Hydrological Periods Research Articles

Assessment of characteristics and distinguished hydrological periods of a river regime

This study was carried out to analyze the hydrological characteristics and assess the distinguished hydrological periods of Upper Indus Basin (UIB) Rivers of Pakistan. For this purpose, statistical analysis (variation coefficient, the auto-correlation coefficient, sequential Mann–Kendall’s test) and a proposed method for distinguishing hydrological periods (described in methodology section) were applied. The results revealed that all rivers reflect moderate variability. The results of auto-correlation displayed that the river flow observed at Astore gauging station only indicated independency, while for Gilgit, Hunza and Kachura guaging at Indus River exhibited 2, 2, 4-year lag. The mutation analysis indicated that after 1980, the change point occurred at all UIB rivers. During analysis, it was also observed that river regimes have the same hydrological periods (i.e., 4), but with different dates of occurrence. The Gilgit River showed a low high-flow hydrological period compared to Astore, Hunza and Kachora (Indus). This difference may be due to the river’s own area natural conditions. The current analysis may be helpful for planning and management of water resources, designing of hydraulic structures and to make better policies in response to agricultural water requirement downstream of UIB River.

Methylmercury in environmental compartments of a hydroelectric reservoir in the Western Amazon, Brazil

Damming rivers to generate electricity creates a lentic environment that favors methylmercury (MeHg) formation. Reservoirs in the Amazon are critical environments for MeHg formation, considering its old soils and the use of Hg in gold mining in the region. The objective of this study was to evaluate MeHg accumulation in three environmental compartments (aquatic macrophytes, suspended particulate matter (SPM) and sediment) of the Samuel reservoir (Western Amazon, Brazil), during the low water, ebb and high water hydrological periods, characterizing the dry season, the end of the rainy season and the rainy season, respectively. MeHg concentrations were determined through GC-AFS. The aquatic macrophytes presented higher %MeHg in their roots (up to 12%) compared to their other tissues. This ratio was 1.7 and 5.9 times higher than those observed for SPM and the sediment, but MeHg concentrations were the lowest (0.5–4.5 ng g−1) among the three environmental compartments. Contrary, the highest MeHg concentration was observed in SPM (104 ng g−1) during the low water period. The MeHg concentration in the sediment profile decreased with increasing depth (0.93–0.48 ng g−1) and with decreasing organic matter lability (increasing C:N ratio). In the SPM, on the other hand, MeHg concentration showed a positive association with increasing C:N ratio. We conclude that MeHg dynamics in the SPM are associated with the hydrological periods, with peaks during the low water period. The organic matter lability of the sediments is more limiting to the production of MeHg than the total Hg concentrations.

Quantifying flood events in Bangladesh with a daily-step flood monitoring index based on the concept of daily effective precipitation

Bangladesh, located in the Bay of Bengal, is a developing nation that is prone to devastating flood events that cause loss of lives and several other forms of humanatarian disasters. Identifying, developing and validating new scientific techniques that can be used for flood-risk warning and regular monitoring, including flood risk mitigation and adaptation, can help reduce the catastrophic effect of floods in Bangladesh and other developing countries. In this study, a daily Flood Index (IF) based on daily effective precipitation (PE) is utilized for quantifying floods for two cites in Bangladesh: Dhaka (23.7° N, 90.38° E) and Bogra (24.51° N; 89.22° E), where flooding is a common phenomenon. Based on total daily precipitation (P) data, in this study the IFis determined by calculating the PE using an exponentially decaying time-reduction function, which considers the gradual depletion of water resources over time. PE per day is normalized and compared with the average and standard deviation of yearly maximums, within the considered hydrological period. The start of a flood event is identified for IF ≥ 0. Subsequently, the IF severity ( $$ {I}_F^{acc} $$ ) as consecutively positive IF, duration (DF) as number of days with positive IF, and peak danger ( $$ {I}_F^{\mathrm{max}} $$ ) as maximum IF are estimated for identified flood events, using the run-sum theory. The analysis carried out has accurately identified historical flood events at Dhaka station in 1984 and 2007 as having the largest $$ {I}_F^{acc} $$ value (i.e., greatest severity). Flood severity ( $$ {I}_F^{acc} $$ ) and peak danger ( $$ {I}_F^{\mathrm{max}} $$ ) parameters have been verified by accumulated precipitation corresponding to the same period. For Bogra station, the 1998 and 1979 events were found to be the most intense. Seasonality analysis of the flood index shows most floods happened during the summer monsoon, although for the Dhaka station, flood events occurred between early June and November, and in Bogra, from late June to October. A rational study of effective precipitation provides a useful severity and danger indicator. The results indicate the practicality of daily IF for flood-risk assessments where the severity, peak danger, and duration need to be considered as a unified index for flood-risk monitoring. The proposed daily flood index can be useful for hydrologists for the purpose of daily operational flood monitoring in high flood-risk nations.

БИОЛОГИЧЕСКОЕ РАЗНООБРАЗИЕ НА БЕНИНСКОМ КОНТИНЕНТАЛЬНОМ ШЕЛЬФЕ ВО ВРЕМЯ ИССЛЕДОВАНИЯ ОЦЕНКИ ЗАПАСОВ ДЕМЕРСАЛЬНЫХ РЫБ

The global objectives of this study are to assess biodiversity composition in the tested trawling areas during the survey period. This study cannot take in account all species that can occur in the fishing areas because of the shortness of the work. To have a most complete list of species it will be better to carry out the survey covering four hydrologic periods (2 hot and 2 cold hydrologic periods) to have a chance to meet most of the species. However, the work was done during the most important period for the study. This study was conducted in terms of the demersal fish stock assessment survey initiated by the West African Economic and Monetary Union in the continental shelves of states members and neighboring countries (Côte d'Ivoire, Ghana, Togo and Benin) for the south part of Africa in order to determine fish population and abundance. In the waters of Benin, there have been listed 100 fish species including 76 demersal species (69 bony and 7 cartilaginous fish) and 13 pelagic species consisting entirely of bony specimens. Species richness, according to the reports of trawling stations, varies between 28 and 7 species. Fish abundance is the largest at the depth of 25-50 m. According to the data of station 10, species number makes 7.76% of the total, followed by station 19 with 26 taxa at the depth of 50-100 m. The lowest taxon number is registered in station 4 at a depth of 10-25 m with 4 taxa representing 1.94% of all targeted. The Simpson's index is close to 0, varying between 0 and 0.049, it shows a great diversity especially in the first stratum of 10 to 25 m. This study allows to evaluate species diversity in different fishing areas and consequences of the significant increase of fishing pressure on the stand and not only to focus on a few populations of species of commercial interest.

Priorization of River Restoration by Coupling Soil and Water Assessment Tool (SWAT) and Support Vector Machine (SVM) Models in the Taizi River Basin, Northern China.

Identifying priority zones for river restoration is important for biodiversity conservation and catchment management. However, limited data due to the difficulty of field collection has led to research to better understand the ecological status within a catchment and develop a targeted planning strategy for river restoration. To address this need, coupling hydrological and machine learning models were constructed to identify priority zones for river restoration based on a dataset of aquatic organisms (i.e., algae, macroinvertebrates, and fish) and physicochemical indicators that were collected from 130 sites in September 2014 in the Taizi River, northern China. A process-based model soil and water assessment tool (SWAT) was developed to model the temporal-spatial variations in environmental indicators. A support vector machine (SVM) model was applied to explore the relationships between aquatic organisms and environmental indicators. Biological indices among different hydrological periods were simulated by coupling SWAT and SVM models. Results indicated that aquatic biological indices and physicochemical indicators exhibited apparent temporal and spatial patterns, and those patterns were more evident in the upper reaches compared to the lower reaches. The ecological status of the Taizi River was better in the flood season than that in the dry season. Priority zones were identified for different hydrological seasons by setting the target values for ecological restoration based on biota organisms, and the results suggest that hydrological conditions significantly influenced restoration prioritization over other environmental parameters. Our approach could be applied in other seasonal river ecosystems to provide important preferences for river restoration.

Temporal and spatial patterns of freshwater decapods associated with aquatic vegetation from floodplain rivers

The presence of freshwater decapods may be considered dependent on the habitat and vegetation characteristics in floodplain rivers. Water level can influence the availability of macrophytes and the associated species composition of freshwater decapods. Changes in the sex ratios, abundances and body sizes of Macrobrachium borellii, Palaemon argentinus and Trichodactylus borellianus were investigated focusing on the type (floating, emergent) and the presence/absence of macrophytes in the Middle Parana River floodplains. Organisms were sampled and analysed from river sites with floating, emergent vegetation and vegetation-free waters during different hydrological periods. The presence of macrophytes and some environmental variables during different hydrological and seasonal periods affected the variations in the species composition of decapods. M. borellii and T. borellianus tended to increase with the increase in floating vegetation in high waters, while P. argentinus was abundant in emergent vegetation and vegetation-free waters in low waters. Macrophytes provide food and shelter for freshwater decapods, influencing the species abundance according to the ecological response of each species. Variations in macrophytes composition due to water-level fluctuations modify the abundance of freshwater decapods, altering the species composition of decapod assemblages. Floodplain rivers are complex systems that act as macrofactors that regulate other factors that impact species composition.

Effect of flood pulses on the trophic ecology of four piscivorous fishes from the eastern Amazon

This study investigated the effect of hydrological periods on the feeding activity and trophic interactions of four piscivorous fishes from the middle Xingu River, Brazil: pike-characid Boulengerella cuvieri, dogtooth characin Hydrolycus armatus, dogtooth characin Hydrolycus tatauaia and South American silver croaker Plagioscion squamosissimus. Repletion Index (IR %), Alimentary Index (IAi %) and food web properties were calculated for each species. A total of 825 specimens were collected. The IR showed changes in feeding intensity of B. cuvieri, H. armatus and H. tatauaia among hydrological periods. Flood pulse showed no influence on composition and importance of food items consumed. Trophic connections showed that connectivity ranged from 0.025 to 0.038. The highest number of trophic connections (75) occurred in the high-water period, when 51 food items were recorded and the lowest number of trophic connections (43) occurred in receding water, with 31 food items. In all food webs, over 45% of food items were consumed by only one species (ultra-peripheral items), which is common in piscivorous fishes.

Temporal dynamics of soil moisture and rainfall erosivity in a tropical volcanic archipelago

Soil water availability has a strong role on vegetation conservation and biodiversity, particularly at vulnerable environments such as archipelagos, subject to significant temporal changes of climate and rainfall, which influence soil weathering and erosion processes. Few field studies on hydrology of volcanic islands in the Atlantic Ocean have been developed focusing on soil and water temporal dynamics and conservation, mainly because such studies require data with high temporal resolution, and also due to the financial costs involved with field data acquisition at such remote places. Considering the importance of soil moisture content to several hydrological processes and islands environmental sustainability, this study aimed to investigate the soil water temporal dynamics in relation to different rainfall patterns and also the rainfall erosivity and its temporal variation, and the resulting infiltration depths, during a typical hydrological period, in an experimental plot at the main watershed of Fernando de Noronha, in the Brazilian Atlantic Coast. Rainfall was recorded every 5 min, and soil moisture was intensely monitored by 16 moisture probes, installed at 10–40 cm and 40–70 cm layers, during three years, representing the typical local hydrological regime and seasons. Rainfall bursts pattern were identified and described. Experimental data allowed a hydrological model to be calibrated and validated, providing estimates of infiltration depths, which can be valuable for water resources planning and management. Hydrological patterns were determined for each erosive rainfall, depending on the precipitation peak position, as advanced, intermediate and delayed. The soil water effectiveness was also evaluated and related to the different rainfall patterns. Soil moisture is highest from April to June, close to saturation; whilst for the other months the values were close to the residual value. The rainfall erosivity in the archipelago was identified as moderate to strong, and the most frequent rainfall pattern was the advanced. Fast wetting-drying cycles during the rainfall events were observed, due to rainfall intermittency, evapotranspiration, and to soil hydraulic conductivity. It was observed the prevalence of high moisture indexes, with percentages higher than 40% (extremely effective level) for both investigated depths within the first 70 cm of soil, essential for plant water uptake. The observed rainfall erosivity highlights the importance of defining local strategies for soil and water conservation aimed at water security in the island. Based on a simulation model, which was successfully calibrated (Nash-Sutcliffe Efficiency Index NS = 0.76) and validated (NS = 0.81) for periods in the wet season, high infiltration depths have been identified, which contributes to canopy conservation in the archipelago.

A comparative assessment of Australia's Lower Lakes water quality under extreme drought and post-drought conditions using multivariate statistical techniques

Abstract Drought generally results in a decline to freshwater quality, but the spatial nature of these impacts and recovery processes in large lakes systems remain poorly understood. This study applied multiple statistical methods such as cluster analysis (CA), discriminant analysis (DA), principal component analysis (PCA) and factor analysis (FA), to assess spatial and temporal variations of water quality in the Lower Lakes (Australia) during drought (April 2008–September 2010) and post-drought (October 2010–October 2013) periods. The comprehensive analysis of water quality from 22 locations and including 22 key parameters showed that Lower Lakes were eutrophic in both drought and post-drought periods with higher nutrient and algae concentrations than guideline levels for aquatic ecosystem. The Lower Lakes were identified three distinct spatial zones, i.e., (1) low eutrophication for the southeast of Lower Lakes (SE), (2) moderate eutrophication for northeast of Lower Lakes (NE), and (3) high eutrophication for northwest of Lower Lakes (NW) in the drought as well as low eutrophication for NW and high eutrophication for SE in the post-drought. DA allowed a better reduction in the dimensionality of the large dataset during post-drought than during the drought period with better results for spatial analysis rather than for temporal analysis regardless of hydrological periods. PCA/FA reflected three major factors of mineral dissolution, erosion and anthropogenic sources accounting for water constituents. Our results demonstrate the powerful utility of multivariate statistical techniques for revealing the persistent and spatially complex nature of drought-induced impacts on lake water quality and highlight that optimal utilization of water resources in the upper catchment of Lower Lakes are urgently needed for the sustainable lake ecosystems.

Spatio-temporal analysis of annual rainfall in Crete, Greece

Analysis of rainfall data from the island of Crete, Greece was performed to identify key hydrological years and return periods as well as to analyze the inter-annual behavior of the rainfall variability during the period 1981–2014. The rainfall spatial distribution was also examined in detail to identify vulnerable areas of the island. Data analysis using statistical tools and spectral analysis were applied to investigate and interpret the temporal course of the available rainfall data set. In addition, spatial analysis techniques were applied and compared to determine the rainfall spatial distribution on the island of Crete. The analysis presented that in contrast to Regional Climate Model estimations, rainfall rates have not decreased, while return periods vary depending on seasonality and geographic location. A small but statistical significant increasing trend was detected in the inter-annual rainfall variations as well as a significant rainfall cycle almost every 8 years. In addition, statistically significant correlation of the island’s rainfall variability with the North Atlantic Oscillation is identified for the examined period. On the other hand, regression kriging method combining surface elevation as secondary information improved the estimation of the annual rainfall spatial variability on the island of Crete by 70% compared to ordinary kriging. The rainfall spatial and temporal trends on the island of Crete have variable characteristics that depend on the geographical area and on the hydrological period.

Daily Monitoring of Shallow and Fine-Grained Water Patterns in Wet Grasslands Combining Aerial LiDAR Data and In Situ Piezometric Measurements

The real-time monitoring of hydrodynamics in wetlands at fine spatial and temporal scales is crucial for understanding ecological and hydrological processes. The key interest of light detection and ranging (LiDAR) data is its ability to accurately detect microtopography. However, how such data may account for subtle wetland flooding changes in both space and time still needs to be tested, even though the degree to which these changes impact biodiversity patterns is of upmost importance. This study assesses the use of 1 m × 1 m resolution aerial LiDAR data in combination with in situ piezometric measurements in order to predict the flooded areas at a daily scale along a one-year hydrological period. The simulation was applied over 663 ha of wet grasslands distributed on six sites across the Marais Poitevin (France). A set of seven remote sensing images was used as the reference data in order to validate the simulation and provide a high overall accuracy (76–94%). The best results were observed in areas where the ditch density was low, whereas the highly drained sites showed a discrepancy with the predicted flooded areas. The landscape proportion index was calculated for the daily steps. The results highlighted the spatiotemporal dynamics of the shallow flooded areas. We showed that the differences in the flooding durations among the years were mainly related to a narrow contrast in topography (40 cm), and occurred over a short period of time (two months).

Insectos acuáticos asociados a Eichhornia azurea (Schwartz) Kunth en ciénagas del río Atrato, Chocó - Colombia

El objetivo de este estudio fue caracterizar la comunidad de insectos acuáticos asociados a Eichhornia azurea (Schwartz) Kunth en cuatro ciénagas de la cuenca media y baja del río Atrato (Chocó-Colombia) durante los periodos de aguas altas y bajas; igualmente se evaluó la influencia de las variables ambientales y fisicoquímicas sobre esta comunidad. Durante dos meses se hicieron colectas de insectos acuáticos asociados a las raíces de E. azurea, utilizando un cuadrante de un m2, dotado de una malla de 0,5 mm, con tres replicas por ciénaga y simultáneamente se midieron algunas variables físicas y químicas del agua. La comunidad estuvo compuesta por 6 órdenes, 21 familias y 28 géneros. El mayor número de organismos (55,39%) y de taxones (23) se registró en el periodo de aguas bajas. Los órdenes más abundantes fueron Ephemeroptera (37,55%) y Coleoptera (26,77%), sobresaliendo las familias Baetidae y Noteridae respectivamente; mientras que la mayor riqueza taxonómica fue para coleópteros, dípteros y hemípteros. No se presentaron diferencias significativas en la diversidad y dominancia entre periodos hidrológicos (p>0,05), pero si en la riqueza específica (p<0,05). Los grupos funcionales de mayor abundancia fueron predadores (54,81%) y colectores (43,70%). Las variables fisicoquímicas hídricas no mostraron diferencias significativas entre periodos hidrológicos y se presentaron asociaciones entre la entomofauna acuática y las variables abióticas analizadas, principalmente con el oxígeno disuelto, la conductividad y los sólidos totales disueltos.

Characterizing Major Controls on Spatial and Seasonal Variations in Chemical Composition of Surface and Pore Brine of Maharlu Lake, Southern Iran

Maharlu Lake with Na–Cl water type is the terminal point of a closed basin in southern Iran. A total of 10 water samples from two rivers discharging to the lake and 78 water samples of surface and pore brine of Maharlu Lake have been collected from different depths (surface, 20, 50 and 100 cm) of four sampling stations along the lake during a period of lake water-level fluctuation (November 2014–July 2015). To investigate chemical interaction between lake surface water and shallow pore water and to understand the major factors governing chemical composition of Maharlu brine, concentrations of major and minor (boron, bromide and lithium) solutes, pH and total dissolved solids have been measured in collected water samples. Saturation indices of evaporite minerals in collected water samples have been also calculated. The chemical behavior of dissolved solutes and evaporative evolution of the lake brine during a hydrological period have been simulated using PHREEQC. The results of our investigations indicated that chemical composition of lake surface water and pore brine of Maharlu Lake are mainly connected with lake water-level fluctuations and distance from input rivers (and depth), respectively. Hydrochemical investigations and statistical analysis showed that the brines chemistry of Maharlu is mainly controlled by three processes: brine evaporative evolution, dissolution–precipitation and diagenetic evolution of secondary carbonates.

Velocity‐amplified microbial respiration rates in the lower Amazon River

AbstractMost measurements of respiration rates in large tropical rivers do not account for the influence of river flow conditions on microbial activity. We developed a ship‐board spinning incubation system for measuring O2 drawdown under different rotation velocities and deployed the system along the lower Amazon River during four hydrologic periods. Average respiration rates in incubation chambers rotated at 0.22 m s−1 and 0.66 m s−1 were 1.4 and 2.4 times higher than stationary chambers, respectively. On average, depth‐integrated respiration rates in chambers spun at 0.22 m s−1 and 0.66 m s−1 accounted for 64% ± 22% and 104% ± 36% of CO2 outgassing rates, respectively, in mainstem sites. Continuous measurements of in situ pCO2 were also made along with cross‐channel profiles of river velocity. A positive correlation between river velocity and pCO2 was observed along the lower river (r2 = 0.67–0.96) and throughout a tidal cycle.

Simulation of Nitrate Isotopic (δ15N and δ18O) by Coupling the Hydrology and Transport Processes Described by the SWAT Model

To improve the reliability of methods to trace surface water pollutants in river basins, hydrological and water quality processes in the Fuxi River Basin were continuously monitored from 2013 to 2015, and the main pollution sources in the watershed and δ15N as well as δ18O in the rivers were measured simultaneously. The Soil and Water Assessment Tool (SWAT) model was used to simulate the NH4+ and NO3- migration processes in the hydrological processes of the land surface and rivers. On this basis, the processes of mixing, transformation, and fractionation of δ15N and δ18O in NO3- were coupled, and the simulation methods of δ15N and δ18O in the rivers were developed. The results showed that δ15N and δ18O in the rivers were mainly affected by the pollution sources in the river basin and the variation in runoff conditions during different hydrological periods. The contribution of the mixing process of different isotopes to the isotope abundance was 82.74%. The contribution of isotope fractionation in the process of nitrogen conversion was 16.26%. The influence of NH4+ and NO3- concentration deviation from the SWAT simulation on the simulation errors of δ15N and δ18O was 10.44%. The δ18O simulation errors were 18.72% larger than those of δ15N because of the higher variation range of δ18O in rainfall and the complexity of δ18O. The systematic errors and deviations of the simulated δ15N and δ18O results using the proposed method were less than 10% and 15%, respectively. The simulation method of δ15N and δ18O in the river basin has a clear physical meaning, which provides a useful approach for tracing nitrogen sources in rivers.

Intra-annual variation in planktonic ciliate species composition (Protista: Ciliophora) in different strata in a shallow floodplain lake

Abstract Aim: We aimed to evaluate the variation in planktonic ciliate species composition in different strata of the Guaraná Lake, encompassing high and low water periods, at the Upper Paraná River floodplain. Methods Samplings were collected monthly between March 2007 and February 2008, from the epilimnion, metalimnion and hypolimnion. Ciliates samples were filtered using a plankton net of 10µm mesh size and identified in vivo under an optical microscope. Results Among 112 species identified, 13 were found exclusively during the high water periods and 39 during the low water period. Results of nonparametric extrapolation indices evidenced that the observed richness represented between 70% and 90% of the estimated richness. Regarding the variation in species composition, Beta1 index showed that the alteration in composition between strata during the low water period was slightly greater than that registered during high waters. Cluster analysis evidenced a higher dissimilarity in ciliate species composition between periods than among the different strata. The greatest variation in species composition was verified during the distinct hydrological periods, whereas no significant differences were observed for the different strata analysed. Conclusions We found that in the pelagic compartment, ciliate species composition changed significantly between hydrological periods, and a higher similarity in species composition among strata was observed during the high water period. Therefore, alterations in the vertical distribution seem to be related to the homogenizing effect of the floods in the water column stability.

Assessment of the cytotoxic and mutagenic potential of the Jialu River and adjacent groundwater using human-hamster hybrid cells

The Jialu River in China has been seriously polluted by the direct discharge of industrial and domestic wastewater. The predominant contaminants of the Jialu River and its adjacent groundwater were recently investigated. However, the potential genotoxic impact of polluted water on human health remains to be clarified. Here, we used human–hamster hybrid (AL) cells, which are sensitive for detecting environmental mutagens. We found that the cytotoxicity and mutagenicity of the groundwater in the Jialu River basin were influenced by the infiltration of the Jialu River. Hydrological periods significantly affected the cytotoxicity, but not the mutagenic potential, of surface and groundwater. Further, the mutagenic potential of groundwater samples located <1km from the Jialu River (SM-2 water samples) was detected earlier than that of groundwater samples located approximately 20km from the Jialu River (SN water samples). Because of high cytotoxicity, the mutagenic potential of water samples from the Jialu River (SM-1 water samples) was not significantly enhanced compared with that of untreated controls. To further assess the mutagenic dispersion potential, an artificial neural network model was adopted. The results showed that the highest mutagenic potential of groundwater was observed approximately 10km from the Jialu River. Although further investigation of mutagenic spatial dispersion is required, our data are significant for advancing our understanding of the origin, dispersion, and biological effects of water samples from polluted areas.

Diversidad de macroinvertebrados fitófilos en arroyos de cabecera en pastizales de altura en Córdoba, Argentina

Macrophytes play an important role in lotic systems increasing habitat heterogeneity and providing food and shelter for wildlife. The aim of the study was to analyze the structure and composition of the invertebrate community associated with macrophytes in headwater streams in mountain grasslands (Ctalamochita sub-basin, Córdoba, Argentina) in two hydrological periods. The structure of the invertebrate assemblages in different macrophyte species (Hydrocotyle spp., Rorippa nasturtium-aquaticum and Ranunculus flagelliformis) was also evaluated. Three streams were sampled during high water (March 2012) and low water (August 2012) period. In each period, samples of invertebrates associated with the dominant macrophyte in each stream were collected. Seventy-two taxa of phytophilous macroinvertebrates were identified. The most frequent and abundant taxa were Naidinae, Hyalella curvispina, Americabaetis spp., Corynoneura spp. and Rheotanytarsus spp. Assemblages composition differed between hydrological periods and greater abundance of invertebrates was detected in R. nasturtium-aquaticum. The results showed that macrophyte patches in grassland headwater streams harbor an abundant and diverse invertebrate fauna and provide important base information for biomonitoring.

The change of quantity and quality outflow of water in Ochożanka River basin

AbstractThe aim of this research work is to evaluate changes in the quantities of water and chemical parameters of outflow water from the forest catchment. Research was carried over a hydrological five-year period in the Ochożanka River basin (Western Polesie). The structure of the catchment area of 33.1 km2 is dominated by forestland constituting 81% of the area. During this period the precipitation amounted to 627 mm, which was 100 mm higher than the multi-year average. Precipitation of the summer half-year was almost three times higher than in the winter half-year. Data analysis shows that the average unit outflow from the catchment unit was 3.0 dm3·s−1·km−2. Outflow in the winter half-year was 52% higher than in the summer half-year. The waters of the river are used, they are usually characterized by good chemical status. In case 30% samples concentration of Kjeldahl nitrogen (&gt;2 mg N·dm−3), total phosphorus (&gt;0.4 mg P·dm−3) exceed the limit values for second class quality water. Indicators of oxygen conditions reach medium and high values. In spring, it happens that the limits are exceeded for second class water quality. These values are respectively COD &gt; 20 mg O2·dm−3 and oxygen &lt;5 mg O2·dm−3. An important issue related to the value parameters is the seasonal variability of their concentration in water outflow from the catchment. The maximum value chemical parameters are recorded in March, when the occurred largest outflows water.

Role of environmental and spatial processes structuring fish assemblages in streams of the eastern Amazon

Considering the increasing importance of analysing spatial structure in ecological studies, the aims of the present study were to test whether fluvial distances and environmental factors are important drivers of the β-diversity of stream fish assemblages, and whether β-diversity is different in distinct hydrological periods. Specimens were sampled at 33 stream sites in the eastern Amazon. Eight environmental variables were measured at each site and fluvial distances between pairs of stream sites were determined. Environmental variables were the main factors structuring fish assemblages in both periods. However, fluvial distances were important only during the flood period. This can be related to the formation of extensive flood plains in this period, which increases connectivity between streams, breaking habitat isolation and increasing the regional signal for fish species. The higher correlation of β-diversity with environmental variables during the flood period may be related to decreased dispersal limitations and intermediate dispersal. Finally, β-diversity was higher during the flood period, highlighting the importance of the heterogeneity of the flood plain to stream biota. The results of the present study indicate that spatial and environmental factors play complementary roles in structuring fish assemblages in Amazon streams, and that β-diversity was affected by changes in the habitat connectivity experienced in different hydrological periods.