Hydraulic Diversity Research Articles

Habitat associations of the Rio Grande Silvery Minnow, an endangered desert river fish, from a retrospective analysis based on a period of high abundance

AbstractObjectiveCharacterizing habitat associations is useful to aid in understanding the habitat requirements of native fishes, particularly those of conservation concern. Our study objective was to characterize mesoscale habitat associations of the only remaining wild population of the Rio Grande Silvery Minnow Hybognathus amarus (a federally endangered desert river fish), and provide comparisons with mesohabitat availability in the middle Rio Grande, New Mexico, from 1994 to 1996.MethodsWe collected fish monthly at two sites (separated by 160 km) near the northern and southern limits of the species' current range, and we recorded depth, velocity, substrate, and mesohabitat type for each habitat surveyed. Mesohabitat availability was recorded across 10 equally spaced and fixed transect lines at both study sites.ResultRio Grande Silvery Minnow most frequently occupied mesohabitats characterized by relatively shallow depths (≤25 cm) and low to near‐zero water velocities (≤15 cm/s). Statistical analyses indicated that mesohabitats occupied by the species were not the most frequently available at the study sites, suggesting a preference for shallow, low‐velocity habitats. Relatively high abundance of Rio Grande Silvery Minnow (n = 10,971), especially compared with post‐2009 abundance, facilitated robust characterization of species‐specific habitat associations.ConclusionComparison of our results with other studies of pelagic broadcast‐spawning leuciscids (pelagophils) endemic to the Great Plains and desert rivers of North America suggested broad overlap in mesohabitat associations among members of this reproductive guild. Our work contributes to a growing body of research aimed at conserving this declining reproductive ecotype of freshwater fishes and suggests that increasing hydraulic diversity through innovative management approaches (e.g., habitat creation, restoration of fluvial processes, and preservation of natural streamflow characteristics) will be crucial for their long‐term recovery and conservation.

Hydraulic variability of tropical forests is largely independent of water availability.

Tropical rainforest woody plants have been thought to have uniformly low resistance to hydraulic failure and to function near the edge of their hydraulic safety margin (HSM), making these ecosystems vulnerable to drought; however, this may not be the case. Using data collected at 30 tropical forest sites for three key traits associated with drought tolerance, we show that site-level hydraulic diversity of leaf turgor loss point, resistance to embolism (P50 ), and HSMs is high across tropical forests and largely independent of water availability. Species with high HSMs (>1 MPa) and low P50 values (< -2 MPa) are common across the wet and dry tropics. This high site-level hydraulic diversity, largely decoupled from water stress, could influence which species are favoured and become dominant under a drying climate. High hydraulic diversity could also make these ecosystems more resilient to variable rainfall regimes.

Coordination of plant hydraulic and photosynthetic traits: confronting optimality theory with field measurements.

Summary Close coupling between water loss and carbon dioxide uptake requires coordination of plant hydraulics and photosynthesis. However, there is still limited information on the quantitative relationships between hydraulic and photosynthetic traits.We propose a basis for these relationships based on optimality theory, and test its predictions by analysis of measurements on 107 species from 11 sites, distributed along a nearly 3000‐m elevation gradient.Hydraulic and leaf economic traits were less plastic, and more closely associated with phylogeny, than photosynthetic traits. The two sets of traits were linked by the sapwood to leaf area ratio (Huber value, v H). The observed coordination between v H and sapwood hydraulic conductivity (K S) and photosynthetic capacity (V cmax) conformed to the proposed quantitative theory. Substantial hydraulic diversity was related to the trade‐off between K S and v H. Leaf drought tolerance (inferred from turgor loss point, –Ψtlp) increased with wood density, but the trade‐off between hydraulic efficiency (K S) and –Ψtlp was weak. Plant trait effects on v H were dominated by variation in K S, while effects of environment were dominated by variation in temperature.This research unifies hydraulics, photosynthesis and the leaf economics spectrum in a common theoretical framework, and suggests a route towards the integration of photosynthesis and hydraulics in land‐surface models.

Instream wood increases riverbed temperature variability in a lowland sandy stream

AbstractThe (re)introduction of wood into rivers is becoming increasingly popular in river restoration and natural flood management schemes. While instream wood is known to promote geomorphic and hydraulic diversity, the impact of wood in driving surface water‐streambed exchange and subsequent streambed temperatures remains under‐researched, particularly in lowland rivers. We make use of the occurrence of three naturally occurring wood structures in a small, lowland sandy stream to determine how the presence of wood alters the geomorphic, hydraulic and thermal properties of the streambed. Our results show that instream wood plays an important role in promoting localized geomorphic complexity and thermal variation in the streambed. Locations within and immediately downstream of wood structures displayed the highest temperature range and daily variation. Locations upstream of wood structures were characterized by weaker daily temperature variation, while areas without wood displayed relatively stable streambed temperatures, with little diurnal fluctuation. Our study indicates that at this lowland site, instream wood increased seasonal temperature extremes (increased summer and decreased winter temperatures) at shallow depths by enhancing infiltration of warmer (summer) and colder (winter) surface water. This reduction in thermal buffering is likely to have significant implications to streambed‐dwelling communities and highlights that the thermal impacts of wood reintroduction in lowland rivers should be considered prior to river restoration.

Effects of an engineered log jam on spatial variability of the flow field across submergence depths

AbstractEngineered log jams (ELJs) are commonly implemented in rivers to diversify fish habitat, but few studies have verified the hydraulic benefits of ELJs by assessing their effects on the spatial variability and turbulence structure of the flow field. This field and modelling study assessed the effects of an ELJ on various characteristics of the flow field with increasing submergence. A 2‐D hydrodynamic model was applied to simulate flow conditions of the Calapooia River, Oregon, with an ELJ installed at the upstream end of a meander. Output was analyzed using coherent flow structure identification, maps of turbulence measures, and wavelet analysis along linear transects. At the highest discharge (62% ELJ submergence), more and smaller coherent flow structures were identified than in the no ELJ model run, but the magnitudes of turbulence metrics were unaffected. At low flow (1% jam submergence), the presence of the ELJ did not affect the number of coherent flow structures identified and produced only small and localized effects on turbulence measures. Taken together, results indicate that the ELJ primarily affected the flow field by increasing the number of flow structures at higher discharges and submergence depths. However, these changes were small and local to the ELJ. The limited effects of this wood jam over limited spatial scales raise questions about the conditions under which such structures increase hydraulic diversity and highlight the need for more detailed understanding on spatial variability around habitat structures with complex shapes.

How alternative urban stream channel designs influence ecohydraulic conditions

Streams draining urban catchments ubiquitously undergo negative physical and ecosystem changes, recognized to be primarily driven by frequent stormwater runoff input. The common management intervention is rehabilitation of channel morphology. Despite engineering design intentions, ecohydraulic benefits of urban channel rehabilitation are largely unknown and likely limited. This investigation uses an ecohydraulic modeling approach to investigate the performance of alternative channel design configurations intended to restore key ecosystem functioning in urban streams. Channel reconfiguration design scenarios, specified to emulate the range of channel topographic complexity often used in rehabilitation are compared against a reference ‘natural’ scenario using ecologically relevant hydraulic metrics. The results showed that the ecohydraulic conditions were incremental improved with the addition of natural oscillations to an increasing number of individual topographic variables in a degraded channel. Results showed that reconfiguration reduced excessive frequency of bed mobility, loss of habitat and hydraulic diversity particularly as more topographic variables were added. However, the results also showed that none of the design scenarios returned the ecohydraulics to their reference conditions. This indicate that channel-based restoration can offer some potential changes to hydraulic habitat conditions but are unlikely to completely mitigate the effects of hydrologic change. We suggest that while reach-scale channel modification may be beneficial to restore urban stream, addressing altered hydrology is critical to fully recover natural ecosystem processes.

Can catchment-scale urban stormwater management measures benefit the stream hydraulic environment?

The potential for catchment-scale stormwater control measures (SCMs) to mitigate the impact of stormwater runoff issues and excess stormwater volume is increasingly recognised. There is, however, limited understanding about their potential in reducing in-channel disturbance and improving hydraulic conditions for stream ecosystem benefits. This study investigates the benefits that SCM application in a catchment have on in-stream hydraulics. To do this, a two-dimensional hydraulic model was employed to simulate the stream hydraulic response to scenarios of SCM application applied in an urban catchment to return towards pre-development hydrologic pulses. The hydraulic response analysis considered three hydraulic metrics associated with key components of stream ecosystem functions: benthic mobilization, hydraulic diversity and retentive habitat availability. The results showed that when applied intensively, the developed SCM scenarios could effectively restore the in-stream hydraulics to close to natural levels. Compared to an unmanaged urban case (no SCMs), SCM scenarios yielded channels with reduced bed mobility potential, close to natural hydraulic diversity and improvement of retentive habitat availability. This indicates that mitigating the effect of stormwater driven hydrological change could result in significant improvements in the physical environment to better support ecosystem functioning. We therefore suggest that intensive implementation of SCMs is an important action in an urbanizing catchment to maintain the flow regime and hydraulic conditions that sustain the ‘natural’ stream habitat functioning. We propose that stormwater management and protection of stream ecosystem processes should incorporate hydraulic metrics to measure the effectiveness of management strategies.

Embolism resistance drives the distribution of Amazonian rainforest tree species along hydro-topographic gradients.

Species distribution is strongly driven by local and global gradients in water availability but the underlying mechanisms are not clear. Vulnerability to xylem embolism (P50 ) is a key trait that indicates how species cope with drought and might explain plant distribution patterns across environmental gradients. Here we address its role on species sorting along a hydro-topographical gradient in a central Amazonian rainforest and examine its variance at the community scale. We measured P50 for 28 tree species, soil properties and estimated the hydrological niche of each species using an indicator of distance to the water table (HAND). We found a large hydraulic diversity, covering as much as 44% of the global angiosperm variation in P50 . We show that P50 : contributes to species segregation across a hydro-topographic gradient in the Amazon, and thus to species coexistence; is the result of repeated evolutionary adaptation within closely related taxa; is associated with species tolerance to P-poor soils, suggesting the evolution of a stress-tolerance syndrome to nutrients and drought; and is higher for trees in the valleys than uplands. The large observed hydraulic diversity and its association with topography has important implications for modelling and predicting forest and species resilience to climate change.

Hydraulic diversity of forests regulates ecosystem resilience during drought.

Plants influence the atmosphere through fluxes of carbon, water and energy1, and can intensify drought through land-atmosphere feedback effects2-4. The diversity of plant functional traits in forests, especially physiological traits related to water (hydraulic) transport, may have a critical role in land-atmosphere feedback, particularly during drought. Here we combine 352 site-years of eddy covariance measurements from 40 forest sites, remote-sensing observations of plant water content and plant functional-trait data to test whether the diversity in plant traits affects the response of the ecosystem to drought. We find evidence that higher hydraulic diversity buffers variation in ecosystem flux during dry periods across temperate and boreal forests. Hydraulic traits were the predominant significant predictors of cross-site patterns in drought response. By contrast, standard leaf and wood traits, such as specific leaf area and wood density, had little explanatory power. Our results demonstrate that diversity in the hydraulic traits of trees mediates ecosystem resilience to drought and is likely to have an important role in future ecosystem-atmosphere feedback effects in a changing climate.

Linking geomorphic change due to floods to spatial hydraulic habitat dynamics

AbstractLarge flood events have the capacity to induce geomorphic restructuring that can impact riverine ecosystems. However, the detailed morphodynamics associated with infrequent, high‐magnitude floods are variable and difficult to capture, and more research is needed into potential relationships between geomorphic change, flow organization, and aquatic habitat dynamics. In this study, we focus on the reach‐scale response of a gravel bed river to a large flood, employing a combined remote sensing, field measurement, and numerical modelling approach to measure and interpret conditions bracketing the flood. Documented geomorphic turnover was extensive, reworking low‐flow channel patterns and causing widespread bank erosion and sediment deposition. This resulted in a shift to wide, shallow flow conditions in the post‐flood morphology and a loss of hydraulic diversity, particularly in ecologically important pool and riffle units identified using a fuzzy statistical classification method. These impacts are most evident at low flows; higher discharges display relatively similar hydraulic conditions despite geomorphic change. Smaller‐scale adjustments in the year following the flood appear to be driving the reintroduction of hydraulic diversity, which is interpreted as beneficial for in‐stream brown trout. Results from this study highlight the utility of applying flexible and objective remote sensing and modelling methods to measure fluvial change and provide a real‐world example that can inform broader theoretical understanding of large flood ecohydrology.

Assessing the impacts of reservoir expansion using a population model for a threatened riverine fish

Increasing demand for water and a desire for greater human water security has facilitated the global expansion of dams, with river regulation acknowledged as the leading cause of biodiversity decline in rivers. Native biota within these stressed systems are also impacted by reductions in habitat availability, decreased hydraulic diversity, increased sedimentation, movement barriers, invasive species and altered flows that may profoundly change the character and functioning of rivers. Construction or enlargement of reservoirs is continuing, and whilst downstream impacts are often considered, upstream impacts receive far less attention. We develop a population model to examine the impacts of reservoir expansion on a threatened riverine species in South Eastern Australia: the two-spined blackfish. We examined two processes, loss of breeding habitat and increased predation, directly linked to reservoir expansion as well as a broader threat of recruitment failure due to sedimentation. These threatening processes were assessed using the expected minimum population size as an indicator of risk. As is often the case for threatened species, limited data were used to parameterise the model and sensitivity analysis performed to assess the appropriateness of the model parameterisation. The outcomes indicate that the two-spined blackfish population is vulnerable to the loss of breeding habitat particularly if two-spined blackfish are unable to spawn in the larger dam, although this vulnerability is ameliorated if the whole river is accounted for. Including possible impacts from the resident trout population for the whole river, indicates the two-spined blackfish to be vulnerable to low level predation particularly if the trout population have a high growth rate. Population modelling has rarely been used to predict the consequences of dam construction on aquatic species/communities. The example here shows it to be a powerful tool to visualise and quantify potential biodiversity outcomes.

Ecohydraulic quantification of hydropeaking alterations by the use of hydrosignatures: a two scale approach

Hydropeaking flow fluctuations can affect aquatic fauna in various ways, depending on the river's morphological characteristics. We have developed a method for quantifying hydropeaking events by drawing up hydro­signatures. In a given flow, a hydrosignature quantifies the hydraulic diversity in any area/part of the aquatic space defined by either volume or area percentages on a depth and current velocity cross grid. When a two-dimensional hydraulic model for hydropeaking events is available, in a given reach, a comparative hydrosignature index can be calculated between the hydrosignature of the present time step and the initial hydrosignature, or between two hydrosignatures separated by a constant time interval. This method is useful to determine where major changes have occurred along a river, and to classify hydropeaking intensities. This approach can be used to analyse the level of hydraulic transformation of an entire reach but does not focus on the sides of the channel inhabited by the juvenile fish, which are particularly exposed to the effects of flow fluctuations. Juvenile habitats can be defined by suitability indexes which are attributed to hydraulic classes of hydrosignatures. The total weighted usable area of a juvenile habitat can be calculated at all the time steps in a hydraulic simulation by partitioning any hydraulic mesh into hydraulic classes. An index quantifying the damage to juvenile populations can then be defined by calculating the maximum change in habitat area observed during the hydropeaking event.

Grapevines hydraulic diversity – a critical consideration for irrigation management?

Grapevines hydraulic diversity – a critical consideration for irrigation management?

Behaviour of two small pelagic and demersal fish species in diverse hydraulic environments

ABSTRACTIncreased hydraulic diversity could be a means to promote fish diversity in rivers, but little is known of the behaviour of fish in hydraulic environments. This study concerns the behaviour of two species of small native Australian freshwater fish in variable hydraulic environments and ecological habit, with regard for (a) whether the apparent differences in swimming ability are reflected in the behaviour of the species and (b) the influence of changing hydraulic conditions on their patterns of use. An artificial channel was constructed with three levels of discharge, and fish were allowed to swim freely for 3 h without human interference. Their movements and habitat choices reflected their swimming ability and ecological habit, in that the stronger swimming, pelagic common galaxias (Galaxias maculatus) spent most time cruising in the open channel, preferring the turbulent inflow, and the demersal flat‐headed gudgeon (Philypnodon grandiceps) remained in the shelter of boulders. In effect, the galaxias changed their behaviour with changes in hydraulic conditions, while the gudgeons continued to use their preferred habitat. This study, therefore, provides support for the use of hydraulic diversity as a tool to foster fish diversity. Copyright © 2010 John Wiley &amp; Sons, Ltd.

A framework for evaluating the spatial configuration and temporal dynamics of hydraulic patches

ABSTRACTA framework for evaluating the spatial configuration and temporal dynamics of hydraulic patches was tested in a UK lowland river. Detailed hydraulic assessment was carried out at four discharges between 0.303 m3 s−1 and 1.410 m3 s−1 in a 56 m reach. Five hydraulic patches, as combinations of depth and mean column velocity, and the transitional zones between them were delineated using fuzzy cluster analysis. The composition and configuration of the hydraulic patch mosaic was quantified using spatial metrics. Results showed that the proportion, size, shape and relative location of hydraulic patches all varied with discharge, however intermediate flows appeared to support the most diverse hydraulic patch composition and configuration. This suggests the spatial influence of mesoscale bedforms on hydraulic patches is mediated by temporal variations in discharge. Transitional areas between hydraulic patches occupied a significant proportion of the reach at all flows (33–38%) and may function as in‐stream ecotones. The framework addresses the need for a quantitative, spatially explicit approach to hydraulic assessment which could be used to assess the implications of flow regulation and hydromorphological alteration on hydraulic diversity. Copyright © 2010 John Wiley &amp; Sons, Ltd.

The Effects of Hydraulic Heterogeneity on Tracer Transport in 3D Fractured Reservoir

Both hydraulic heterogeneity and topological one affect the tracer transport in real heterogeneous reservoir. Previous numerical studies for the fluid transport in 3D fractured medium focused on interpreting the topological heterogeneity, which were not able to analyze the combining effects by the local hydraulic heterogeneity of apertures. The authors developed a simple 3D discrete fracture set that had minimum geological heterogeneity but log-normal aperture distribution, and investigated the effect of hydraulic heterogeneity on the tracer transport using automatic quadrilateral meshing, finite element method, and streamline routing on irregular grids. Breakthrough curve assumed no retardation has a positively skewed characteristic, which confirms that the fluid transport is influenced by not only geological heterogeneity, but also pressure distribution and hydraulic diversity. A trajectory of streamlines and a distribution of residence time confirm that the tracer moves mainly in the direction of decreasing pressure gradient. The developed model can investigate the mixed effect of topological and hydraulic heterogeneity.

Hydraulic habitat composition and diversity in rural and urban stream reaches of the North Carolina Piedmont (USA)

AbstractThe differences between urban and rural streams regarding hydrological process, channel morphodynamics and ecosystem functioning have been highlighted by a number of studies in recent decades. The need to understand lotic ecosystem functioning in these environments at scales relevant to individual organisms has led to research focusing on hydraulic composition and structure over small areas of channel bed. In this study we map and analyze the hydraulic biotope composition of two urban and two rural stream reaches in the North Carolina (USA) Piedmont to determine if urban flow regimes and attendant channel modification processes might translate into important differences in hydraulic environment, and if so, what those differences are. Hydraulic biotope assemblages were found to vary only moderately in diversity per unit stream length between sites, but were distinctly different in composition. One important control on the differences between rural and urban streams was found to be the localized incision of urban channels into bedrock and saprolite. Resistant rock outcrop in the beds of urban streams creates rapid and riffle biotopes and long stretches of upstream pool habitat by impoundment. Urban reaches were found to be more homogeneous than rural reaches in hydraulic composition and were dominated by pools. Rural reaches, characterized by copious sandy alluvium in the bed, were dominated by runs or glides. Quantitative differentiation of biotopes based on four hydraulic indices generally yields coherent associations, although these may vary in content. Comparisons between hydraulic and biotic diversities suggest relationships favoring biotic functional group aggregation over species richness‐based indices of diversity. Because the majority of published hydraulic diversity analyses are based on coarse‐bed streams, further study of hydraulic diversity in streams with finer substrate is likely to be beneficial. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Managing river flows for hydraulic diversity: an example of an upland regulated gravel‐bed river

AbstractThe establishment of ecologically responsive environmental flow regimes is a challenge for river managers. Biological communities in river environments are partly constrained by hydraulic characteristics such as water depth, flow velocity and turbulence, so a key step in understanding the links between discharge and biotic response is to relate discharge and hydraulic character. This paper explores the nature of the relationship observed between discharge and hydraulic character in the Cotter River, Australia. Surface flow types or hydraulic patches, expressing a variety of hydraulic characteristics, were mapped in six reaches in this upland gravel‐bed river, during 18 different flow releases ranging from 8 to 260 ML per day. The distributions of these hydraulic patches were variable, both spatially and over time. The patches represent hydraulic habitats (of varying depth, flow velocity and turbulence) the diversity of which may contribute to in‐stream biodiversity. The study identified a range of flow releases that produce the greatest in‐stream diversity of hydraulic habitats, which, if included in managed release strategies, potentially benefits in‐stream biodiversity. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Natural variability in the distribution, loading and induced scour of large wood in sand‐bed forest streams

AbstractCharacteristics of large wood and its influence on bed scour and pool formation have been investigated in four sand‐bed forest streams in southeastern Australia. Sites included high‐energy bedrock‐confined streams near Sydney and medium to low energy partially terrace‐confined streams on the south coast of NSW and in East Gippsland, Victoria. Total large wood loadings were inversely correlated with bankfull specific stream power. At the two lower energy sites, up to 18% of the total large wood volume comprised Tristaniopsis laurina trees living within the channel. At all sites, the majority of large wood pieces were small in length and diameter. However, the overall large wood volume was dominated by larger pieces. At the two lower energy sites less than 3% of large wood pieces formed part of debris dams, the majority occurring as individual logs. Debris dams were absent from the higher energy sites. The length of channel classified as pool habitat and the amount of head loss over log‐steps were positively correlated with large wood loading. A greater proportion of large wood pieces was aligned parallel to the flow at the higher energy sites. Such characteristics significantly influenced the type and extent of pools present. Longitudinal, bedrock and boulder scour pools were dominant at the bedrock‐confined sites, while transverse scour pools, log‐step pools and debris dam pools were dominant at the less laterally confined sites. The log‐affected pools were significantly smaller, in terms of length and maximum depth, at three of the study sites, than the non‐log‐affected pools. However, this study indicates that reintroduction of large wood into sand‐bed streams will increase bed scour, pool formation and hydraulic diversity. Copyright © 2005 John Wiley &amp; Sons, Ltd.

The hydraulic impact and performance of a lowland rehabilitation scheme based on pool–riffle installation: the River Waveney, Scole, Suffolk, UK

AbstractPool–riffle installation is increasingly becoming the standard form of river habitat enhancement undertaken, largely for the benefit of fisheries. This study documents the effect of riffle installation on the morphological and hydraulic diversity of a low gradient engineered river. Despite their prevalence there have to date been few published studies of the impacts of these features on channel hydraulics, despite concerns as to their potential impact on flood levels. In this paper the impacts of the installation of gravel bedforms on water surface elevations and flow resistance are considered. The performance of the riffle–pool sequences is assessed against a set of criteria derived from the scientific literature. The analysis reveals that the gravel bedforms do display the hydraulic functionality associated with natural pool–riffle sequences. At bankfull discharge, water surface elevation is not significantly increased over those existing prior to installation, and physical habitat is shown to be more diverse following rehabilitation. The stability and appropriate classification of the gravel bedforms created in the scheme are discussed, together with the implications for floodplain and river rehabilitation in general. Copyright © 2004 John Wiley &amp; Sons, Ltd.