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Preview: Regulated Rivers: Research & Management

River Research and Applications



Wiley Online Library : River Research and Applications



Published: 2018-01-01T00:00:00-05:00

 



Nature-like fishways as compensatory lotic habitats

2018-01-18T22:54:26.679299-05:00

Damming of rivers disrupts migration of fish and results in lotic habitats being both scarcer and spaced further apart, ultimately affecting riverine fish communities. Nature-like fishways are often designed as bypass channels, constructed with natural materials that reroute part of the water around weirs and dams, restoring longitudinal connectivity as well as forming nature-mimicking habitats. We evaluated the potential of such bypasses to function as compensatory lotic habitats by comparing fish fauna in 23 bypasses to adjacent lotic stream habitats in a same-river pairwise design. Bypasses were narrower, shallower, and less shaded than adjacent stream habitats, but very few significant differences could be detected in the fish communities, indicating the potential of such nature-like fishways to constitute compensatory lotic habitats for fish. Analyses also indicated how bypass design may be altered to favour or disfavour certain target species. Generally, narrower and shallower bypasses with high gradient favoured brown trout (Salmo trutta), whereas European eel (Anguilla anguilla) were more abundant at sites with lower gradient. Finally, to increase the impact of these compensatory habitats on running water ecosystems, we suggest that the size of bypasses should be maximized in areas where natural stream habitats have been lost.



Effects of hydropeaking on benthic invertebrate community composition in two central Norwegian rivers

2018-01-18T21:56:51.765602-05:00

Hydropower regulations can have dramatic impacts on river ecological communities. The operation of hydropower stations is related to power demands, but their releases in the receiving water body causes sudden changes in flow, which in turn affect the biota. The effects of such flow variations on benthic invertebrates is not fully understood. Here, we studied the effects of duration and intensity of hydropeaking on benthic invertebrates in two rivers over a 3.5-year period. We used both quantitative (Surber) and semiquantitative (kick samples) sampling methods to compare the ramping zone with the permanently water covered zone downstream of the hydropower plant, and with corresponding unaffected upstream areas. The ramping zone had a different invertebrate community composition and lower benthic density than other areas, especially after hydropeaking. Mayflies and chironomids were most negatively affected by hydropeaking and oligochaetes largely unaffected. Chironomids and the mayfly Baetis rhodani were able to recolonize the ramping zone and almost reach densities similar to deeper areas within 48 days following hydropeaking. The relative abundance of filter feeders tended to increase and gatherers/collectors tended to decrease from the ramping zone towards the deep, permanently water covered areas. In corresponding areas upstream of the power plant, the relative abundance of different functional feeding groups was the same in the mid-channel and shore sites. Our study shows that hydropeaking has clear impacts on the functional structure of benthic invertebrates below the power plants. The ecological impact of hydropeaking on invertebrate communities should thus be taken into account, for example, by reducing the amplitude and duration of flow fluctuations.



Underwater video monitoring of fish passage in the Mekong River at Sadam Channel, Khone Falls, Laos

2018-01-17T00:56:22.703609-05:00

This paper describes the first measurement of fish passage in the Mekong River at Khone Falls. The site was in the Sadam Channel, which was modified in 2013 to improve fish passage and mitigate closure of Sahong Channel for the Don Sahong hydropower project. Underwater cameras recorded 149 hr of discontinuous video from January 18 to 26, 2015, which showed a major upstream migration by small cyprinid fish. Daily catch surveys in the same channel showed most fish migrated on days when video records were almost complete. We used stratified hourly sampling to review 17% of the available video and counted 14,783 fish and identified 16 taxa. The most abundant species were Labiobarbus leptocheilus, Henicorhynchus lobatus, and Henicorhynchus siamensis, and these fishes migrated almost exclusively during daylight. We calculated passage rates for West Sadam Channel from video samples and extrapolated those results to Sadam Channel, by assuming equivalent passage rates for both East and West Sadam Channels. This assumption was based on observations that fish were evenly distributed between both banks below the confluence, and they migrated close to each bank, so we assumed that there was an even split at the confluence and neither channel was preferred for upstream passage. Although channel modification improved fish passage efficiency, we estimated that artisanal fishers caught 79% of migrating fish in Sadam Channel, so fishing pressure remains the greatest risk to successful fish passage. Active fisheries management will be necessary to sustain and further improve passage efficiency in future.



Towards a systems approach for river basin management—Lessons from Australia's largest river

2018-01-17T00:55:28.241298-05:00

Globally, large river systems have been extensively modified and are increasingly managed for a range of purposes including ecosystem services and ecological values. Key to managing rivers effectively are developing approaches that deal with uncertainty, are adaptive in nature, and can incorporate multiple stakeholders with dynamic feedbacks. Australia's largest river system, the Murray–Darling Basin (MDB), has been extensively developed for shipping passage, irrigation, hydroelectric development, and water supply. Water development in the MDB over the last century resulted in overallocation of water resources and large-scale environmental degradation throughout the Basin. Under the pressure of a significant drought, there was insufficient water to supply critical human, environmental, and agricultural needs. In response, a massive programme of water reform was enacted that resulted in considerable institutional, social, and economic change. The underlying policy was required to be enacted in an absence of certainty around the scientific basis, with an adaptive management focus to incorporate new knowledge. The resulting institutional arrangements were challenged by a need to generate new governance arrangements within the constraints of existing state and national structures. The ongoing reform and management of the MDB continues to challenge all parties to achieve optimization for multiple outcomes, and to communicate that effectively. As large-scale water reform gains pace globally, the MDB provides a window of insight into the types of systems that may emerge and the challenges in working within them. Most particularly, it illustrates the need for much more sophisticated systems thinking that runs counter to the much more linear approaches often adopted in government.



How do instream flow increase and gravel augmentation impact biological communities in large rivers: A case study on the Upper Rhine River

2018-01-09T19:05:53.298049-05:00

Actions are being developed to address the adverse consequences of engineering works on large European rivers by developing and implementing restoration activities in order to enhance the functionality and biodiversity of fluvial hydrosystems. However, as has frequently been mentioned in the scientific literature, quantitative and qualitative evaluation of the project benefits, if any, and their sustainability are hindered by the difficulty in assessing the responses of aquatic and riparian communities to the methods employed. A case study was conducted on a by-passed section of the Upper Rhine River (France and Germany) to investigate the effects of instream flow increase and gravel augmentation on selected aquatic and riparian communities (macroinvertebrates, macrophytes, and riparian plants). This paper presents the results of a 6-year interdisciplinary, before-after control-impact design monitoring study. The complexity of the study lies in carrying out a separate assessment of the cumulative effects on a site-based, project-specific basis. The results showed that (a) the instream flow increase resulted in greater richness of macrophyte species in the newly created backwaters, (b) the artificial gravel bar favoured the recruitment of pioneer species, including invasive species, although gravel redistribution by floods prevented their development, and (c) gravel augmentation tended to promote the taxonomic richness of macroinvertebrate communities with the appearance of species adapted to the new substrate areas. These findings should help to fill the knowledge gaps in large-scale restoration and contribute key responses to the most frequently arising issues in this area, especially those concerning the efficiency and sustainability of river restoration projects.



Influence of tributaries on the longitudinal patterns of benthic invertebrate communities

2018-01-08T19:40:36.929664-05:00

There has been little effort to understand how tributaries influence mainstem rivers at large scales beyond the immediate influence of the tributary and downstream of the mixing zone. Such knowledge is needed to create breaks in stream networks that can aid in the classification of stream valley segments and conservation studies that rely on the delineation of zones. We use benthic invertebrate assemblages to infer longitudinal gradients and discontinuities and relate these patterns to confluence symmetry ratio (CSR; the size ratio of the tributary basin to the mainstem basin upstream of the confluence). In addition, we briefly explore reach and catchment-scale environmental influences. We found evidence for both gradual and abrupt longitudinal changes in benthic invertebrate communities. There was not a smooth continuous gradient but a sawtooth pattern with an overarching trend. Two major discontinuities were found: one associated with a large CSR = 0.74 and reach scale factors including predominance of sand and an abundance of benthic organic matter that provided a unique habitat; and a second associated with a large CSR = 0.64 and a transition from coarse textured morainal deposits to glaciolacustrine deposits. There were synchronous additions of some benthic invertebrates (e.g., Eukiefferiella brehmi, Antocha, Hydropsyche morosa, and Oligochaeta) showing an affinity for downstream reaches, whereas others showed an affinity for headwater reaches (e.g., Simulium tuberosum, Baetis tricaudatus, and Micropsectra). Benthic invertebrate communities were driven by a combination of confluence symmetry ratio, landscape, and reach scale factors that can confound interpretation.



The bright side of linking science and management in large river ecosystems: The Hudson River case study

2018-01-08T19:40:25.062236-05:00

Large river ecosystems (LRE) are important components of global cycles, influence large parts of the earth's surface, and provide many services in support of human civilization. However, understanding their condition, functioning, and trajectory of change is difficult in part due to their scale and diversity of forcing factors but also due to multiple and potentially conflicting human uses. Although these challenges are generally applicable and probably true to some degree for any large river ecosystem, there are also attributes of LRE that foster scientific understanding, can lead to knowledge-based management, and may catalyse their interaction. The absolute size of LRE means they will be complex, unique and the water quality, physical character, or habitat availability at any particular point may be the result of drivers acting further up the basin or legacies from previous times. On the bright side however, their absolute size also means there will be existing information on many important features, not least land cover and hydrology. Moreover, it is highly likely there will be a sizeable human population in the basin that derives some benefits from the river even if just in a narrow anthropocentric fashion and so there will be some motivation for understanding characteristics and potential change. Large size also suggests that the LRE will be viewed (perhaps with some basis in law) as a national or regional resource making it (at least nominally) worthy of study and management. I provide some examples of how science and management of the Hudson River in New York, USA, have benefitted from some of these perceived difficulties perhaps offering optimism for application in other systems.



Kayak drifter surface velocity observation for 2D hydraulic model validation

2018-01-04T18:46:30.80308-05:00

Advances in remote sensing, informatics, software, and microprocessors enable meter-resolution two-dimensional (2D) hydrodynamic models that produce nearly a census of ecohydraulic conditions over long river segments with 105 to 108 computational elements. It is difficult to test statistical and spatial model performance at such scope using fixed-point velocity measurements, because field methods are so expensive, laborious, slow, and restricted by safety factors. This study evaluated low-cost water surface particle tracking by kayak with real-time kinematic GPS for 2D model validation using 7.2 km of the lower Yuba River in California. Observed flows were between 15 to 140 m3/s, which were in-channel up to and including bankfull conditions. The coefficients of determination between 5,780 observations and 2D model predictions were 0.79 and 0.80 for velocity magnitude and direction, respectively. When surface speed was downscaled and compared to modelled depth-averaged velocity, median unsigned difference was 15.5%. Standard hydrological model performance metrics affirmed satisfactory validation. Surface tracking provided the novel benefit of enabling validation of velocity direction, and that testing found satisfactory performance using all metrics. Having 10 to 1,000 times more data enables robust statistical testing and spatial analysis of both speed and direction, which outweighs the loss of depth-averaged data. Both fixed-point and kayak particle tracking methods are useful tools to help evaluate 2D model performance.



Complexity and trends analysis of hydrometeorological time series for a river streamflow: A case study of Songhua River Basin, China

2017-12-20T00:21:06.54395-05:00

In China's national economic growth, an important role is being played by the Songhua River because of the river's abundant resources and natural conditions. Therefore, study of hydrometeorological time series is very important to understand the basin behaviour. This research uses the snow cover data derived from MODIS, streamflow, and meteorological records in the Songhua River Basin to evaluate similarity, complexity, and trends in the snow cover, temperature, precipitation, and streamflow. In this paper, we suggest a new method of ranking the statistics symbolic sequences to examine the degree of similarity (distance measurement) between meteorological stations and compare it with non-parametric correlation methods and also investigate the deviations in the complexity of a hydrometeorological time series. Information-based similarity index and multiscale entropy confirm that the hydrometeorological time series of different stations have self-similarity and abundant complexity. Wavelet entropy is also used to investigate the basin behaviour by taking streamflow records and population. It is found that with the increase in population and urbanization, the complexity values are increased. The results also exhibit that due to increase in urbanization, it affects the hydrological process and nature of environment resulting in complex catchment behaviour. Furthermore, the streamflow trend results displayed significant decline (22.21 m3/s × year−1) in the Songhua River. The results also indicated that the seasonal snow cover trend has no impact on changes of the streamflow. However, the decline of the streamflow may be influenced by the significant human activity upstream of the Songhua River.



The case of extreme hydrologic drought downstream from reservoirs in Quebec (Canada): The intermittent flow

2017-12-13T03:41:32.290657-05:00

Intermittent flow is a hydrological phenomenon observed at all latitudes. This phenomenon is characterized by a complete or partial interruption of flow in time and/or space in channels. In Quebec, even though the climate is humid, intermittent flow occurs downstream from headwater reservoirs. These reservoirs store water during spring and summer (from April to September) and release it in winter to supply hydroelectric power plants located downstream. During the water storage period, intermittent flow is common (discharges falling to <1 L/s/km2). The goal of the study is to analyse the characteristics (magnitude, frequency, and duration) of this flow downstream from 3 reservoirs built in the Saint-Maurice River watershed, during the period from 1930 to 2010. Downstream, the contribution (magnitude) of intermittent flow to total altered flow is less than 2%. Intermittent flow frequency ranges from 24 to 65 days per year downstream from the 3 reservoirs. As far as duration is concerned, intermittent flow persists on average from 40 to 128 consecutive days. Canonical correlation analysis revealed that the frequency of intermittent flow is correlated with the North Atlantic Oscillation and its magnitude and negatively correlated with the Southern Oscillation.



What factors affect the suspended sediment concentrations in rivers? A study of the upper Warta River (Central Poland)

2017-12-01T05:07:02.841328-05:00

The suspended sediment concentration (SSC) of the Warta River was analysed using data collected at the Sieradz gauging station (Central Poland) during the period of 1961–1980. The aim of the study was to characterize the trend in the suspended sediment transported over this multi-annual period and search for possible correlations between the suspended sediment values and the discharge and thermal seasonality factors. This study also investigated whether the SSC is affected by anthropogenic factors. The SSC in the river water increased over the analysed 20-year period. It was caused mainly by the training works in the Warta valley upstream of Sieradz and the opening of the Bełchatów lignite mine. No direct relationship between the SSC and fluctuations in the discharge was noted. A connection existed between the SSC and ice phenomena on the river. The river ice breakup was often coincident with increases in SSC; however, the SSC increased rapidly during the freezing of the river. There was also a positive correlation between the SSC and the temperature of the water during the summer half-year, which resulted from the growth of phytoplankton. This process was supported by the general warming trend observed in the river water and by an increase in the quantity of nutrients noted since the early 1970s. It is worth emphasizing that the relationships established between the SSC and the studied factors are not always unequivocal and repetitive. It follows that, as a rule, the SSC is influenced by more factors than are actually considered in this study.



To swim or to jump? Passage behaviour of a potamodromous cyprinid over an experimental broad-crested weir

2017-11-17T04:10:56.813695-05:00

Physical stressors, such as man-made obstacles, are considered one of the main causes that negatively affect freshwater fish. Even small weirs may impact fish populations, including potamodromous cyprinids, by partially or totally blocking upstream migratory movements. Some studies have addressed the effect of key hydraulic parameters on upstream movements past small weirs, but little is known on how these parameters interact to induce swimming or jumping behaviour in negotiating such obstacles. This study aims to evaluate the passage behaviour (swimming vs. jumping) of Iberian barbel (Luciobarbus bocagei), a potamodromous species, over an experimental small broad-crested weir, considering the effect of different plunge pool depths (D), waterfall heights (H), and weir discharges (Q). Results revealed that passage behaviour was highly dependent on combinations of plunge pool depths and waterfall heights. Barbel navigated most configurations by swimming (overall outcomes: 81.5% swimming vs. 18.5% jumping), except the ones with the higher waterfall heights (25 cm) tested. Therefore, higher waterfalls proved to be preponderant in the switching of passage behaviour from swimming to jumping. Regarding the discharge over the 1-m-wide weir (overall outcomes: 85% swimming vs. 15% jumping), contrary to what was expected, there was no evidence that passage behaviour was discharge-related, for the range of discharges tested (25–100 L/s). These results are useful to identify potential migration obstacles and should be taken into consideration in river restoration projects and when designing fishways for potamodromous cyprinids.



A novel SON2-based similarity index and its application for the rationalization of river water quality monitoring network

2017-11-17T04:06:56.796934-05:00

In this paper, a novel self-organizing network (SON) based similarity index and its application for the optimization of sampling locations in an existing river water quality monitoring network (WQMN) is presented. A rationalization of the River Danube WQMN on its stretch through Serbia was performed using the proposed SON2-based similarity index. A high-dimensional dataset was used, which is composed of 18 water quality parameters that were collected during the period 2002–2010 at 17 monitoring locations. The SON-based seasonal classification that divides 12 months into the cold, moderate, and warm seasons was employed, whereas its second application on each seasonal class yielded subclasses that were used to compare the monitoring locations. The obtained SON2-based similarity index can be utilized for analysing seasonal variations, as well as overall similarities among neighbouring sites. Based on the calculated similarities of locations and characteristics of the River Danube basin a rationalized WQMN, which uses 30% less monitoring sites, has been proposed.



Stakeholder-enhanced environmental flow assessment: The Rufiji Basin case study in Tanzania

2017-09-27T22:00:30.334448-05:00

Environmental flows are now a standard part of sustainable water management globally but are only rarely implemented. One reason may be insufficient engagement of stakeholders and their priority outcomes in the environmental flow-setting process. A recent environmental flow assessment (EFA) in the Kilombero basin of the Rufiji River in Tanzania concentrated on a broad-based investigation of stakeholders' use and perceptions of the ecosystem services provided by the river as a framework for the assessment of flow regimes that would maintain them. The EFA process generally followed the Building Block Methodology but within an enhanced stakeholder engagement framework. Engagement began with the involvement of institutional stakeholders to explain the purpose of the EFA and to elicit their priority outcomes. Extensive interactions with direct-use stakeholders followed to investigate their uses of and priorities for the rivers. Results were used by the EFA specialist team in choosing flow indicators and defining measurable environmental objectives. The specialists then met to reach a consensus of the flow requirements. The EFA results were lastly reported back to stakeholders. During the Kilombero EFA, we learned that stakeholders at all levels have a good awareness of the natural services provided by a healthy river and can contribute to the setting of environmental objectives for the rivers and floodplain. These can be factored into the biophysical assessments of river flows required to maintain habitats, processes, water quality, and biodiversity. It is therefore important to allocate significant resources to stakeholder engagement. It now remains to be seen if enhanced stakeholder engagement, including the increased understanding and capacity built among all stakeholders, will increase support for the implementation of the recommended flows.



Effect of morphologic and hydraulic factors on hysteresis of sediment transport rates in alluvial streams

2017-08-30T02:45:41.069218-05:00

Unsteady flow events, such as those caused by extreme precipitation events or reservoir flushing, can result in hysteresis of sediment transport rates in alluvial streams. Over the past 20 years, several experimental studies have been conducted that monitored sediment transport rates in response to unsteady flow event hydrographs. Previous literature has identified numerous morphological and hydraulic factors, including sediment composition, sediment supply, hydrograph characteristics, bed morphology, and mode of sediment transport, that affect hysteresis of sediment transport rates. This manuscript reviews and evaluates the degree of influence of these factors on hysteresis in order to develop a comprehensive understanding of the dominant factors responsible for this phenomenon. This systematic evaluation suggests that the mode of sediment transport and sediment composition are the most dominant factors influencing the resulting type of hysteresis. Further research is required to investigate the effect of other factors, such as non-uniform stream bed composition and planform geometry, and develop predictive models to assess the sediment transport response to unsteady flow events.



Linking ecological science with management outcomes on New Zealand's longest river

2017-07-21T05:27:40.025255-05:00

New Zealand's Waikato River has had a short but intense history of development, primarily through land-use change and flow regulation in the upper river, and in the lower river through flood control works, non-native species invasion, and land-use intensification. The river undergoes sharp transitions across montane-flood plain-coastal environments over a short distance and under similar climate. Together with specialized life-history requirements of many native fish, these features provide valuable insights into large river ecology and management. Testing approaches to determine outcomes of water quality changes have highlighted the value of functional indicators over traditional biotic measures for monitoring anthropogenic impacts. Initiatives to enhance native fish populations in the lower river have included remediation of migration barriers to improve access to tributary habitat, enhancement of tidal spawning habitat, and traps and gates to limit movement of large pest fish into flood plain lakes for spawning. This example of a southern temperate large river system highlights the importance of recruitment habitat and connectivity for native fish communities dominated by migratory species. Their slender bodies provide opportunities to create semipermeable barriers that enable access to flood plain habitats while restricting larger invasive fish. Recent initiatives have increased momentum to restore the ecological health of this river, but the underpinning science to guide priority actions is often lacking, and there is limited monitoring over the scales and time frames required to evaluate effectiveness.



Issue Information

2018-01-17T18:37:53.538947-05:00

No abstract is available for this article.



Soundpeaking – Hydropeaking induced changes in river soundscapes

2017-11-28T19:05:31.060745-05:00

Underwater soundscapes and their unique acoustic signatures are mainly generated through movement of streambed sediment, subsequent particle collisions, and turbulence created by water flowing over submerged obstructions such as rocks and woody debris. This study characterized river soundscapes in Alpine rivers of Trentino, (North East Italy) with the combined use of hydrophones and a new microelectricalmechanical systems based device (Hydroflown) that is capable of measuring particle velocity components of the sound field. Pool and riffle habitats affected and unaffected by hydropeaking were characterized in terms of their particle velocity and sound pressure levels across 10 octave bands (acoustic signature) to assess temporal variations in overall sound levels, changes in frequency composition, and relationship to hydromorphological habitat parameters. Data revealed that soundscapes affected by hydropeaking are highly homogenized, and sound pressure levels are strongly correlated with turbine discharge, which results in rapid, multiple-fold spikes in low frequency amplitude levels within the typical hearing range of common teleost fish species. The outcomes of this study provide the basis for further examination of the resulting behavioural and physiological responses of organisms to anthropogenic changes in river soundscapes.



Abiotic factors controlling the seasonal and spatial patterns of phytoplankton community in the Tigris River, Turkey

2017-10-09T06:21:22.414732-05:00

In this study, the seasonal and spatial dynamics of the phytoplankton community in the Tigris River (Turkey) and the relationships with environmental factors were analysed. Bacillariophyta were the most important taxonomic group both in terms of abundance and species number. Phytoplankton abundance increased from winter to autumn associated with a decline in discharge and an increase in nutrient concentrations and water temperature. There was a downstream increase in phytoplankton abundance and species number in the river. Similar spatial and seasonal patterns were observed in chlorophyll-a concentration and phytoplankton abundance. Redundancy analysis and correlation analysis revealed that chemical variables, mainly nutrients were the most important abiotic factors controlling phytoplankton abundance in the Tigris River.



Characterizing aquatic habitats for long-term monitoring of a fourth-order, regulated river in the Pacific Northwest, USA

2017-11-30T21:20:58.833461-05:00

A pragmatic approach to the long-term monitoring of rivers leverages available information with targeted field investigations to address key uncertainties relevant to management decisions. An over-arching management issue for many rivers is how reservoir operation affects the amount and location of in-channel sediment and the resulting distribution of aquatic habitats. We integrate remotely acquired and field-survey morphologic data for the Cedar River, Washington, to constitute the current status of aquatic habitats and benchmarks for long-term monitoring that will inform streamflow management. Four key habitats (river edge, side channels, riffles, and pools) are feasible to monitor with high-resolution aerial imagery, a longitudinal profile of the river, and a side channel inventory, but full characterization of the functional differences within these habitats requires additional information. Habitat use information such as redd surveys will continue to be important for long-term monitoring where it cannot be inferred reliably from physical habitat characteristics.



Responses of fishes and lampreys to the re-creation of meanders in a small English chalk stream

2017-10-09T06:26:07.236483-05:00

River rehabilitation initiatives have become commonplace in European water courses as a result of European Union Water Framework Directive requirements. However, the short-term responses of fishes to such work have thus far been varied, with some river rehabilitation efforts resulting in demonstrable improvements in diversity and size structure, whereas others have resulted in little or no change. Electrofishing and channel character surveys were conducted annually between 2009 and 2014 on a reach of the River Glaven (North Norfolk, UK) before and after rehabilitation work (embankment removal in 2009 and re-meandering in 2010) as well as on a control reach immediately upstream. To assess the effects of rehabilitation work, before-after-control-impact analysis tested for changes in channel character (geomorphology, substratum composition, and mesohabitat structure) and in fish species richness, relative abundance, population density, and size structure (calculated after fish data entry into the UK Environment Agency's National Fisheries Population Database). Following re-meandering work (i.e., treatment), habitat heterogeneity and depth variation increased in the treatment reach, but fish responses were not significant except for biomass and density increases of brown trout Salmo trutta and abundance decreases of European eel Anguilla anguilla, in the treatment but not the control reach. These results are consistent with comparable river rehabilitation initiatives elsewhere, and they suggest that larger-scale rehabilitations are probably needed to produce greater increases in fish density and diversity. It is recommended that future rehabilitation initiatives address catchment-scale factors that can enhance ecosystem recovery, for example, removal of barriers to colonization, and increases in connectivity and water quality issues linked to eutrophication, elevated fine sediment inputs, and various pollutants.



Pacific lamprey recolonization of a Pacific Northwest river following dam removal

2017-10-06T07:25:30.56612-05:00

Recolonization of Pacific lampreys Entosphenus tridentatus into historically used freshwater habitats in the United States Pacific Northwest was evaluated in the White Salmon River basin after removal of Condit Dam. Pacific lamprey population declines are of concern, and passage barrier removal is often recommended for conservation. Condit Dam on the White Salmon River in Washington was a complete barrier to fish migrating upstream for nearly 100 years, was breached in 2011, and was removed by 2012. Distribution of larval Pacific lampreys was estimated before and after removal of Condit Dam using either backpack or deepwater electrofishing. Larval detection probabilities were calculated for the basin, and sample efforts were refined to ensure at least 80% confidence that larvae were absent when not detected. Pacific lampreys were not present upstream of Condit Dam before it was removed but were present in areas downstream of the dam. After dam removal, Pacific lamprey larvae were collected upstream of the former dam site from four reaches of the mainstem White Salmon River, indicating a recent recolonization event. Pacific lampreys were absent from the river mouth area before the dam was removed but were found in newly created habitat at the mouth after dam removal. Pacific lampreys naturally recolonized the White Salmon River basin within a few years after dam removal. Removing dams and providing passage opportunity can allow Pacific lampreys to distribute into vacant areas and may help reverse population declines.



Mortality of silver eels migrating through different types of hydropower turbines in Lithuania

2017-10-06T07:15:21.053251-05:00

Hydropower plants (HPP) are considered to be one of the major threats to the survival of European eels when they migrate downstream along inland water bodies during the early part of their annual journey to the spawning area in the Sargasso Sea. There are 98 HPPs in Lithuania and thousands throughout Europe. Numerous studies describe HPP induced mortality rates among European eels as variable depending on local, environmental, and technical factors. This heterogeneity in effect complicates theoretical extrapolation to eel mortality arising from specific types of HPP, necessary for effective management of local stocks. Silver eel mortality was estimated for 4 different HPPs in Lithuania. Mortality was estimated using RFID (Radio Frequency Identification, passive integrated transponders) tags and acoustic telemetry in a large HPP (>100 MW) with Kaplan turbines, a small HPP (<1 MW) with a Kaplan turbine and a fish passage, and for the first time in two small HPPs (<1 MW) with CINK turbines. The results supported a hypothesis that the mortality rate of migrating eels depends mainly on the type and size of the turbine. HPP induced mortality varied from 100% in a small CINK turbine down to 25% in the large HPP with Kaplan turbines. The importance of simple mitigation measures was highlighted by 34% of all tagged eels bypassing one of the HPP via an adjacent fish passage constructed for upstream migration of salmonids. The observed differences in mortality provide essential information for long term strategies designed to restore depleted eel populations in Lithuania and other European countries.



Habitat fragmentation has interactive effects on the population genetic diversity and individual behaviour of a freshwater salmonid fish

2017-10-26T23:45:42.623435-05:00

Sufficient genetic diversity can aid populations to persist in dynamic and fragmented environments. Understanding which mechanisms regulate genetic diversity of riverine fish can therefore advance current conservation strategies. The aim of this study was to investigate how habitat fragmentation interacted with population genetic diversity and individual behaviour of freshwater fish in large river systems. We studied a population of the long-distance migratory, iteroparous freshwater salmonid European grayling (Thymallus thymallus) in south-eastern Norway. Genotyping (n = 527) and radio-tracking (n = 54) of adult fish throughout a 169-km river section revealed three major migration barriers limiting gene flow and depleting genetic diversity upstream. Individuals from upstream areas that had dispersed downstream of barriers showed different movement behaviour than local genotypes. No natal philopatry was found in a large unfragmented river section, in contrast to strong fidelity to spawning tributaries known for individuals overwintering in lakes. We conclude that (a) upstream sub-populations in fragmented rivers show less genetic variation, making it less likely for them to adapt to environmental changes; (b) fish with distinct genotypes in the same habitat can differ in their behaviour; (c) spawning site selection (natal philopatry) can differ between fish of the same species living in different habitats. Together this implies that habitat loss and fragmentation may differently affect individual fish of the same species if they live in different types or sections of habitat. Studying behaviour and genetic diversity of fish can unravel their complex ecology and help minimize human impact.



Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River, Brazil

2017-10-26T21:15:58.407971-05:00

Flow-dependent fish specialists require specific conditions for reproduction, so the success and reproductive intensity of these animals are determined by the flood regime. Thus, this study investigated the spatial and temporal reproductive patterns of fish, especially migratory Prochilodus species (flow-dependent specialists) in an unusual period of low flow in the Pará River sub-basin, one of the main tributaries of the upper São Francisco River. For this, ichthyoplankton collections were carried out between November 2013 and February 2014. Data were analysed considering the spatial and temporal variations in density of eggs and larvae for the upper, middle, and lower portions of the Pará River sub-basin, and correlating this to some environmental variables. The results showed that the small headwater stretch of the Pará River is one relevant spawning area for migratory fish species. However, this area is isolated by the Cajuru reservoir, which makes it uncertain the recruitment of these embryos, due to interruption of natural drift between spawning/nursery areas caused for reservoirs. Larvae of newly hatched migratory species found in tributaries of the lower Pará River sub-basin also indicate these species use these tributaries as spawning grounds and migratory routes. The period in which the research was conducted represented the most atypical low flow, one in the last 75 years, resulting in the low variability in the environmental parameters. Although few parameters increased briefly in this low flow period influenced by greater rainfall in December, this precipitation was possibly responsible for the final gonadal maturation and spawning of migratory species.



How much groundwater can we pump and protect environmental flows through time? Presumptive standards for conjunctive management of aquifers and rivers

2017-08-25T04:07:39.204678-05:00

Groundwater is a critically important source of water for river, wetland, lake, and terrestrial ecosystems, yet most frameworks for assessing environmental flows have ignored or not explicitly included the potential impacts of groundwater pumping on environmental flows. After assessing the processes and existing policies for protecting streamflow depletion from groundwater pumping, we argue that a new groundwater presumptive standard is critical as a placeholder to protect environmental flows in rivers lacking detailed assessments. We thus extend the previous presumptive standard to groundwater pumping, a different and important driver of changes to streamflow. We suggest that “high levels of ecological protection will be provided if groundwater pumping decreases monthly natural baseflow by less than 10% through time.” The presumptive standard is intended to be a critical placeholder only where detailed scientific assessments of environmental flow needs cannot be undertaken in the near term. We also suggest a new metric, the environmental flow response time, that allows water managers to quantify the timescales of the impacts of groundwater pumping on the loss or gain of environmental flows.



Building Hydrologic Foundations for Applications of ELOHA: How Long A Record Should You Have?

2017-03-16T00:31:16.77729-05:00

The Ecological Limits of Hydrologic Alteration framework for making regional assessments of environmental flows requires a ‘hydrologic foundation’ of flow data for current and undeveloped conditions. This raises the question how long a record is needed for an adequate hydrologic foundation? The answer depends on the variance in the flow record and on how much uncertainty is tolerable in metrics developed from the flow data. Copyright © 2017 John Wiley & Sons, Ltd.