Flow regime alteration effects on the organic C dynamics in semiarid stream ecosystems

There is evidence of an ongoing alteration of the flow regime owing to climate change forcing, which has resulted in substantial increases in the frequency and magnitude of extreme events such as floods and droughts. Such changes in the flow regime may have major implications in freshwater ecosystems and, in particular, in the organic carbon dynamics in semiarid stream ecosystems. Much is known about the role of extreme flow events on structuring stream ecosystems, but few studies explored the effects of extreme flow events magnitude, timing, and sequence on stream ecosystems. To assess the effect of extreme events on stream organic C dynamics, a simple and flexible modeling approach was applied to simulate the organic carbon dynamics in a simplified river reach. The river reach model was initially calibrated and tested using long-term data for stream water velocity and amount of organic carbon in sediment. After that, multiple scenarios differing in the extreme flow events (floods and droughts) sequence and magnitude were used to simulate the effects of possible flow regime changes on the stream organic carbon dynamics. Initial expectations were that: (i) an increase in the magnitude or frequency of extreme flow events would reduce the amount of organic carbon respired within the simulated river reach, and (ii) relationship between the timings of the extreme flow events and of the litterfall input would influence considerably the effects of the extreme flow events. Results pointed out that: (i) the amount of processed carbon respect the amount entering the ecosystem was affected by extreme events such floods and droughts, but the relevance of those events differed along the year, with a maximal effect during the litterfall period; (ii) extreme event timing rather than the magnitude was more relevant to the stream organic carbon dynamics; and (iii) the amount of respired carbon in the ecosystem could be amplified or reduced depending on event sequence. Increasing awareness of the role of inland waters in the global carbon cycle and the shaping role of hydrology on the stream organic carbon dynamics stress the need to better quantify carbon fluxes and the hydrological controls on these fluxes.     

Potential impacts to freshwater ecosystems caused by flow regime alteration under changing climate conditions in Taiwan

Observed increases in the Earth’s surface temperature bring with them associated changes in precipitation and atmospheric moisture that consequentially alter river flow regimes. Climate-induced flow regime changes are examined using the Indicators of Hydrologic Alteration. This article uses observed daily streamflow data to examine the flow regime alteration and how these changes might potentially affect freshwater ecosystems. Flow data from 23 gauging stations throughout Taiwan show that the annual extreme water conditions (1-, 3-, 7-, 30-, 90-day annual minima or maxima) have increased alteration compared to baseline periods (1961–1990). Specifically, more severe flood and drought events occur in the period after 1991 than the period from 1961 to 1990. The frequency and duration of flood and drought events also show increased fluctuation. Flow regimes are currently being altered by stressors that will continue into the foreseeable future and it is also happing elsewhere in the world. Aquatic organisms not only need to defend themselves from anthropogenic damage to the river system, but also face the on-going threat from climate change-induced thermal and flow regime alteration. This article raises this issue so that water resources managers may identify precautionary measures that reduce the cumulative effects of both anthropogenic flow alteration and changing climate conditions.     

Geographical patterns of flow-regime alteration by flood-control dams in Japan

Natural variability in water flow is an inherent feature of river ecosystems, but many rivers in the world have been dammed, altering the flow regime and leading to ecosystem degradation. Dam reoperation to maintain environmental flows has been proposed for ecosystem and biodiversity improvement. Reoperation requires an understanding of flow alteration due to dam operations. However, knowledge of natural flow regimes and their degree of alteration remain poor in Japan. The Japanese islands extend from the sub-Arctic to the subtropics with four seasons and thus are considered to show high spatial and temporal variation in flow regime and alterations caused by those variations. We examined the spatial and temporal dependency of flow alteration by flood-control dams in Japan. We confirmed that flood-control dams reduced the rate of change in discharge and peak discharge and that such dams fulfilled their primary role of preventing flood disaster by reducing and delaying flooding. However, other flow characteristics, such as high- and low-flow frequency and duration, were also altered. We demonstrated that the magnitude, frequency, duration, and seasonality of high and low flows in undammed flow regimes differed with latitude and that discharge alteration was spatially and temporally dependent, presumably because dam operation responded to the inherent differences in seasonal flow variability at different latitudes.     

Application of r/K selection to macroinvertebrate responses to extreme floods

1. Due to climate change, contemporary climate scenarios forecast an increase in extreme weather, which may have considerable impacts on the world's riverine ecosystems. Because the flow regime is a primary determinant of the structure and function of lotic ecosystems, changes in the weather could fundamentally alter these ecosystems through changes in hydrologic disturbance regimes. 2. In this paper, we use the abundance/biomass comparison (ABC) method, based on r/K selection theory, and event probability distribution to characterise the responses of macroinvertebrates in Taiwan mountain streams to extreme floods. 3. Severe impacts on macroinvertebrates, resulting in a large shift in community structure toward r‐selected taxa, usually were observed the year after extreme floods. 4. Macroinvertebrate communities dominated by K‐selected taxa had more individuals with traits conferring resistance to flooding disturbance, while those dominated byr‐selected taxa had more individuals with traits conferring resilience. 5. This relationship between the changes in flow regime and the ecological response of r‐ and K‐selected taxa may be exploited to understand the potential effects of flood extremes in the future, and to keep decision makers informed about the ecological consequences of climate‐mediated changes to hydrological regimes.     

Assessment of regulated rivers with indices based on macroinvertebrates,fish and riparian forest in the southeast of Spain

The complexity of natural river ecosystems is driven by the natural flow regime. Alteration of the flow regime generates changes in geomorphological processes and poses a challenge to conservation of the integrity of biotic communities. The modifications of flow regimes can produce serious changes to the structure and function of aquatic ecosystems. The present study aims to evaluate these changes in two regulated rivers under different management regimes. The reaches are located upstream and downstream of two reservoirs in the Mundo and Segura Rivers (Southeast Spain) and were sampled in spring, 2006. According to the Water Framework Directive, ecological condition should be evaluated by observed deviation from the expected natural condition. In this study, we applied this concept to determine the degree of alteration in the regulated reaches. The evaluation of ecological status has been performed by applying a multimetric focus using indices derived from the community of macroinvertebrates (MCLM) and fish (SI) as biological elements as well as a riparian forest index (RQI), which analyzes a hydromorphological element. The assessment of ecological status revealed degradation in the quality of reaches downstream of reservoirs. These three biological indicators are sensitive to the alteration of natural flows produced by regulation. Flow regimes are modified due to a need to store water resources for economic purposes; however flow regimes should be planned in accordance with the natural cycle so that ecosystem quality is preserved and not further degraded in the future.     

Ecological effects of perturbation by drought in flowing waters

• 1 Knowledge of the ecology of droughts in flowing waters is scattered and fragmentary, with much of the available information being gathered opportunistically. Studies on intermittent and arid‐zone streams have provided most of the information.
• 2 Drought in streams may be viewed as a disturbance in which water inflow, river flow and water availability fall to extremely low levels for extended periods of time. As an ecological perturbation, there is the disturbance of drought and the responses of the biota to the drought.
• 3 Droughts can either be periodic, seasonal or supra‐seasonal events. The types of disturbance for seasonal droughts are presses and for supra‐seasonal droughts, ramps.
• 4 In droughts, hydrological connectivity is disrupted. Such disruption range from flow reduction to complete loss of surface water and connectivity. The longitudinal patterns along streams as to where flow ceases and drying up occurs differs between streams. Three patterns are outlined: ‘downstream drying’, ‘headwater drying’ and ‘mid‐reach drying’.
• 5 There are both direct and indirect effects of drought on stream ecosystems. Marked direct effects include loss of water, loss of habitat for aquatic organisms and loss of stream connectivity. Indirect effects include the deterioration of water quality, alteration of food resources, and changes in the strength and structure of interspecific interactions.
• 6 Droughts have marked effects on the densities and size‐ or age‐structure of populations, on community composition and diversity, and on ecosystem processes.
• 7 Organisms can resist the effects of drought by the use of refugia. Survival in refugia may strongly influence the capacity of the biota to recover from droughts once they break.
• 8 Recovery by biota varies markedly between seasonal and supra‐seasonal droughts. Faunal recovery from seasonal droughts follows predictable sequences, whilst recovery from supra‐seasonal droughts varies from one case to another and may be marked by dense populations of transient species and the depletion of biota that normally occur in the streams.
• 9 The restoration of streams must include the provision of drought refugia and the inclusion of drought in the long‐term flow regime.

     

Habitat quality affects the condition of Barbus sclateri in Mediterranean semi-arid streams

We investigated the site level relationships between fish condition and environmental variables in Sclater's barbel, Barbus sclateri, from semi-arid streams in the south-eastern Iberian Peninsula. These freshwater ecosystems are characterized by strong seasonal fluctuations in flow levels (droughts and floods) as a consequence of their irregular hydrological regime on both an annual and pluriannual scale. We analysed the relationships between 11 ecosystem variables [conductivity, oxygen concentration, water temperature, pH, seasonal water flow, dominant substrate, submerged vegetation, QBR (Riparian Ecosystems Quality Index), BMWP' (Spanish version of the Biological Monitoring Working Party), fish refuge index and fish density] and fish condition by comparing mass–length relationships of nine populations of Sclater's barbel located in five sub-basins with different environmental conditions. Fish condition differed between the populations studied and was mainly dependent on the ecological variables related with water flow and, consequently, the physical structure of the streams, which is directly related to substrate and fish refuge.     

Condition of Barbus sclateri from semi-arid aquatic systems: effects of habitat quality disturbances

This study investigated the relationships between fish condition and environmental variables in Barbus sclateri from semi-arid freshwater ecosystems in the south-eastern Iberian Peninsula. Two main habitats were studied: semi-arid streams characterized by strong seasonal fluctuations in flow level (droughts and floods) and reservoirs (artificial ecosystems characterised by waters of high conductivity). The mass–length relationships were used to test differences in fish condition between nine stream populations and five reservoir populations of B. sclateri from the Segura River basin. The relationships between seven ecosystem variables (conductivity, oxygen concentration, water temperature, pH, seasonal water flow, submerged vegetation and sub-basin location) and fish condition were analysed. The ecological variables that accounted for most of the variation in fish condition were seasonal water fluctuation and water conductivity. The condition of B. sclateri populations may be a good indicator of fish habitat quality in Mediterranean semi-arid freshwater ecosystems and should be considered when such populations are subjected to sports fishing regulations, recovery plans or any other management programme.     

Downstream fish assemblage response to river impoundment varies with degree of hydrologic alteration

River impoundments can fundamentally restructure downstream fish assemblages by altering flow regimes. However, the degree of alteration and associated ecological change may depend on pre-existing hydrologic regimes. We used long-term datasets to compare downstream hydrological and fish assemblage responses to impoundment in two catchments classified as having intermittent and perennial-flashy natural hydrologic regimes. We observed significant shifts in fish assemblage structure at both sites after stream impoundment. The historically intermittent stream shifted to a stable perennial flow regime. Changes in fish assemblage structure covaried with changes in five different components of the flow regime; most species that increased in abundance require fluvial habitats and likely benefited from increased flows during historically low flow seasons. Shifts in fish assemblage structure were also observed in the perennial stream, despite minimal flow alteration after impoundment; however, most species shifts were associated with lentic environments, and were more likely related to proximity of reservoirs in the drainage system rather than changes in stream flow. Findings from this study confirm that downstream fish assemblage response to river impoundment can be associated with high levels of hydrologic alteration, but other factors including expansion of lentic species into lotic environments also influence shifts in assemblage structure.     

How to comprehensively evaluate river discharge under the influence of a dam

The dams in the upper reaches of the Yangtze River are highly concentrated. Dam construction can effectively solve water shortage problems; however, the natural hydrological regimes of rivers have changed to varying degrees under the influence of water conservancy projects. In this study, a comprehensive method is proposed to analyze the hydrological regime changes in a river impacted by a dam through the evaluation of hydrological periodicity, hydrological frequency and hydrological parameters. Hydrological periodicity is used to evaluate the time series from the vertical multiyear perspective, while hydrological frequency is used to evaluate the time series from the horizontal one-year perspective. The two parameters have complementary roles. The indicators of hydrologic alteration and environmental flow component parameters are used to analyze the changes in various hydrological factors affected by the dam. The results demonstrate that the construction of dams can change the multiyear periodicity of the flow and reduce the peak flow. As a result, downstream fish may be unable to sense the reduced floods and fail to spawn. The indicators of hydrologic alteration and environmental flow component parameters can complement each other and can be used to evaluate changes in a hydrological regime influenced by a dam. This comprehensive method can be used to analyze how the hydrological regime is affected by this dam.     

Wetland plant growth under contrasting water regimes associated with river regulation and drought: implications for environmental water management

An important characteristic of many wetland plants in semi-arid regions is their capacity to withstand fluctuations between extended dry phases and floods. However, anthropogenic river regulation can reduce natural flow variability in riverine wetlands, causing a decline in the frequency and duration of deep flooding as well as extended droughts, and an increase in shallow flooding and soil saturation. Our aim in this paper was to use an experimental approach to examine whether reductions in flooding and drought disadvantage species adapted to both these extremes, and favours those with water requirements that match the new regime of frequent low-level flooding. We compared the growth characteristics and biomass allocation of three native Australian aquatic macrophytes (Pseudoraphis spinescens, Juncus ingens and Typha domingensis), which co-occur at Barmah Forest, south-eastern Australia, under three water treatments: drought, soil saturation and deep flooding. The responses of species to the treatments largely reflected changes in their relative abundance at Barmah Forest since river regulation. Typha domingensis, which has remained uncommon, performed relatively poorly in all treatments, while J. ingens, which has increased its range, exhibited more vigorous growth under soil saturation. Pseudoraphis spinescens, which was once widespread but has declined markedly in its distribution, grew strongly under all water treatments. These findings suggest that a return to more natural, variable river flow regimes can potentially be an important conservation and restoration strategy in ecosystems characterised by species that have adaptations to extreme hydrological growing conditions.     

Assessment of multi-objective reservoir operation in the middle and lower Yangtze River based on a flow regime influenced by the Three Gorges Project

The construction of multi-function reservoirs is important to guaranteeing the development and utilization of water and hydropower resources, but the construction of any hydrologic projects will inevitably affect the downstream flow regime that provides the driving force for riverine ecosystems. This paper therefore aims to propose a framework for assessing multi-objective reservoir operation models based on flow regime using the middle and lower Yangtze River as a case study. Using indicators of hydrologic alteration (IHA) and the histogram matching approach (HMA), critical influential factors for flow were investigated at the Yichang and Datong gauges, which are typical of the middle and lower Yangtze River. This found the magnitude of annual extreme minimum water flow rates to be the most dramatically changed indicator, with an overall degree of hydrologic alteration at the Yichang and Datong gauges of 41.98% and 34.58%, respectively. The monthly mean discharges of February and October at Yichang have been significantly changed as a result of the Three Gorges Reservoir (TGR) operation. Meanwhile, an improved range of variability approach (IRVA) was developed to obtain ideal target ranges for monthly average flow. A multi-objective ecological reservoir operations model was created for the TGR; the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was applied to the model. Three typical years of wet, normal and dry years were selected, and the operation results with corresponding ideal target ranges were analyzed for the downstream Yichang and Datong cross sections. The results showed that there should be a reduction by 23.57%, 28.10% and 39.92% in the monthly mean flow of February and an increase by 34.48%, 112.36% and 52.12% in the monthly mean flow of October at Yichang cross section in wet, normal and dry years, respectively.Close attention therefore needs to be given to integrating ecological objectives with appropriate flow regimes into multi-objective operation models.     

Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

相似文献   

Detrimental effects of a novel flow regime on the functional trajectory of an aquatic invertebrate metacommunity

Novel flow regimes resulting from dam operations and overallocation of freshwater resources are an emerging consequence of global change. Yet, anticipating how freshwater biodiversity will respond to surging flow regime alteration requires overcoming two challenges in environmental flow science: shifting from local to riverscape‐level understanding of biodiversity dynamics, and from static to time‐varying characterizations of the flow regime. Here, we used time‐series methods (wavelets and multivariate autoregressive models) to quantify flow‐regime alteration and to link time‐varying flow regimes to the dynamics of multiple local communities potentially connected by dispersal (i.e., a metacommunity). We studied the Chattahoochee River below Buford dam (Georgia, U.S.A.), and asked how flow regime alteration by a large hydropower dam may control the long‐term functional trajectory of the downstream invertebrate metacommunity. We found that seasonal variation in hydropeaking synchronized temporal fluctuations in trait abundance among the flow‐altered sites. Three biological trait states describing adaptation to fast flows benefitted from flow management for hydropower, but did not compensate for declines in 16 “loser” traits. Accordingly, metacommunity‐wide functional diversity responded negatively to hydropeaking intensity, and stochastic simulations showed that the risk of functional diversity collapse within the next 4 years would decrease by 17% if hydropeaking was ameliorated, or by 9% if it was applied every other season. Finally, an analysis of 97 reference and 23 dam‐affected river sites across the U.S. Southeast suggested that flow variation at extraneous, human‐relevant scales (12‐hr, 24‐hr, 1‐week) is relatively common in rivers affected by hydropower dams. This study advances the notion that novel flow regimes are widespread, and simplify the functional structure of riverine communities by filtering out taxa with nonadaptive traits and by spatially synchronizing their dynamics. This is relevant in the light of ongoing and future hydrologic alteration due to climate non‐stationarity and the new wave of dams planned globally.     

Effect of flow regime on the morphology of a colonial cnidarian

Abstract. Phenotypic plasticity is the ability of some organisms to exhibit different phenotypes in response to environmental conditions. Many sessile marine invertebrates are morphologically plastic. In colonial cnidarians, compact morphologies are often associated with high-velocity flow regimes, whereas elongated morphologies are associated with calmer water. This ability to alter morphology in response to flow regime likely represents an adaptive strategy: these morphologies may permit efficient suspension feeding and gas exchange while reducing the risk of dislodgment in a particular flow regime. Which flow-related factors (e.g., CO₂ accumulation, drag forces, prey delivery) actually signal a colony to alter its morphology are unclear. In this study, we test the hypothesis that differences in flow regime or some correlate of flow regime (in the absence of differences in prey delivery) signal a colonial cnidarian to change its morphology. To separate prey delivery from water flow, hydroid ( Bougainvillia muscus ) colonies were fed equivalent amounts in still water, regardless of the flow regime treatment to which they were exposed the rest of the time. Our results show that, regardless of prey delivery, colonies grew in ways characteristic of calm water (with a higher percentage of tall pedicels and secondary hydranths, and fewer basal stolon branches) and of high flow (with more hydranths, free stolons, and a denser basal stolon network) environments. This work suggests that, for this hydroid, prey flux is not a proximate cue mediating morphological plasticity in response to flow regime.     

Linking Water Quality and Quantity in Environmental Flow Assessment in Deteriorated Ecosystems: A Food Web View

Most rivers worldwide are highly regulated by anthropogenic activities through flow regulation and water pollution. Environmental flow regulation is used to reduce the effects of anthropogenic activities on aquatic ecosystems. Formulating flow alteration–ecological response relationships is a key factor in environmental flow assessment. Traditional environmental flow models are characterized by natural relationships between flow regimes and ecosystem factors. However, food webs are often altered from natural states, which disturb environmental flow assessment in such ecosystems. In ecosystems deteriorated by heavy anthropogenic activities, the effects of environmental flow regulation on species are difficult to assess with current modeling approaches. Environmental flow management compels the development of tools that link flow regimes and food webs in an ecosystem. Food web approaches are more suitable for the task because they are more adaptive for disordered multiple species in a food web deteriorated by anthropogenic activities. This paper presents a global method of environmental flow assessment in deteriorated aquatic ecosystems. Linkages between flow regimes and food web dynamics are modeled by incorporating multiple species into an ecosystem to explore ecosystem-based environmental flow management. The approach allows scientists and water resources managers to analyze environmental flows in deteriorated ecosystems in an ecosystem-based way.     

基于多水文改变指标评价东江流域河流流态变化及其对生物多样性的影响

新丰江、枫树坝和白盆珠3座大型水库的建立对东江流域河道流量和河流流态过程有了较大改变,威胁河道下游生态系统的健康。基于广义指标生态剩余和生态赤字评价了东江流域受水库影响后流域生态需水需求目标总的盈余和缺失变化过程,基于IHA32指标计算的Do和DHRAM评价了水库对下游河段河流水文过程总的改变程度以及威胁河道生态系统健康的风险性大小,并进一步分析了对河道生物多样性的影响。研究结果如下:(1)水库对流量历时曲线(FDC)有显著影响,曲线上部下降,尾部上升,尤其体现在秋季和冬季。降水对年与夏季生态剩余影响较大,水库对各季节生态剩余和生态赤字均有较大影响:秋季和冬季生态赤字几乎为0,生态剩余显著增加。生态剩余和生态赤字与大部分IHA中32个指标具有很强的相关性,可作为衡量东江流域年和季节径流变化的生态指标。(2)龙川、河源、岭下和博罗4站点总体改变程度分别为58.48%、54.04%、54.32%和52.47%。河流流态变化导致总季节生态剩余增加并维持在较高水平,进一步引起河流生物多样性下降,并维持在较低水平。龙川和河源两站河流流态的变化对河流生态系统造成了高风险性影响,岭下和博罗两站则为中等风险。     

Impacts of biological invasions on disturbance regimes

Human management activities have altered the frequency and intensity of ecosystem disturbance often with enormous impacts on landscape structure and composition. One additional and under-appreciated way in which humans have altered disturbance regimes is through the introduction of invasive non-native species, themselves capable of modifying existing disturbance regimes or introducing entirely new disturbances. In many cases, modifications of disturbance regimes results in maintenance of ecosystems in a new or transitional state. There is now evidence that alteration of disturbance regime may be the most profound effect that a species or functional group can have on ecosystem structure and function.     

Drought‐induced changes in flow regimes lead to long‐term losses in mussel‐provided ecosystem services

Extreme hydro‐meteorological events such as droughts are becoming more frequent, intense, and persistent. This is particularly true in the south central USA, where rapidly growing urban areas are running out of water and human‐engineered water storage and management are leading to broad‐scale changes in flow regimes. The Kiamichi River in southeastern Oklahoma, USA, has high fish and freshwater mussel biodiversity. However, water from this rural river is desired by multiple urban areas and other entities. Freshwater mussels are large, long‐lived filter feeders that provide important ecosystem services. We ask how observed changes in mussel biomass and community composition resulting from drought‐induced changes in flow regimes might lead to changes in river ecosystem services. We sampled mussel communities in this river over a 20‐year period that included two severe droughts. We then used laboratory‐derived physiological rates and river‐wide estimates of species‐specific mussel biomass to estimate three aggregate ecosystem services provided by mussels over this time period: biofiltration, nutrient recycling (nitrogen and phosphorus), and nutrient storage (nitrogen, phosphorus, and carbon). Mussel populations declined over 60%, and declines were directly linked to drought‐induced changes in flow regimes. All ecosystem services declined over time and mirrored biomass losses. Mussel declines were exacerbated by human water management, which has increased the magnitude and frequency of hydrologic drought in downstream reaches of the river. Freshwater mussels are globally imperiled and declining around the world. Summed across multiple streams and rivers, mussel losses similar to those we document here could have considerable consequences for downstream water quality although lost biofiltration and nutrient retention. While we cannot control the frequency and severity of climatological droughts, water releases from reservoirs could be used to augment stream flows and prevent compounded anthropogenic stressors.     

Behavioral adaptations imply a direct link between ecological specialization and reproductive isolation in a sympatrically diverging ground beetle

Adaptation to a previously unoccupied niche within a single population is one of the most contentious topics in evolutionary biology as it assumes the simultaneous evolution of ecologically selected and preference traits. Here, we demonstrate behavioral adaptation to contrasting hydrological regimes in a sympatric mosaic of Pogonus chalceus beetle populations, and argue that this adaptation may result in nonrandom gene flow. When exposed to experimental inundations, individuals from tidal marshes, which are naturally subjected to frequent but short floods, showed a higher propensity to remain submerged compared to individuals from seasonal marshes that are inundated for several months. This adaptive behavior is expected to decrease the probability that individuals will settle in the alternative habitat, resulting in spatial sorting and reproductive isolation of both ecotypes. Additionally, we show that this difference in behavior is induced by the environmental conditions experienced by the beetles during their nondispersive larval stages. Hence, accidental or forced ovipositioning in the alternative habitat may induce both an increased performance and preference to the natal habitat type. Such plastic traits could play an important role in the most incipient stages of divergence with gene flow.