Global changes and local pressures related to the exploitation of water resources are significantly reducing streams' biodiversity and threatening their ecological balance. This trend concerns both the lowland rivers flowing in densely populated areas, and the alpine headwaters, where the effects of global change are dramatically evident and often accompanied by alterations in river hydro-morphology. In mountainous river stretches, regulation and morphological alterations such as bank reinforcement, water abstractions, dams, and weirs are increasing. In the Alps, protected areas and especially large National Parks constitute an effective strategy to face the loss of biodiversity, but little is known about their effectiveness regarding lotic environments. To examine the recent trend in aquatic communities in Alpine protected areas, we carried out biological samplings and hydro-morphological evaluation in twelve high-altitude streams within the oldest Italian National Park, the Gran Paradiso Park, located in the heart of the Western Alps, and we compared results with a previous survey performed in 2005, keeping the same experimental design. Our results detected minimal changes in the hydro-morphology of the studied watercourses. Biomonitoring indices associated with benthic communities likewise do not evidence significant differences. Concerning diatom flora, we found however in 2020 a greater uniformity in species composition compared to communities of 2005, and a slight turnover between species. In conclusion, our findings underline the effectiveness of protected areas for the conservation of running water environments because they limit hydro-morphological alterations thus increasing the resilience of aquatic communities to climate change.

One of the negative effects of hydropower on river environment includes rapid changes in flow and habitat conditions. Any sudden flow change could force fish to move towards a refuge area in a short period of time, causing serious disturbances in the life cycle of the fish. A probability-based multiscale model was developed to quantify the impact of hydropeaking on habitat suitability for two fish species. The model used habitat preference curves, river flow and depth to develop the suitability maps. The suitability index maps reveal that habitat suitability deteriorates as flow increases in this part of the river. The probability model showed that, on average, suitability indices are higher for adult grayling than juvenile trout in hydropeaking events in the studied area. In addition, the life stages of fish determine their response to the sudden flow change. The method developed shows the potential to be used in river management and the evaluation of hydropeaking impacts in river systems affected by hydropower.

Headwater streams can constitute up to 80% of river channel length and are vulnerable to anthropogenic pressures due to their high connectivity to adjacent land, large relative catchment size and low dilution capacity. In these environments unrestricted cattle access is a potential significant cause of water quality deterioration, resulting from increases in stream bank erosion, riparian damage and sediment deposition among others. Several studies have reported improvements in physico-chemical and hydromorphological conditions of streams following elimination of cattle access; few, however, have focussed on the ecological impacts of such management practices. Here, such impacts are assessed. We look at the short-term effects by comparing habitat condition, sediment deposition, and instream macroinvertebrate communities upstream and downstream of cattle access points prior to, and one year following exclusion via fencing. The long-term effects are also measured by reassessing a small stream catchment entirely fenced off from cattle access in 2008 under a concerted management effort. In the short term, cattle exclusion led to reduction in deposited sediment downstream of cattle access points and a related homogenisation of macroinvertebrate community structure between upstream and downstream sampling points. Increased abundances of specific indicator taxa ( Ancylus fluviatilis, Glossosomatidae and Elmidae) in the fenced catchment following 9 years of exclusion highlight the long-term ecological benefits of such mitigation practices. These findings highlight the importance of incentivised agri-environment schemes in reducing the negative impacts of cattle access to these vulnerable ecosystems.

Hydrological drought has wide-ranging impacts on water quality, nutrient and carbon metrics that are critical to investigate with the increased drought frequency predicted with climate change. This study compared physicochemical parameters (temperature, conductivity, pH and DO), nutrients (TN, NO X, NH 3, TP) and carbon (TOC and DOC) between hydrological drought conditions (2006–2009) and hydrological normal conditions (2016–2019) at five sites along the lower Savannah River (Georgia, USA). We unexpectedly found temperature (F 1,220=4.27, p=0.04) was significantly lower during drought conditions. Levels of pH (F 1,220=11.99, p<0.01) and DO (% saturation; F 1,220=9.17, p=0.01; and mg L –1; F 1,220=4.04, p<0.01) were significantly higher during drought. We found TN (F 1,220=5.23, p=0.02), TOC (F 1,220=30.22, p<0.01) and DOC concentrations (F 1,220=30.22, p<0.01) were significantly lower during drought, but NO X concentrations (F 1,219=4.04, p=0.05) were significantly higher during drought. Conductivity only varied at the lower river sites, being significantly higher during drought at Sites 3 (F 1,47=12.56, p<0.01), 4 (F 1,47=12.96, p<0.01) and 5 (F 1,34=17.60, p<0.01). These complex changes could be attributed to volume reductions coupled with an increase in the percentage of total flow originating from groundwater and limnetic reservoir inputs, persistent point source pollution, reduced natural catchment inputs and/or reduced floodplain interactions. The changes that occurred during drought may be disruptive to aquatic life, not only from reduced water quantity but also due to a scarcity of some biologically essential materials and lower food resources, combined with artificially high levels of some other potentially stressful materials.

Place identity is the emotional connection between people and a place. It is significant for local development and people’s satisfaction and happiness in where they reside. The physical environment is one of the most important factors affecting people’s emotions toward a place. In order to clarify the theoretical analytical framework of the process from village space morphology to place identity, this study takes the area of Aihui along the Heilongjiang River, China, as an example. The research was conducted regarding two aspects: First, we analyzed the space morphology of the villages in the Aihui district and interpreted their locality. On this basis, we conducted a survey of villagers’ subjective perceptions of the village space and their place identity through in-depth interviews. From the collected interview texts, we extracted, verified, and analyzed the role of morphological constituents in the construction of place identity. Finally, a comprehensive framework was established. The features of space morphology are the projections of locality in physical space. People use morphological constituents to construct an image of the village and scenes of local life; morphological constituents with local characteristics can help enhance people’s place identity.

This study provides a comprehensive review of the existing river measurement data of South Korea. The specific sediment yield in the country is 5–1,500 tons/km 2·year. The watershed area decisively affects the shapes of the curves for flow duration, sediment rating, and cumulative distribution of water and sediment discharge, and it can determine the effects of topographic and anthropogenic characteristics on erosion and sedimentation processes. Regarding flow regime, small watersheds have flashy hydrographs and high sediment concentrations at a given flow discharge. The coefficient of the sediment rating curves for various rivers decreases from 1 to 0.02 as the watershed area increases from 100 to 20,000 km 2, with the exponent of the curves ranging from 1.5 to 2.0. Moreover, sediment transport in small watersheds depends on large floods. The half-yield discharge typically ranges from 5 to 40 times the mean discharge, and it decreases with increasing watershed area. This study proposes equations to calculate the annual discharges, flow duration curves, sediment yield, and cumulative distribution curves of the flow and sediment, as well as the sediment yield at reservoirs in South Korea. Additionally, the sediment regimes in the country are compared to those in other continental regions.

Numerical hydrodynamic models enable the simulation of hydraulic conditions under various scenarios and are thus suitable tools for hydropeaking related assessments. However, the choice of the necessary model complexity and the consequences of modelling choices are not trivial and only few guidelines exist. In this study we systematically evaluate numerical one-dimensional (1D) and two-dimensional (2D) hydrodynamic models with varying spatial resolution regarding their suitability as input for hydropeaking-sensitive, ecologically relevant hydraulic parameters (ERHPs), and their computational efficiency. The considered ERHPs include the vertical dewatering velocity, the wetted area variation between base and peak flow and the bed shear stress as a proxy for macroinvertebrate drift. We then also quantified the habitat suitability of brown trout for different life stages. The evaluation is conducted for three channel planforms with morphological characteristics representative for regulated Alpine rivers, ranging from alternating bars to a braiding river morphology. Our results suggest, that while a highly resolved 1D model is sufficient for accurate predictions of the dewatering velocity and wetted area in the less complex alternating bar morphology, a 2D model is recommended for more complex wandering or braiding morphologies. For the prediction of habitat suitability and bed shear stress, a 1D model appears to be always insufficient, and a highly resolved 2D model is suggested. Reducing the spatial resolution of 2D models leads to computational efficiency similar to 1D, while providing more accurate results. This study can serve as guideline for researchers and practitioners in the selection and setup of hydrodynamic models for hydropeaking.

Blue sucker ( Cycleptus elongatus) occurs in the Mississippi River and Gulf of Mexico drainages of North America and is negatively affected by habitat fragmentation and flow regime alteration caused by dams. During fish assemblage surveys in August of 2022, we collected five specimens of juvenile blue sucker (312-428 mm total length) in the Angelina River upstream of Sam Rayburn Reservoir in east Texas (46,335-hectare surface area) where the occurrence of the species was previously unconfirmed. Given this unexpected finding, we (1) analyzed blue sucker mesohabitat associations to compare habitats we sampled with reports in the literature, and (2) reviewed blue sucker occurrence in state, national, and global databases across historical (1950-1980) and contemporary (1981-2022) periods to assess occurrence across gradients of habitat fragmentation and streamflow regulation. The blue sucker population in the Angelina River upstream of Sam Rayburn Reservoir was previously unconfirmed but is within the native range of the species. Mesohabitats occupied by blue sucker were consistent with literature reports, including fast velocity, shallow depth, and coarse substrates. The low degree of regulation (19% of natural runoff stored by upstream reservoirs) and a high degree of habitat connectivity (287 rkm of mainstem habitat) for the Angelina River upstream of Sam Rayburn Reservoir matched range-wide patterns of persistence within relatively intact (unfragmented and unregulated) or remnant (fragmented but unregulated) riverscapes. Our review reveals that blue sucker populations might persist (1) in remnant river fragments where local habitat templates are appropriate and (2) where effects of habitat fragmentation and flow regulation are not coupled.

Classification of natural flow regimes of non-perennial rivers and streams (NPRS) is an incipient field of research. NPRS represent approximately 70% of the total Mediterranean rivers and are expected to increase in the next decades as a result of climate change. Due to the ecological importance of NPRS and the need to improve national ecological assessment methods within the scope of the Water Framework Directive (WFD), this paper aims to classify the hydrological regime of 69 non-regulated streams, testing several hydrological indices related to the frequency, duration, timing, and rate of change in periods of flow cessation. Using daily flow records, a total of 315 indices were calculated and their relationships were examined with Principal Component Analysis (PCA) for different thresholds used to define zero-flow condition set at 0, 1, 2, and 5 l/s. Redundancy analysis identified five indices that better describe the patterns of hydrological variability in Mediterranean NPRS: number of days per year without flow, annual percentage of months without flow, mean daily of annual flows, coefficient of variation of Julian date of the annual start of zero flow and annual rise rate. Using these indices, a self-organizing map (SOM) was trained in order to categorize the NPRS into three groups with similar hydrological features. The results of this study provide a statistically-based hydrological classification of NPRS in Mediterranean environments. We expect that this classification will provide useful insights to water authorities to improve the assessments of the ecological status in this set of water bodies.

Salt dilution is a well-established streamflow measurement method in creeks, which works particularly well downstream of turbulent flow sections as mixing of the salt tracer is enhanced. Usually salt dilution measurements are performed manually, which considerably limits the observations of rare peak flow events. However, these events are particularly important for constructing robust rating curves and avoiding large uncertainties in the extrapolation of river discharge values. An additional challenge is the variability of the river cross-section, especially after larger discharge events, leading to non-stationary rating curves. Therefore, discharge measurements well distributed over time are needed to both construct a reliable streamflow-water level relationship and to detect changes caused by erosion and deposition processes. To overcome these two issues, we used an automated streamflow measuring systems at three different sites in the Alps for event-based discharge measurements. This system allowed us to measure close to the highest peak flows at all three sites in the observation period (2020-2021) and to detect abrupt changes in the rating curve. Based on a very large data set of almost 300 measurements, we were able to evaluate the reliability of the system and to identify the main sources of uncertainty in the experimental setup. One key aspect was the site selection for the downstream electrical conductivity sensors as measurement location strongly controls the signal-to-noise ratio (SNR) in the recorded breakthrough curves.

Although the dispersal is important for riparian plants, few studies have evaluated the patterns in species richness and composition of propagules deposited by different dispersal types. In the present study we evaluate the temporal and spatial patterns in the diversity of propagules deposited by hydrochory and by other types of dispersal along mountain rivers. To do this, we sampled the propagules deposited in the riparian zone in a distance gradient with respect to the site of origin of the rivers in two seasons. Regarding the temporal analyses, we found no differences in the number of propagules between seasons. In the rainy season we observed a greater number of species deposited by hydrochory, while for other types of dispersal there was a greater number of species in the dry season. Differences in composition were observed for hydrochory but not for other types of dispersal. Regarding the spatial analyses, there were no changes in the number of propagules deposited along the river by hydrochory, while for other types of dispersal an increase was observed in the dry season. A lower number of species deposited by hydrochory along the river in the rainy season was observed. Finally, we observed that turnover increases by other types of dispersal in the dry season but not for hydrochory. The results underline the importance of types of dispersal other than hydrochory in the contribution of propagules dispersed and the temporal and spatial particularities of the hydrochory in mountain rivers.

Over the last decade, rapid vegetation colonization and changes in channel morphology have been observed in the Naeseongcheon Stream in South Korea, which were linked to short-term hydrological fluctuations under a changing monsoon climate. The surface area covered by vegetation has been increasing; this increase intensified after the 2014–2015 drought, which provided a window of opportunity for vegetation establishment. During the drought, pioneer herbaceous vegetation densely colonized the lower floodplains, including bare sandbars and temporarily exposed riverbed. Although the colonized lower floodplain and river banks were partially rejuvenated by several subsequent floods, succession to woody vegetation continued, resulting in stable vegetation cover in areas that had previously been bare. Moreover, sediment carried by flood water was deposited on and around the vegetated areas, and the low-water channel was incised, causing vertical development of river topography. In addition, the main channel width decreased in previously relatively wide sites, and secondary channels formed. The results of this study show that river rejuvenation by floods may decrease owing to systemic changes in the river system. Therefore, we concluded that the Naeseongcheon watershed was primed by human-induced changes, which made the river system more susceptible to changes in rainfall and discharge due to climate change. Furthermore, after the initial vegetation colonization, changes in nutrients and temperature created a positive feedback loop, which reinforced vegetation establishment.

The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite abundance; with greater host diversity, parasite levels per host are predicted to be lower due to a higher probability of dispersing parasites encountering non-competent hosts. Dilution effects could also occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competency. The introduction of non-native hosts can change community competency of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish occurring in the presence and absence of non-native Faxonius crayfish in the New River, USA. We performed an experiment investigating the effect of host density (1 vs 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced F. cristavarius is a non-competent host for these worms. Six C. ingens were stocked on a C. chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment . There was no significant effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.

A document by Behnam Balouchi. Click on the document to view its contents.

Numerical modeling of braided channels showed no significant differences in the number of cross-sectional branches between different water periods in the middle reaches of the Yarlung Tsangpo River. During most of the year (wet, normal and dry periods), flow velocities in the higher-branching (HB) channels were significantly lower than in the other two branching categories, while the overall distribution of depth in the higher-branching channels maintained a high degree of consistency with the moderate-branching channels (MB), which partly explains why the HB channels are important habitats for fish spawning, nursery and baiting (lower flow velocity distribution with a wider range of depth). Based on the examination of the water surface width, the water surface width may not be a limiting factor for fish habitat within braided rivers. Simulation of the hydrodynamic parameters of the fish-spawning grounds revealed that the average cross-sectional flow velocity and water depth fluctuated the least at different flows during the fish-spawning period for the HB channels. By counting the hydraulic parameters of the spawning grounds during the spawning period, it can be seen that the most preferred flow velocity for fish in the braided river in the study section was 0.1-0.4 m/s, and the water depth was 0-1.2 m. This article analyses the characteristics of the hydraulic parameters of the braided river and provides theoretical support for the restoration of fish habitats in braided rivers.

The Clarence River (New South Wales, Australia) was the main transport corridor for the sugar cane industry operating in the area from the 1860s to the 1970s. Using archaeological, documentary and oral historical resources we explore some of the anthropogenic impacts of this industry upon river channels and hydrology, in particular through the deliberate abandonment of obsolete vessels. These deliberately discarded former cane barges have been used as erosion control devices in several areas around the Harwood Island sugar mill, resulting in the accumulation of sediments and the establishment of mangrove environments in what were degraded areas.

A poor understanding of factors leading to species decline can result in inefficient or ineffective species restoration. Endangered Colorado Pikeminnow ( Ptychocheilus lucius) was nearly extirpated from the San Juan River, NM, USA and recent efforts to reestablish the species via hatchery augmentation of juveniles has yet to reach the targeted number of adults in the system. To assess how changes to the river’s food web could be limiting reestablishment of this top predator, we used stable isotope (δ 13C and δ 15N) signatures of the fish community pre- (museum specimens) and post river regulation with coincident extirpations and invasions. Following river regulation, four of five community-wide trophic structure metrics used to quantify resource use diversity were reduced and species turnover likely had little effect per se. For species sampled in both time periods, shared trophic resources generally increased (mean niche overlap = +35.7%). However, Colorado Pikeminnow experienced a large decrease in niche breadth (-72%) and diet mixing models suggested a shift from piscivory towards insectivory in contemporary collections. Our results suggested an overall reduction in basal resource availability after river regulation. We suggest increased reliance on similar resources may be limiting fish prey for Colorado Pikeminnow, ultimately contributing to the slow and limited reestablishment in the San Juan River. This study adds to the growing body of knowledge provided by museum specimens and stable isotope analyses to identify food-web dynamics that are a departure from historical conditions which can provide novel information critical to imperiled species management in modified systems.

Mapping fluvial hydromorphology is an important part of defining river habitat. Mapping via field sampling or hydraulic modelling is however time consuming, and mapping hydromorphology directly from remote sensing data may offer an efficient solution. Here we present a system for automated classification of fluvial hydromorphology based on a deep learning classification scheme applied to aerial orthophotos. Using selected rivers in Norway, we show how surface flow patterns (smooth or rippled surfaces versus standing waves) can be classified in imagery using a trained convolutional neural network. We show how integration of these classified surface flow patterns with information on channel gradient, obtained from airborne topographic LiDAR data, can be used to compartmentalize the rivers into hydromorphological units that represent the dominant flow features. Automated classifications were consistent with those produced manually. They were found to be discharge-dependent, showing the temporally dynamic aspect of hydromorphology. The proposed system is quick, flexible, generalizable, and free from researcher-subjectivity. The deep learning approach used here can be customized to provide more detailed information on flow features, such as delineating between standing waves and advective diffusion of air bubbles/foam, to provide a more refined classification of surface flow patterns, and the classification approach can be further advanced by inclusion of additional remote sensing methods that provide further information on hydromorphological features.