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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.

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Highly regulated basins have traditionally required management practices to mitigate the negative environmental impacts and ensure human well-being. This paper proposes and assesses environmental and water supply deficit indicators to assist in the management of environmental flows (e-flows). For that, a water allocation model is applied, and hydrological alteration, habitat alteration and water supply indicators are quantified, normalized and integrated into a general basin management indicator. This basin management indicator is analyzed for four management approaches and seven e-flow scenarios in the Júcar River Basin (eastern Spain). Hydrological alteration indicators show a less pronounced alteration in the river sections located upstream of the basin while a higher alteration in the downstream sections. As for the habitat indicators, they experience an improvement compared to the natural regime. Based on the values of the basin management indicator, the best e-flow scenario to adopt in the Júcar River Basin is selected. The indicators proposed in this work are useful for supporting decision-making regarding the planning and management of e-flows in regulated river basins worldwide.

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Ecological flow is an important indicator for reflecting the stability of a watershed ecosystem. The calculation of ecological discharge under hydrological variation has become a research hot-spot. The Ganjiang River south of Poyang Lake in China was taken as an example in this study. Hydrological Alteration Diagnosis System methods were used to detect the change-points. The Distributed Time Variation Gain Model (DTVGM) was used to carry out runoff restoration. The Probability-weighted Flow Duration Curve was applied to calculate the ecological flow. The results showed that: (1) The hydrological alteration of the Waizhou Station occurred in 1991, the annual runoff increased by 10%, and the Gini coefficient (GI) increased by 0.07 after the change-point. The change in precipitation was the main driving factors. (2) The R value and NSE of the DTVGM were greater than 0.84, which represents the feasibility of the model used to restore runoff. (3) Compared to the traditional hydrological method, the proposed method can better reflect the inter-annual difference of ecological flow, flow ranges for high, normal, and low flow years are 398-3771 m3/s, 352-2160 m3/s, and 277-1657 m3/s, respectively. The calculation method of ecological flow in rivers considering hydrological variation can more scientifically reflect the impact of hydrological variation on ecological flow process, ecological flow under different human activities that can be calculated, such as dam control, water intake and water transfer, furthermore, it also provides a scientific basis for water resources planning and allocation under changing environment.

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Inundations of wetlands play a significant role in wetland ecosystems, but they are vulnerable to hydrological alterations. In Southeast Asia, many hydro-dams, which significantly alter the hydrology, have been built, but little is known about the influences of dams on wetland inundations. In this study, we quantified the characteristics of inundations and related the alterations to the dams by distinguishing them from influences of climate variabilities and local human activities. A multi-sensor approach using Landsat 8, Sentinel-1, and MODIS was devised to delineate the weekly inundations of 362 Southeast Asian wetlands from 2014 to 2021. The four hydrological characteristics (cyclical patterns, trends, intra-annual variability, and amplitude of inundations) were quantified, and the alteration of the characteristics caused by dams was separated from climate variabilities and local human activities using correlation analysis and logistic regression models. The results found that cyclical patterns, trends, intra-annual variability, and amplitude of wetland inundations changed significantly over the period, but the magnitudes vary significantly depending on their geographic locations with respect to the dams. Findings showed that dams critically affect the wetlands even though dams are located distantly from the dams. This indicates that wetlands should be monitored and conserved for reducing the influences of dams. This study advances our understanding of the effects of dams on wetlands by using the multi-sensor approach and distinguishing them from climate variabilities and local human activities.

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The Ganga-Brahmaputra moribund deltaic floodplain region hosted many socio-ecologically precious freshwater wetland ecosystems experiencing hydrological alteration. The present study aimed to model hydrological strength (HS) to show the spatial difference and account for the degree and direction of hydrological alteration of Indian moribund deltaic wetland in three phases e.g. (1) phase I (1988-1997), (2) phase II (1998-2007) and phase III (2008-2017). Three key hydrological parameters, such as Water Presence Frequency (WPF), water depth, and hydro-period were considered for hydrological strength modelling using two ensemble Machine Learning (ML) techniques (Random Forest (RF) and XGBoost). Image algebra was employed for phasal change detection. Hydrological strength models show that around 75% of the wetland area was lost in-between phases I to III and the loss was found more intensive in moderate and weak HS zones. Existing wetland shows a clear spatial difference of HS between wetland core and periphery and river linked and delinked or not linked wetlands. Regarding the suitability of the ML models, both are acceptable, however, the XGBoost outperformed in reference to applied 15 statistical validation techniques and field evidence. HS models based on change detection clarified that more than 22% and 55% of the weak HS zone in phases II and III respectively were turned into non-wetland. The degree of alteration revealed that about 40% of wetland areas experienced a negative alteration during phases I to II, and this proportion increased to 63% in between phases II to III. Since the study figured out the spatial nature of HS, degree and direction of alteration at a spatial scale, these findings would be instrumental for adopting rational planning towards wetland conservation and restoration.

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Rivers are among the most threatened ecosystems worldwide and are experiencing rapid biodiversity loss. Flow alteration due to climate change, water abstraction and augmentation is a severe stressor on many aquatic communities. Macroinvertebrates are widely used for biomonitoring river ecosystems although current taxonomic approaches used to characterise ecological responses to flow have limitations in terms of generalisation across biogeographical regions. A new macroinvertebrate trait-based index, Flow-T, derived from ecological functional information (flow velocity preferences) currently available for almost 500 invertebrate taxa at the European scale is presented. The index was tested using data from rivers spanning different biogeographic and hydro-climatic regions from the UK, Cyprus and Italy. The performance of Flow-T at different spatial scales and its relationship with an established UK flow assessment tool, the Lotic-invertebrate Index for Flow Evaluation (LIFE), was assessed to determine the transferability of the approach internationally. Flow-T was strongly correlated with the LIFE index using both presence-absence and abundance weighted data from all study areas (r varying from 0.46 to 0.96). When applied at the river reach scale, Flow-T was effective in identifying communities associated with distinct mesohabitats characterised by their hydraulic characteristics (e.g., pools, riffles, glides). Flow-T can be derived using both presence/absence and abundance data and can be easily adapted to varying taxonomic resolutions. The trait-based approach facilitates research using the entire European invertebrate fauna and can potentially be applied in regions where information on taxa-specific flow velocity preferences is not currently available. The inter-regional and continental scale transferability of Flow-T may help water resource managers gauge the effects of changes in flow regime on instream communities at varying spatial scales.

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Large lakes provide various types of ecosystem services (ESs), of which stocks and variations induced by hydrological alterations are largely unquantified. The present study investigates the long-term changes of five key ESs (i.e., flood regulation, water supply, fish production, nutrient retention and biodiversity conservation) in a large river connected lake (Poyang Lake), with special attention to impacts of hydrological alteration induced by the Three Gorges Dam (TGD). Hydrological data series, hydrodynamic model, the nutrient balance, fishery statistics, and wetland winter waterbird survey data from 1980 to 2016 were employed. Results showed that Poyang Lake provide significant ESs, with long-term average flood regulation, water supply and nutrient retention services of 167.7 × 108 m3, 31.53 × 108 m3, and 15.12% of total phosphorus load, respectively. The fish production service ranged from 1.74 × 104t to 7.19 × 104t, with an average value of 3.12 × 104t. All five key ESs exhibited a downward trend since the 2000s, especially for water supply, fish production and nutrient retention services (p < 0.05), which might be largely attributed to the hydrological condition changes induced by TGD operation. Nevertheless, more detailed monitoring data and biophysical models are required to further acknowledge the changes in biodiversity conservation and fish production services and their linkages with the TGD. The present study sheds light on long-term ES changes in large lakes and their possible linkages with human influences through hydropower projects.

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This paper presents a methodology to assess the effects of management strategies of environmental flows on the hydrological alteration of river basins on a daily scale. It comprises the collection and analysis of data, the implementation and calibration of a water allocation model; the computation of the natural flow regime; and the estimation, normalization, and aggregation of hydrological alteration indicators to obtain a global indicator of the hydrological alteration. The methodology was applied to a case study in the Iberian Peninsula: The Orbigo River basin, which belongs to the Duero River basin district. For that, three management scenarios were defined: the current scenario, a scenario without any environmental flow and the scenario with the environmental flows initially projected for the period 2022-2027. These scenarios were modelled with the SIMGES water allocation model, which is calibrated in the study site, and the hydrological alterations in four river stretches with different locations and characteristics were assessed. The implications of each environmental flow scenario on the demand reliabilities were also analysed. The global indicator of hydrological alteration obtained in the projected scenario was greater (better) than those of the other two scenarios, but the reliabilities of the water demands were worse. The methodology proposed in this work can be helpful to design environmental flow regimes considering both the effects on the hydrological alteration and the implication on the water demand reliabilities.

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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 (P2O5, 20 kg ha-1y-1), N + P addition, and control (CK)) on three major GHGs including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) 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 CH4 emissions 13-fold and reduced CO2 and N2O emissions by 37.3% and 72.2% averaged over the growing seasons compared with no flooding. PF enhanced CH4 emissions 5.7-fold and decreased N2O emissions by 69.0% in comparison with no flooding. Nutrient additions had no significant effect on CO2 or CH4 flux, but P addition significantly lowered N2O 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 CO2 emissions. CF reduced GWP from 597 to 439 g CO2-eq m-2, and N + P addition enhanced GWP from 489 to 625 g CO2-eq m-2. The qPCR analysis revealed that decreased CH4 oxidation potential may lead to the enrichment of CH4 emissions under the hydrological alterations, and reduced nitrification and denitrification potential contributed to the reduction of N2O 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 CO2 emissions of growing season in riparian ecosystem.

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Human-induced changes in land and water resources adversely affect global hydrological regimes. Hydrological alteration of the natural flow regime is considered to have a significant damaging and widespread impact on river ecosystems and livelihoods. Therefore, understanding the hydrological alteration of rivers and the potential driving factors affecting such alterations are crucial to effective water resources management. This study analyses the impact of changes in land use, climate, and hydropower development on the hydrological regime of the Srepok River Basin in the Lower Mekong Region. The Lower Mekong Basin (LMB) in Southeast Asia is known for its agriculture, forests, fisheries, wildlife, and diverse natural ecosystems. Historical land use and climate change are quantified (utilising European Space Agency land cover and observed meteorological data) and correlated with the hydrological indicators using the Indicators of Hydrologic Alteration (IHA) software. Moreover, pre and post impacts on the hydrological regime by hydropower development are quantified using the Range of Variability Approach (RAV) in IHA software. The results reveal that land use, rainfall, and temperature affect different aspects of the hydrological regime, with corroborating evidence to support variation among the most correlated IHA and environmental flow component (EFC) parameters with the three drivers. The highest and lowest correlations among the IHA and EFC parameters under each driver are against land use (0.85, -0.83), rainfall (0.78, -0.54), and minimum and max temperatures (0.42, -0.47). Among the parameters, the fall rate has the most significant effect on hydrological alteration of all drivers. Hydropower development in the basin mostly affects the fall rate and reversal. Identifying the connection between these multiple drivers and hydrological alteration could help decision-makers to design more efficient and sustainable water management policies.

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Extensive efforts have been undertaken in the northern Gulf of Mexico to restore coastal wetlands that have been lost rapidly. The evaluation of these restorations mostly focused on individual-project scales. A modeling framework that can coherently synthesize multi-scale monitoring data and account for various uncertainties would improve quantitative evaluations at broader spatial scales needed for regional decision-making. We aim to develop such a framework to investigate the impact of different restoration methods (hydrological alteration, breakwater infrastructure, vegetative planting, or marsh creation using dredged materials) on wetland loss on the outermost mainland coastlines in Louisiana. We did this by implementing multi-level Bayesian models to predict areal wetland loss (1996-2005 before Hurricane Katrina) as a function of local geophysical variables (relative sea-level rise, wave height, tidal range) and a dummy variable indicating presence/absence of restoration. We assumed the effects of these variables varied by broader watershed scales. The restoration's effect also depended on temporal scales of implementation. The results indicate the sites with hydrological alteration, when implemented for longer than 7 years, had significantly smaller areal wetland loss, compared to the reference sites controlled for the local geophysical variables, in the Chenier Plain watershed, but not in the lower Mississippi River watershed. The effects of the other restoration methods on wetland loss were not significant based on limited numbers of sites. The Bayesian modeling framework we developed can integrate monitoring data/key drivers across projects with uncertainties accounted for, it is adaptable, and presents a useful tool in restoration evaluations spatially and temporally.

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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.

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The response of floodplain wetlands to changes in river hydrology caused by different dam operation strategies in arid regions has attracted worldwide attention in recent decades. However, less is known about quantifying the effects of dam operations on wetlands in different lateral zones located in low-gradient floodplains in arid regions using remote sensing and hydrological time series. In this study, hydrological time series from 1975 to 1985 and 2008-2014 were used to quantify 67 flow metrics during different dam operation periods. Time series of remote sensing data (39 periods in total) from 1975 to 1977 and 2008-2014 were analysed to quantify the spatiotemporal dynamics in floodplain wetland types (river, bare wet land and wetland vegetation areas). In addition, a correlation analysis was performed to quantify the relationship between each wetland type and the flow metrics in different lateral zones. The results indicate that approximately 90% of the water and bare wet land area were located in the continuously and frequently inundated zones. Vegetation was the main wetland type in the regularly and extremely rarely inundated zones, and a 45.7% decrease in the vegetation area of these two belts occurred; in contrast, a 20.14 km2 of increase in vegetation occurred in the frequently inundated zone after the uniform scheduling was implemented for the entire river. Linear correlation and regression analysis showed that the different dam operation strategies resulted in various wetland changes in the different lateral zones. The decrease in high flows and increase in low flows caused a decrease in the vegetation cover area in the regularly and extremely rarely inundated zones and led to vegetation encroachment in the frequently inundated zone. Our study can improve the management of wetlands and water resources in arid region floodplains.

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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, QR50; low-flow, QR90). 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 (QU) within and among different class-sizes, and (2) river discharge (QR) within low-order streams (ω < 3) resulting from differences in drainage areas. For QR50, 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 QR50 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 QR90 conditions [(QR50/QR90) ~ 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.

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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.

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Based on the measured daily flow prototype sequence of five hydrologic stations in the three outfalls of Chingjiang River from 1990 to 2014, its hydrological characteristics and its changing trend was analyzed by using the Mann-Kendall statistical test and the cumulative anomaly method, while the effect of the operation of the Three Gorges on the variation of the 33 indexes of ecological hydrology was also analyzed by the index system of ecological hydrology and range of variability approach. The results showed an obvious decreasing trend in annual mean discharge with the confidence degree of 95% with a decrease rate of 19% during 1990-2014. The jump point appeared in 2003, with the annual mean discharge being 1981.1 m3·s-1 before 2003 but 1603.25 m3·s-1 after. There was an obvious increase in monthly mean discharge from January to April (the degree of deviation was 1.58, 1.86, 0.83 and 0.62 respectively), an obvious increase in the late May and the early June, a slight decrease in July and August (the degree of deviation was -0.12 and -0.10 respectively), and a significant decrease in October (the degree of deviation was -0.40). There was a great change in annual minimum flows while a slight change in most of the annual maximum flows and a moderate decrease in 1-day and 3-day maximum flow. It also had a great change in duration and frequency of the low-flow pulse and slight change in high-flow pulse.

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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.

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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.

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