Evaluation of aquatic ecological systems through dynamics of ichthyofaunal diversity in a Himalayan torrential river,Murti     

《Limnologica》2020

The biodiversity hotspot region of the Eastern Himalayas consists of a vast freshwater network enriched with species diversity. Many small-scale torrential rivers and water reaches contribute to the species pool of all the major rivers by converging downstream. These reaches are most likely to be degraded at a faster rate as compared to the large-scale rivers following an increased rate of urbanization, habitat alterations, and changing climatic conditions. Therefore, this study aims to explore River Murti, which is a representative small scale river system characterized by a large altitudinal gradient and a diverse watershed area. Ichthyofaunal diversity (i.e., diversity, evenness & richness) and 21 environmental variables are measured through a tri-seasonal sampling effort conducted along 14 selected locations. A total of 41 fish species (including species belonging to 4 Near Threatened, 8 Vulnerable, and 1 Endangered) are found inhabiting this river. Ichthyofaunal assemblage is found to be primarily modulated by habitat diversity and landscape variables. Three Aquatic Ecological Systems (AES) have been identified along this river in a top-down approach based on recorded environmental variables. We have calculated an observed/expected ratio for each diversity indices along 14 locations based on predicted temporal variability using boosted regression (BRT) models. The evaluation of diversity status has been kept at 0.5 to account for a 50% loss or deviation from observed (O/E50). This evaluation has been successfully used to delineate AES1 with majorly “Impaired” status and thus ensures its importance in terms of species conservation. Our study indicates the contribution of 11 major environmental drivers modulating the species assemblage patterns in these AES. Amongst them, altitude, substrate coarseness, river morphology, and shelter availability are strongly associated with species diversity as per the BRT models. These underlying factors are also correlated with “basin pressure,” suggesting that anthropogenic disturbances, as well as the changing climate, might play an important role in the gradual change in environmental conditions, which in turn could cause a shift in species assemblage structure.  相似文献   

Wave-forced dynamics in the nearshore river mouths,and swash zones     

Maurizio Brocchini 《地球表面变化过程与地形》2020,45(1):75-95

The role of wave forcing on the main hydro-morphological dynamics evolving in the shallow waters of the nearshore and at river mouths is analyzed. Focus is mainly on the cross-shore dynamics that evolve over mildly sloping barred, dissipative sandy beaches from the storm up to the yearly timescale, at most. Local and non-local mechanisms as well as connections across three main inter-related subsystems of the nearshore – the region of generation and evolution of nearshore bars, river mouths and the swash zone – are analyzed. The beach slope is a major controlling parameter for all nearshore dynamics. A local mechanism that must be properly described for a suitable representation of wave-forced dynamics of all such three subsystems is the proper correlation between orbital velocity and sediment concentration in the bottom boundary layer; while specific dynamics are the wave–current interaction and bar generation at river mouths and the sediment presuspension at the swash zone. Fundamental non-local mechanisms are both infragravity (IG) waves and large-scale horizontal vortices (i.e. with vertical axes), both influencing the hydrodynamics, the sediment transport and the seabed morphology across the whole nearshore. Major connections across the three subsystems are the upriver propagation of IG waves generated by breaking sea waves and swash–swash interactions, the interplay between the swash zone and along-river-flank sediment transport and the evolution of nearshore sandbars. © 2019 John Wiley & Sons, Ltd.  相似文献   

Density effects on solute release from streambeds     

Guangqiu Jin  Wenhai Yang  Huiyu Xu  Zhongtian Zhang  Saiyu Yuan  Hongwu Tang  Ling Li  David Andrew Barry 《水文研究》2020,34(5):1144-1153

Contaminants that entered the streambed during previous surface water pollution events can be released to the stream, causing secondary pollution of the stream and impacting its eco-environmental condition. By means of laboratory experiments and numerical simulations, we investigated density effects on the release of solute from periodic bedforms. The results show that solute release from the upper streambed is driven by bedform-induced convection, and that density effects generally inhibit the solute release from the lower streambed. Density gradients modify the pore water flow patterns and form circulating flows in the area of lower streambed. The formation of circulating flows is affected by density gradients associated with the solute concentration and horizontal pressure gradients induced by stream slope. The circulating flows near the bottom of the streambed enhance mixing of the hyporheic zone and the ambient flow zone.  相似文献   

Intercomparison of measurements of bulk snow density and water equivalent of snow cover with snow core samplers: Instrumental bias and variability induced by observers     

J. Ignacio López-Moreno  Leena Leppänen  Bartłomiej Luks  Ladislav Holko  Ghislain Picard  Alba Sanmiguel-Vallelado  Esteban Alonso-González  David C. Finger  Ali N. Arslan  Katalin Gillemot  Aynur Sensoy  Arda Sorman  M. Cansaran Ertaş  Steven R. Fassnacht  Charles Fierz  Christoph Marty 《水文研究》2020,34(14):3120-3133

Manually collected snow data are often considered as ground truth for many applications such as climatological or hydrological studies. However, there are many sources of uncertainty that are not quantified in detail. For the determination of water equivalent of snow cover (SWE), different snow core samplers and scales are used, but they are all based on the same measurement principle. We conducted two field campaigns with 9 samplers commonly used in observational measurements and research in Europe and northern America to better quantify uncertainties when measuring depth, density and SWE with core samplers. During the first campaign, as a first approach to distinguish snow variability measured at the plot and at the point scale, repeated measurements were taken along two 20 m long snow pits. The results revealed a much higher variability of SWE at the plot scale (resulting from both natural variability and instrumental bias) compared to repeated measurements at the same spot (resulting mostly from error induced by observers or very small scale variability of snow depth). The exceptionally homogeneous snowpack found in the second campaign permitted to almost neglect the natural variability of the snowpack properties and focus on the separation between instrumental bias and error induced by observers. Reported uncertainties refer to a shallow, homogeneous tundra-taiga snowpack less than 1 m deep (loose, mostly recrystallised snow and no wind impact). Under such measurement conditions, the uncertainty in bulk snow density estimation is about 5% for an individual instrument and is close to 10% among different instruments. Results confirmed that instrumental bias exceeded both the natural variability and the error induced by observers, even in the case when observers were not familiar with a given snow core sampler.  相似文献   

Beaver dam analogues drive heterogeneous groundwater–surface water interactions     

Jeffrey Wade  Laura Lautz  Christa Kelleher  Philippe Vidon  Julianne Davis  Julio Beltran  Casey Pearce 《水文研究》2020,34(26):5340-5353

Beaver dam analogues (BDAs) are a cost-effective stream restoration approach that leverages the recognized environmental benefits of natural beaver dams on channel stability and local hydrology. Although natural beaver dams are known to exert considerable influence on the hydrologic conditions of a stream system by mediating geomorphic processes, nutrient cycling, and groundwater–surface water interactions, the impacts of beaver-derived restoration methods on groundwater–surface water exchange are poorly characterized. To address this deficit, we monitored hyporheic exchange fluxes and streambed porewater biogeochemistry across a sequence of BDAs installed along a central Wyoming stream during the summer of 2019. Streambed fluxes were quantified by heat tracing methods and vertical hydraulic gradients. Biogeochemical activity was evaluated using major ion porewater chemistry and principal component analysis. Vertical fluxes of approximately 1.0 m/day were observed around the BDAs, as was the development of spatially heterogeneous zones of nitrate production, groundwater upwelling, and anaerobic reduction. Strong contrasts in hyporheic zone processes were observed across BDAs of differing sizes. This suggests that structures may function with size-dependent behaviour, only altering groundwater–surface water interactions after a threshold hydraulic step height is exceeded. Patterns of hyporheic exchange and biogeochemical cycling around the studied BDAs resemble those around natural beaver dams, suggesting that BDAs may provide comparable benefits to channel complexity and near-stream function over a 1-year period.  相似文献   

Evaluating soil water routing approaches in watershed-scale,ecohydrologic modelling     

Garett Pignotti  Indrajeet Chaubey  Keith Cherkauer  Mark Williams  Melba Crawford 《水文研究》2021,35(3):e14034

Soil water dynamics are central in linking and regulating natural cycles in ecohydrology, however, mathematical representation of soil water processes in models is challenging given the complexity of these interactions. To assess the impacts of soil water simulation approaches on various model outputs, the Soil and Water Assessment Tool was modified to accommodate an alternative soil water percolation method and tested at two geographically and climatically distinct, instrumented watersheds in the United States. Soil water was evaluated at the site scale via measured observations, and hydrologic and biophysical outputs were analysed at the watershed scale. Results demonstrated an improved Kling–Gupta Efficiency of up to 0.3 and a reduction in percent bias from 5 to 25% at the site scale, when soil water percolation was changed from a threshold, bucket-based approach to an alternative approach based on variable hydraulic conductivity. The primary difference between the approaches was attributed to the ability to simulate soil water content above field capacity for successive days; however, regardless of the approach, a lack of site-specific characterization of soil properties by the soils database at the site scale was found to severely limit the analysis. Differences in approach led to a regime shift in percolation from a few, high magnitude events to frequent, low magnitude events. At the watershed scale, the variable hydraulic conductivity-based approach reduced average annual percolation by 20–50 mm, directly impacting the water balance and subsequently biophysical predictions. For instance, annual denitrification increased by 14–24 kg/ha for the new approach. Overall, the study demonstrates the need for continued efforts to enhance soil water model representation for improving biophysical process simulations.  相似文献   

A critical zone observatory dedicated to suspended sediment transport: The meso-scale Galabre catchment (southern French Alps)     

Cédric Legout  Guilhem Freche  Romain Biron  Michel Esteves  Oldrich Navratil  Guillaume Nord  Magdalena Uber  Thomas Grangeon  Nico Hachgenei  Brice Boudevillain  Céline Voiron  Lorenzo Spadini 《水文研究》2021,35(3):e14084

The 20 km² Galabre catchment belongs to the French network of critical zone observatories (OZCAR; Gaillardet et al., Vadose Zone Journal, 2018, 17(1), 1–24). It is representative of the sedimentary lithology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands on various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution were installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and turbidity (10 min time-step). Stream water samples are collected automatically to estimate SS concentration-turbidity relationships, allowing quantification of SS fluxes with known uncertainty. The sediment samples are further characterized by measuring their particle size distributions and by applying a low-cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands located on different lithologies to total SS flux are quantified at a high temporal resolution, providing the opportunity to better analyse the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both stream water electrical conductivity and major ion concentrations are measured each week and every 3 h during storm events. This extension of measurements to the dissolved phase will allow progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes of solutes in the critical zone. All data sets are available at https://doi.osug.fr/public/DRAIXBLEONE_GAL/index.html .  相似文献   

Quantifying suitable dynamic water levels in marsh wetlands based on hydrodynamic modelling     

Peng Hu  Zefan Yang  Qiande Zhu  Weize Wang  Qin Yang 《水文研究》2021,35(2):e14054

The water level of marsh wetlands is a dominant force controlling the wetland ecosystem function, especially for aquatic habitat. For different species, water level requirements vary in time and space, and therefore ensuring suitable water levels in different periods is crucial for the maintenance of biodiversity in marsh wetlands. Based on hydrodynamic modelling and habitat suitability assessment, we determined suitable dynamic water levels considering aquatic habitat service at different periods in marsh wetlands. The two-dimensional hydrodynamic model was used to simulate the temporal and spatial variation of water level. The habitat suitability for target species at various water levels was evaluated to obtain the fitting curves between Weighted Usable Area (WUA) and water levels. And then suitable water levels throughout the year were proposed according to the fitting curves. Using the Zhalong Wetland (located in northeastern China) as a case study, we confirmed that the proposed MIKE 21 model can successfully be used to simulate the water level process in the wetland. Suitable water levels were identified as being from 143.9–144.2 m for April to May, 144.1–144.3 m for June to September, and 144.3–144.4 m for October to November (before the freezing season). Furthermore, proposed water diversion schemes have been identified which can effectively sustain the proposed dynamic water levels. This study is expected to provide appropriate guidance for the determination of environmental flows and water management strategies in marsh wetlands.  相似文献   

Relating the depth of the water table to the depth of weathering     

M.I. Lebedeva  S.L. Brantley 《地球表面变化过程与地形》2020,45(9):2167-2178

Weathering of bedrock creates and occludes permeability, affecting subsurface water flow. Often, weathering intensifies above the water table. On the contrary, weathering can also commence below the water table. To explore relationships between weathering and the water table, a simplified weathering model for an eroding hillslope was formulated that takes into account both saturated and unsaturated subsurface water flow (but does not fully account for changes in dissolved gas chemistry). The phreatic line was calculated using solutions to mathematical treatments for both zones. In the model, the infiltration rate at the hill surface sets both the original and the eventual steady-state position of the water table with respect to the weathering reaction front. Depending on parameters, the weathering front can locate either above or below the water table at steady state. Erosion also affects the water table position by changing porosity and permeability even when other hydrological conditions (e.g. hydraulic conductivity of parent material, infiltration rate at the surface) do not change. The total porosity in a hill (water storage capacity) was found to increase with infiltration rate (all else held constant). This effect was diminished by increasing the erosion rate. We also show examples of how the infiltration rate affects the position of the water table and how infiltration rate affects weathering advance. Published 2020. This article is a U.S. Government work and is in the public domain in the USA  相似文献   

Multimodal water age distributions and the challenge of complex hydrological landscapes     

Nicolas B. Rodriguez  Paolo Benettin  Julian Klaus 《水文研究》2020,34(12):2707-2724

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