Predicting the natural flow regime: models for assessing hydrological alteration in streams

Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long‐term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20–50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national‐ and regional‐scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were ≤25% for most metrics. We selected three gaged, non‐reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate pre‐disturbance conditions and are sensitive to changes in streamflow variability associated with long‐term land‐use change. We also demonstrate how the models can be applied to predict expected natural flow characteristics at ungaged sites. Copyright © 2009 John Wiley & Sons, Ltd.     

EFFECTS OF GRADE CONTROL STRUCTURES ON FISH PASSAGE,BIOLOGICAL ASSEMBLAGES AND HYDRAULIC ENVIRONMENTS IN WESTERN IOWA STREAMS: A MULTIDISCIPLINARY REVIEW

Land use changes and channelization of streams in the deep loess region of western Iowa have led to stream channel incision, altered flow regimes, increased sediment inputs, decreased habitat diversity and reduced lateral connectivity of streams and floodplains. Grade control structures (GCSs) are built in streams to prevent further erosion, protect infrastructure and reduce sediment loads. However, GCS can have a detrimental impact on fisheries and biological communities. We review three complementary biological and hydraulic studies on the effects of GCS in these streams. GCS with steep (≥1:4 rise : run) downstream slopes severely limited fish passage, but GCS with gentle slopes (≤1:15) allowed greater passage. Fish assemblages were dominated by species tolerant of degradation, and Index of Biotic Integrity (IBI) scores were indicative of fair or poor biotic integrity. More than 50% of fish species had truncated distributions. After modification of GCS to reduce slopes and permit increased passage, IBI scores increased and several species were detected further upstream than before modification. Total macroinvertebrate density, biomass and taxonomic diversity and abundance of ecologically sensitive taxa were greater at GCS than in reaches immediately upstream, downstream or ≥1 km from GCS. A hydraulic study confirmed results from fish passage studies; minimum depths and maximum current velocities at GCS with gentle slopes (≤1:15) were more likely to meet minimum criteria for catfish passage than GCS with steeper slopes. Multidisciplinary approaches such as ours will increase understanding of GCS‐associated factors influencing fish passage, biological assemblage structure and other ecological relationships in streams. Copyright © 2011 John Wiley & Sons, Ltd.     

FISH ASSEMBLAGES IN NON‐REGULATED AND REGULATED RIVERS FROM PERMANENT AND TEMPORARY IBERIAN SYSTEMS

The effects of river regulation on the hydrological cycle of a river and on the respective fish assemblage may differ according to dam operation purpose and type of river analysed. To assess the spatial and temporal variation of fish assemblages and their response to the hydrological changes caused by two different types of flow regulation, we selected three sampling sites in four rivers with different levels of regulation, two in a permanent river system and another two on a temporary one, which we sampled in four different annual seasons. In the permanent system, hydroelectrical regulation decreased hydrological variability, which affected fluvial specialist species, benefitting the generalist ones, and created a more homogeneous community that presented less intra‐annual variation. In the temporary system, agricultural regulation caused an inversion of the hydrological cycle, maintaining a moderate flow volume throughout the drought period that benefited the introduced, generalist and more tolerant species. Monthly volume was recognized, in a temporal scale, as the most important hydrological feature for assemblages’ structure, predicting the intra‐annual variation of several ecological guilds. This study provides important considerations for dam management and riverine ecosystems conservation. Copyright © 2012 John Wiley & Sons, Ltd.     

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

FISH ASSEMBLAGES RESPOND TO HABITAT AND HYDROLOGY IN THE WABASH RIVER,INDIANA

Detailed relationships between fish assemblages and habitat and hydrology variation are largely unknown for large rivers. We evaluated hydrology, habitat variation and fish assemblages at 28 sites on the Wabash River, Indiana, USA, during 2005–2008. We calculated hydrologic variation with the Indicators of Hydrologic Alteration software and tested for temporal hydrologic effects on habitat variation of substrate particle size, water depth and water velocity by reducing data into principal component axes that were tested for differences among years with ANOVAs. We then tested for effects of habitat and hydrology variation on fish assemblages with canonical correspondence analysis. These analyses showed significant relationships between hydrologic variation and local habitats, and hydrology and habitat variables had significant relationships with fish assemblage structure. Our Mantel tests resulted in significant concordance among hydrology, local habitat variation and fish assemblage structure, suggesting associations of these variables. These results supported strong connections for hydraulic control over habitat variation and subsequent effects on fish assemblages. Copyright © 2011 John Wiley & Sons, Ltd.     

INVERTEBRATE AND FISH ASSEMBLAGE RELATIONS TO DISSOLVED OXYGEN MINIMA IN LOWLAND STREAMS OF SOUTHWESTERN LOUISIANA

Dissolved oxygen (DO) concentrations in lowland streams are naturally lower than those in upland streams; however, in some regions where monitoring data are lacking, DO criteria originally established for upland streams have been applied to lowland streams. This study investigated the DO concentrations at which fish and invertebrate assemblages at 35 sites located on lowland streams in southwestern Louisiana began to demonstrate biological thresholds. Average threshold values for taxa richness, diversity and abundance metrics were 2.6 and 2.3 mg/L for the invertebrate and fish assemblages, respectively. These thresholds are approximately twice the DO concentration that some native fish species are capable of tolerating and are comparable with DO criteria that have been recently applied to some coastal streams in Louisiana and Texas. DO minima >2.5 mg/L were favoured for all but extremely tolerant taxa. Extremely tolerant taxa had respiratory adaptations that gave them a competitive advantage, and their success when DO minima were <2 mg/L could be related more to reductions in competition or predation than to DO concentration directly. DO generally had an inverse relation to the amount of agriculture in the buffer area; however, DO concentrations at sites with both low and high amounts of agriculture (including three least‐disturbed sites) declined to <2.5 mg/L. Thus, although DO fell below a concentration that was identified as an approximate biological threshold, sources of this condition were sometimes natural (allochthonous material) and had little relation to anthropogenic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

ECOLOGICAL FUNCTIONS OF FISH BYPASS CHANNELS IN STREAMS: MIGRATION CORRIDOR AND HABITAT FOR RHEOPHILIC SPECIES

The introduction of weirs into stream ecosystems resulted in modifications of serial continuity and in the decline of riverine fish species. Successful river restoration requires information on the ecological functionality of fish bypass channels that are considered an ecological improvement according to the European Water Framework Directive. In this study, we compared the functionality of three nature‐oriented fish passes as compensatory habitats and migration corridors for fishes. Fish passes differed significantly from upstream and downstream reaches of the weirs, revealing higher current speed, lower water depth, smaller channel width and greater habitat variability. Following these structural differences, they provided key habitats for juvenile, small and rheophilic fishes that are typically underrepresented in highly modified water bodies. All fish passes were used as migration corridors, with increased fish movements during high discharge and at spawning periods. Because river stretches with high variability of current speed and water depth are scarce in highly modified water bodies, fish passes can play an important role as compensatory habitats and should thus be considered more intensively in habitat assessments and river restoration. Ideally, fish bypasses should mirror the natural discharge dynamics and consider all occurring fish species and sizes. Copyright © 2011 John Wiley & Sons, Ltd.     

THE RELATIONS BETWEEN MODEL PARAMETERS AND CERTAIN PHENOMENA IN TRAFFIC FLOW

Based on the dimensionless dynamic model of traffic flow, the model parameters were compared with numerically simulating solutions, and the effects of the former on the latter was investigated. Some relations between the parameters were obtained. Investigation several idealized results from dimensionless dynamic model of traffic flow were concluded.     

MORE EXOTIC AND FEWER NATIVE PLANT SPECIES: RIVERINE VEGETATION PATTERNS ASSOCIATED WITH ALTERED SEASONAL FLOW PATTERNS

Natural flow regimes are important for sustaining riverine vegetation. The regulation of river flows to provide water for agriculture often results in changes to flow timing. This study assesses the impact of altered seasonal flow patterns on riverine flora. Within temperate Australia, we surveyed the vegetation of five lowland rivers, three of which have large dams that alter their seasonal flow patterns; the other two are unregulated. From four to six sites were selected on each river, and these were classified into three levels of regulation based on the extent to which the timing of their seasonal flow patterns were altered. Sites were surveyed in winter and the following summer. Permanent quadrats were also established at a number of the surveyed sites and resurveyed every 3 months. Of the 267 plant taxa identified, 145 were exotic (non‐native). More exotic taxa and fewer native taxa were associated with increasing level of seasonal flow inversion (regulation). In particular, greater numbers of short‐lived exotic terrestrial taxa and fewer native woody taxa were associated with increasing level of regulation. Some exotic woody species (e.g. willows) were more common in the unregulated rivers and may have life‐history traits favoured by the natural seasonal flow patterns of study area. Multivariate analyses showed that level of regulation had a significant effect on the overall composition of the riverine vegetation. Our results provide support for the hypotheses that flow regulation adversely affects native species diversity and increases the vulnerability of riparian zones to invasion by exotic species; however, these effects are dependent on plant species' life‐history strategies. Our study highlights the importance of natural seasonal flow patterns for sustaining native riverine plant communities. Flow management aimed at maintaining or restoring ecological values should consider seasonal flow patterns. Winter/spring flow peaks may be particularly important for the recruitment of native riverine plants, especially trees and shrubs, and reducing the extent of exotic annuals and grasses. Copyright © 2012 John Wiley & Sons, Ltd.     

FISH ASSEMBLAGE RELATIONSHIPS WITH PHYSICAL CHARACTERISTICS AND PRESENCE OF DAMS IN THREE EASTERN IOWA RIVERS

Fish assemblages in rivers of the Midwestern United States are an important component of the region's natural resources and biodiversity. We characterized the physical environment and presence of dams in a series of reaches in three eastern Iowa rivers tributary to the Mississippi River and related these characteristics to the fish assemblages present. Some physical characteristics were similar among the 12 study reaches, whereas others differed substantially. We found a total of 68 species across the 12 study reaches; 56 in the Turkey River, 51 in the Maquoketa River and 50 in the Wapsipinicon River. Seventeen species could be described as ‘downstream‐distributed’; 15 being found only in the lowest reach of one or more rivers and the other two being found only in the lowest reaches or two or more contiguous reaches including the lowest reach. Two species could be described as ‘upstream‐distributed’, being found only in an uppermost reach. Non‐metric multidimensional scaling ordination illustrated similarities among reaches, and five physical variables were significantly correlated with assemblage similarities. Catchment area and number of dams between reaches and the Mississippi River were strongly correlated with assemblage similarities, but the directions of their effects were opposite. Catchment area and number of dams were confounded. The collective evidence to date suggests that the pervasiveness of dams on rivers significantly alters fish assemblages, making underlying patterns of species change and relationships with naturally varying and human‐influenced physical characteristics along a river's course difficult to discern. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

FISH ASSEMBLAGES AT ENGINEERED AND NATURAL CHANNEL STRUCTURES IN THE LOWER MISSOURI RIVER: IMPLICATIONS FOR MODIFIED DIKE STRUCTURES

Large rivers throughout the world have been modified by using dike structures to divert water flows to deepwater habitats to maintain navigation channels. These modifications have been implicated in the decline in habitat diversity and native fishes. However, dike structures have been modified in the Missouri River USA to increase habitat diversity to aid in the recovery of native fishes. We compared species occupancy and fish community composition at natural sandbars and at notched and un‐notched rock dikes along the lower Missouri River to determine if notching dikes increases species diversity or occupancy of native fishes. Fish were collected using gill nets, trammel nets, otter trawls, and mini fyke nets throughout the lower 1212 river km of the Missouri River USA from 2003 to 2006. Few differences in species richness and diversity were evident among engineered dike structures and natural sandbars. Notching a dike structure had no effect on proportional abundance of fluvial dependents, fluvial specialists, and macrohabitat generalists. Occupancy at notched dikes increased for two species but did not differ for 17 other species (81%). Our results suggest that dike structures may provide suitable habitats for fluvial species compared with channel sand bars, but dike notching did not increase abundance or occupancy of most Missouri River fishes. Published in 2011 by John Wiley & Sons, Ltd.     

SEASONALLY DRIVEN VARIATION IN SPATIAL RELATIONSHIPS BETWEEN AGRICULTURAL LAND USE AND IN‐STREAM NUTRIENT CONCENTRATIONS

Geographic information system (GIS) based distance weighted models were applied to determine critical areas of agricultural influence in nine agriculturally dominated, prairie subcatchments in southern Manitoba, Canada. Models were generated using a range of coefficients to represent nutrient overland and in‐stream attenuation between agricultural source areas and stream sampling stations. Coefficients were also used to represent increased attenuation during overland travel through areas with natural vegetation. Water samples collected at intervals throughout the open water season were used to establish associations between areas of influence and in‐stream total nitrogen and phosphorus concentrations in each season and under different flow conditions. Critical areas of influence varied seasonally with areas of influence expanding with individual rainfall events. Inclusion of natural vegetated areas on the landscape resulted in substantial increases in model power for only one scenario. Agriculture in areas within approximately 100 m of the stream channel appears to be the most critical driver of in‐stream nutrient conditions during most seasons and under most flow conditions. Best management practices, such as vegetated buffer strips, should be most effective in controlling nutrient losses to southern Manitoba streams when situated within stream corridor, as opposed to upland areas, which appear to have minimal impact on in‐stream conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

THE RELATIONSHIP BETWEEN THERMAL REGIME ALTERATION AND SPAWNING DELAY OF THE FOUR MAJOR CHINESE CARPS IN THE YANGTZE RIVER BELOW THE THREE GORGES DAM

Large dams often alter flow and thermal regimes downstream, resulting in fish spawning delays and larval abundance declines. Accurate prediction of the delayed spawning period under changed thermal regime is critical for selecting a correct timing to modify dam operation and to release the environmental flow needed to enhance fish spawning. We used correlation analysis to investigate the relationship between thermal regime alteration and spawning delay of the four major Chinese carps (FMCC) below the Three Gorges Dam in the Yangtze River, China, using a 13‐year ecological data series (1997–2009). Eighteen variables were defined to quantify thermal regime and related to two variables representing spawning timing. Our results demonstrate that the start of FMCC spawning has been delayed from early May to middle June since the Three Gorges Dam initiated operation in 2003. Water temperature declines of 2 °C–4 °C in March, April and May (a critical period for gonad development) were the principal reason for the observed spawning delay. The variable most associated with spawning timing was the arrival date of the cumulative temperature needed for gonad development from stages IV to V (D_DegDayIV–V), which describes the long‐term impacts of the timing, magnitude and duration of thermal regime upon gonad development. Only the cumulative temperature for gonad development and the minimum temperature for FMCC spawning (18 °C) are both satisfied, the occurrence of suitable flow conditions, that is, flow increase or flash flood, would produce a successful spawning event. Consequently, we suggest that the experimental flow increase process of the Three Gorges Reservoir aimed at enhancing FMCC spawning should initiate after 15 June when the requisite thermal regime can be met. Copyright © 2013 John Wiley & Sons, Ltd.     

ASSESSING THE IMPACTS OF RIVER REGULATION ON NATIVE BULL TROUT (SALVELINUS CONFLUENTUS) AND WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) HABITATS IN THE UPPER FLATHEAD RIVER,MONTANA, USA

Hungry Horse Dam on the South Fork Flathead River, Montana, USA, has modified the natural flow regimen for power generation, flood risk management and flow augmentation for anadromous fish recovery in the Columbia River. Concern over the detrimental effects of dam operations on native resident fishes prompted research to quantify the impacts of alternative flow management strategies on threatened bull trout (Salvelinus confluentus) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) habitats. Seasonal and life‐stage specific habitat suitability criteria were combined with a two‐dimensional hydrodynamic habitat model to assess discharge effects on usable habitats. Telemetry data used to construct seasonal habitat suitability curves revealed that subadult (fish that emigrated from natal streams to the river system) bull trout move to shallow, low‐velocity shoreline areas at night, which are most sensitive to flow fluctuations. Habitat time series analyses comparing the natural flow regimen (predam, 1929–1952) with five postdam flow management strategies (1953–2008) show that the natural flow conditions optimize the critical bull trout habitats and that the current strategy best resembles the natural flow conditions of all postdam periods. Late summer flow augmentation for anadromous fish recovery, however, produces higher discharges than predam conditions, which reduces the availability of usable habitat during this critical growing season. Our results suggest that past flow management policies that created sporadic streamflow fluctuations were likely detrimental to resident salmonids and that natural flow management strategies will likely improve the chances of protecting key ecosystem processes and help to maintain and restore threatened bull trout and westslope cutthroat trout populations in the upper Columbia River Basin. Copyright © 2011 John Wiley & Sons, Ltd.