Hydromorphological Factors Research Articles

Beyond taxonomic diversity patterns - investigating how α and β components of macrophyte functional diversity respond to environmental gradients in lotic ecosystems of Greece.

In addition to quantifying the taxonomic diversity of aquatic communities, understanding the patterns of alpha functional diversity (α-diversity) and exploring changes in functional dissimilarity (β-diversity) can improve our understanding on how ecosystems respond to environmental changes. In this study, we quantified functional alpha (α) and beta (β) diversity of macrophytic assemblages from river sites in Greece and then, examined relationships with water quality parameters and hydromorphological factors. We assigned 6 traits (Ellenberg nutrients indicator, Ellenberg light indicator, growth form, leaf size, leaf type, fruit size) to a total of 36 hydrophyte species and calculated three indices of functional diversity (functional richness, functional dispersion and functional evenness). We also estimated the total β-functional diversity and its' main components, turnover and nestedness. To assess the effects of water quality (including physical and chemical variables) we used Generalized Additive Models (GAM) for alpha functional diversity indices and Generalized Dissimilarity Models (GDM) for beta functional diversity. We performed Kruskal-Wallis tests and permutational multivariate analysis of variance (PERMANOVA) to search for significant variations of α- and β-diversity among the hydromorphological factors. Our results showed that macrophyte growth form and light preference were important trait characteristics that explained a large share of the total variance of functional composition. We also found relatively low taxonomic and functional richness, whereas taxonomic and functional dissimilarity were mostly attributed to species turnover, which expresses the changes in taxonomic and functional composition. We found significant relationships between functional dispersion and functional evenness with pH and oxygen saturation, whereas functional dissimilarity was driven only by geographic distance, although the GDM explained a small portion of the total variance. Functional richness, dispersion and evenness were significantly higher at systems with fine substrates and deep waters with low or high flow compared to systems with coarser substrates and riffle habitats. We also found significant variation in functional dissimilarity among the hydromorphological factors, although much of the total variance remained unexplained. Overall, our study highlights the importance of considering the functional diversity of aquatic plant assemblages within the frame of freshwater monitoring and conservation plans.

Aquatic plants entrap different size of plastics in indoor flume experiments

Plastics accumulate in the environment affecting biota and ecosystems. Although rivers are vectors of land-based plastics to the sea, macroplastics and microplastics in rivers are recently studied. Most studies focused on floating plastic transport to the sea through rivers considering only abiotic hydromorphological factors. In this view, among biotic factors, vegetation has recently been found to entrap plastics. Indeed, the role of vegetation is pivotal in affecting riverine plastic transport. While marine vegetation blocking plastics has been studied, research in freshwater ecosystems is neglected. Since hydrological factors have a pivotal role in riverine plastic transport and few is known on plant entrapment, the interaction between hydrological variables and plastic entrapment by vegetation has not yet been investigated. Given that the composition, transport, and fate of “submerged” plastics in the water column are neglected, we aimed at investigating the behaviour of plants in entrapping plastics within a specific laboratory flume tank. Specifically, we assessed whether (i) aquatic plants block different plastic sizes within the water column and (ii) different factors (e.g. water level, density of plants) affect plastic entrapment. Our results showed that, according to plant density, the higher the plant density the higher the entrapment of plastics by plants - independently of plastic size. Considering the water level, macro-, meso-, and microplastics were trapped similarly. Moreover, Potamogeton crispus blocked fewer microplastics compared with Myriophyllum spicatum. Our results might have impact as plants acted as temporary plastic trappers and can be used as tools for mitigating plastic pollution. Future research might investigate if this laboratory approach can be applied in field for recollecting plastics and consequently mitigating the problem. In conclusion, good management of plants in watercourses, canals, and rivers should be ideal for enhancing river functionality and ecosystem services for human well-being (i.e. the plastic entrapment service by plants).

Development of transient habitat modeling for stream Macrozoobenthos

AbstractIn addition to the hydromorphological pressure on the ecological conditions of free‐flowing river courses, increasing water temperature is affecting the water bodies, particularly by changing freshwater community compositions. The low discharge of numerous European rivers in the dry and hot hydrological year 2022 proves this relevance. Therefore, ecological assessment tools such as habitat modeling should take these factors into account when assessing the quantity and quality of habitats. In this paper, the habitat modeling tool “Transient River Habitat Modeling for Macrozoobenthos” (TRiMM) is improved by incorporating a fuzzy logic approach and adding water temperature to the set of parameters determining habitat suitability for macrozoobenthos. Habitat‐relevant parameters, including hydromorphological factors (depth, velocity, mineral and organic substrate) and a water quality factor (temperature), are combined in the habitat model so that it can more broadly characterize river physical conditions and their interactions with biological indicators. Habitat modeling employed the mentioned parameters to simulate suitability for the macrozoobenthos in a small river in central Saxony, Germany. Due to its deteriorated condition, this river was selected as a representative for thousands of kilometers of small rivers across the region, which have been restored. The model simulated the status quo of river conditions from spring to summer for three macrozoobenthos species (Ancylus fluviatilis, Ephemera danica and Gammarus fossarum). The results showed that the natural flow resulted in dynamic habitat suitability both spatially and temporally, which differs for each species. Remarkably, the five‐parameter model (depth, velocity, temperature, mineral, and organic substrate) generally performed better compared to a similar model without temperature.

Hybrid approach for flood susceptibility assessment in a flood-prone mountainous catchment in China

• We developed a hybrid approach integrating physical-based flood models with random forest for flood susceptibility assessment. • We identified the relatively significant flood-inducing factors. • The geographical and hydromorphological factors had greater effects on riverine flooding. • This flood susceptibility assessment is suitable in ungauged areas. Flooding is one of the most destructive natural hazards that has caused catastrophic effects worldwide. Recently, machine learning methods have become widespread in flood susceptibility assessments due to their efficiency and robustness. However, flood inventory data acquired from historical flooding records and field surveys in existing studies are sparse and not enough to develop accurate machine learning models. Thus, we developed a hybrid approach that integrates hydrodynamic model (HEC-HMS/RAS), rapid flood model (height above the nearest drainage, HAND) and machine learning model (random forest, RF) for flood susceptibility assessment. The proposed approach was then implemented in the Xinluo watershed, a flood-prone mountainous catchment in China. The results showed that the spatially continuous flood inventory map generated from HEC-HMS/RAS model satisfies the big data requirements of the RF model, and the proposed hybrid approach demonstrates the effectiveness and efficiency in flood susceptibility assessment with overall accuracy and area under the ROC curve values of 0.915 and 0.912, respectively. The geographical and hydromorphological factors had greater effects on riverine flooding with average contribution of 27.8% and 27.6%. In comparison, the average contribution of land cover and meteorological factors were 24.3% and 20.3%, respectively. The method proposed in this study is effective in assessing and forecasting flood susceptibility and can facilitate resilience planning as well as integrated flood management.

Data arrangements to train an artificial neural network within solving the tasks for calculating the Chézy roughness coefficient under uncertainty of parameters determining the hydraulic resistance to flow in river channels

Hydraulic calculations and mathematical modelling of open flows in river channels keep still being among the most topical hydro-engineering today’s problems in terms of practice. While solving them, independently on the research topic and purpose, and methods used, a number of simplifications and assumptions are usually accepted and applied. Moreover, there is a range of methodological, structural, and parametric uncertainties, which to be overcome require complex empirical pre-researches. First of all, these uncertainties relate to assessing hydraulic resistances and establishing numerical characteristics of them, which depend on many factors varying spatially and temporally.One of the most frequently used integral empirical characteristics expressing the hydraulic resistance to open flows in river channels is the Chézy roughness coefficient C. However, despite a large number of empirical and semi-empirical formulas and dependencies to calculate the Chézy coefficient, there is no ideal way or method to determine this empirical characteristic unambiguously. On the one hand, while opting for an appropriate formula to calculate the Chézy coefficient, we need to take into account practical experience based on comprehensive options analysis considering different empirical equations used alternatively to represent the hydraulic resistance to open flows. On the other hand, the fullness and comprehensiveness of field researches of numerous hydro-morphological factors and parameters characterizing various aspects of the hydraulic resistance to open flows can also have an essential role. In particular, the accuracy assessment of the Chézy coefficient computing based on field data, despite methods and formulas, indicates that the accuracy of field measurements of the parameters included in selected formulas largely determines the relative error of such calculations.This paper deals with the problem of data arrangements and the development of general rules for the formation of training and test samples of data to train artificial neural networks being elaborated to compute the Chézy coefficient taking into account the parametric uncertainty of data on the hydro-morphological factors and parameters characterizing the hydraulic resistance in river channels. The problem is solved on the example of an artificial neural network of direct propagation with one hidden layer and a sigmoid logistic activation function.

Comparative Phylogeography of Birds Across the Tocantins–Araguaia Interfluve Reveals a New Biogeographic Suture in the Amazon Far East

Few phylogeographic studies have focused on understanding the role of the Tocantins–Araguaia Interfluve (TAI) in the diversification of Amazonian biodiversity. Herein we evaluate the phylogeographic relationships of 14 avian lineages present in the TAI and its two neighboring Amazonian Areas of Endemism: the Xingu (XAE) and Belém (BAE). Four alternative scenarios coupling degree of genetic differentiation and area relationships were tested: (1) populations distributed in TAI, BAE, and XAE are not genetically differentiated from each other (assumed as the null hypothesis); (2) populations from TAI are more closely related to those from BAE; (3) populations from TAI are more closely related to those from XAE; and (4) TAI populations represent independent or endemic lineages not present in either the BAE or XAE. Molecular analyses considered Bayesian Inference methods and Bayesian Information Criterion (BIC) evolutionary models, haplotype sharing and genetic differentiation estimates. We found three distinct phylogeographic patterns: (i) four lineages presented no population structure across XAE, TAI and BAE; (ii) six lineages were represented in the TAI with distinct phylogroups replacing each other between XAE and BAE, but with varying degrees of contact and evidence of gene-flow within the TAI; and (iii) for four lineages, the Tocantins River acted as a barrier isolating BAE phylogroups from those inhabiting both TAI and XAE. These different patterns demonstrate a heterogeneous response to the barrier effects posed by both the Tocantins and Araguaia rivers on the local fauna. Historical geomorphological and hydromorphological factors, such as the presence and absence of paleochannels and anastomosed channel stretches and variations in sedimentation rates support a dynamic history for the Araguaia-Tocantins floodplains, likely accounting for the observed heterogeneity in species’ specific responses. Finally, the scenario of phylogeographic breaks and population subdivision recovered herein along the Tocantins and Araguaia rivers, associated with the existence of contact zones and the occurrence of gene flow, define the TAI as hitherto unknown biogeographic suture zone, localized in southeasternmost Amazonia.

The Effect of Hydro-Morphology and Habitat Alterations on the Functional Diversity and Composition of Macrophyte Communities in the Large River

Macrophyte communities have major role in the functioning of freshwater ecosystems. However, there is gap in knowledge about how natural and anthropogenic hydro-morphological disturbances affect their functional diversity and trait structure, particularly in the temperate large rivers. In this study we investigated the effect of hydro-morphology on functional diversity and trait structure of macrophyte communities in the middle section of the Danube course. We collected macrophyte and environmental data from 947 sampling units in the main river channel and connected side waterbodies. We extracted data on 18 traits with 65 trait states and calculated seven functional diversity metrics and cumulative weighted means of trait states (CWMs). We applied redundancy analysis (RDA) to investigate the response of functional diversity metrics to the environmental variables, and Variation Partitioning to determine whether natural, or anthropogenic subset of hydro-morphological factors is more important predictor of functional diversity. To relate CWMs and environmental variables, we performed RLQ and fourth-corner analysis, followed by false discovery rate procedure. Hydro-morphological variables explained 36.7% of the variability in the functional diversity metrics. Combined effect of two subsets of environmental variables explained largest part of the variability in functional diversity metrics. Six associations between traits and environmental variables were found. We found that functional diversity metrics indicate prevailing ecological processes, from environmental to biotic filtering, along the natural—anthropogenic hydro-morphological gradient. We concluded that functional diversity metrics are potentially useful tools in the identification of the causes of ecological degradation, and could be applied in river bioassessments and management.

Scour Characteristics of the Underwater Crossing of Trunk Gas Pipeline Across the River Lena

The design data of the underwater crossing of the trunk gas pipeline (TGPL), which is an extension of the main gas pipeline of Hatassy GDS-2, for gasification of regions on the eastern side of the river Lena of the Republic of Sakha (Yakutia) are considered. Scours behaviour of the underwater crossing of TGPL across the river Lena is examined taking into account hydromorphological factors. The influence of hydrological and exogenous processes on the state of the underwater passage of Hatassy-Pavlovsk TGPL is shown by the example of the line-II. Changes of the river bottom profiles in the area of TGPL fixed at four discharge section lines, as well as water consumption were analyzed. It is shown that the presence of the underwater gas pipeline significantly affects the nature of the movement of micro- and meso-forms of the river bottom. It has been established that the constantly changing hydrological and hydromorphological processes resulted in sagging of the inverted siphon section in the line-II of the underwater crossing of Hatassy-Pavlovsk TGPL. During the designing and construction of the first line of the underwater gas pipeline across the river Lena, major omissions were committed, the peculiarities of the hydromorphological and hydrologic features of the river bed evolution in the section of the underwater passage of Tabaga-Kangalassy TGPL across the river Lena had not been taken into account. The effects of hydrodynamic and permafrost processes, heaving phenomena on floodplain and shore slope together increase the non-functional loads on the underwater gas pipeline. As a result of these factors, high longitudinal tensile stresses arise, especially in the welded joints of the inverted siphon pipes, and lead to accidents and incidents at the underwater gas pipeline across the river Lena.

Are aquatic and semiaquatic true bugs (Hemiptera: Nepomorpha; Gerromorpha) distinct aquatic communities? A case study in homogeneous habitats

ABSTRACTWe investigated the environmental factors influencing Nepomorpha and Gerromorpha in lentic, highly vegetated habitats from the Danube Delta. We collected 7032 individuals from 12 species from 23 habitats over 6 months. Separate multivariate analyses were conducted on the entire species dataset and separately on aquatic and semiaquatic species. Statistical analyses showed that aquatic and semiaquatic true bugs are influenced by different sets of environmental variables. Hydromorphological factors are most important in influencing communities of aquatic species, whereas aquatic plant species most strongly influence communities of semiaquatic species. Thus, including closely related taxa in a wider, more general analysis might lead to biased and/or distorted conclusions, and detailed analysis of the different related taxa is recommended to establish whether they do not represent distinct communities.

Performance of A Two-Dimensional Hydraulic Model for the Evaluation of Stranding Areas and Characterization of Rapid Fluctuations in Hydropeaking Rivers

Extreme, short-duration fluctuations caused by hydropeaking occurs when hydropower is regulated to cover demand peaks in the electricity market. Such rapid dewatering processes may have a high impact on the downstream biological conditions, particularly related to stranding of fish and other species. The present work analyzes these fluctuations using a two-dimensional unsteady hydraulic modelling approach for quantification of two important hydro-morphological factors on fish stranding risk: the variation in wetted area and the dewatering ramping rate. This approach was applied on the two-kilometer-long reach of Storåne downstream of the Hol 1 power plant, where topo bathymetric LiDAR (Light Detection and Ranging) data was available providing a high-resolution digital elevation model. Based on this model, hydraulic conditions could be simulated in high detail allowing for an accurate assessment of the hydro morphological factors. Results show the dried area distribution at different flows and dewatering ramping rates. The attenuation of the water level fluctuation due to the damping effect along the river reach controls the dewatering rate. We recommend an alternative scenario operation which can reduce the impact of the peaking operation and estimate the operational mitigation cost. We find that the modelling based on the fine resolution grid provides new opportunities in assessing effects of hydropower regulations on the ecosystem.

Pesticides in agricultural headwater streams in southwestern Germany and effects on macroinvertebrate populations

Pesticides are a major burden for stream ecosystems in the central European cultivated landscape. The objective of the present study was to investigate the applicability of ecological indicator methods in relation to toxicity of pesticides under the specific hydro-morphological conditions in small water bodies. Thus, an association of toxicity evaluating methods with different ecological indicators was to be attempted. Based on three random samples taken within the 2016 vegetation period, 23 headwater areas in the Saarland were investigated to test for pesticides and their metabolites. The macroinvertebrate population was also surveyed in 16 of these streams. Evidence was found of 41 substances in total. Most dominant substances include atrazine, isoproturone, quinmerac and tebuconazol as well as metabolites of dimethenamid, chloridazon and metazachlor. At 9 of the 23 sampling points, over 10 plant protection products and metabolites were found. Only 17% of the water bodies investigated contained fewer than 5 substances. Around half of the bodies of water investigated show noticeably high concentrations of metabolites of plant protection products. Maximum concentrations exceeding environmental quality standards or the Health-oriented Guideline Values were measured for 13 substances at individual sampling points.Analysis of the biological data for only 4 of the water bodies investigated resulted in the Ecological Status Class (ESC) “good”. All others fell short of the quality target, although they were classified as “good” or “very good” according to the Saprobic index. SPEARpesticides as a measurement of the sensitivity of the biocoenosis to pesticides shows their influence in a few water bodies. Likewise, high toxic unit values have also been calculated, indicating the presence of toxic substances at relevant concentrations. However, an actual correlation between SPEARpesticides and toxic unit could not be derived. Clearly in these very headwater streams other habitat-determining hydromorphological factors overlay the toxic impact of pesticides.

Effect of watershed urbanization on N2O emissions from the Chongqing metropolitan river network, China

Watershed urbanization, an integrated anthropogenic perturbation, is another considerable global concern in addition to that of global warming and may significantly enrich the N loadings of watersheds, which then greatly influences the nitrous oxide (N2O) production and fluxes of these aquatic systems. However, little is known about the N2O dynamics in human-dominated metropolitan river networks. In this study, we present the temporal and spatial variations in N2O saturation and emission in the Chongqing metropolitan river network, which is undergoing intensified urbanization. The N2O saturation and fluxes at 84 sampling sites ranged from 126% to 10536% and from 4.5 to 1566.8 μmol N2O m−2 d−1, with means of 1780% and 261 μmol N2O m−2 d−1. The riverine N2O saturation and fluxes increased along with the urbanization gradient and urbanization rate, with disproportionately higher values in urban rivers due to the N2O-rich sewage inputs and enriched in situ N substrates. We found a clear seasonal pattern of N2O saturation, which was co-regulated by both water temperature and precipitation. Regression analysis indicated that the N substrates and dissolved oxygen (DO) that controlled nitrogen metabolism acted as good predictors of the N2O emissions of urban river networks. Particularly, phosphorus (P) and hydromorphological factors (water velocity, river size and bottom substrate) had stronger relationships with the N2O saturation and could also be used to predict the N2O emission hotspots in regions with rapid urbanization. In addition, the default emission factors (EF5-r) used in the Intergovernmental Panel on Climate Change (IPCC) methodology may need revision given the differences among the physical and chemical factors in different rivers, especially urban rivers.

Riparian and microhabitat factors determine the structure of the EPT community in Andean headwater rivers of Ecuador

AbstractThis research was conducted in the high‐Andean basin of the Zhurucay River in southern Ecuador. In 4 river reaches, 19 sampling campaigns were conducted per reach spread over a period of 35 months. The biotic samples were selected in the periods with greatest flow stability. Parallel to each sampling, 37 environmental variables grouped into 3 factors (riparian corridor, hydromorphology, and water quality) were recorded. The study aimed to analyse during periods of stable flow the influence of these environmental factors on the structure and density of the EPT community (Ephemeroptera, Plecoptera, Trichoptera) in a quasi‐pristine aquatic ecosystem. Multivariate statistical analysis revealed that the Froude number, gravel type, and width/depth ratio are the most relevant hydromorphological variables explaining variations in EPT density. Xiphocentronidae,Contulma, andHelicopsychewere observed to have a relationship with the order of the river, whileOchrotrichia,Nectopsyche, andPhylloicusvaried with the type of riparian vegetation.Phylloicus,Ochrotrichia, andNectopsychewere common in lentic sites, while the proportion of gravel and the width/depth ratio restricted the genusHelicopsyche. The only relevant water quality factor was the total phosphorus, which was related with 2 taxa. In conclusion, although macroinvertebrates are currently employed in water quality studies, riparian vegetation and hydromorphological factors are determinant for their communities in pristine Andean rivers. Such factors are therefore crucial in the study of environmental flows and the assessment of the ecological integrity.

Distribution of Soil Organic Carbon in Riparian Forest Soils Affected by Frequent Floods (Southern Québec, Canada)

Measuring soil organic carbon (SOC) in riparian forest soils affected by floods is crucial for evaluating their concentration and distribution along hydrological gradients (longitudinal and transversal). Hydromorphological factors (e.g., sedimentation vs. erosion, size of floodplain, flood recurrence) may be the cause of major variations in the concentration of organic matter and SOC in soils and could have a direct impact on C levels in soil profiles. For this study, SOC concentrations were assessed in riparian soils collected along transects perpendicular to the riverbanks which cross through inundated and non-inundated zones. Other soil properties (e.g., acidity, nitrogen, texture, bulk density) that may affect the concentration of SOC were also considered. The main purpose of this study was to assess SOC concentrations in soils subjected to flooding with those outside the flood zones, and also measure various soil properties (in surface soils and at various depths ranging from 0 to 100 cm) for each selected area. Across the various areas, SOC shows marked differences in concentration and spatial distribution, with the lowest values found in mineral soils affected by successive floods (recurrence of 0–20 years). SOC at 0–20 cm in depth was significantly lower in active floodplains (Tukey HSD test), with average values of 2.29 ± 1.64% compared to non-inundated soils (3.83 ± 2.22%). The proportion of C stocks calculated in soils (inundated vs. non-inundated zones) was significantly different, with average values of 38.22 ± 10.40 and 79.75 ± 29.47 t·ha−1, respectively. Flood frequency appears to be a key factor in understanding the low SOC concentrations in floodplain soils subjected to high flood recurrence (0–20 years).

Macroinvertebrate community traits and nitrate removal in stream sediments

Abstract In‐stream nitrate removal capacity may be used as a proxy for the ecosystem service of water quality regulation. It is well known that this natural function is driven by abiotic and biotic factors in running water environments. With regard to biotic drivers, most of the literature focuses on the microbial community influences, but there has been very little emphasis on the relationship with the benthic macroinvertebrate community. Since this community feeds on microbial assemblages (autotrophic and/or heterotrophic biofilms) that live on the streambed and in the hyporheic zone of the river, macroinvertebrates also have the potential to influence nitrate removal via its influences on microbiological processes. The objective of this study was to examine the potential relationship between the macroinvertebrate communities and nitrate removal. A dataset of in‐stream nitrate removal rates measured in nine‐third‐order streams was analysed. The simultaneous influences of abiotic (hydromorphological, physical and chemical characteristics) and biotic (biofilm and macroinvertebrate) drivers were examined and together explained 56% of the in‐stream nitrate removal variance. An analysis of the independent contributions of each driver showed that abiotic drivers (e.g. ammonium, dissolved organic carbon, temperature and transient zone) contributed 40% of this nitrate removal variance, whereas the macroinvertebrate community contributed 39%. The potential relationship between macroinvertebrates and nitrate removal was subsequently explored using trait‐based approaches of the macroinvertebrate community. This method allows for the selection of trait modalities assuming a top‐down control of microbial communities by macroinvertebrates, with in‐stream abiotic conditions correlated with nitrate removal (assuming that environmental conditions affect macroinvertebrate community composition). The main trait modalities positively correlated with nitrate removal were scraper (feeding habit), flagstones/boulders/cobbles/pebbles (substrate preference), crawler and interstitial (locomotion) and detritus (food). The main modalities negatively correlated with nitrate removal were silt and mud with microphytes (as substrate preference), and with fine sediment with microorganisms, and dead animals (as food sources). These results agreed with the hypothesis of top‐down control and enhanced understanding of the influence of hydromorphological factors on nitrate removal. This study highlights the involvement of the macroinvertebrate community in in‐stream nitrate processing, and demonstrates the usefulness of applying a functional approach to explain relationships between biodiversity and ecosystem function.

English

Several hydromorphological and soil factors may be the cause of variations in the total organic carbon (TOC%) and total nitrogen (TN%) content of riparian soils. Despite the importance of these two essential components in soil-forming processes, few studies have focused on the variability of carbon and nitrogen content for soils subjected to frequent flooding. Successive floods may in fact result in soil depletion. Measurements of TOC% and TN% content as well as of other physico-chemical soil properties (e.g. litter thickness, texture, pH, Fe and Al concentrations, C/N ratio, bulk density, colour) were performed in various flood zones (recurrence intervals of 0-20 and 20-100 years) and in no-flood zones (outside of floodplains). To do so, soil samples were systematically collected along transects perpendicular to the riverbank which cross through the various flood zones. The results show that TOC% and TN% content varies significantly from one zone to another. The concentrations of these two components are significantly lower in the flood zone with a recurrence interval of 0-20 years (29% ±0.80 TOC and 0.17% ±0.05 TN) compared to the other two zones, name 3.45% ±1.56 TOC and 0.26% ±0.10 TN (recurrence interval of 20-100 years), and 3.52% ±1.57 TOC and 0.27% ±0.11 TN (no-flood zone). There is often no soil biomass (litter) in flood zones with a flood recurrence interval of 0-20 years (72% of sites without litter), whereas litter is almost always present in the flood zone with a recurrence interval of 20-100 years and in the no-flood zone, with average thicknesses of 2.84 and 3.65 cm, respectively. The absence or virtual absence of litter in the frequent-flood zones progressively results in soil depletion in terms of CO and N, which over time could adversely affect forest stand regeneration and deeply alter current river ecosystems. Key words: Alluvial soils, total organic carbon (TOC), total nitrogen (TN), soil biomass, floodplain, flood, recurrence intervals.

Variation partitioning of diatom species data matrices: Understanding the influence of multiple factors on benthic diatom communities in tropical streams

Elucidating the confounding influence of multiple environmental factors on benthic diatom communities is important in developing water quality predictive models for better guidance of stream management efforts. The objective of this study was to explore the relative impact of metal pollution and hydromorphological alterations in, addition to nutrient enrichment and organic pollution, on diatom taxonomic composition with the view to improve stream diatom-based water quality inference models. Samples were collected twice at 20 sampling stations in the tropical Manyame Catchment, Zimbabwe. Diatom, macroinvertebrate communities and environmental factors were sampled and analysed. The variations in diatom community composition explained by different categories of environmental factors were analysed using canonical correspondence analysis using variance partitioning (partial CCA). The following variations were explained by the different predictor matrices: nutrient levels and organic pollution - 10.4%, metal pollution - 8.3% and hydromorphological factors - 7.9%. Thus, factors other than nutrient levels and organic pollution explain additional significant variation in these diatom communities. Development of diatom-based stream water quality inference models that incorporate metal pollution and hydromorphological alterations, where these are key issues, is thus deemed necessary.

Water inundation hazard and micro level basin hydromorphological relationships: a geographical assessment

This paper is to evaluate the relationships between basin hydromorphological factors and water inundation issue delineating five broad watersheds in a micro level study area, Moyna basin of West Bengal, India, using remote sensing and GIS techniques along with mapping and measurement of the hazard affected areas. It is observed that hydromorphological characteristics have systematic non-linear complex co-relationships with this hazard. Drainage frequency, drainage density, drainage texture, form factor, elongation ratio, ruggedness index, and mean slope proportionate with water inundation; and constant of channel maintenance, length of overland flow, shape factor, basin relief, relief ratio, and embankment density disproportionate with it. Some factors response not significantly. Besides, high rainfall and low depth of groundwater level of Moyna basin increases inundation problem. Bhuvan web data, based on Resourcesat 1 (LISS III), during 2005–2006, has been considered here as the primary value and Resourcesat 2 (LISS IV) image data during pre and post rainy seasons of 2012–2014 as observed value. There it is observed that in Moyna basin water inundation is a permanent hazard but its area changes with time. Finally, there a water inundation model has been formed to evaluate and to compare water inundation/waterlogging based on considering ranks. In result, it is found that the central Moyna watershed has maximum water inundation/waterlogging problem. Small scale basin area study sometimes shows difficulties and also distortions from the general.

Caddisflies (Trichoptera) as good indicators of environmental stress in mountain lotic ecosystems

We analysed the influence of environmental stress (mainly deforestation of catchment due to windstorm) on taxonomic structure as well as composition of functional groups (FG) based on zonation preferences and feeding types of caddisfly species in 11 streams (12 sites) with various environmental conditions situated in the High Tatra Mts, Slovakia. Us- ing Spearman correlation, we confirmed an expected positive association between taxonomic and functional groups richness (Ri), diversity (Shannon - Wiener Index) (Di) and equitability (Eq), but not with habitat diversity (HQA indices). By test- ing measured physiographical, physico-chemical and hydromorphological factors using CCA analysis we found that stream order and temperature best explained the functional and taxonomic structure of caddisfly assemblages. The occurrence of Rhyacophila glareosa decreased with increasing daily mean water temperature positively correlated with deforestation, whereas R. tristis (dominating at sites most affected by erosion) showed the opposite pattern. Composition of functional groups based on zonation preferences and feeding types distinguished well near natural sites from impacted ones, domi- nated by crenal/rhithral predators, and explained more of the overall variance of the species-environment relationships than taxonomic composition of caddisfly assemblages.

Evaluación del peligro de las aguas de avenida en cruces de puentes sobre ramblas: el caso de estudio de la costa murciana (SE de España)

Bridges are usually built when traffic or the importance of the road network justifies the cost. Most road bridges are permanent structures and are vulnerable to extreme hydrologic events. Streams, particularly in semiarid regions, can significantly overflow their banks and may change course, defying the bridge’s ability to perform its intended function. This article proposes a way of assessing flood hazards at bridge crossings over ephemeral streams. Two hazard indices associated with floodwaters at bridge crossings have been tested for ephemeral channels on the South-East coast of Spain: a Flood Hazard Index for bridge crossings (FHIBC), and a Geomorphological Hazard Index (GHIBC). FHIBC is based on the exposure and effectiveness of drainage works for dealing with floods of different return period. The second index, GHIBC, integrates parameters related to hydraulic resistance and potential bed erosion in large floods. Variables such as granular bed susceptibility to incision, critical velocity and transitory scouring have previously been estimated based on field data. The results show that FHIBC is an appropriate index for obtaining an overall evaluation of the flood hazard at this crossing type, while GHIBC provides useful information on the main hydromorphological factors which endanger the stability of the bridges over ephemeral streams. The joint implementation of both indices may also be an efficient tool for identifying high-risk crossings and improving the planning of future infrastructures over channels in the study area.