–20. Soil water storage was highest at the agricultural sites, while lowest at the forest, though this reflected both the influence of soil properties (as forests dominated sand soils while crops loam soils) and the greater evapotranspiration from forests. We also estimated soil water ages and found the greatest isotopic variability and fastest turnover of water in the upper soils of arable sites. The forest soil water had the most limited variability in isotopic composition and tended to be older, revealing lower levels of groundwater recharge. Conventional and innovative cropping sites were similar to each other, likely due to the early tree development stage in agroforestry schemes under the latter. Our investigation revealed the forest sites are potentially most vulnerable to limited water availability in the DMC and land use changes in agricultural land lacked major differences in ecohydrological fluxes over the study year. The study further underlines the need for long‐term observations of recent adaptive land use changes and drought‐sensitive vegetation to improve our understanding and evolve drought resilient land management strategies considering time lags in impacts and non‐stationarity. [ABSTRACT FROM AUTHOR]

Wastewater treatment plant (WWTP) effluents alter water chemistry and in-stream nutrient uptake rates of receiving freshwaters, thus changing the magnitude and fate of the nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams can vary strongly over time due to the seasonal occurrence of floods and droughts, causing temporal variability of nutrient uptake. We assessed the temporal patterns and the controlling factors of net nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled the longitudinal concentration profiles of ambient dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) along a 800 m reach on 47 sampling dates between 2001 and 2017, encompassing a wide range of hydrological conditions. We estimated net nutrient uptake in the receiving stream. In 72% of the dates, high rates of net ammonium uptake co-occurred with net releases of either nitrate or nitrite. This pattern suggests that the receiving stream has a high nitrification capacity. Conversely, 75% of the dates did not show any longitudinal pattern in SRP concentration, suggesting that uptake and release processes for this element were either counterbalanced or both occurred at very low rates. Finally, net ammonium uptake was low when the stream had a low dilution capacity (< 40%) and ammonium concentration was high. Overall, we demonstrate that consideration of the receiving stream's dilution capacity is imperative to the management of freshwaters to guarantee an adequate dilution of WWTP effluent inputs and avoid saturation of in-stream nutrient uptake capacity under low flow conditions in urban landscapes. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the contribution of urban runoff in pollutant delivery to standing water pools within the Edwards Aquifer region of Texas. Grab samples of water were collected weekly over 5 months at one urban pool, one undeveloped pool, and one control pond that received minimal runoff. Samples were tested for nitrates, total dissolved phosphorus, Escherichia coli, and other coliform bacteria. The urban site had higher nitrate, E. coli, and other coliform bacteria concentrations than the undeveloped site. Significant positive linear relationships between weekly antecedent rainfall and both nitrate and E. coli were found at the urban site but not the undeveloped site. Water quality parameters at the control site remained stable, suggesting increases in nitrate and E. coli at the urban site were caused by runoff. Using publicly available data, relationships between water quality and weekly antecedent discharge were tested at 24 additional sites varying in land use. Positive relationships for E. coli were found at several urban sites, supporting runoff as a contributor to bacterial loading. Relationships for nitrate were variable, but all additional sites had flowing water, suggesting a unique response of water quality to urban runoff at the sampled urban pool. [ABSTRACT FROM AUTHOR]

Documenting flow regimes and the ecology of source headwater streams has gained considerable attention for scientific and regulatory purposes. These streams do not appear on standard maps, and local physiographic and climatologic conditions can control their origins. We investigated macroinvertebrate assemblages seasonally and in relation to flow duration, catchment and habitat variables within 14 source headwaters (< 1 ha) in the Western Allegheny Plateau over a 19-month period. We classified 6 perennial (P) and 8 intermittent (I) streams directly with continuous flow data loggers. Several biological and trait-based metrics could distinguish flow class, but few instream physical measures could. Macroinvertebrate metrics and assemblage dispersion varied seasonally and responded significantly along a gradient of total flow duration. Separate indicator species analyses generated 22 genera and 15 families with significant affinities to P streams. Richness of P-indicator taxa was also strongly correlated with flow duration gradients, and we estimated a total flow duration changepoint at 77% (3 indicator families) followed by a sharp increase in richness. Two rapid field-based flow duration methods (NC Stream Identification index and OH Headwater Habitat Evaluation index) could distinguish upstream ephemeral reaches from P and I reaches, but misclassified P as I more frequently. Our findings highlight that diverse coldwater macroinvertebrate assemblages inhabited extremely small, low-discharge springs in the region, and responded with flow duration. These source headwater habitats are susceptible to human disturbance and should be monitored as is routinely done in larger lotic systems. [ABSTRACT FROM AUTHOR]

Data on Maghrebian mayfly communities are scarce and fragmentary, but evidence of alterations of the North African riverine landscape depleting the freshwater biota is rapidly mounting.In contrast to the overexploited lowlands, the highlands of north‐eastern Algeria are hotspots of freshwater biodiversity and the last refugia to micro‐endemics, North African endemics, and Eurosiberian relicts.The mayflies of relict mountain streams of north‐eastern Algeria were investigated and 20 species or taxa in five families were recorded. Two species of the genus Habrophlebia and one species of Centroptilum are new to science, whereas two Rhithrogena species are new to Algeria, including the Numidian endemic Rhithrogena sartorii.Co‐inertia analysis suggested a highly significant co‐structure between mayfly assemblages and habitats defined by altitude, flow velocity, bed width, water depth, and water conductivity. In addition, a Poisson generalized linear model indicated a strong positive relationship between species richness and water depth and a weaker negative one with bed width (stream size). The results are congruent with the hypothesis that habitat provides the templet that drives mayfly communities, and they support the use of mayflies as bioindicators in the implementation of monitoring schemes to assess the ecological integrity of Maghrebian freshwater biodiversity hotspots.The upstream part of the Kebir‐East river basin is subjected to forest fires, pollution, and flow alteration, whereas the downstream part, which includes the vast Mekhada marsh, is increasingly fragmented and invaded by alien fish species. Conservation efforts focusing on the management of Oued Kebir‐East, a transboundary Maghrebian river, and the restoration of the Mekhada marsh, a Ramsar site, need to be launched during the United Nations Decade on Ecosystem Restoration (2021–2030). [ABSTRACT FROM AUTHOR]

Study region: This study focused mainly on Burkina Faso in West Africa. Study focus: This study aims to identify environmental variables that best explain the geographic variations of the flow intermittency regime, focusing on intermittency duration. Discharge data from 49 gauging stations were considered, mostly over large rivers. The mean number of dry months (Ndry¯) was used as a predictor to define four classes of flow intermittency, for which the potential explanatory environmental variables were assessed based on correlation analysis and principal component analysis (PCA). New hydrological insights for the region: The first two components (PCs) account for 82 % of the total variance with PC1 (52 %), and most of the catchments with similar flow intermittency are ordered according to PC2 (30 %), predominantly related to catchment permeability. Moreover, permeability was highly correlated with Ndry¯ (r = - 0.75). Results suggest that catchment permeability and catchment areas are the most critical variables in determining flow intermittency classes in Burkina Faso, as the effect of precipitation can be overruled by the ones of permeability, catchment area, and Strahler order. This study is a first step in understanding the controls of river intermittency in data-scarce and poorly gauged regions of West Africa. The identified variables could be used as input in statistical models to predict and map river intermittency and provide valuable information for stream conservation.

The stoneflies of the Maghreb (Tunisia, Algeria and Morocco) are characterized by high endemicity but their ecology remains poorly known. We have surveyed the stonefly assemblages of northeastern Algeria mountain streams, a relatively unstudied region, and attempted to identify through co-inertia analysis the environmental correlates of their distribution. Species richness varied from nine taxa in the most species-rich localities to a single taxon in some anthropogenically impacted localities. Results indicated a significant co-structure between ecological descriptors and stonefly distribution and frequency of occurence. Mountain stream stonefly assemblages differed according to water conductivity, altitude, anthropogenic impacts, and spring proximity. The frequent occurrence of Afroperlodes lecerfi, Brachyptera auberti and Tyrrenoleuctra tangerina was indicative of high altitude, intermittent streams whereas Amphinemura berthelemy, Eoperla ochracea and Leuctra sartori favoured permanent, low-altitude headwaters. Conversely, Leuctra cf. vaillanti seemed to tolerate low altitude sites characterized by high water conductivity, large bed width and fast flow. This study also highlights the diversity of the Maghrebian endemic or microendemic stoneflies harbored by relict lotic streams and their sensitivity towards anthropogenic stressors. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are threatened by the global change‐induced extreme climatic events worldwide. The unpredictable changes in water supply create strongly disturbed environments and ultimately result in diversity changes. Here, we studied the formation of benthic algal and cyanobacterial assemblages under intermediately disturbed (IDC) and highly disturbed conditions (HDC) in a small lowland intermittent stream. We addressed our hypotheses to the Intermediate Disturbance Theory supposing that intermediate frequencies or intensities of disturbances maximise diversity independently of its level. We expected a larger influence of extremes in water supply on functional than on taxonomic and phylogenetic diversity. Our results only partially proved our first hypothesis highlighting the (i) importance of short‐time but intense disturbing effect on biofilm formation and trait composition under IDC period and (ii) the instability within the assemblages caused by large and opposing influences during HDC. Although extreme weather events caused trait extremes (supporting second hypothesis), they did not result in a decrease in functional richness (rejecting the second hypothesis). These findings in accordance with the insurance hypothesis clearly stress that a system with high functional redundancy can keep its functionality even under drastic hydrological conditions and the accompanying loss of species. [ABSTRACT FROM AUTHOR]

• Multi-criteria calibration of a lumped hydrological model based on discharge or stream-level and temporary stream data for 92 catchments in France. • The flow state of temporary streams was assumed to reflect groundwater storage. • Temporary stream observations did not improve overall model performance for most catchments but led to a better low-flow simulation for some catchments. • Temporary stream data constrained the uncertainty in the storage coefficient for the slowest reservoir, which affected the simulated groundwater level dynamics and total dynamic storage. Multi-criteria model calibration can lead to a better representation of hydrological processes and reduce parameter uncertainty compared to calibration on streamflow data alone. However, the additional data may be difficult to collect or aggregate into a representative catchment average value that can be used to calibrate a lumped model. Temporary streams are highly dynamic, and their flow state can be observed visually. However, data on the state of temporary streams are still uncommon and rarely used in hydrological catchment modelling. In this study, we used a unique dataset with discrete flow state observations for temporary streams in France and evaluated how informative these data are for calibrating a lumped, bucket-type hydrological model. We calibrated the HBV model for 92 catchments using discharge or stream-level data at different temporal resolutions (daily, one daily value per month, or one daily value per season) and used the observed flow states of temporary streams as a proxy of groundwater storage. Temporary stream data generally did not result in a better overall discharge simulation for the validation period. For catchments for which the model performance based on the calibration on only discharge or stream-level data was poor, it was more likely to lead to an improvement in model performance. The use of temporary stream data in combination with discharge data reduced the uncertainties in the low-flow simulations for up to half of the catchments. This improvement was caused by a better-constrained storage coefficient for the slowest groundwater reservoir and the elimination of parameter sets that led to substantial variations in groundwater storage. However, the improvements in low-flow simulations or parameter uncertainty due to the inclusion of temporary stream data in model calibration were not related to catchment characteristics. Thus, it remains unclear for which catchments temporary stream data can help to improve low-flow simulations and reduce parameter uncertainty. [ABSTRACT FROM AUTHOR]

The Demnitzer Millcreek catchment (DMC), is a 66 km2 long‐term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de‐intensification of farming and riparian restoration in the low‐lying landscape dominated by rain‐fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below‐average rainfall and above‐average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two‐year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in‐stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage‐dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio‐temporal patterns of stream connectivity and flow duration during droughts that may have implications for in‐stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future. [ABSTRACT FROM AUTHOR]

Non‐perennial streams comprise over half of the global stream network and impact downstream water quality. Although aridity is a primary driver of stream drying globally, surface flow permanence varies spatially and temporally within many headwater streams, suggesting that these complex drying patterns may be driven by topographic and subsurface factors. Indeed, these factors affect shallow groundwater flows in perennial systems, but there has been only limited characterisation of shallow groundwater residence times and groundwater contributions to intermittent streams. Here, we asked how groundwater residence times, shallow groundwater contributions to streamflow, and topography interact to control stream drying in headwater streams. We evaluated this overarching question in eight semi‐arid headwater catchments based on surface flow observations during the low‐flow period, coupled with tracer‐based groundwater residence times. For one headwater catchment, we analysed stream drying during the seasonal flow recession and rewetting period using a sensor network that was interspersed between groundwater monitoring locations, and linked drying patterns to groundwater inputs and topography. We found a poor relationship between groundwater residence times and flowing network extent (R2 < 0.24). Although groundwater residence times indicated that old groundwater was present in all headwater streams, surface drying also occurred in each of them, suggesting old, deep flowpaths are insufficient to sustain surface flows. Indeed, the timing of stream drying at any given point typically coincided with a decrease in the contribution from near‐surface sources and an increased relative contribution of groundwater to streamflow at that location, whereas the spatial pattern of drying within the stream network typically correlated with locations where groundwater inputs were most seasonally variable. Topographic metrics only explained ~30% of the variability in seasonal flow permanence, and surprisingly, we found no correlation with seasonal drying and down‐valley subsurface storage area. Because we found complex spatial patterns, future studies should pair dense spatial observations of subsurface properties, such as hydraulic conductivity and transmissivity, to observations of seasonal flow permanence. [ABSTRACT FROM AUTHOR]

The effect of anthropogenic activities on natural intermittent stream and diversity of adult caddisfly were studied at the University of Phayao, Thailand. The caddisfly adults were collected monthly from 2 intermittent streams (the Huai Thub Chang and Huai Luang streams) from February to May 2015 (cooldry to hot-dry season) using a black-light trap. Huai Thub Chang stream received wastewater from the oxidation pond, while Huai Luang stream was affected by an agricultural field of the university. Both streams are located in a deciduous forest. The 14 species of 7 families were collected and identified. Cheumatopsyche lucida (Hydropsychidae) and Leptocerus dirghachuka (Leptoceridae) were found in both streams. C. lucida was the most abundant species. Micrasema turbo, Amphipsyche meridiana, C. globosa, Diplectrona lavinia, Macrostemum dohrni, Marilia sumatrana, and Wormaldia relicta were found only in Huai Thub Chang stream, whereas C. dhanikari, Lepidostoma doligung and Chimarra toga were found only in Huai Luang stream. A high number of C. lucida in both streams from February to April reflected a drought effect on the emergence of the caddisflies. Huai Thub Chang stream had a higher diversity of Trichoptera species than Huai Luang stream because of the variety of substrate types which were suited for the larval stage, especially hydropsychids. [ABSTRACT FROM AUTHOR]

Stream drying and wildfire are projected to increase with climate change in the western United States, and both are likely to impact stream chemistry patterns and processes. To investigate drying and wildfire effects on stream chemistry (carbon, nutrients, anions, cations, and isotopes), we examined seasonal drying in two intermittent streams in southwestern Idaho, one stream that was unburned and one that burned 8 months prior to our study period. During the seasonal recession following snowmelt, we hypothesized that spatiotemporal patterns of stream chemistry would change due to increased evaporation, groundwater dominance, and autochthonous carbon production. With increased nutrients and reduced canopy cover, we expected greater shifts in the burned stream. To capture spatial chemistry patterns, we sampled surface water for a suite of analytes along the length of each stream with a high spatial scope (50-m sampling along ~2,500 m). To capture temporal variation, we sampled each stream in April (higher flow), May, and June (lower flow) in 2016. Seasonal patterns and processes influencing stream chemistry were generally similar in both streams, but some were amplified in the burned stream. Mean dissolved inorganic carbon (DIC) concentrations increased with drying by 22% in the unburned and by 300% in the burned stream. In contrast, mean total nitrogen (TN) concentrations decreased in both streams, with a 16% TN decrease in the unburned stream and a 500% TN decrease (mostly nitrate) in the burned stream. Contrary to expectations, dissolved organic carbon (DOC) concentrations varied more in space than in time. In addition, we found the streams did not become more evaporative relative to the Local Meteoric Water Line (LMWL) and we found weak evidence for evapoconcentration with drying. However, consistent with our expectations, strontium-DIC ratios indicated stream water shifted toward groundwater-dominance, especially in the burned stream. Fluorescence and absorbance measurements showed considerable spatial variation in DOC sourcing each month in both streams, and mean values suggested a temporal shift from allochthonous toward autochthonous carbon sources in the burned stream. Our findings suggest that the effects of fire may magnify some chemistry patterns but not the biophysical controls that we tested with stream drying.

First-order streams in Brazil are protected by the Native Vegetation Protection Law of Brazil (NVPL), which regulates the land-use in rural properties and is linked with aquatic conservation. We investigated the importance of the data-set resolution to identify first-order streams (State of São Paulo, Brazil) and estimated its length compared to other water bodies. We found that first-order streams represent around 58% of the total length of the drainage system. In addition, we compared this database with that of the Environmental Rural Registry (CAR in Portuguese). Compared with the lower resolution data-set, the length of first-order streams self-declared in CAR was 80% lower. We also found a concerning number of small dams in first-order streams, which severely changes their dynamics. Therefore, we recommend the use of finer resolution data-sets in order to create tools to support legal compliance that goes beyond the limited information provided by CAR.

Abandoned mining operations continue to severely degrade many ecosystems worldwide by releasing acidic water and/or heavy metals into surface and groundwater. Contaminant concentrations in affected streams vary with discharge in patterns that reflect both geochemical reactions and variable mixing of contaminated and non‐contaminated waters. However, controls on concentration‐discharge (C‐Q) patterns remain unclear, particularly for constituents that experience changing solubility across redox and pH gradients. Understanding the C‐Q behaviour of contaminants aids in predicting both downstream transport and effects on aquatic life under variable flow. Here, we examined the C‐Q behaviours of non‐reactive (Na, K, Ca, Mg, Cl−) and reactive (Fe, Mn, Al, H+, SO42−) solutes in a stream contaminated with acid mine drainage in northeastern Ohio, USA. Concentration‐discharge patterns at the watershed outlet primarily reflected mixing of contaminated baseflow with intermittent inputs of high pH water draining from a passive limestone treatment system into the stream. The treatment system acted as an ephemeral tributary that mitigated contamination in the stream by diluting solutes, raising pH, and driving metal precipitation, but only when flow was present during wet seasons. Consequently, AMD‐derived reactive solutes (H+, Fe, Mn, Al) decreased with increasing stream discharge while relatively conservative solutes (e.g., Ca, Mg, K, Na) decreased only slightly or were chemostatic. This study highlights both the unique C‐Q patterns of reactive solutes when compared to those of non‐reactive solutes and the potential for intermittent streams to control C‐Q behaviour in headwater catchments. [ABSTRACT FROM AUTHOR]

Temporary Mediterranean streams dry out in summer due to low precipitation and high temperatures, thus affecting biota and ecosystem functioning. The consequences of exposing leaf litter to an extreme summer drought, that is, high solar radiation, low humidity, and high temperatures, were evaluated. It was hypothesised that litter exposure to summer drought conditions in a dry streambed would change litter chemical composition, affecting decomposition and associated benthic communities after autumnal flow resumption. Recently fallen black poplar leaves were enclosed in litterbags and separated into two sets: (1) control leaves, kept air-dry in the dark, and (2) drought leaves, exposed to harsh summer conditions in a simulated dry streambed. Both sets were then immersed in a temporary Mediterranean stream in autumn, and leaf litter decomposition monitored. As expected, summer drought exposure increased nitrogen, total fibre, lignin, and cellulose content in drought leaves. After litterbag immersion, higher cellulose-degrading enzyme activity was observed in drought leaves while lignin-degrading enzyme activity was greater in the control leaves. Fungal and bacterial assemblages clearly differed between treatments. Inter-replicate variability was lower in drought leaves for most of the measured variables, suggesting that drought homogenised decomposer and detritivore communities. Despite these drought-related effects, decomposition rates did not vary, apparently due to counterbalancing effects (that is, drought treatment enhanced recalcitrant compounds and nutrient content in leaf litter) probably related to terrestrial microbial colonisation and photodegradation. Our study demonstrates that summer drought has bottom-up critical legacy effects in temporary Mediterranean streams, affecting the structure and function of decomposer communities. [ABSTRACT FROM AUTHOR]

Little is known about the conservation of intermittent and ephemeral streams on private lands despite the importance of these waterways for ecosystem and hydrologic outcomes. Our case study of a watershed of central New York State considers landowners' attitudes toward perennial and intermittent streams on their property. We combine social science survey responses with aerial imagery to assess the underlying drivers of landowners' attitudes about their streams, and the extent to which these attitudes shape riparian conservation behaviors on their properties. We find that stream flow regularity directly and positively shapes landowners' stream attitudes, with landowners of perennially flowing streams holding their streams in higher regard than landowners with streams of intermittent flows. Landowners with forest and wetlands as the primary land cover had more riparian buffer coverage on their properties than agricultural landowners. Landowners with a weaker perceived land use efficacy also had greater buffer coverage. Our findings suggest that landowners in headwater regions do not perceive their influence on downstream water quality, and that outreach efforts should emphasize the importance and conservation of headwater streams and associated water quality outcomes. [ABSTRACT FROM AUTHOR]

Extreme drying can dramatically shift abiotic characteristics of streams and species respond differently as conditions change. We modified a conceptual model describing responses of aquatic invertebrate assemblages to stream drying to facilitate predictions of fish assemblage shifts in which thresholds of physiochemical gradients lead to punctuated losses of fish diversity as stream connectivity diminishes. We tested the applicability of this model during a record-breaking drought that reduced a perennial reach of a headwater prairie stream to a series of 12 isolated pools with variable levels of hyporheic connectivity that was associated with pool volume. We tracked fish assemblage structure in pools over seven weeks and measured abiotic conditions. Inter-specific differences in drought resistance traits were tested in the lab (i.e., thermal and hypoxia tolerance) for common species experiencing drought conditions. Species richness declined rapidly with pool volume associated with hyporheic connectivity. Abundance of the most common species prior to drought, Chrosomus erythrogaster (southern redbelly dace) declined 95% and was extirpated from five pools during drought due to its low thermal tolerance. Despite being the least tolerant to hypoxia, Campostoma anomalum (central stoneroller) populations persisted in most pools. The remaining pools became dominated by a non-native extremophile fish, Gambusia affinis (western mosquitofish) and abundances of less resistant native species declined. Our study demonstrates that richness in drying pools is driven by factors associated with pool volume, and assemblage composition shifts from dominance by native species adapted to variable hydrological conditions to non-native species able to resist increasing temperatures and hypoxia. Sudden species loss associated with reduced stream connectivity can shift abundance patterns of prairie stream fish communities with potentially lagged effects on population and community dynamics. [ABSTRACT FROM AUTHOR]

Streams in hot, arid environments often exist as a series of isolated pools along main channels. During these periods, shallow alluvial through flow may strongly influence key ecological processes within pools. We measured diel changes in δ13C values of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) in two pools of ephemeral, dryland streams. We quantified alluvial water connectivity through stable isotope analysis (δ18O and δ2H) of pool and alluvial water. We also estimated gross primary productivity (GPP) and ecosystem respiration (ER) rates across a wider set of pools in both streams. δ13CDIC values displayed regular diel cycles, where both pools displayed small but similar daily amplitude (0.7–0.9‰) despite contrasting amplitudes of change in DO (0.8 mg L−1 vs. 2.8 mg L−1) and contrasting alluvial water connectivity (connected vs. disconnected). Water temperature was the strongest predictor of both δ13CDIC values and rates of change in δ13CDIC across both pools. Across both streams, all pools were net heterotrophic. GPP (0.35–1.73 g O2 m−2 d−1) and ER (0.49–2.64 g O2 m−2 d−1) rates were linked to aquatic vegetation cover. The disconnect between diurnal amplitudes of δ13C values and DO concentrations thus suggests that ecological drivers of gas exchange became increasingly localised as pools contracted. [ABSTRACT FROM AUTHOR]

Ecosystems experience natural disturbances and anthropogenic impacts that affect biological communities and ecological processes. When natural disturbance modifies anthropogenic impacts, current widely used bioassessment metrics can prevent accurate assessment of biological quality.Our aim was to assess the ability of biomonitoring metrics to detect anthropogenic impacts at both perennial and intermittent sites, and in the latter including both flowing and disconnected pool aquatic phases. Specifically, aquatic macroinvertebrates from 20 rivers were sampled along gradients of natural flow intermittence (natural disturbance) and anthropogenic impacts to investigate their combined effects on widely used river biomonitoring metrics (i.e. taxonomic richness and standard biological indices) and novel functional metrics, including functional redundancy (i.e. the number of taxa contributing similarly to an ecosystem function, here a trophic function) and response diversity (i.e. how functionally similar taxa respond to natural disturbance and anthropogenic impacts).Only the widely used IBMWP index (Iberian Biological Monitoring Working Party) was able to detect anthropogenic impacts in intermittent rivers when used during flowing phases. Several functional metrics also detected anthropogenic impacts regardless of flow intermittence. Besides, functional redundancy of the entire community remained effective even in disconnected pools.Synthesis and applications. Our results show that natural flow intermittence can confound river bioassessment, and that a set of new functional metrics could be used as effective alternatives to standard metrics in naturally disturbed intermittent rivers. Our findings suggest that water managers should incorporate alternative functional metrics in the routine biomonitoring of naturally disturbed rivers. [ABSTRACT FROM AUTHOR]

The study of variation of species composition among sites is key to understanding community ecology, but few studies have assessed beta diversity patterns in highly dynamic stream networks in the Neotropical region. We assessed aquatic insect patterns of local contribution to beta diversity (LCBD) and species contribution to beta diversity (SCDB) in a Neotropical drainage network composed of both perennial and intermittent streams in a dry period. We evaluated if environmental and/or spatial predictors drive patterns of LCBD. We sampled aquatic insects in 12 intermittent headwater streams and 34 perennial streams. The intermittent compared to perennial streams had higher LCBDs and lower richness. The pure environmental component significantly explained 19% of the variation of LCBD, while the pure spatial components were not significant. Forty-six taxa contributed to beta diversity above the mean of the 199 taxa. We detected the association of oxygen tolerant and good dispersal ability taxa to intermittent streams and species riffle-adapted taxa as indicators of perennial streams. We showed a disproportional contribution of intermittent streams to the regional species pool. In summary, we demonstrated that when streams dry out, compositional uniqueness may increase during the dry period making them critical to conservation planning of dynamic stream networks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Woody encroachment in prairies reduces streamflow despite wetter climate. • Woody encroachment deepens water flow paths. • Woody encroachment increases groundwater flow fraction even as total flow declines. Grasslands, covering 40% of ice-free Earth surface, are experiencing woody encroachment globally. The hydrological impacts of woody encroachment are highly uncertain because they are compounded by the concurrent influence of climate change. Here we ask the questions 1) How water balance (evapotranspiration versus streamflow) and streamflow partitioning (into surface runoff and subsurface flows) evolve over time in woody-encroached grasslands? 2) What is the relative influence of climate change and woody encroachment? We used the hydrology model HBV-light and decades of hydrometeorological and streamflow data from two intermittent streams draining catchments with different degrees of woody encroachment at the Konza Prairie, Kansas, US. Results indicate that both streams have become drier and have experienced more hydrological droughts over time, more so in the substantially encroached site, with increasing evapotranspiration despite a wetter climate. In contrast, a modelled hypothetical "Climate Only" scenario without woody encroachment suggests streamflow would have increased under climate change alone. Moreover, results suggest that flow paths have deepened with increasing fractions of deeper groundwater flow in the substantially encroached site. These findings raise questions about mechanisms of these changes and commonality of drier streams in a wetter climate in woody-encroached areas and beyond. Answers to these questions can have far-reaching implications for the occurrence of droughts, water availability, water quality, and ecosystem health. [ABSTRACT FROM AUTHOR]

Many organisms living in temporary streams rely on remnant surface water to survive during extended dry periods and recolonize newly established habitats when flow resumes. However, research on the spatiotemporal variations in surface water extent for entire river networks is scarce. In this study, we first present a new field method for rapid surface water assessment. Next, we develop predictive models relating observed water extent to environmental attributes at a large number of surveyed stream segments (n = 241) in eastern Australian coastal catchments. We use the models to predict daily variations in surface water dynamics throughout entire river networks over the period of 1911–2017, based on available long‐term environmental attributes influencing hydrological processes. We find descriptors of surface water extent can be accurately predicted based on robust internal and external validations. Environmental predictor variables representing water gaining processes were more important in predicting surface water extent than variables representing water losses. Simulated long‐term variations in surface water extent were highly dynamic through space and time, particularly in inland streams, which were predicted to be the driest on average. Total stream length with surface water ranged from 8,974 to 13,742 km across the study period. Our study presents a novel and practical approach to quantifying and predicting variations in surface water extent, with potential applicability to other parts of the world. The simulated surface water extent through space and time can be used to identify and prioritize potential aquatic refuge areas that sustain aquatic biodiversity in river networks during extended dry periods. Key Points: We propose a field method for surface water assessment and develop predictive models of spatiotemporal variations in surface water extentSimulated long‐term variations in surface water extent were highly dynamic through space and timeModel outputs can inform the identification and prioritization of aquatic refuges to sustain aquatic biota [ABSTRACT FROM AUTHOR]

Running waters in Mediterranean regions are strongly regulated by dams, which produce significant alterations to natural flow regimes. Climate change will reduce discharge and increase flow intermittence in Mediterranean streams, which will lead to an intensified flow regulation to meet water demands. Very little is known about how the functional features of aquatic communities vary along combined anthropogenic flow alteration and natural intermittence gradients.As intermittent streams are subjected to natural stress (droughts and flash floods), the flow regime alteration effect may differ from that observed in perennial rivers. Consequently, studies that aim to determine the effects of flow regulation on the functioning of aquatic communities in a global change context are crucial.By applying linear mixed‐effect models and null models to the macroinvertebrate communities from 65 stream sites in the Segura River Basin (south‐east Spain), we assessed the separate effects of natural flow intermittence and flow regulation, as well as their interaction, on biological traits and functional diversity indices.Natural flow intermittence and flow regulation were mainly associated with loss of taxa with semivoltine or univoltine cycles and more sensitive aquatic stages (i.e. eggs), and with the replacement by taxa with multivoltine cycles and more resistant aquatic stages (i.e. adults). Flow regulation intensified the impact of natural flow intermittence on some biological traits, producing synergistic effects (i.e. decreasing interstitial taxa and tegument breathers and increasing taxa with aquatic adult stages). At the same time, antagonistic (life cycle) and opposing (shredders) interaction effects were also observed. Functional diversity, functional dispersion, and functional redundancy underwent a non‐random decrease as the flow regime alteration increased, and a significant antagonistic interaction was also found between both stressors for functional redundancy.In general, flow regulation effects were stronger in perennial than in intermittent streams because natural intermittence imposes a previous eco‐evolutionary pressure on aquatic biota by selecting those resistant or recovery traits that confer resilience to anthropogenic flow regime alterations. Thus, the natural flow regime influences the functional sensibility of communities to anthropogenic flow alteration. [ABSTRACT FROM AUTHOR]

Highlights • Composition of diatom assemblages were analysed in intermittent and permanent streams. • Changes in water regime induced marked differences in trait composition. • Lower functional diversity was typical in the intermittent than in permanent streams. • Results highlighted the vulnerability of intermittent streams in temperate lowlands. Abstract Climate change is predicted to increase drought occurrence and severity in small continental watercourses. Here, we studied the structure and the functional diversity of benthic diatom assemblages in lowland intermittent and permanent watercourses of the Carpathian Basin. We assumed that the community structure of intermittent and permanent watercourses would be markedly different, and the functional diversity in both would be strongly influenced by autumn drought. We found that intermittent streams were primarily characterized by small-sized generalists and aerophilic taxa, while permanent watercourses were inhabited by large-sized planktic or fast moving groups. The functional richness was significantly lower in intermittent than in permanent streams. This decrease in the functional richness of benthic algal communities may negatively affect the functioning of lotic algal communities. We conclude that diatom assemblages in lowland intermittent watercourses are sensitive indicators of changes in ecosystem properties, and should be considered in appropriate evaluation and management of extreme climatic events on aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The objective of the present study was to document the knowledge about the biodiversity of benthic insect communities and their distribution patterns in the semi-arid bioclimatic stage in the streams of the Aurès Region (NE Algeria). The distribution patterns of communities were analyzed in relation to some environmental factors: physicochemical water parameters and global habitat characteristics, including human impact. The taxonomic biodiversity of six sampled streams (wadis) comprises 42 insect taxa, belonging to seven orders and 30 families, of which Coleoptera is the most diverse order (15 taxa), whereas Diptera, Trichoptera and Ephemeroptera dominate in terms of abundance. The human impact, flow velocity and some quality parameters of water (potential of hydrogen, nitrite, concentration of orthophosphates and conductivity) were identified as the most influential environmental variables, which allows the prediction of taxonomic diversity indicators. The classification and regression tree analysis (CART) for benthic insects shows the effect of environmental variables (habitat parameters and human impact in the arid region) on the diversity and distribution of insect orders. The RDA analysis showed that altitude, substrate type, human impact and physicochemical parameters of water (pH, flow velocity, conductivity and total dissolved solids) are the most important predictor variables that play an important role in the distribution patterns of benthic insects. [ABSTRACT FROM AUTHOR]

The seasonal dynamics and spatial variability of macroinvertebrate assemblages in Alpine streams are becoming better understood. However, the implications of this knowledge for indices used in monitoring programs have yet to be fully considered. Establishing the ecological status of such streams using macroinvertebrates may then be difficult if what is expected to be found, and where, varies across small distances between streams at a given altitude, or between years in response to different climatic characteristics. In this paper, we evaluated the degree of spatial variability in macroinvertebrate abundance and diversity for 14 tributaries at similar altitude that feed a 6-km reach of an Alpine stream, and how this spatial variability differs within and between years. Environmental variables and macroinvertebrates were sampled on 10 dates for assessment. The data showed that differences in environmental characteristics over relatively short distances lead to between tributary differences in the "windows of opportunity" and hence when a tributary should be sampled for monitoring purposes. Superimposed on this spatial variability was inter-annual variability linked to climate differences that shifted this "window of opportunity" in time, and thus altered when monitoring was optimal for any one tributary in any one year. If biological indices are not rendered sensitivity to these variations, the results obtained may reflect more natural variability than possible human impacts. [ABSTRACT FROM AUTHOR]

Climate change has fundamentally altered the water cycle in tropical islands, which is a critical driver of freshwater ecosystems. To examine how changes in streamflow regime have impacted habitat quality for native migratory aquatic species, we present a 50‐year (1967–2016) analysis of hydrologic records in 23 unregulated streams across the five largest Hawaiian Islands. For each stream, flow was separated into direct run‐off and baseflow and high‐ and low‐flow statistics (i.e., Q10 and Q90) with ecologically important hydrologic indices (e.g., frequency of flooding and low flow duration) derived. Using Mann–Kendall tests with a running trend analysis, we determined the persistence of streamflow trends through time. We analysed native stream fauna from ~400 sites, sampled from 1992 to 2007, to assess species richness among islands and streams. Declines in streamflow metrics indicated a general drying across the islands. In particular, significant declines in low flow conditions (baseflows), were experienced in 57% of streams, compared with a significant decline in storm flow conditions for 22% of streams. The running trend analysis indicated that many of the significant downward trends were not persistent through time but were only significant if recent decades (1987–2016) were included, with an average decline in baseflow and run‐off of 10.90% and 8.28% per decade, respectively. Streams that supported higher native species diversity were associated with moderate discharge and baseflow index, short duration of low flows, and negligible downward trends in flow. A significant decline in dry season flows (May–October) has led to an increase in the number of no‐flow days in drier areas, indicating that more streams may become intermittent, which has important implications for mauka to makai (mountain to ocean) hydrological connectivity and management of Hawai'i's native migratory freshwater fauna. [ABSTRACT FROM AUTHOR]

Ephemeral and intermittent flow in dryland streams plays a vital role in supporting delicate ecosystems and recharging groundwater in underlying aquifers. Despite extensive research, accurately predicting surface runoff, streambed water infiltration, and groundwater recharge during ephemeral streamflow events remains challenging due to the complex physical processes involved. Such processes are logistically difficult to observe in the field and should not be assessed through numerical studies alone. To tackle this complexity, we utilized an 8 m long, 0.25 m wide, and 0.6 m deep laboratory flume filled with fine sand as a physical model for event flows along a dry stream. This flume allowed us to measure both streamflow and streambed infiltration volumetrically as the stream wetting front advanced along its length during 8 steady inflow rates. The flume was divided into separate compartments to measure water across the sediment surface (streamflow) and water exiting through the flume's bottom (groundwater recharge). To validate our physical tests, we compared them with simulated flows in an integrated surface–subsurface hydrological numerical model. The model results exhibited good agreement with the observed stream and groundwater dynamics. Through a parametric numerical investigation, we identified that hydraulic conductivity significantly controlled the rate of surface infiltration and the advancement of the stream wetting front. Interestingly, we found a linear relationship between surface discharge and stream wetting front location, as well as groundwater recharge, under steady-state conditions, in line with the governing equations. However, our simulations of variable streambed heterogeneity and elevation unveiled the crucial influence of these factors in determining the timing of downstream flow progression. This insight is essential for establishing ecological connectivity along non-perennial rivers and has significant implications for delivering environmental flows in arid regions where ephemeral rivers are prevalent. Our study underscores the value of flume experiments in elucidating the transient physical processes during surface water and groundwater interactions in intermittent streams. By employing a combination of physical modelling and numerical simulations, we advance our understanding of these vital hydrological interactions, contributing to sustainable water management practices in semi-arid and arid environments. • Flume experiments demonstrated stream and groundwater dynamics during ephemeral flood wave advancement. • Location of the stream wetting front is linearly proportional to stream discharge. • Stream wetting front arrival is sensitive to depression storage and sediment heterogeneity. • Parametric analysis identified hydraulic conductivity as the primary control on stream wetting front. [ABSTRACT FROM AUTHOR]