Alteration Of Natural Flow Regime Research Articles

Hydrologic changes in the Brazos River Basin and implications for Great Plains fishes

Alteration of natural flow regimes from surface water and groundwater resource development has adversely impacted aquatic habitats of resident fish throughout the Great Plains. Two endangered cyprinids, Sharpnose Shiner Notropis oxyrhynchus and Smalleye Shiner N.buccula, were historically found throughout the Brazos River Basin in Texas. However, their range has been greatly reduced by construction of impoundments and stream depletion from groundwater pumping. Successful recruitment requires flowing, unobstructed river reaches of sufficient velocity to suspend semi-buoyant fertilized fish ova. The wide, shallow stream habitats the shiners utilize are now limited to the Upper Brazos River Basin upstream of Possum Kingdom Reservoir. This study assesses the relative importance of long-term climate variability, reservoir construction, and groundwater development on Upper Brazos streamflow regimes by (1) calculating flow metrics (2) evaluating groundwater-surface water interactions and long-term groundwater inflows, and (3) using mixed-effects regression models and Poisson regression. Results show that fish habitat has been threatened through several impacted hydrologic processes: (1)groundwater development has resulted in reduced mean daily flows, peak flows, and zero-flow days, (2)upstream impoundments have increased zero-flow days and reduced mean daily flows, and (3)lower mean daily flows and peak flows now occur during droughts, suggesting water resource development—particularly after 1970—has exacerbated drought effects. We illustrate this approach using the Upper Brazos River Basin; however, the methodology applied can inform management actions to maintain spawning flows for streams in similar altered basins.

The duality of drought: Pelagic‐ and benthic‐spawning stream fishes show opposing responses to drought in the southern Great Plains

AbstractObjectiveStreamflow is a primary determinant of fish assemblage structure in riverine systems, but alteration of natural flow regimes can result in fish assemblage shifts through the process of environmental filtering. Because natural drought conditions reduce and homogenize streamflow in a manner comparable to projections for climate change in some regions, drought could serve as a proxy for expected future flow conditions.MethodsWe investigated the effects of drought as a temporally dynamic environmental filter of the occurrence of two guilds of fishes, benthic spawners that deposit adhesive ova along the benthic zone of rivers and pelagic spawners that release semibuoyant, nonadhesive ova into the pelagic zone of rivers. We developed species‐specific random forest models to estimate annual probability of occurrence for three benthic‐spawning and four pelagic‐spawning minnow species at three sites in the upper Brazos River, Texas, for the period 1950–2018. We then used a generalized additive mixed‐effects model to assess the relationship between drought intensity and likelihood of occurrence to test whether reproductive modes differed in response to drought (hypothesis 1) and whether response to drought was spatially (hypothesis 2) or temporally (hypothesis 3) variable.ResultWe found support for hypothesis 1 as two of four pelagic‐spawning species (Shoal Chub Macrhybopsis hyostoma, Smalleye Shiner Notropis buccula) declined and two of three benthic‐spawning species increased as drought intensified, support for hypothesis 2 as responses to drought varied by gauge location, and no support for hypothesis 3 as drought response was consistent for periods 1950–1979 and 1980–2018.ConclusionThese findings offer insight into the future of riverine fish assemblages as climate change is expected to exacerbate regional drought conditions. Management of pelagic‐spawning fishes during extreme drought in the southern Great Plains may require strategies such as (1) rescues of fish from drying reaches, (2) captive holding and propagation, and (3) assisted recolonization following subsidence of drought conditions.

Fish movements in response to environmental flow releases in intermittent rivers

Abstract Variation in river flow is a strong behavioural determinant for the movement of many freshwater fish species and often is linked to key aspects of their life cycle. The alteration of natural flow regimes to meet human water demands can result in changes to this variability, and cause declines in water‐dependent biota. Environmental flows are used as a remediation tool in some regulated rivers with the intention of restoring aspects of the natural flow regime to benefit riverine species, although empirical data are required to inform the efficacy of these interventions. Using acoustic telemetry, we quantified the movement responses of two large‐bodied native fish species (freshwater catfish, Tandanus tandanus and Murray cod, Maccullochella peelii) to variations in river flow over 4 years in two intermittent regulated rivers in the northern Murray–Darling Basin, Australia. Both rivers received periodic environmental flow releases and also there were several large natural flow events during the study period. Both species displayed a range of intra‐specific movement behaviours. Analysis of individuals' movements revealed five distinct functional groups, which were represented in both species. We found that periods of environmental flow delivery played an important role in the movement behaviour of both species. Murray cod were more likely to move during periods of environmental flow releases, whereas freshwater catfish were less likely to move on an environmental release following higher antecedent flows. No large‐scale philopatric movements were observed, yet Murray cod were more likely to move during the breeding period, indicative of nest site selection. We also found that the likelihood of movement in both species was higher in the smaller of the two rivers for a given magnitude of flow. Our results suggest that environmental flows may benefit certain fish species by facilitating, rather than cueing breeding behaviours, allowing individuals improved access to, and provision of, higher‐quality nesting habitats. These findings will aid water managers in creating economical and targeted environmental flow releases, timing larger flow pulses for the species with flow‐cued reproductive strategies, and providing a continuity of smaller baseflows for species whose reproduction is not dependent on flow cues but may be enhanced by greater connectivity.

Spatially structured relationships between white banana prawn (Penaeus merguiensis) catch and riverine flow in the Northern Prawn Fishery, Australia

Water resource development can lead to the significant alteration of natural flow regimes, which can have impacts on the many aquatic species that rely on both freshwater and estuarine environments to successfully complete their lifecycles. In tropical northern Australia, annual catches of commercially harvested white banana prawns (WBP) are highly variable in response to environmental conditions, namely rainfall and subsequent riverine flow. However, little is known about the spatial extent to which flow from individual rivers influences offshore WBP catch. In this study, we quantify how the relationship between WBP catch in the Gulf of Carpentaria is influenced by flow from the Mitchell River, Queensland Australia. We used a Bayesian framework to model both prawn presence and catch per unit effort, and found evidence that multiple components of the flow regime contribute to fishery catch. We also found evidence to suggest that the relationships between prawn presence and flow were spatially structured across the fishing ground. Our results suggest that attributing fishery catch to a single river remains challenging, though highlights the importance of maintaining natural flow regimes to support a highly valuable commercial fishery species in the face of potential water resource development.

Effects of reservoir operation methods on downstream ecological disturbance and economic benefits

AbstractThe natural flow regime can sustain the ecological integrity of riverine ecosystems. Different reservoir operation polices differ in their effects on the degree of alteration of natural flow regimes. Dynamic programming plays an important role in developing operation policies. When using dynamic programming models to develop operation policies, the discrete number of storage states (DNSS), which is a key factor affecting the reservoirs operation policies, is always been determined based on computational efficiency and economic benefits. Little consideration has been given to the ecological disturbance caused by different DNSS‐based operation policies. To analyze the impact of DNSS, we built a deterministic dynamic programming model to explore the relationship among DNSS, the flow regime alteration (ecological disturbance), and the cumulative annual power generation (economic benefits) by setting a range of DNSS scenarios. We used three reservoirs with different storage coefficients (ratios of usable storage to annual average runoff) as examples and used the range of variability approach to assess the ecological disturbance under these scenarios. We compared the results with those of a stochastic dynamic programming (SDP) model and a Bayesian SDP (BSDP) model. We found that when DNSS is low, increasing DNSS improves economic benefits but causes a more severe ecological disturbance; when DNSS is high, increasing DNSS improves the economic benefits only slightly, without exacerbating the ecological disturbance; for a given DNSS, the BSDP model provides higher economic benefits than the SDP model and a similar disturbance of the riverine ecosystem; and larger reservoirs more often cause more severe disturbance of riverine ecosystems because monthly mean flows and annual extreme flows change more drastically. Our results will help to protect the riverine ecosystems and improve economic benefits if reservoir operation managers consider DNSS using dynamic programming models.

Environmental water allocations are insufficient to control an invasive wetland plant: evidence from a highly regulated floodplain wetland

Summary Regulation of the world's rivers and alteration of natural flow regimes have led to the degradation of floodplains and wetlands. Here, we investigate plant–flood interactions in a floodplain wetland to determine whether a return to more natural flooding regimes using environmental water allocations can contribute to restoration from a degraded state. We use detailed field surveys to quantify the effects of flooding on a native rush, Juncus ingens, which has become invasive in floodplain grasslands in south‐eastern Australia. We then apply these results to determine the likelihood of generating the flood regime required to control J. ingens in its new range, considering the regulated nature of the river system. Complete submergence for several months substantially reduced J. ingens stem densities, survival and recovery. However, rhizomes were able to survive, with new stems produced during subsequent partial submergence. Under current regulated conditions, the volume of environmental water needed to cause substantial stem decline, and potentially rhizome death, is extremely large – particularly for tall stems – even when used in conjunction with a natural flood peak. Synthesis and applications. Although repeated submergence events may cause stem decline of the invasive plant Juncus ingens, the present day operational constraints of the regulated river make it difficult to deliver the required volume and depth of water using environmental water allocations. Furthermore, shallow floods may actually provide favourable conditions for growth. This research is particularly relevant for other restoration projects where historical disturbance regimes can only be partially mimicked. Whilst a managed flood regime can be successful in achieving a range of conservation and restoration goals, there may be situations in which river regulation can limit the ability to effectively manage particular species using environmental water allocations alone.

The impact of river regulation on the biodiversity intactness of floodplain wetlands

Alteration of natural flow regime is considered a major threat to biodiversity in river floodplain ecosystems. Measurements of quantitative relationships between flow regime change and biodiversity are, however, incomplete and inconclusive. This hampers the assessment of human impact on riverine floodplain wetlands in global biodiversity evaluations. We systematically reviewed the scientific literature and extracted information from existing data sets for a meta-analysis to unravel a general quantitative understanding of the ecological consequences of altered flow regimes. From 28 studies we retrieved both ecological and hydrological data. Relative mean abundance of original species (mean species abundance, MSA) and relative species richness were used as effect size measures of biodiversity intactness. The meta-analysis showed that alteration of a natural flow regime reduces the MSA by more than 50 % on average, and species richness by more than 25 %. Impact on species richness and abundance tends to be related to the degree of hydrological alteration. These results can be used in strategic quantitative assessments by incorporating the relationships into global models on environmental change and biodiversity such as GLOBIO-aquatic.

Response of an invasive native wetland plant to environmental flows: Implications for managing regulated floodplain ecosystems

The natural flow regimes of rivers underpin the health and function of floodplain ecosystems. However, infrastructure development and the over-extraction of water has led to the alteration of natural flow regimes, resulting in the degradation of river and floodplain habitats globally. In many catchments, including Australia's Murray–Darling Basin, environmental flows are seen as a potentially useful tool to restore natural flow regimes and manage the degradation of rivers and their associated floodplains. In this paper, we investigated whether environmental flows can assist in controlling an invasive native floodplain plant in Barmah Forest, south-eastern Australia. We experimentally quantified the effects of different environmental flow scenarios, including a shallow (20 cm) and deeper (50 cm) flood of different durations (12 and 20 weeks), as well as drought and soil-saturated conditions, on the growth and survival of seedlings of Juncus ingens, a native emergent macrophyte that has become invasive in some areas of Barmah Forest following river regulation and alteration of natural flow regimes. Three height classes of J. ingens (33 cm, 17 cm and 12 cm) were included in the experiment to explicitly test for relationships between treatments, plant survival and growth, and plant height. We found that seedling mortality occurred in the drought treatment and in the 20-week flood treatments of both depths; however, mortality rates in the flood treatments depended on initial plant height, with medium and short plants (initial heights of ≤17 cm) exhibiting the highest mortality rates. Both the 20 cm and 50 cm flood treatments of only 12 weeks duration were insufficient to cause mortality in any of the height classes; indeed, shoots of plants in the 20 cm flood treatment were able to elongate through the water surface at rapid rates. Our findings have important implications for management of Barmah Forest and floodplain ecosystems elsewhere, as it demonstrates the potential for using environmental flows to limit the spread of invasive plants by targeting a life-stage that is particularly sensitive to prolonged submergence. However, there may be narrow thresholds between the conditions that provide effective control of an invasive species, and those that instead facilitate growth and may promote further invasion.

Performance and Water Table Responses of Retrofit Rain Gardens

AbstractThe alteration of natural flow regimes associated with land use change increases storm water runoff volume, increases peak flows, and reduces the time to peak flow. This can cause flooding, erosion, and higher pollutant loading in streams, rivers, lakes, and estuaries. Rain gardens represent a sustainable and economic method to decrease the volume of water that flows into rivers and streams from impervious areas during storm events. For developments that were built without permanent storm water controls, rain gardens may be a viable retrofit instead of centralized and more costly alternatives. However, there is a lack of knowledge about the performance of rain gardens in urban retrofit applications. In this rain garden study, the hydrologic performance of terraced, street-side rain gardens was examined by monitoring inflow and outflow volumes and water tables during simulated runoff events. Areas of uncertainty that were addressed include general relationships between inflow and hydrologic perform...

Development and application of a hybrid model to analyze spatial distribution of macroinvertebrates under flow regulation in the Lijiang River

Alteration of natural flow regime due to reservoir operation imposes serious impacts on the aquatic ecosystem. To investigate the effects on the spatial distribution of macroinvertebrates, this study developed a hybrid ecohydraulics model which integrated a two-dimensional water quality module with an artificial neural network (ANN) based macroinvertebrate habitat module. The developed model was applied to a compound channel in the middle of the Lijiang River, where the flow in dry season has been largely modified by the Qingshitan Reservoir in the upstream. Semisulcospira amurensis ( S. amurensis) which is the dominant macroinvertebrate species in the whole river basin was studied. The simulation and comparison results indicate that in general the flow regulation in dry season has negative impacts on the distribution of S. amurensis. The distribution area decreases, and in particular it becomes seriously fragmented. The model can be used through scenario analyses to adjust reservoir operation, so as to improve river management for ecological interest. In addition, the hybrid approach proposed in the paper has great potentials in studying this type of problems.

Critical habitat during the transition from maternal provisioning in freshwater fish, with emphasis on Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

AbstractIn freshwater fish, the transition from dependence on maternal yolk reserves to independent foraging can be an early critical period, with survival during this stage having a strong influence on population abundance and cohort strength. Information concerning Atlantic salmonSalmo salarand brown troutSalmo truttaas model species is reviewed to show how population dynamics are influenced by habitat use during the transitional stage and illustrate the role of maternal provisioning along with density‐dependent and ‐independent factors. The allocation of resources in yolk and timing and position of spawning strongly influence the biotic and abiotic environments of juveniles and their subsequent performance. Vulnerability to predators, adverse environmental conditions and restricted conditions over which they can successfully forage result in specific habitat requirements for newly independent juveniles. The availability of slow‐flowing habitats at stream margins during the first month of independence is crucial. Alteration of natural flow regimes and physical habitat structure, associated with a wide range of anthropogenic influences, can have significant deleterious effects on the availability of critical juvenile habitat. A model combining habitat structure and the relationship between density‐dependent and ‐independent mortality is presented to explore the range of conditions under which the transitional period would have a strong influence on population abundance. This model provides a framework for establishing thresholds or optima for habitat availability that will favour sufficient recruitment out of the transitional stage. Using the modelling framework, managers can make informed decisions on the utility and cost effectiveness of fisheries and habitat management activities designed to increase juvenile survival during the transition to independence. A range of management options is outlined for improving habitat quality and increasing juvenile survival during the transitional period, including restoration of structural complexity, provision of suitable flow regimes, and tailoring stocking and reintroduction strategies to mimic natural dynamics.

FLOW–SEDIMENT–BIOTA RELATIONS: IMPLICATIONS FOR RIVER REGULATION EFFECTS ON NATIVE FISH ABUNDANCE

Alteration of natural flow regimes by river regulation affects fish distribution and assemblage structure, but causative pathways are not always direct and may go un- recognized. The Colorado River population of the endangered Colorado pikeminnow, Ptych- ocheilus lucius, suffers from low rates of recruitment and reduced carrying capacity. We hypothesized that availability of prey fish for this large-bodied native piscivore may, in part, be limited by reduced standing crops of periphyton and macroinvertebrates resulting from accumulation of fine sediment in the riverbed. We stratified the 373-km-long study area into 11 strata and sampled various physical and biological parameters in runs and riffles of three randomly selected 1- to 3-km-long study reaches in each stratum during base flows of spring and fall 1994-1995. Significant correlations were found between biomass of both chlorophyll a and macroinvertebrates and various physical metrics that described the degree of fine sediment accumulation in gravel-cobble substrates. Riffles were relatively free of fine sediment throughout the study area, but substrates of runs contained progressively more fine sediments with distance downstream. There was a cor- responding longitudinal change in biota along the river continuum with greatest biomass of fish, invertebrates, and periphyton upstream. Adult pikeminnow were concentrated in upstream strata where potential prey fishes were most abundant. We suggest that fine- sediment effects on biota have increased in recent years as a result of river regulation. Historically, spring snowmelt frequently produced flows with magnitudes sufficient to mo- bilize the bed and winnow silt and sand from coarse substrates. Following regulation, the mean recurrence interval of such flows lengthened from 1.3-2.7 yr (depending on the stratum) to 2.7-13.5 yr, extending the duration of fine sediment accumulation and potentially depressing biotic production. Our results describe and help explain the spatial distribution of the Colorado River fish community and establish a link between flow, sediment, and the riverine food web supporting the community's top predator. To maintain intact native fish communities in this and other river basins, managers need to identify functional aspects of the natural hydrograph and incorporate these findings into river restoration efforts.

Restoration of riparian vegetation in the south-western United States: importance of flow regimes and fluvial dynamism

Riparian ecosystems in the south-western United States have undergone extensive physical and biological changes, due, in part, to alteration of natural flow regimes and suppression of fluvial processes. Many riparian ecosystem restoration projects are achieving success because they recognize the importance of restoring the hydrologic regime. In other words, these projects are restoring flows of water and sediment in sufficient quantities and with appropriate temporal and spatial patterns. Other projects have proceeded without recognition of the need to incorporate environmental stream flow requirements into management plans. To increase success rate of riparian ecosystem restoration, this paper describes some changes that have occurred within riparian ecosystems of the southwestern United States, reviews the role of stream flow regimes in structuring riparian plant communities, and assesses various ways in which riparian plant communities can be restored by naturalizing ecological processes.

Managing Water for the Environment: Impediments and Challenges

The management of Australia's water resources has, until recently, focused upon meeting the needs of consumptive users. This focus has been driven by economic imperatives, combined with a government commitment to industrial/agricultural development and expansion. While expansionary policies have produced significant economic benefits for Australia, it has become increasingly apparent that such development has come at a price. The regulation of Australian rivers has resulted in the alteration of natural flow regimes to the extent that many ecological processes have been severely disrupted. This has not only had biological repercussions, but also produced agricultural problems such as algal blooms, salinity and rising groundwater tables. The situation in which Australian water managers find themselves is, therefore, one in which competing demands and limited resources combine to place them in an often untenable position. The key issue with which such managers must grapple is how to trade off environmental and consumptive water needs. In order to examine the types of difficulties and challenges which face these managers, this account seeks to outline the key impediments to managing water for the environment efficiently and effectively. In so doing, it reviews the complicated and, often controversial, conditions within which decisions about water management are currently being made. It also seeks to alert future and existing environmental water managers to the experiences of others in their industry.