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• High-intensity dam operations have severely disturbed the power-law tails of natural river flows. • Damming reduced downstream connection duration, magnitude, accumulation, and efficiency. • Damming weakened seasonal patterns of lateral exchanges. • Increasing damming would lead to the exponential loss of downstream connectivity. • The power-law tails of natural flows have important implications for the entire ecosystem's integrity, diversity, and sustainability. High-intensity dam operations have severely disturbed the power-law behaviors of natural river flows, which have important implications for the entire ecosystem's integrity, diversity, and sustainability. This study investigated the effects of vanishing power-law tails of river flows caused by damming on downstream hydrological connectivity in the Wanquan river–floodplain (China) and determined the consequent ecological responses. A two-dimensional hydrodynamic model was established to estimate inundation regimes under different hydrological scenarios, and a statistics-based method was used to generate vanishing power-law tails. Connectivity assessments quantified the duration, magnitude, accumulation, and efficiency of connection events in the river–floodplain system for historical hydrological processes, current dam operating schemes, and simulated flow series with compressed power-law tails. The results showed significant reductions in downstream connection duration, magnitude, accumulation, and efficiency with compression of the natural power-law tail, especially for small (P < 20 %) and large (P > 90 %) connection events. Under a fully modified scenario, the cumulative large connection events were reduced by as much as 50 %. Damming also diminished the seasonal fluctuations of lateral exchanges and weakened the synergetic relationships among inflows, inundation extents and connectivity in the river–floodplain system. Furthermore, increasing damming led to an exponential and accelerated loss of downstream connectivity, with noticeable inflection points. Reduced or insulated hydrological exchanges would weaken material cycling, energy flow, and information transmission in the river–floodplain system, ultimately impacting the entire aquatic ecosystem. Our study emphasizes the importance of the power-law tail in the estimation of natural flows, which, although accounting for only a small part of the whole flow series (approximately 6 % in this case), is of great significance for maintaining the downstream connectivity necessary for healthy aquatic ecosystems. [ABSTRACT FROM AUTHOR]

River regulation through reservoir construction is one of the greatest challenges to the natural flow state and ecological health of river systems globally. The Three Gorges Dam (TGD), the largest dam in the world, has been in operation since 2003 to regulate water resources downstream. However, most of the current research on the TGD compares the post-2003 hydrologic patterns downstream of the TGD with the pre-2003 hydrologic patterns and lacks direct evidence of the TGD impacts on the downstream areas. In this paper, the ecological impacts of TGD on downstream large lakes are explored in terms of hydrological alteration degree, biodiversity, connectivity, and ecological surplus and ecological deficit by building a 1/2-dimensional nested model to simulate the hydrological processes with and without the TGD from 2008 to 2011. The results showed that (1) TGD storage led to a decrease in the number of high pulses at downstream stations, resulting in wetland degradation in the riverine region; (2) the SI (Shannon's diversity index) based on hydrological calculations became smaller, indicating that the downstream biodiversity showed a decreasing trend; (3) the diversion ratio and the confluence ratio of Dongting Lake and the Yangtze River decreased at the same time, and the connectivity decreased, which would lead to an increase in the degree and frequency of droughts during the dry season;(4) after the regulation of the TGD, the low-risk months were transformed into medium-risk months of the Dongting Lake basin, indicating a deterioration of the ecological situation in this region. The study demonstrates that the construction of the TGD has exacerbated downstream water stress, while the degradation of wetlands and the reduction in biodiversity highlight the heightened pressure on ecological and environmental protection downstream of the TGD. The results of this study provide necessary information for evaluating the impact of the TGD project on large lakes downstream and provide feasible suggestions for water resource management and ecological protection in the Yangtze River basin to ensure the realization of sustainable development in the future. [ABSTRACT FROM AUTHOR]

Anthropogenic activities and climate change have caused physical and ecological changes in lakes and have aggravated water level fluctuations, which are essential factors to consider for nutrient import, ecological protection, and biodiversity maintenance. Maintaining water levels within a reasonable range is essential for maintaining lake function and ecological health, because ecosystem stability is compromised when water level fluctuations exceed specific thresholds. Thus, the ecological water level (EWL) is an important index for maintaining aquatic habitats and biodiversity. A method for quantifying the EWL of lakes based on hydrological statistical analysis was constructed to bridge the gaps in existing studies, considering both the hydrological alteration and spatio-temporal heterogeneity of water level fluctuations. Taking Poyang Lake as an example, which has recently attracted increasing global attention owing to its water level alterations and subsequent ecological problems, the applicability of the method and rationality of the results were verified. The results indicate that hydrological alteration occurs at the water level of the representative stations, which is jointly affected by climate change and anthropogenic activities in this region. For instance, the construction and operation of the Three Gorges Project affected the water level alteration at Hukou and Xingzi station, and drought further aggravated that of Xingzi station. The calculated EWL of Poyang Lake showed obvious spatio-temporal heterogeneity, which is consistent with the topographic, geographical, and climatic characteristics of the basin. And the rationality of the EWL in this study was verified through literature reviews and satisfiability of characteristic species requirements. The proposed EWL calculation method is simple and feasible with easy data acquisition, strong universality, and broad application prospects, offering a scientific basis and quantitative reference for water resource management and lake ecosystem protection. • An ecological water level quantifying method for lakes based on hydrological statistical analysis is proposed. • Water level alteration occurs in Poyang Lake, which is jointly affected by climate change and anthropogenic activities. • The monthly ecological water level thresholds of Poyang Lake are quantified with obvious spatio-temporal heterogeneity. • The calculated ecological water level is reasonable, offering a quantitative reference for water resources management. [ABSTRACT FROM AUTHOR]

• Variations in DOM chemistry across the four periods were explored in Poyang Lake. • More terrestrial DOM inputs were detected during higher water levels periods. • CHOS formulas enhanced the autochthonous DOM features in the dry period. • Hydrological alteration affects DOM chemistry and its overall lability. As the largest reactive organic carbon pool, dissolved organic matter (DOM) plays an important role in various biogeochemical processes in lake ecosystems. Recently, climate change-induced extreme events (e.g., floods and droughts) have significantly modified the hydrological patterns of lakes worldwide, and regulated the quality and quantity of DOM. However, the responses of DOM chemistry to hydrological alteration in lakes remain poorly understood. Here we investigated the influences of hydrological alteration on sources, composition, and characteristics of DOM in Poyang Lake, the largest freshwater lake in China, using a combination of bulk chemical, optical and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques. Results show various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) and significant variations in DOM chemistry across four hydrological periods (the retreating, dry, rising, and flooding periods) in Poyang Lake. During the retreating, rising, and flooding periods, DOM was characterized by higher aromaticity, humification degree, and recalcitrance, and exhibited pronounced allochthonous signatures. In contrast, DOM contained more S-containing molecules and aliphatic compounds during the dry period, displaying relatively stronger autochthonous features. Terrestrial inputs and the lignin-CHOS formation process are likely the primary underlying mechanisms shaping the differences in DOM chemistry in Poyang Lake. Our research demonstrates the significant impacts of hydrological alteration on DOM dynamics, and provides an improved understanding of DOM biogeochemical cycles and carbon cycling in large aquatic systems under global climate change. [Display omitted] [ABSTRACT FROM AUTHOR]

Environmental flow refers to the fundamental hydrological process that sustains the ecosystem of rivers and lakes. Safeguarding environmental flow is crucial for optimal water resource utilization and lake ecosystem preservation. The study delivers a comprehensive exploration of ecohydrology, focusing on the common analysis of runoff and water level (RWL) to evaluate ecohydrological conditions in Hongze Lake (HZL) over five decades (1970–2020). Techniques such as the change point test and wavelet analysis were employed to discern trends and periodicity in hydrological elements. A series of ecologically pertinent indicators was applied to measure the changes in RWL, assessing their impacts on the lake's ecosystem. The Budyko hypothesis and cumulative slope rate of change (CSRC) were integrated for a quantitative analysis that shed light on the ecological response to RWL variations. Differential effects of human activities and climate change on runoff were discerned through subsurface parameter analysis across different decades. The study's results indicate that human activities, particularly gate dam operations and agricultural irrigation, have precipitated a significant reduction in environmental flow components (EFCs). The gate dam manipulation during the dry season has notably influenced the lake's hydrological regime, with a substantial alteration of RWL by 37% and 41%, respectively. This hydrological modification aligns with observed ecological trends such as species population reduction, habitat fragmentation, and organism miniaturization within HZL. Analysis of subsurface parameters also reflected an increasing influence of climatic factors on runoff over time. Human activities, evapotranspiration, and precipitation were found to contribute 75.5%, 10.3%, and 14.2% to runoff alterations, and 70.1%, 11.4%, and 18.5% to water level (WL) changes, respectively. [Display omitted] • Runoff and water level exhibit significant synchronicity and correlation. • The water level rises by an average of 0.43 m during the impact period. • Downstream irrigation demand and dam regulation induce observable intra-annual alteration. • Hydrological indicators indicate a moderate 35–38% variation in both runoff and water level. • Human activities surpass climate factors accounting for 70.1–75.5% of water level and runoff changes. [ABSTRACT FROM AUTHOR]

Lake Baiyangdian, the largest natural freshwater wetland on the North China Plain, has faced multiple stressors from anthropogenic disturbances and climate change, affecting its aquatic ecosystem over the past century. An improved understanding of the relationship between environmental stresses and ecosystem responses and the mechanisms underlying ecological shifts has significant implications for managing the aquatic ecosystem in Lake Baiyangdian. In this paper, we reconstructed the ecological changes in Lake Baiyangdian over the past 70 years based on diatom assemblages in a sediment core and identified ecological shifts by the Sequential t test Analysis of Regime-shifts algorithm (STARS) and a sequential F test. Our results revealed two ecological shifts. The first ecological shift in the diatom community occurred in approximately 1963, which was associated with the rather abrupt changes, i.e., damming in the basin. This hydrological modification prolongs hydraulic residence time and accelerates nutrient retention, consequently leading to an increase in eutrophic species. Subsequently, the second ecological shift occurred in the 1990 s, which was attributed to sustained nutrient loading due to human activity intensification as well as an increase in the regional temperature. Ongoing nutrient loading finally pushed the lake toward a driver threshold, leading to an abrupt shift in the diatom assemblage. Our study details the complex trajectories of aquatic ecosystem shifts driven by hydrological alteration, increasing nutrient loading, and climate change in Lake Baiyangdian and highlights the processes by which ecological shifts occur in response to both abrupt and gradual stressors. [ABSTRACT FROM AUTHOR]

Increasing demand for renewable energy has led to a massive expansion of the small-scale hydropower plants and particularly those of run-of-river type. Meanwhile, the awareness concerning river conservation and restoration is being continually increasing. This study focuses on the assessment of environmental flows releases and energy production considering eight hydrological based environmental flows methods. The main goal of this study is to propose a practical approach that allows for quick estimation of the environmental flows releases and alteration due to water diversion for energy production, in the case of run-of-river hydropower plants. For this purpose, the indicators of hydrological alteration approach was applied to characterise flow alteration, and three economic metrics were used to assess the impact on energy production. Downstream Diversion Index was proposed to characterise the degree of water diversion due to energy production. Also, five new simplified indexes derived from indicators of hydrologic alteration approach were proposed to simplify flow alteration characterisation. The results of this study showed that a minor reduction of energy production could significantly improve environmental flows releases for the riverine ecosystem needs. Particularly, proportional dynamic approaches maximise energy production and imposes relatively less flow alteration. Also, it was concluded that following flow parameters: frequency, timing, duration and rates, can be maintained close to the natural regime without necessarily reducing the energy production by choosing the right environmental flows method. Finally, the methodology developed in this study can be a useful decision-making tool to help water managers, by including other relevant information also (i.e., biological, water supply, irrigation, and social) to choose the most appropriate method for the environmental flows determination in the case of run-of-river hydropower plants. Image 1 • Eight environmental flow methods were applied to estimate the implication on e-flow release and energy production. • Downstream Diversion Index (DDI) was introduced to characterise the degree of water diversion. • Five new indexes were derived from Indicators of Hydrological Alteration (IHA) to simplify flow alteration characterisation. • Proportional dynamic approach preserves essential flow regime parameters and maximises profitability. • Hydropower licensing should guarantee adequate e-flow release and ensure feasible investment. [ABSTRACT FROM AUTHOR]

• We established large-scale patterns of hydrological alteration caused by dams. • We used a hydrological classification and we define types of altered regimes. • Variability of daily flows and high flow events were the most commonly altered features. • The hydrological alteration is influenced by the pre-dam nature of the altered rivers. • Types of altered regime and the purposes of the dams were not directly related. Nowadays, alteration of the natural flow regime is considered one the most widespread and damaging impacts for river ecosystems. Hence, increasing our understanding of large-scale hydrological alteration patterns would help us design more effective water use policies. The present study aims to establish general patterns of hydrological alteration caused by dams on a national level, with Spain as a case study. First, we developed a classification of the natural flow regime of the Spanish river network, which served as the reference to assess the degree of hydrological alteration of 139 altered-river gauges. In addition, using the flow series of the altered-river gauges we defined a set of 7 types of altered regimes (TARs), which allowed the stratification of the analyses. The results revealed that the magnitude and direction of hydrological alteration depended on the natural flow class of the altered rivers. In this regard, major effects of dams on Spanish rivers were related to the modification of the intra-annual variability of daily flow, the magnitude of seasonal maximum and minimum flows and the patterns of high flow events. Our results also showed that the distribution of the TARs partially followed a geographic order, but associations between TARs and natural flow classes were not straightforward. In addition, we highlighted that the nature of the hydrological alteration was independent of the registered dam uses. [ABSTRACT FROM AUTHOR]

Highlights • Cause of emerging canopy gaps in the natural desert riparian forests was discussed. • Effect of hydrological alteration on the canopy gap disturbances was estimated. • Implications for ecological restoration of floodplain forests were put forward. Abstract Due to climate change and excessive human activities, runoff dynamics of the Tarim River in northwest China become more pronounced. Understanding the effects of hydrological alteration on the life strategy and dynamics of the Populus euphratica riparian forests is becoming increasingly important. Forest gaps led by such disturbances change the structure and function of the desert riparian forest ecosystems. However, there is a lack of research on the gap formation and dynamics of this special forest type, for which the main driving force of the gap disturbance has always been unknown. In this study, we investigated several parameters of P. euphratica forest gap, such as gap size, gap age, gap fraction, and gap makers to quantify the gap disturbance regimes in the natural floodplain forests along the Tarim River in arid northwest China. In the middle reaches of the Tarim River, a total number of 263 gap makers and 60 gaps in six 50 m × 50 m plots with a total area of 1.5 hm2 were investigated. The result showed that gap fraction was <5%, and approximately 28.5% of the expanded gaps were from 1.0 to 1.2 in size (ratio of gap diameter to tree height), especially when formed around 1997–2006. The median size of the expanded gap (140.57 m2) in the desert riparian forests was smaller than in tropical forests. P. euphratica was the most abundant gap maker, and its share among gap makers was 12–14 times larger than another species. Furthermore, gap makers contributed to the forest gap size, as shown by a significant correlation between the number of gap makers and the size of expanded gaps, especially those that had been created 50–60 years ago (R2 = 0.455, P < 0.01). The DBH distribution of living trees versus dead trees showed that most P. euphratica mortality occurred in small size classes. However, living trees were equally frequent in large classes, which suggested that large trees were not exclusively injured or died in these P. euphratica stands that were affected by poor habitats, such as water scarcity. We concluded that climate change and anthropogenic activities (increasing water use for irrigation) since the 1970s led to the progressive decrease in water resources at the regional scale and resulted in a higher frequency of forest gaps in the riparian forests along the Tarim River. The results of this study provide useful implications for ecological restoration of P. euphratica to improve sustainable management of desert riparian forests. [ABSTRACT FROM AUTHOR]

Abstract Hydropower plants frequently operate at high output during peak hours and at low output (or even shutoff) during off-peak hours. This scheme, called "hydropeaking", is harmful to downstream ecosystems. Operational constraints (minimum flows, maximum ramps) are frequently used to mitigate the impacts of hydropeaking. However, they reduce the operational flexibility of hydroelectric dams and increase the operational cost of power systems. Another approach to mitigating ecological impacts from hydropeaking is using structural measures, such as re-regulation reservoirs or afterbays. The first contribution of our work is to study the cost-effectiveness of these re-regulation reservoirs in mitigating ecological impacts from subdaily hydropeaking. Our second contribution is assessing energy storage (specifically, batteries) to mitigate the financial impacts of implementing peaking restrictions on dams, which represents the first attempt in the literature. Understanding these mitigation options is relevant for new hydropower dams, as well as for existing ones undergoing relicensing processes. For this, we formulate an hourly mixed-integer linear optimization model to simulate the annual operation of a power system. We then compare the business-as-usual (unconstrained) hydropower operations with ecologically constrained operations. The constrained operation, by limiting hydropower ramping rates, showed to obtain flows close to the natural streamflow regime. As next step, we show how re-regulation reservoirs and batteries can help to achieve these ecological constraints at lower costs. While the former are cost-effective for a very broad range of investment costs, the latter will be cost-effective for hydropeaking mitigation from 2025 onwards, when their capital costs have fallen. If more stringent environmental constraints are imposed, both solutions become significantly more attractive. The same holds for scenarios of more renewable generation (in which the operational flexibility from both alternatives becomes more valuable). After 2030, batteries can match the cost-effectiveness of expensive re-regulation reservoirs. Our findings are valuable for policy and decision makers in energy and ecosystem conservation. Highlights • We compare re-regulation reservoirs with batteries for hydropeaking mitigation. • We develop profitability curves that track profitability alongside capital costs. • Re-regulation reservoirs are highly cost-effective (easily recoup capital costs). • Batteries will become economically viable for hydropeaking mitigation by 2025. • Results will inform public/private sector management of dams' environmental impacts. [ABSTRACT FROM AUTHOR]

Highlights • Hydropower reservoirs and diversions are severely altering Mekong basin streamflow. • Dam-induced flow alteration on both mainstream and tributaries are reviewed. • Alteration assessments must consider hydropeaking, diversions and timing impacts. • Dams can offset or exacerbate impacts of changing climate, water use and land cover. • Observed and projected impacts must be assessed systematically and synergistically. Abstract Hydropower production is altering the Mekong River basin's riverine ecosystems, which contain the world's largest inland fishery and provide food security and livelihoods to millions of people. The basin's hydropower reservoir storage, which may rise from ∼2% of its mean annual flow in 2008 to ∼20% in 2025, is attenuating seasonal flow variability downstream of many dams with integral powerhouses and large storage reservoirs. In addition, tributary diversions for off-stream energy production are reducing downstream flows and augmenting them in recipient tributaries. To help manage tradeoffs between dam benefits (hydropower, irrigation, flood control, domestic water supply, and navigation) and their consequences for livelihoods and ecosystems, we review observed and projected impacts on river flows along both the Mekong mainstream and its tributaries. We include the effects of diversions and inter-basin transfers, which prior reviews of flow alteration in the Mekong basin have largely neglected. We also discuss the extent to which concurrent changes in climate, water demand, and land use, may offset or exacerbate hydropower-induced flow alteration. Our major recommendations for assessing hydrological impacts in the Mekong and other basins undergoing rapid hydropower development include synchronizing and integrating observational and modeling studies, improving the accuracy of reservoir water balances, evaluating multi-objective reservoir operating rules, examining hydropeaking-induced flow alteration, conducting multi-dam safety assessments, evaluating flow indicators relevant to local ecosystems and livelihoods, and considering alternative energy sources and reservoir sedimentation in long-term projections. Finally, we strongly recommend that dam impact studies consider hydrological alteration in conjunction with fish passage barriers, geomorphic changes and other contemporaneous stressors. [ABSTRACT FROM AUTHOR]

We analyzed the conjoint effects of sewage inputs and hydrological alteration on the occurrence of teratological forms and on the assemblage composition of stream benthic diatoms. The study was performed in 11 Mediterranean streams which received treated or untreated urban sewage (Impact sites, I), whose composition and morphological anomalies were compared to upstream unaffected (Control, C) sites. The impact sites had high concentrations of ammonium, phosphorus, and pharmaceutical compounds (antibiotics, analgesics, and anti-inflammatories), particularly in those receiving untreated sewage. Impact sites had a higher proportion of teratological forms as well as a prevalence of diatom taxa tolerant to pollution. The differences in the diatom assemblage composition between the paired C and I sites were the largest in the impacted sites that received untreated sewage inputs as well as in the systems with lower dilution capacity. In these sites, the diatom assemblage was composed by a few pollution-tolerant species. Mediterranean river systems facing hydrological stress are highly sensitive to chemical contamination, leading to the homogenization of their diatom assemblages. [ABSTRACT FROM AUTHOR]

Water exploitation for energy production from Small Hydropower Plant (SHP) is increasing despite human pressure on freshwater already being very intense in several countries. Preserving natural rivers thus requires deeper understanding of the global (i.e., ecological and economic) efficiency of flow-diversion practice. In this work, we show that the global efficiency of SHP river intakes can be improved by non-proportional flow-redistribution policies. This innovative dynamic water allocation defines the fraction of water released to the river as a nonlinear function of river runoff. Three swiss SHP case studies are considered to systematically test the global performance of such policies, under both present and future hydroclimatic regimes. The environmental efficiency is plotted versus the economic efficiency showing that efficient solutions align along a (Pareto) frontier, which is entirely formed by non-proportional policies. On the contrary, other commonly used distribution policies generally lie below the Pareto frontier. This confirms the existence of better policies based on non-proportional redistribution, which should be considered in relation to implementation and operational costs. Our results recommend abandoning static (e.g., constant-minimal-flow) policies in favour of non-proportional dynamic ones towards a more sustainable use of the water resource, also considering changing hydroclimatic scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ecological consequences of river system degradation manipulated by in-river weirs. • Integration of WA and EP methods to determine environmental flow demand and impact. • Hydrodynamic and habitat models to quantify the structural habitat of endemic fishes. • Offer alternative mitigations such as random discharge schemes and rehabilitation programs. In-river hydraulic structures may negatively impact aquatic ecosystems, including changing river flow regimes and the habitat quality of endemic fish habitats. This study integrates the wavelet analysis and the time-series exceedance probability method to quantify the degree of evolution in the river flow regime caused by weirs and determine the critical time scale most affected in the environmental flow. Hydrodynamic and habitat models were conducted to analyze the influence of the variant flow characteristics between the dry and wet seasons on the habitat structure. Four endemic fishes were selected as the indicator species to represent different habitat preferences and reveal the spatiotemporal changes in habitat quality. The flow difference between dry and wet seasons became more extensive after the weir construction, indicating the alternative flow regime downstream. The annual deviation of daily flow dramatically raised, showing the flow rates decline in the dry season and enlarge in the wet season. The findings exhibit that the downstream flow amplitude changes regardless of time scale after constructing the weir. The flow data from the 2-days scale to the 1-week scale were most adjusted, meaning that these periods to meet the environmental flow decline significantly. The critical environmental flow corresponding to lower flow events was apparently influenced in the dry season, in which the Q 75 and Q 90 displayed the highest degradation in fish habitat quality. In addition, the simulation results of the habitat model found that glide is the primary habitat type. The total water area and the habitat diversity were reduced, while the habitat quality also had a lowered tendency after the weir operation. The habitat run was most degraded, and the riffle was also significantly negatively impacted. Regarding the endemic fish species, F. lacustre suffered the most harmful effects on suitable-habitat quality and quantity from the weir. This study suggests considering natural flow regimes at the planning and design phases of weir construction and rehabilitating these essential habitat patterns to mitigate the downstream ecosystem impacts. [ABSTRACT FROM AUTHOR]

The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides , Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The main scope of this study was to assess potential climate change impacts on the hydrological patterns and typical biota for a south-western Balkan mountain river, the Acheloos. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrological model and based on regional climate simulations over the study area. The Indicators of Hydrologic Alteration (IHA) methodology was then used to assess the potential streamflow alterations in the studied river due to predicted climate change conditions. A fish habitat simulation method integrating univariate habitat suitability curves and hydraulic modeling techniques were used to assess the impacts on the relationships between the aquatic biota and hydrological status utilizing a sentinel species, the West Balkan trout. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate change impacts on the south-western Balkan river ecosystems. [ABSTRACT FROM AUTHOR]

The natural flow regime of rivers across the world has been largely modified. Understanding the extent to which the flow regime deviates from natural conditions is necessary for designing sound management and restoration measures. In this regard, ‘Indicators of Hydrologic Alteration’ is currently considered one of the most effective approaches for assessing hydrologic alteration (HA). However, several generalized drawbacks such as the climatic variability between the pre- and post-impacted series and the scarcity of hydrological data in many impaired rivers should be addressed. In this study, a protocol with the following five alternative designs based on data availability is presented: (1) Paired-Before–After Control–Impact (BACIP), (2) Before–After (BA), (3) Control–Impact (CI), (4) Hydrological Classification (HC) and (5) Predicted Hydrological indices (HP). BACIP compares the status of the impacted gauge before and after the perturbation is started, in addition to controlling for natural climatic changes. Hence, it has been considered as the reference benchmark for all other designs. When this protocol was applied to 11 reservoirs situated in the northern third of the Iberian Peninsula, the BA design was able to correctly identify most of the non-significant HA but failed in almost one quarter of the significant alterations. Similarly, BACIP and CI showed an agreement of >80%. This suggests that the method is suitable when proper data are unavailable for BACIP or BA. In addition, our results indicated that the critical thresholds for HA varied depending on the hydrological index being considered. Significant HAs ranged from <5% for the number of days with increasing and decreasing flows to >64% for the duration of low-flow pulses. To delineate adequate thresholds, further research combining hydrological analyses with the biological response to the HA is warranted. Finally, the application of HC and HP designs revealed a significant degree of uncertainty related to the intra-class variability and the predictive error of the models. Therefore, 25% of the analysis could not be evaluated. However, in the evaluable cases, the HC and HP designs correctly assessed >75% of the HA, which highlighted the potential of this method in cases of scarce streamflow data. [ABSTRACT FROM AUTHOR]

Present-day habitats of the Ebro Delta, NE Iberian Peninsula, have been ecologically altered as a consequence of intensive human impacts in the last two centuries (especially rice farming). Benthic foraminiferal palaeoassemblages and sediment characteristics of five short cores were used to reconstruct past wetland habitats, through application of multivariate DCA and CONISS techniques, and dissimilarity coefficients (SCD). The timing of environmental changes was compared to known natural and anthropogenic events in order to identify their possible relationships. In deltaic wetlands under altered hydrological conditions, we found a decrease in species diversity and calcareous-dominated assemblages, and a significant positive correlation between microfaunal changes and organic matter content. Modern analogues supported palaeoenvironmental interpretation of the recent evolution of the Delta wetlands. This research provides the first recent reconstruction of change in the Ebro Delta wetlands, and also illustrates the importance of benthic foraminifera for biomonitoring present and future conditions in Mediterranean deltas. [ABSTRACT FROM AUTHOR]

Dam construction may alter the hydrological regime of rivers, and thus may cause profound and accumulative impacts on a river ecosystem. Therefore, research on hydrological and ecological response to river regulation has received increasing interest. This research, takes the middle reach of the Lijiang River as a case and an indigenous cyprinid fish Spinibarbus hollandi ( S. hollandi ) as a target species for the development of an integrated hydro-environmental-habitat model. In contrast to previous studies focusing only on habitat suitability, this research takes into account habitat quality such as habitat fragmentation. The model analyses the effects of flow regime changes due to upstream reservoir operation on habitats for juvenile fish. Unregulated flow (UF) and regulated flow (RF) were simulated, and the corresponding effects on habitat of S. hollandi were analysed and discussed. Using the developed model, an ecologically-based flow regime was derived ensuring several conservation levels for S. hollandi habitats. Based on the recommended ecological flow regime, rules for reservoir operation are suggested. [ABSTRACT FROM AUTHOR]

Biotic indices developed to assess the ecological status of coastal waters according to the European Water Framework Directive (WFD) often show discrepancies when they are applied in transitional environments. Although several indices have been widely used in transitional waters throughout Europe, there is still a lack of knowledge about their suitability assessing ecological status. We evaluated the performance of most common used biotic indices and community parameters (e.g. Multivariate AZTI's Marine Biotic Index (M-AMBI), BENTIX, Benthic Opportunistic Polychaetes Amphipods index (BOPA), diversity indices, species richness, abundance) that have been proposed in the scope of WFD, using data of macroinvertebrate community coming from a special case of transitional water body, the highly stratified Ebro estuary. Additionally, we tested their ability to respond to the main pressures affecting the Ebro estuary, the hydrological alteration due to regulation and the pollution pressure due to nutrient enrichment. Estimation of hydrological alteration was based on flow historical data (period from 1913 to 1963), that we assumed as 'hydrological reference conditions' for Ebro estuary. Pollution pressure was estimated by means of PCA analysis including organic and nutrient enrichment related variables, expressed as a synthetic index by PCA factor scores extraction. All the community parameters were able to detect changes in macrofauna composition along the estuarine gradients and were able to differentiate between the impoverished stations and the healthier ones. Regarding indices, the ratings were contradictory and only M-AMBI classified the stations in the correct way. Strong significant correlations were found between indices and metrics and the calculated pressures; nevertheless, these correlations showed a paradoxical result, since increasing hydrological alteration benefited the macrofauna, achieving great complexity. Other identified limitations of biotic indices were the opposite classifications, overestimation of ecological status and low resolution ability. We conclude that for transitional water ecosystems, where each water body has particular characteristics, is difficult the use of 'common biological' assessment tools as the results of this study, among others (more details in discussion section), have demonstrated. Nevertheless, M-AMBI seemed to work in the correct way, so further investigation about its use for transitional waters is necessary. The development of new strategies such as the use of historical data, the use of metrics as a complement for the assessment could be a reliable alternative. [ABSTRACT FROM AUTHOR]

This study models the effect of climate change on runoff in southeast Korea using the TANK conceptual rainfall-runoff model. The results are assessed using the indicators of hydrological alteration (IHA) developed by U.S. Nature Conservancy. Future climate time series are obtained by scaling historical series, provided by four global climate models (GCMs, IPCC, 2007 ) and three greenhouse gas (GHG) emissions scenarios ( IPCC, 2000 ), to reflect a maximum increase of 3.6 °C in the average surface air temperature and 33% in the annual precipitation. To this end, the spatio-temporal change factor method is used, which considers changes in the future mean seasonal rainfall and potential evapotranspiration as well as the daily rainfall distribution. In this study, the variance range for precipitation is from +3.55% to +33.44% compared to the present for years between 2071 and 2100. The variance range for the daily mean temperature is estimated between +1.59 °C and +3.58 °C. Although the simulation results from different GCMs and GHG emissions scenarios indicate different responses of the flows to the climate change, the majority of modeling results show that there will be more runoff in southeast Korea in the future. According to the analysis results, the predicted impacts of hydrological alteration caused by climate change on the aquatic ecosystem are as follows: 1) an increase in the availability of aquatic ecosystem habitats in Nakdong River in future summers and winters, 2) an increase in stress on the aquatic ecosystem due to extremely high stream flow, 3) an increase in the stress duration of flood events for the Nakdong River downstream and 4) an increase in aquatic ecosystem stress caused by rapid increases or decreases in stream flow. [ABSTRACT FROM AUTHOR]

• Proposed a new approach using cloud model with multiple weighting method (CM-MW). • Quantified the contribution rates of climate change and human activity to hydrological alteration. • CM-MW was able to select the more reasonable weights for the IHA parameters. • CM-MW method evaluate the percent data that the ODHA would fall into the respective category. Understanding the hydrological alterations caused by climate change and human activities and the underlying impact factors are essential for sustainable water resource management in river basins. Several statistical methods, particularly the Indicator of Hydrologic Alteration (IHA), have been successfully employed to assess the degree of hydrologic alteration. This study proposed a new approach, the cloud model combined with the multiple weighting method (CM-MW), for better quantification of the overall degree of hydrologic alteration. This approach adopts game theory to select reasonable weights for the IHA parameters, therefore improving the accuracy and reliability of the evaluation. By estimating the similarity between the evaluation cloud and the category cloud, this method quantifies the percent data for which the overall degree of hydrological alteration (ODHA) would fall into the respective category. Analysis based on the Budyko framework indicated that in the Illinois River Basin, the dominant causes of hydrologic alteration for watersheds with moderate ODHA and low ODHA were human activities and climate change. The proposed method had a distinct advantage over the conventional approach in classifying the overall hydrological alteration, which would provide more accurate information for comprehensive and adaptive river basin management. [ABSTRACT FROM AUTHOR]

Abstract: After the construction and operation of the Three Gorges and Gezhouba dams, their impacts on hydrologic alterations in the middle and lower reach of Yangtze River are under high attention worldwide, of which the balance between the human and environmental flow requirements is one of the most important issues. This study uses an optimization model for the operation of reservoirs to compare the different environmental flow requirements of river ecosystems. Based on the different environmental flow requirements, four scenarios were established: (1) the no environmental flow case; (2) the minimum environmental flow (MEF) case; (3) the appropriate environmental flow (AEF) case; and (4) the environmental design flow (EDF) case. The EDF case is first proposed in this paper, which considers the reservoir adjustment ability and comprehensively balances the economic, social and ecological benefits. The Range of Variability Approach (RVA) is used to evaluate the potential hydrological alterations of each of the four scenarios. The comparison results of the power production and the degree of hydrological alteration in the four different scenarios, indicate that the system operation under the EDF case imposes the least hydrological alteration while providing adequate power production. The encouraging results demonstrate that this method will be a robust tool for practitioners to better perform reservoir operations in balancing the human and environmental requirements. [Copyright &y& Elsevier]

Summary: Water demand for hydropower production has been increasing along with a growing awareness of the importance of preserving riparian ecosystems and their biodiversity. Some Cantons in Switzerland have begun replacing the inadequate concept of Minimum Flow Requirement (MFR) with a dynamic one, by continuously releasing a percentage of the total inflow. In this work, we evaluate both ecological and economical benefits of dynamic release policies within a diverted river reach in the Swiss Canton of Graubünden. We compare such policies to another one that generates inflow-dependent variable releases as a result of an economic competition between traditional (e.g., hydropower) and non-traditional (e.g., environment) water uses (Perona et al., 2013). We propose to compute flow statistics from different release polices by using Indicators of Hydrologic Alteration (Richter et al., 1996; Richter et al., 1997). Then, we aggregate the hydrological differences from the natural flow regime as a proxy for assessing environmental benefits and we look at the mean of the ratio of the allocated net flows between environment and hydropower as a suitable engineering parameter to represent their relative value. Eventually all the simulated release policies find an economical significance explained by marginal utility functions. We show that dynamic redistribution policies can perform better than MFR-like ones. Moreover, by introducing the concept of inflow-dependent water allocation, both economic and ecological indicators can be further improved, without necessarily implying higher installation costs. This method aims to provide a simple but effective step towards eco-sustainability in the growing market of mini hydropower plants, where MFR-rules are still widespread. [ABSTRACT FROM AUTHOR]

Abstract: Chaohu Lake, the fifth largest freshwater lake in the Yangtze floodplain, is faced with multiple stresses from anthropogenic disturbances and climate change. To explore the ecological changes in Chaohu Lake since the mid 20th century, we examined diatoms, geochemical indicators and particle size in 210Pb-dated sediment core from the lake. Diatom succession revealed that the lake had switched to a eutrophic state since the late 1970s. Redundancy analysis using limnological data, hydrological and meteorological variables showed that sedimentary total phosphorus (TP) and total organic carbon (TOC), annual mean temperature, annual mean wind velocity, and water-level amplitude (WLA) were five significant factors influencing diatom succession. Diatom assemblages from 1950 till 1978 were driven by WLA and wind. The establishment of Chaohu Dam baffled hydrological connectivity between the lake and the Yangtze River in 1962, and reducing water exchange-induced flow. Meanwhile, weak wind velocity reduced the wind-induced flow in the 1960s. Due to the weak hydrodynamic intensity, the dominant species (Aulacoseira granulata, a species with high sinking rate) became less important during this period. From 1979 till 2006, diatom assemblages were mainly driven by TP, TOC and temperature, which were highly correlative. Increasing nutrient loading promoted the blooms of eutrophic species (e.g., Cyclostephanos dubius). In addition, rising temperature would indirectly influence diatom assemblages by mediating nutrient release process. As a consequence, multiple stresses in concert have caused the lake switch to a further eutrophic state indicated by prominent increases in more eutrophic species (e.g., Stephanodiscus parvus) since 2000. This study provided information on complex trajectories of aquatic ecosystem shifts driven by increasing nutrient loading, hydrological alteration and climate warming in the Yangtze floodplain lake. [Copyright &y& Elsevier]

Summary: The management of water through the impoundment of rivers by dams and reservoirs is necessary to support key human activities such as hydropower production, agriculture and flood risk mitigation. Advances in multi-objective optimization techniques and ever growing computing power make it possible to design reservoir operating policies that represent Pareto-optimal tradeoffs between multiple interests. On the one hand, such optimization methods can enhance performances of commonly targeted objectives (such as hydropower production or water supply), on the other hand they risk strongly penalizing all the interests not directly (i.e. mathematically) included in the optimization algorithm. The alteration of the downstream hydrological regime is a well established cause of ecological degradation and its evaluation and rehabilitation is commonly required by recent legislation (as the Water Framework Directive in Europe). However, it is rarely embedded in reservoir optimization routines and, even when explicitly considered, the criteria adopted for its evaluation are doubted and not commonly trusted, undermining the possibility of real implementation of environmentally friendly policies. The main challenges in defining and assessing hydrological alterations are: how to define a reference state (referencing); how to define criteria upon which to build mathematical indicators of alteration (measuring); and finally how to aggregate the indicators in a single evaluation index (valuing) that can serve as objective function in the optimization problem. This paper aims to address these issues by: (i) discussing the benefits and constrains of different approaches to referencing, measuring and valuing hydrological alteration; (ii) testing two alternative indices of hydrological alteration, one based on the established framework of Indicators of Hydrological Alteration (Richter et al., 1996), and one satisfying the mathematical properties required by widely used optimization methods based on dynamic programming; (iii) demonstrating and discussing these indices by application River Ticino, in Italy; (iv) providing a framework to effectively include hydrological alteration within reservoir operation optimization. [Copyright &y& Elsevier]

Abstract: Hydrological alteration caused by dam operation and river modification has changed the dynamics of riparian vegetation in most river floodplain systems. In this study, a dynamic vegetation model was used to analyze the change in floodplain area occupied by individual vegetation types and vegetation succession dynamics as consequences of river modification and dam operation. The vegetation model simulates spatially distributed vegetation types based on simulated river floodplain physical processes. Study periods were classified into historic, pre-dam and post-dam conditions. The statistical t-test was used to analyze changes in the normalized mean area occupied by different vegetation types between different time periods. Furthermore, the Mann–Kendall test was used to evaluate the succession trend of vegetation with respect to spatial area and age. The area occupied by colonization and cottonwood young transition vegetation was similar in historic and pre-dam conditions, but decreased gradually from pre-dam to post-dam conditions. In contrast, the reed and grassland vegetation gradually increased from historic to post-dam conditions. The cottonwood old transition vegetation increased from pre-dam to post dam condition. The average age of the vegetation did not significantly increase or decrease in historic and pre-dam conditions; however, it increased in the post-dam condition. There were no significant differences in the succession trends of vegetation area between historic and pre-dam conditions for most of the vegetation types, except for reed and grassland and cottonwood old transition vegetation. The succession trends of vegetation area were significantly different between pre- and post-dam conditions for all vegetation types except for the wetland vegetation. Our vegetation model illustrated the impact of altered physical processes on riparian ecosystems. Such spatial and quantitative measurements of vegetation distributions can be used to quantify the riparian habitat losses from dam operation, which can help to manage and restore riparian vegetation in human disturbed systems. [Copyright &y& Elsevier]

Abstract: The alteration of natural water-level-fluctuation patterns is a key cause of ecological degradation in lake ecosystems. In this research a method is developed to measure the alteration degree of natural water-level-fluctuation patterns in lakes. Utilizing this method, a series of indicators are developed that can reflect the pattern of water level fluctuation. The dissimilarity between the pre- and post-impacted frequency histograms for each indicator is evaluated using a metric called the Earth Mover''s Distance. A case study of Baiyangdian Lake shows the water-level-fluctuation pattern alteration degree calculated by the new method is consistent with the ecological degradation degree, indicating the new method''s ability to reflect the ecological degradation degree based only on hydrological data [Copyright &y& Elsevier]

• Define WQL and HA considering ecological demands of water quantity and fluctuation. • The general process of defining ecological objectives can be applied to other reservoirs. • Incorporate ecological objectives into operation model with economic objective. • Set up different scenarios to search for optimal reservoir operation strategy. The construction and operation of reservoirs arise the problems in downstream river of hydrological regime alteration and threat to freshwater biodiversity. Currently, most researches on reservoir operation model considering downstream ecology just quantify single ecological objective, which is difficult to reflect the downstream ecological demands comprehensively. To address the challenges above, this paper divides the parameters in Indicators of Hydrological Alteration (IHA), a widely used tool reflecting flow regime from multiple perspectives but seldom applied to guide practice reservoir operation, into two categories to reflect ecological demands of water quantity and fluctuation respectively. Then, two ecological objectives of Water Quantity Level (WQL) and Hydrological Alteration (HA) are defined to be incorporated into reservoir operation model with the economic objective of Hydropower Production (HP) for generating optimal operation strategy coordinating economic and ecological benefits. The case study of a typical reservoir in Hunan Province, China shows that: 1) two ecological objectives defined can reflect the alteration of hydrological regime from the perspective of water quantity and fluctuation accurately; and 2) compared with historical operation strategy and optimal operation strategies in the other two scenarios, the optimal operation strategy in scenario C is proved an excellent strategy to guide operation practice reconciling the economic benefits of hydropower plant with the ecological benefits of downstream river, which can balance two objectives of WQL and HA well with high level HP and make the released flow maintain more regime of natural flow. [ABSTRACT FROM AUTHOR]

• Hydrologic changes enhanced CH 4 emission, but inhibited CO 2 and N 2 O fluxes. • N and N + P addition increased N 2 O fluxes, which is contrary to p addition. • No interactive effects of hydrologic changes and nutrient additions on GHGs fluxes. • Global warming potential was reduced by continuous flooding and enhanced by N + P. Changes in global rainfall patterns and construction of artificial dams have led to widespread alteration of hydrological processes in riparian ecosystems. At the same time, many riparian ecosystems, such as those associated with the Yangtze, are being subjected to enhanced inputs of nitrogen (N) and phosphorus (P) due to intensified agricultural activity in surrounding uplands. Together, these environmental changes may alter the magnitude and direction of greenhouse gasses (GHGs) fluxes from riparian soils. We conducted an in situ experiment combined with quantitative PCR approach (qPCR) to elucidate the effects of hydrological alterations (continuous flooding (CF), periodic flooding (PF), and no flooding (NF)) and nutrient addition (N addition (urea, 100 kg N ha−1 y−1), P addition (P 2 O 5 , 20 kg ha−1y−1), N + P addition, and control (CK)) on three major GHGs including carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2 O) fluxes as well as the underlying mechanisms. Our results showed that hydrological alterations greatly affected GHGs emissions, possibly by altering soil moisture, soil organic C, and C:N ratios. The CF, with higher soil moisture and lower C:N ratio, increased CH 4 emissions 13-fold and reduced CO 2 and N 2 O emissions by 37.3% and 72.2% averaged over the growing seasons compared with no flooding. PF enhanced CH 4 emissions 5.7-fold and decreased N 2 O emissions by 69.0% in comparison with no flooding. Nutrient additions had no significant effect on CO 2 or CH 4 flux, but P addition significantly lowered N 2 O flux. Interactions between hydrological alterations and nutrient additions were not detected for any GHGs. As a result, hydrological alterations and nutrient additions affected the global warming potential (GWP) of growing season GHG budgets on a 100-year time horizon, mainly by changing the CO 2 emissions. CF reduced GWP from 597 to 439 g CO 2 -eq m−2, and N + P addition enhanced GWP from 489 to 625 g CO 2 -eq m−2. The qPCR analysis revealed that decreased CH 4 oxidation potential may lead to the enrichment of CH 4 emissions under the hydrological alterations, and reduced nitrification and denitrification potential contributed to the reduction of N 2 O fluxes under all the treatments. Our study indicates that continuous flooding could curb the contribution of riparian GHGs fluxes to global warming but that the combination of N and P additions may increase the greenhouse effect mainly by regulating the CO 2 emissions of growing season in riparian ecosystem. [Display omitted] [ABSTRACT FROM AUTHOR]

• Hydraulic and Habitation models were coupled to assess the Environmental Flow Requirements (EFRs). • Hydrological alteration analysis indicates possible reasons for non-attainment of EFR due to the presence of the dams. • The presence of dam controls flows for anthropogenic activities and affects ecology and biodiversity. Anthropogenic activities in the Krishna River have altered its flow regime and affected the ecosystems in the river. It is essential to maintain an optimum Environmental Flow (EF) in the river to recover from its deteriorated ecosystem. The present study is to estimate Environment Flow Requirement (EFRs) and the Hydrological Alteration (HA) (Flow changes) that take place on the Krishna River at five dam sites. Pre and post construction impact flow data are collected at five gauge stations which are located downstream of these five dams. The flow data which are impacted by climate variability are removed and the study is focussed on the impact of human activities. These EFRs are estimated using statistical relationships between the Krishna River flow regime and ecological indicator with the help of the Global Environmental Flow Calculator (GEFC). HA is used to analyse how the recommended EFRs are different in the post-impact period (after the dam construction). Hydraulic indicators like water depth and velocity are determined by importing estimated EF values into a Hydrologic Engineering Centre's - River Analysis System (HEC-RAS) model. The habitation analysis is carried out to check whether the hydraulic indicators are providing an acceptable habitation for aquatic species in the study area. The results from HA analysis showed that the required EFRs in the Krishna River were not maintained for almost 43% of the time in the post impact period. The hydraulic analysis showed that recommended EFR is providing velocity in the range of 0.12 m/s to 1.08 m/s and water depth in the range of 0.23 m to 3.16 m throughout the basin. From the habitation study, it is observed that the results obtained from the GEFC approach is providing excellent habitation under the dams of Srisailam and Nagarjuna Sagar. Good habitation conditions are seen under Narayanapur, Ujjani, and PD Jurala dams. [ABSTRACT FROM AUTHOR]

In recent decades many studies have proven the paramount impact of flow regimes on the structure of lotic ecosystems, both through extreme events (i.e. floods and droughts) but also during intermediate flows, which temporarily and spatially regulate the habitat availability. Human demand for water is steadily increasing and scientists are challenged to define ecosystem needs clearly enough to guide policies and management strategies. However, field studies demonstrated that a variety of interacting factors, such as, presence of barriers (e.g. dams) and temporal changes in habitat structure affect the abundance, composition and distribution of fish assemblages. This work based on quantile regression tested hypotheses to elucidate the effect of antecedent hydrological conditions on fish communities. A large monitoring database collecting and homogenizing the existing information on fish fauna in the Júcar River Basin District (Eastern Iberian Peninsula) was gathered and used to evaluate biological metrics (species richness, Capture Per Unit Effort-CPUE, and CPUE ratio over the total CPUE) related to life history strategies (i.e. periodic, opportunistic or equilibrium) and species origin (i.e. native, translocated or alien). The resulting dataset was complemented with diverse indicators of the measured daily discharge at the nearest gauging site. Most of the significant relationships confirmed the role of antecedent hydrological conditions as limiting factors, although other environmental factors likely play additional roles. In general, richness and abundance of alien species showed the higher proportion of significant associations, particularly spring flows and annual minima and maxima. These flow-ecology relationships shall be particularly useful to manage ecological responses to hydrological alteration. They also provide with clear ecological foundations for developing environmental flows assessments in Mediterranean river basins worldwide, using holistic approaches which can harmonise eco-hydrological approaches with smaller-scale and habitat-based ecohydraulics methods, especially under the current climate trends. Unlabelled Image • Quantile regression provided with flow-ecology relationships for fish communities. • Native species abundance proved to be related with the timing of minimum flow. • Alien species are favoured by lower annual minima and smaller annual maxima. • To manage minimum and high flows is crucial to obtain ecological benefits. • Robust flow-ecology relationships can greatly improve environmental flows assessments. [ABSTRACT FROM AUTHOR]

• This work delimits multi-criteria based riparian corridor. • The riparian habitat quality was evaluated for pre and post HA phases. • The riparian zone was decreased by 12.29% in post HA phase. • The very poor riparian quality area has increased over time. • The riparian quality models were validated using ROC, wilcoxon signed rank test. Riparian corridor, a vital ecotonian ecosystem is under stress due to flow reduction and inconsistency of flow in Lower Tangon river basin across the neo tectonically active Barind tract of India and Bangladesh. But it is ill defined and its habitat quality is rarely assessed insipite of its immense socio-ecological importance. The present work intends to delineate the riparian corridor and quality assessment of the riparian habitat in reference to the hydrological alteration (HA) triggered by anthropogenic activities, mainly damming in 1989. The present work applied multi-parametric (altitude, topographic roughness, water body, forest patches) approach for delineating the riparian corridor instead of existing uni-criterion approaches for the same. Quality assessment of the habitat is done using nine surface, ecological, hydrological and anthropogenic parameters in the Arc Gis platform employing advance machine learning algorithms like Fuzzy logic (FL), Artificial Neural Network (ANN), Random Forest (RF), Random subspace, Dagging and Support vector machine (SVM). Total 20.63 km2 and 18.36 km2 areas respectively in pre and post-HA periods alongside the main river are identified as the riparian corridor. HA has reduced the area under the riparian corridor by 12.29% in post-HA state. Simultaneously, the quality of the riparian habitat is also deteriorated in the post-HA period. In pre-HA state, 49.05% area was under good to very good riparian habitat but it is reduced to 11.86% in post-HA state. Regularization of the flood, release of ecological flow to the downstream, renovation of tie channels between flood plain and river, restriction in agricultural invasion towards riparian forest and wetland are some of the essential steps for minimizing qualitative deterioration of riparian habitat and amelioration of the ecosystem concerned. [ABSTRACT FROM AUTHOR]

• Flow regulation impacts strongly depend on dam operation and water use. • The magnitude and duration of exposure to flow alterations affect ecological outcomes. • Deviations from natural flow variability should inform damming environmental costs. • Inter-annual flow variability produces changes in fish-based ecological quality. The present study has been taken up to quantify the impacts of the anthropogenic activities on the hydrology of the middle and lower stretches of the Krishna River over the past sixty years. The Flow Health (FH) method which is based on the Range of Variability Approach (RVA) is used to quantify the hydrological alteration (flow changes) of different flow characteristics. The flow characteristics of pre- and post-dam impact periods are compared and evaluated to understand the ecologically sensitive streamflow parameters. The study is primarily focussed on the impact of human activities such as dam constructions. The wet and dry periods are excluded as they are impacted by climate variability. Results of the study confirmed that the impact of the Nagarjuna Sagar on the Krishna River Basin is the highest among the five dams studied, with an average FH score of 0.54 and that of PD Jurala dam is the lowest, with an average FH score of 0.65. This study will be beneficial to help restore regional water resources and eco-environmental system in the middle and lower Krishna River Basin. [ABSTRACT FROM AUTHOR]

We employed the well-established Horton-Strahler, hierarchical, stream-order (ω) scheme to investigate scaling of nutrient loads (P and N) from ~845 wastewater treatment plants (WWTPs) distributed along the river network in urbanized Weser River, the largest national basin in Germany (~46K km2; ~8.4 million population). We estimated hydrologic and water quality impacts at the reach- and basin-scales, at two steady river discharge conditions (median flow, Q R50 ; low-flow, Q R90). Of the five WWTPs class-sizes (1 ≤ k ≤ 5), ~68% discharge to small low-order streams (ω < 3). We found large variations in capacity to dilute WWTP nutrient loads because of variability in (1) treated wastewater discharge (Q U) within and among different class-sizes, and (2) river discharge (Q R) within low-order streams (ω < 3) resulting from differences in drainage areas. For Q R50 , reach-scale water quality impairment assessed by nutrient concentration was likely at 136 (~16%) locations for P and 15 locations (~2%) for N. About 90% of these locations were lower-order streams (ω < 3). At Q R50 and only with dilution, basin-scale cumulative nutrient loads from multiple upstream WWTPs increase impaired locations to 266 (~32% of total) for P. Considering in-stream uptake decreased P-impaired streams to 225 (~27%), suggesting the dominant role of dilution in the Weser River basin. Role of in-stream uptake diminished along the flow paths, while dilution in larger streams (4 ≤ ω ≤ 7) minimizes the impact of WWTP loads. Under Q R90 conditions [(Q R50 /Q R90) ~ 2.5], water quality impaired locations will likely double for the basin-scale analyses. Long-term water quality data suggested that diffuse sources are the primary contributors for water quality impairments in large streams. Our data-modeling synthesis approach is transferable to other urbanized river basins and extends understanding of point source impacts on water quality across spatial scales. Unlabelled Image • Basin-wide point source density is 0.02 km-2 at mean separating distance of 11 km. • Nutrient loads from point sources scale exponentially with river stream-orders. • Ecological threshold (P) is exceeded in 27% (56%) of reaches at median (low) flows. • Ecological threshold (N) is exceeded in ~4% (14%) of reaches at median (low) flows. • In-stream uptake in low-order and dilution in high-order streams control impacts. [ABSTRACT FROM AUTHOR]