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Hydrobiologia ◽  
2021 ◽  
Author(s):  
Lorena González-Paz ◽  
María Comesaña ◽  
Isabel Pardo ◽  
José Barquín ◽  
Alejandra Goldenberg-Vilar ◽  
...  

AbstractSmall rivers support high levels of biodiversity, being especially sensitive to the effects of global change. Temporal records of community composition in minimally impaired streams can be used to explore trends in biodiversity in response to climate change and natural temporal variation. We approached the comparison of two time periods (2003–2008 and 2016–2020) to study whether the composition of diatom assemblages changed over time in twenty-three streams of the mountain range of Picos de Europa (Northern Spain). The stream’s water chemistry indicated significant decreases in N_NO3− and P_PO43− content over time. In these minimally disturbed streams, the specific diatom community was dominated by Achnanthidium pyrenaicum, Achnanthidium minutissimum and Cocconeis euglypta. PERMANOVA analyses did not identify significant changes in diatom assemblage composition between periods or river types. Diatom indices (e.g. IPS, NORTIdiat) indicated high or good ecological status and relatively high alpha diversity values were found in these mountain rivers during the studied years. Although diversity and evenness showed a significant decrease over time, the temporal stability of the river-type diatom reference community between the two periods should be considered as an indicator of biodiversity persistence of high importance when monitoring the ecological status following the reference condition approach.


2021 ◽  
Author(s):  
Jun Liu ◽  
Liguang Jiang ◽  
Filippo Bandini ◽  
Cécile Marie Margaretha Kittel ◽  
Nicola Balbarini ◽  
...  

Abstract Hydraulic roughness (expressed in terms of e.g. Manning's roughness coefficient) is an important input to hydraulic and hydrodynamic simulation models. One way to estimate roughness parameters is by hydraulic inversion, using observed water surface elevation (WSE) collected from gauging stations, satellite platforms or UAS (Unmanned Aerial System) −based altimeters. Specifically, UAS altimetry provides close to instantaneous observations of longitudinal profiles and seasonal variations of WSE for various river types, which are useful for calibrating roughness parameters. However, it is computationally expensive to run high−resolution hydrodynamic models for long simulation periods (e.g. multiple years), and thus global optimization of spatially and temporally distributed parameter sets for such models, e.g., spatio−temporally varying river roughness, is still challenging.This study presented an efficient calibration approach for hydraulic models, using a simplified steady-state hydraulic solver, UAS altimetry datasets, and in-situ observations. The calibration approach minimized the weighted sum of a misfit term, spatial smoothness penalty, and a sinusoidal a priori temporal variation constraint. The approach was first demonstrated for several synthetic calibration experiments and the results indicated that the global search algorithm accurately recovered the Manning–Strickler coefficients M for short river reaches in different seasons, and M varied significantly in time (due to the seasonal growth cycle of the aquatic vegetation) and space (due to, e.g. spatially variable vegetation density). Subsequently, the calibration approach was demonstrated for a real WSE dataset collected at a Danish test site, i.e., Vejle Å. Results indicated that spatio-temporal variation in M was required to accurately fit in-situ and UAS altimetry WSE observations. This study illustrated how UAS altimetry and hydraulic modeling can be combined to achieve improved understanding and better parameterization of small and medium-sized rivers, where conveyance is controlled by vegetation growth and other spatio-temporally variable factors.


Author(s):  
Oblique Shrestha ◽  
Hari Prasad Neopane ◽  
BholaThapa ◽  
Young-Ho Lee ◽  
Aman Kapali

The removal of surface material due to repeated impacts of sediment is known as sediment erosion. This prominent phenomenon is found to exist on a run of the river types of hydro projects where the hydro turbines are exposed to sediment particles. It has drawn the attention of researchers, academic institutions, and hydropower developers to conduct research on this issue. Investigation of the problem at the site may require sophisticated equipment and sensors- set up for quantitative measurements. This process is time consuming and difficult as it is difficult to access the erosion location. Laboratory setup can be a solution to study and investigate erosion behaviour in well-controlled laboratory conditions. Among several erosion testing apparatuses, Rotating Disc Apparatus (RDA) has been used for the investigation of erosion as well as cavitation of hydro components, and to study the erosion resistivity of different materials. This device mainly consists of a rotating disc and an electric motor, which is used to rotate a disc-holding specimen. This paper evaluates the RDA for its applicability in simulating the flow on the surfaces of the components of the hydro turbines as that occurs in actual hydro power plants. The outcomes from the present study indicated that RDA produces promising erosion results and can simulate the wear conditions.


Author(s):  
Péter Takács ◽  
András Abonyi ◽  
Bálint Bánó ◽  
Tibor Erős

AbstractRecent researches suggest that functional diversity represents the response of communities to environmental alterations better than taxonomic diversity. However, there is scarce information about how the functional diversity of freshwater fishes is affected by habitat type and the dominance of non-native species. To address this question, we analysed a large database containing 15 morpho-functional traits of 61 fish species from the Pannon Biogeographic region (Hungary). Based on a fish faunistic list and relative abundance of taxa, we quantified the taxonomic and functional diversity of riverine communities for > 700 sites of six habitat types. We asked how non-native fishes affected the taxonomic and functional diversity in different river types and at the local scale (i.e. at the site level), and how the diversity measures of native fauna elements changes along the invasion gradient. Our results showed that both functional and taxonomic richness increases with habitat complexity, from small headwater streams to large rivers. Therefore taxonomic diversity served as a good proxy for functional diversity along the environmental gradient of river types. Non-natives showed considerable functional diversity relative to their species number in each habitat type. Diversity values of native fauna elements initially increased, and then showed a major decrease along the invasion gradient. River type-specific evaluations highlighted the importance of considering the proliferation of invasive species based on both taxonomic and functional diversity indices. We argue that type-specific action plans are needed in conservation management to preserve the taxonomic and functional diversity of native fishes in Hungary, but also elsewhere.


Forests ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 625
Author(s):  
Vera Zina ◽  
Marc Ordeix ◽  
José Carlos Franco ◽  
Maria Teresa Ferreira ◽  
Maria Rosário Fernandes

In this study, we assess the potential of ants as bioindicators of riparian ecological health in two river types (upland and lowland type) located in the Catalonian region. We proposed to understand to what extent do metrics based on ant responses provide useful information that cannot be presented by traditional biophysical assessments while attempting an approach to creating an ant-based multimetric index (ant-based MMI) of the riparian ecological health. A total of 22 ant species were identified, and 42 metrics related to ant foraging activity, species richness, and functional traits were evaluated as potential core metrics of the index. Riparian features and proximal land use land cover (LULC) were used to distinguish disturbed from less disturbed sites. We found that ant communities strongly responded to human disturbance. When compared with an exclusively physical-based index for the assessment of the riparian health, the ant-based MMI was more sensitive to human disturbance, by also reacting to the effects of the surrounding LULC pressure. This study provides a preliminary approach for an ant-based assessment tool to evaluate the health of riparian corridors although additional research is required to include other river types and a wider stressor gradient before a wider application.


Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 767
Author(s):  
Antoni Munné ◽  
Núria Bonada ◽  
Núria Cid ◽  
Francesc Gallart ◽  
Carolina Solà ◽  
...  

The biomonitoring methods implemented by water authorities are mostly developed for perennial rivers, and do not apply to temporary rivers (TRs). We propose a new classification for TRs to better assess their ecological status. It arises from the LIFE+ TRivers project, which was conducted in the Catalan and the Júcar Mediterranean river basin districts (RBD). The European Water Framework Directive (WFD) provided two systems to set river types (systems A or B from Annex II), which have been officially used by water authorities across Europe to set “national river types” (NRTs). However, essential hydrological variables for TRs are largely omitted. NRTs established according to the WFD were compared with TR categories obtained by using a rainfall-runoff model, “natural flows prescribed regimes” (NFPRs), and with “aquatic phases regimes” (APRs) calculated by using TREHS software. The biological quality indices currently used in Spain, based on macroinvertebrates and diatoms (IBMWP, IMMI-T, and IPS), were compared with a “general degradation” gradient in order to analyze the two TR river classification procedures (NFPR and APR). The results showed that NRTs did not properly classify TRs, and that the APR classification identified ecologically meaningful categories, especially those related to stagnant phases. Four “management temporary river categories” based on APRs are proposed to be used for water managers to properly assess the ecological status of TRs.


Author(s):  
Tolegen Akynzhanov ◽  
Vladimir Dekhnich ◽  
Victoria Bitykova

The article describes the assessment of the areas and spatial distribution of adjoining green spaces as one of the most vulnerable and low studied kind of green spaces in cities. Usually gardening near the residential houses is not legally regulated is being destroyed during the implementation of urban renovation projects. The characteristics of adjoining green spaces were assessed for the city of Nur-Sultan, where, on the one hand, natural properties make green spaces vulnerable, and on the other hand, the acquisition of capital functions increases the value for the urban environment. A large-scale assessment, carried out using unmanned aerial vehicles, has demonstrated its high efficiency in assessing the vertical and horizontal structure of adjacent green spaces and other elements of the city. As a result of aerial imagery sessions for representative key points, a series of orthophotomaps with the horizontal resolution of 3–4 cm and digital terrain models with a horizontal resolution of 3 cm and a vertical resolution of about 4 cm were obtained. These products provided possibility to identify 12 historically established morphotypes of urban buildings, characterized by different levels and types of adjacent landscaping. Using a three-dimensional model of green cover, the average size of the biomass and the density of biomass per 1 m2 of the area in the selected morphotypes of the building were calculated. Territorial differences of adjoining green spaces in the different morphotypes depend on the period of construction, distance from the river, types of the building and urban planning standards typical for the period of the morphotype forming. Losses of the adjoining green spaces during the implementation of the renovation program according to the modern General Plan, excluding restoration, for the city of Nur-Sultan, will be mor than 11.5 % (+/-3.5 %) of the city’s tree cover.


2021 ◽  
Vol 57 (6) ◽  
pp. 31-48
Author(s):  
A. M. Roman ◽  
S. O. Afanasyev ◽  
Yu. K. Kutsokon ◽  
O. M. Lietytska ◽  
O. O. Hupalo
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