Variable Hydrological Regimes Research Articles

DETERMINATION OF THE CHARACTERISTICS OF THE ELECTROMECHANICAL EQUIPMENT OF THE MICRO HYDROELECTRIC POWER PLANT AT THE GUEENI SITE ON THE KOKOULO RIVER

When setting up a small hydroelectric power plant in isolated sites, the choice of electromechanical equipment remains a very important factor. This study is part of this dynamic. Its main objective is the determination of characteristics and the choice of electromechanical equipment for the micro hydroelectric power plant at the Gueeni site on the Kokoulo River in Pita in Guinea, with a variable hydrological regime. The methodology adopted is based on knowledge of the hydraulic parameters and the hydroenergetic characteristics of the site (hydraulic power, net power). Based on these elements, we determined with great precision; the type of turbine (Kaplan), with a rotation speed (586.58 rpm); the specific speed (47 rpm); the number of generator poles (10); the electrical power of the plant (2160 kW), the apparent power of the transformer (2700 kVA) and valve closing time (1.1 s). This study is part of the dynamic of evaluating the hydroenergetic potential of small developable waterfalls in isolated areas of Guinea

Hydrologic connectivity and morphologic variation of oxbow lakes in a pristine alpine fluvial system

The lifespan of oxbow lakes in a meandering system typically exhibits considerable disparity due to the diverse evolutionary processes that lead to their terrestrialization. Although oxbow lakes generally undergo a long-term gradual shrinking trend, their hydrologic connectivity and morphologic variations under variable hydrologic conditions of the river are not well understood. Here we focus on a group of oxbow lakes in a pristine alpine fluvial system in the Qinghai-Tibet Plateau to examine the hydrogeomorphic response of oxbow lakes to a variable hydrologic regime of an active meandering channel. We find that the oxbow lakes are characterized by extensively developed compound forms and connecting “tie” channels and that the lateral migration of the main channel discernably impacts lake morphology and evolution. With increasing discharges in the main channel, the oxbow lakes generally show increases in length under relatively lower flows (RI < 10 years) and more dramatic increases in width under higher flows (RI > 10 years), which collectively lead to their expansion regardless of their hydrologic connectivity. This implies hydrogeomorphic processes other than surface water connection between oxbow lakes and the main channel in adjusting water levels of the lakes. To quantify hydrologic connectivity, we propose a probability-based index and find the overall low hydrologic connectivity of the studied oxbow lakes, owing to the unique paleogeographic setting of the study area. The infrequent but pulsed sedimentation within the lakes and the relatively slow lateral migration of the meandering channel catalyze an inactive floodplain of the study reach.

Hydroclimate variability in the United States continental interior during the early Eocene Climatic Optimum

The early Eocene (56.0 to 47.8 million years ago) was punctuated by a series of transient episodes of rapid global warming superimposed on the long-term early Cenozoic warming trend, culminating in the early Eocene Climatic Optimum (EECO; 53.3 to 49.1 million years ago). Details of the hydroclimate regime operating during the EECO are poorly constrained, especially for continental interior sites. The Green River Formation (GRF) of Utah and Colorado was deposited in a suite of large, unusually productive lakes that offer an ideal opportunity to study the hydrological response to warming. Here we report the hydrogen isotopic composition (δ 2 H) of leaf wax (long-chain n -alkanes) and algal (phytane) lipids preserved in the organic-rich Mahogany Zone (49.3 to 48.7 Ma) and use these data to reconstruct precipitation and lake water δ 2 H records, respectively. We observe large inter-site variations in algal and leaf wax δ 2 H values (~50 to 75‰), suggesting that additional local controls influence precipitation and/or lake water δ 2 H (e.g., salinity). Intriguingly, leaf wax and algal lipid δ 2 H values show little variation through the Mahogany Zone, implying a relatively stable hydrological regime during the latter phase of the EECO. This contrasts with the more variable hydrological regime that prevailed during early Eocene hyperthermals. Unlike the EECO, the early Eocene hyperthermals in the Uinta region do not coincide with the deposition of organic-rich sediments. This suggests that a stable hydrological regime during the EECO may enable the preservation of organic matter within continental-interior lake systems, potentially leading to an important negative climate feedback during the early Eocene and other greenhouse climates. • Gradual variations in leaf wax δ 2 H values indicate a stable hydrological cycle during the latter phase of theEECO. • However, leaf wax and algal δ 2 H values exhibit large lake inter-site variability (~50 to 75‰). • Stable hydroclimate may have promoted organic matter burial within the lake system. • High organic carbon burial may have acted as an important negative climate feedback.

Intraspecific variability in thermal tolerance: a case study with coastal cutthroat trout.

Fish physiological performance is directly regulated by their thermal environment. Intraspecific comparisons are essential to ascertain the vulnerability of fish populations to climate change and to identify which populations may be more susceptible to extirpation and which may be more resilient to continued warming. In this study, we sought to evaluate how thermal performance varies in coastal cutthroat trout (Oncorhynchus clarki clarki) across four distinct watersheds in OR, USA. Specifically, we measured oxygen consumption rates in trout from the four watersheds with variable hydrologic and thermal regimes, comparing three ecologically relevant temperature treatments (ambient, annual maximum and novel warm). Coastal cutthroat trout displayed considerable intraspecific variability in physiological performance and thermal tolerance across the four watersheds. Thermal tolerance matched the historical experience: the coastal watersheds experiencing warmer ambient temperatures had higher critical thermal tolerance compared with the interior, cooler Willamette watersheds. Physiological performance varied across all four watersheds and there was evidence of a trade-off between high aerobic performance and broad thermal tolerance. Given the evidence of climate regime shifts across the globe, the uncertainty in both the rate and extent of warming and species responses in the near and long term, a more nuanced approach to the management and conservation of native fish species must be considered.

Comparing opportunistic and strategic removal efforts to manage invasive fish species using a dynamic multi‐state occupancy model

Abstract Growing ecological and economic impacts of invasive species have heightened the need for new science to inform management that prevents and counteracts their impacts. A persistent challenge is to identify whether removal programs, which range widely in their approach, are successful. Given the variability in dynamic environmental conditions and complex biotic interactions among species, identifying the effectiveness of removal programs intended to lessen nonnative species impacts is inherently difficult. We were interested in whether strategic (i.e. significant coordination and investment) and opportunistic (i.e. temporally periodic and implemented at smaller spatial scales) removal programs result in measurable, and if so, comparable benefits to native fish conservation. We applied a novel dynamic co‐occurrence model to evaluate nonnative fish removal efforts across the Lower Colorado River Basin (USA), while accounting for potential interspecific species interactions and variable hydrologic regimes. We examined the co‐occurrence of two native fishes of conservation concern and two other representative fishes of endemic assemblages, each paired with a nonnative species hypothesized to negatively affect the focal native species. Our model results suggest that both strategic and opportunistic removal programs result in lower extinction probabilities for native fishes (1.2 times greater for strategic programs), especially species of conservation concern, when compared to locations and years not subject to removal. Nonnative species presence mediated native species dynamics, most notably by increasing native species extinction probability during drought years regardless of removal program. Removal efforts resulted in modest changes in extinction probabilities for nonnative fishes, but no measurable effect on colonization dynamics. Synthesis and applications. Both strategic and opportunistic nonnative fish removal programs can help meet recovery goals for native fishes, even over large areas and long after nonnative species are established. Quantifying dynamics of native and nonnative fishes in a multi‐state dynamic co‐occurrence model highlights the collective management value of individual programs at regional scales. Increased evaluation of ongoing nonnative removal programs remains critical to ensuring that management actions are warranted and effective in meeting desired conservation outcomes.

EFFECTS OF THE VERTICAL HETEROGENEITY OF WATER MASSES ON THE STABILITY OF INDUSTRIAL WATER SUPPLY IN INDUSTRY-INTENSIVE AREAS

The stability of water supply systems is one of the main factors for reliable operation of large industrial complexes. This problem is considered through the case of the Azot branch of JSC URALCHEM in the city of Berezniki, which derives raw process water from the Kama River (Kama storage reservoir). A characteristic feature of this water body is a highly variable hydrological regime. During the summer low water period, it is characterized by low current velocities. In winter, when the water level in the reservoir declines, a typical river flow regime is observed. In addition, the water body is exposed to heavy human impact. The bulk of the load comes from non-declared non-point (diffuse) sources. Their characteristic feature is high suspended solids content, and, accordingly, the density of the effluents. Their behavior is fundamentally different from the processes of dilution and migration of effluents with neutral buoyancy. Traditional methods of calculating dilution processes cannot be used to describe them. A two-layer flow is formed, where the content of basic ions in the surface horizon is more than an order of magnitude lower than near the bottom. Early in July 2020, a significant increase in the content of chlorine and sodium ions was observed at the water intake facility of the Azot branch, causing a shutdown of the plant. The causes of the phenomenon had to be identified. The putative causes were emergency discharges of concentrated waste from the sludge dump on the shore or contamination by the wastewater entering the Kama River below the intake facility due to backflow. These situations can be modeled taking into account the vertical heterogeneity of water masses based on the coupling of hydrodynamic models in one-, two-, and three-dimensional formulation. As a result, it was shown that the only cause of the emergency could be water intake from the Kama River bottom flow.

Phototrophic communities of Kulunda Steppe soda lakes (Altai Region): history of algological studies and modern data.

The Kulunda Steppe soda lakes are the only occurrence of hypersaline soda lakes in Russia. They are characterized by a variable hydrological regime with cyclic high-amplitude fluctuations of temperature and brine concentration. The algae of the Kulunda Steppe soda lakes were first studied by Soviet phycologists headed by N.N. Voronikhin in 1927–1932 and new taxa were described: algal genus Lochmiopsis Woronich. et Popova (later revised to Ctenocladus circinnatus Borzì) and cyanobacterial species Aphanocapsa salina Woronich., Synechocystis crassa Woronich., Trichormus (Anabaena) pseudovariabilis (Woronich.) Komárek et Anagnostidis, Anabaenopsis issatschenkoi Woronich., Anabaenopsis milleri Woronich., Anabaenopsis nadsonii Woronich., Oscillatoria deflexa var. crassa Woronich., Limnospira (Arthrospira, Spirulina) fusiformis (Woronich.) Komárek et Lund. Later (since 2007) studies were continued by the microbiologists from the Winogradsky Institute of Microbiology RAS. In this work, a comparison of the algological diversity found in the soda lakes of the Kulunda Steppe during periods 1929–1932 and 2007–2020 is made, and a brief overview of taxonomic problems of selected eukaryotic algae and cyanobacteria is given. In total, 33 morphotypes of cyanobacteria were identified. Most species of algae and cyanobacteria were described based on the exclusively morphological criteria. Thus, their phylogenetic position remains unclear and requires careful analysis using a modern polyphasic approach.

Characteristics, Main Impacts, and Stewardship of Natural and Artificial Freshwater Environments: Consequences for Biodiversity Conservation

In this overview (introductory article to a special issue including 14 papers), we consider all main types of natural and artificial inland freshwater habitas (fwh). For each type, we identify the main biodiversity patterns and ecological features, human impacts on the system and environmental issues, and discuss ways to use this information to improve stewardship. Examples of selected key biodiversity/ecological features (habitat type): narrow endemics, sensitive (groundwater and GDEs); crenobionts, LIHRes (springs); unidirectional flow, nutrient spiraling (streams); naturally turbid, floodplains, large-bodied species (large rivers); depth-variation in benthic communities (lakes); endemism and diversity (ancient lakes); threatened, sensitive species (oxbow lakes, SWE); diverse, reduced littoral (reservoirs); cold-adapted species (Boreal and Arctic fwh); endemism, depauperate (Antarctic fwh); flood pulse, intermittent wetlands, biggest river basins (tropical fwh); variable hydrologic regime—periods of drying, flash floods (arid-climate fwh). Selected impacts: eutrophication and other pollution, hydrologic modifications, overexploitation, habitat destruction, invasive species, salinization. Climate change is a threat multiplier, and it is important to quantify resistance, resilience, and recovery to assess the strategic role of the different types of freshwater ecosystems and their value for biodiversity conservation. Effective conservation solutions are dependent on an understanding of connectivity between different freshwater ecosystems (including related terrestrial, coastal and marine systems).

Detecting the State of the Climate System via Artificial Intelligence to Improve Seasonal Forecasts and Inform Reservoir Operations

AbstractIncreasingly variable hydrologic regimes combined with more frequent and intense extreme events are challenging water systems management worldwide. These trends emphasize the need of accurate medium‐ to long‐term predictions to timely prompt anticipatory operations. Despite in some locations global climate oscillations and particularly the El Niño Southern Oscillation (ENSO) may contribute to extending forecast lead times, in other regions there is no consensus on how ENSO can be detected, and used as local conditions are also influenced by other concurrent climate signals. In this work, we introduce the Climate State Intelligence framework to capture the state of multiple global climate signals via artificial intelligence and improve seasonal forecasts. These forecasts are used as additional inputs for informing water system operations and their value is quantified as the corresponding gain in system performance. We apply the framework to the Lake Como basin, a regulated lake in northern Italy mainly operated for flood control and irrigation supply. Numerical results show the existence of notable teleconnection patterns dependent on both ENSO and the North Atlantic Oscillation over the Alpine region, which contribute in generating skilful seasonal precipitation and hydrologic forecasts. The use of this information for conditioning the lake operations produces an average 44% improvement in system performance with respect to a baseline solution not informed by any forecast, with this gain that further increases during extreme drought episodes. Our results also suggest that observed preseason sea surface temperature anomalies appear more valuable than hydrologic‐based seasonal forecasts, producing an average 59% improvement in system performance.

Assessing the relative impacts of land‐use change and river regulation on Burdekin River (Australia) floodplain wetlands

Abstract The Burdekin River floodplain wetlands are internationally important and act as a sink for sediments and nutrients that would otherwise enter the World Heritage‐listed Great Barrier Reef lagoon. The Burdekin River has the highest natural discharge of any Great Barrier Reef catchment and contributes the greatest mass of sediment to the reef. The river and its catchment have been substantially modified by land clearance, river regulation introduced in the 1960s, the construction of the Burdekin Falls Dam in 1987 and invasive aquatic plants. We hypothesised that the natural variability of Burdekin River discharge would render its wetland ecosystems resistant to human‐induced pressures. Diatoms were analysed from the sediments of two lower Burdekin River floodplain wetlands with contrasting regulation histories. Labatt Lagoon has a long history of flow alteration, whereas Swan's Lagoon has experienced limited regulation. Both wetlands experienced dramatic increases in sedimentation as a result of land clearance, yet the Swan's Lagoon diatom record indicates that the wetland's ecology remains within the range of natural variability. In contrast, Labatt Lagoon is markedly different from its pre‐settlement state. It is now permanent, having been ephemeral for more than 1000 years before European settlement. The conversion to artificial permanence facilitated aquatic plant invasion, resulting in more marked changes than widespread pastoralism. Modern diatom assemblages from 28 lower Burdekin River floodplain wetlands indicate that the contemporary flora of Swan's Lagoon is unusual. Most wetlands have similar assemblages to those in the Labatt Lagoon record in its present, altered state. It is possible, therefore, that the ecological shift registered in Labatt Lagoon is widespread. Diatom records highlight the striking impact that river regulation has had on the trajectory of the Burdekin floodplain wetlands. It is likely that wetland rehabilitation can be facilitated by the re‐introduction of a variable hydrological regime.

The relationship between suspended solids and nutrients with variable hydrologic flow regimes

The hypothesis that “freshwater inflow variability over space and time can drive suspended solids and nutrient concentrations” was tested by comparing three micro-tidal estuaries (Guadalupe, Lavaca-Colorado, and Nueces) in Texas with different hydrologic flow regimes over three years with wet and dry conditions. In all three estuaries, Total suspended solids (TSS) was less than 50 mg/L most of the time. In the Nueces Estuary, TSS of higher than 100 mg/L occurred during frontal events. Dissolved inorganic nitrogen (ammonia+nitrite+nitrate) concentrations were most of the time lowest in the Nueces Estuary (i.e. ≤0.5μmol/L), with low inflow rates and high average salinity of 37.6. Salinity was highest in the river-estuary mouth (average salinity 38.3) of the Nueces Estuary relative to the other oceanic-side stations (average salinity 37), indicating that the system was a “reverse estuary” where evaporation exceeds freshwater inflow, resulting in net inflow of marine water into the estuary. The inverse correlation between ammonium and salinity in all three estuaries and the corresponding negative correlation between nitrite+nitrate concentrations and salinity in the Guadalupe Estuary indicate that the quantity of inflow controls nitrogen concentrations and transformations in the three estuaries. Drought conditions limited riverine transport of nitrogen and sediment to the three estuaries, demonstrating the importance of freshwater inflow to maintaining these constituents. Average silica and orthophosphate concentrations correlated positively with chlorophyll-a in combined data from all three estuaries. Silica and orthophosphate concentrations remained constant over the study period, but correlated with chlorophyll-a when suspended solid was low. Therefore, inflow dynamics drive changes in the salinity regime, suspended solids, and act to maintain nutrient concentrations.

Evaluation of water erosion at a mountain catchment in Poland using the G2 model

The Western Carpathians region in southern Poland is characterized by high erosion risk due to steep slopes, flysch formation and intense precipitation with frequent storm events. The G2 model, based on the principles of the Universal Soil Loss Equation (USLE), was used to investigate soil erosion assessment, except that the yearly rainfall erosivity factor was substituted for by the monthly one. The plant cover factor was determined based on the CORINE land cover 2012 database and field observations of vegetation stages. Slope intercept was estimated by applying a Sobel filter. Terrain properties were calculated from a 5 m DEM of the area. Modeling investigations were carried out in the agricultural basin of the mountain catchment (1.47 km2) in the years 2011–2014. Rainfall data were collected from weather stations, and soil properties were measured in 43 locations. The G2 model estimated total annual soil loss as between 3.37 Mg ha−1 (2012) and 31.05 Mg ha−1 (2014). The erosive events that contributed most to yearly erosion occurred in May (2014: 80.40% of yearly total) and June (2013: 57.08%). Redundancy analysis based on land-use types provided factors affecting soil erosion by water. In conclusion, the G2 model was useful in erosion estimation in a steep-sloped agricultural basin with a variable hydrological regime.

Streamflow-base flow ratio in a lowland area of North-Eastern Romania

The ratio between streamflow and base flow for 3 catchments from lowland area of North-Eastern Romania were calculated with six different separation methods: the local minimum method, Talaksen filter, Chapman filter, recursive digital filter, WHAT model, and the Ekchardt filter. In agreement with an increase in precipitation levels in the past decades all filter-based methods indicate a slight increase in Base Flow Index (BFI) values throughout the study period (1981–2013). The Eckhardt filter associated with Chapman filter are the most appropriate methods to evaluate the ratio between streamflow and base flow for this area. Both methods suggest the identification of parameters a and BFImax (a = 0.925, BFImax = 0.5–0.7). Taking into account the highly variable hydrological regime throughout the year, and the fact that 35% of the hydrographic network displays ephemeral stream, the values obtained for the BFI based on these algorithms are the following: BFI = 0.58 for basins developed on porous aquifers with perennial stream (asuming a = 925 and BFImax = 0.7) and BFI = 0.52 for basins developed on porous aquifers, but with ephemeral stream (asuming a = 925 and BFImax = 0.5).

In-situ atrazine biodegradation dynamics in wheat (Triticum) crops under variable hydrologic regime

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0.11% and 0.15% of ATZ, respectively. The residual Cl mass fraction in ATZ and 4 byproducts was 2.4% of the applied mass. ATZ half-life ranged from 150 to 247days in the soil surface. ATZ reached 5m soil depth within 200years and its concentration increased from 1×10−6 to 4×10−6mg/kgdry-soil over time. The correlation between ATZ specific biomass degradation affinity Φ0 and half-life t1/2, although relatively uncertain for both hydrolyzing and oxidizing bacteria, suggested that microorganisms with high Φ0 led to low ATZ t1/2. Greater ATZ applications were balanced by small nonlinear increments of ATZ biodegraded fraction within the root zone and therefore less ATZ leached into the shallow aquifer.

Modeling Allochthonous Dissolved Organic Carbon Mineralization Under Variable Hydrologic Regimes in Boreal Lakes

Here, we explore the interaction between hydrology and the reactivity of allochthonous dissolved organic carbon (DOCalloch) in determining the potential of DOCalloch to generate CO2 through biological and photo-chemical mineralization in boreal lakes. We developed a mechanistic model that integrates the reactivity continuum (RC) concept to reconstruct in-lake mineralization of DOCalloch under variable hydrologic conditions using empirical measurements of DOCalloch concentrations and reactivity as model inputs. The model predicts lake DOCalloch concentration (L-DOCalloch) and its average overall reactivity $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ , which integrates the distribution of DOCalloch ages within the lake as a function of the DOC loading (DOCin), the initial reactivity of this DOCin (k 0), and the lake water residence time (WRT). The modeled DOCalloch mineralization rates and concentrations were in agreement with expectations based on observed and published values of ambient lake DOC concentrations and reactivity. Results from this modeling exercise reveal that the interaction between WRT and k 0 is a key determinant of the ambient concentration and reactivity of lake DOCalloch, which represents the bulk of DOC in most of these lakes. The steady-state $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ also represents the proportion of CO2 that can be extracted from DOCalloch during its transit through lakes, and partly explains the patterns in surface water pCO2 oversaturation that have been observed across gradients of lake size and volume. We estimate that in-lake DOCalloch mineralization could potentially contribute on average 30–40% of the observed surface carbon dioxide partial pressure (pCO2) across northern lakes. Applying the RC framework to in-lake DOCalloch dynamics improves our understanding of DOCalloch transformation and fate along the aquatic network, and results in a predictable mosaic of DOC reactivity and potential CO2 emissions across lakes within a landscape.

Sediment source identification and load prediction in a mixed-use Piedmont watershed, South Carolina

Many streams in the Piedmont region of the southeastern United States transport a disproportionately large amount of suspended sediment in response to moderately increased streamflows. Transport and deposition of excess sediment affect the stability of the channel and the health of the biological community; therefore, identifying the main source(s) of sediment and assessing the relationships between source, transport, and streamflow are critical to aquatic life and habitat management, dynamic equilibrium preservation, and development of feasible mitigation scenarios. The objectives of this study were to: (1) predict the annual suspended sediment yield and (2) identify significant contributing upland sources of sediment in the Lawsons Fork Creek basin, a 217 km2 mixed-use watershed in the South Carolina Piedmont. A regularly monitored cross-section located in the downstream reach was equipped with a passive sediment sampler, gage-height recorder, and sediment tiles. Streamflow and sediment concentration were measured over a 24-month period under variable hydrologic regimes. Results indicated that the average annual sediment yield (168 t/km2/yr) is significantly higher than yields documented in Piedmont watersheds of comparable size. To identify and prioritize sources of sediment contribution, stable isotopes of nitrogen (δ15N) and carbon (δ13C) were used as tracers. Source material was compared with suspended sediment near the watershed outlet (target material) and SIAR, a Bayesian Inference model, was used to estimate source apportionment. Results of this source study indicate that approximately 60% of the total sediment load in the water column during high flow events is derived from stream bank erosion. Findings are consistent with observed unstable stream bank conditions in the watershed. This study supports the use of a dual-isotopic fingerprinting approach in tandem with traditional sediment monitoring as a cost-effective method to identify and target sediment sources in a mixed-use watershed.

COMPOSITION, BODY-SIZE STRUCTURE AND BIOMASS OF ZOOPLANKTON IN A HIGH-ELEVATION TEMPORARY POND (MINAS GERAIS, BRAZIL)

Small ponds are vital inland water bodies, recognized as small repositories of freshwater biodiversity, but neglected in terms of conservation. Although high-elevation ponds are difficult to sample and monitor, it is important to extend their study, in view of their importance to aquatic biodiversity. The aim of this study was to analyze the composition, size structure biomass and diversity of zooplankton community in a temporary pond (Lagoa Seca) of a low-alpine area in the southern part of Serra do Espinhaco mountain in Minas Gerais State, Brazil. Three ecological aspects were analyzed: (I) the taxonomic composition of the zooplankton assemblage, (II) the size structure and biomass of the main groups in the zooplankton community and (III) whether the morphometric characteristics and biomass of the zooplankton result from the dominance of the microzooplankton, as expected in habitats subjected to frequent and strong disturbances, such as temporary ponds. Zooplankton samples were taken during the rainy period (Oc­tober 2010 to January 2011) in different mesohabitats, from the shallowest areas covered by emergent macrophytes to the open water area covered mainly by submerged macrophytes. The zooplankton community consisted of a small number of taxa (29). Rotifera showed the highest richness, with 21 taxa recorded, of which the most constant species were the cosmopolitan Lecane lunaris , L. obtusa and Lepadella patella . Among the Cladocera, Bosmina freyi and Moina minuta were the pelagic species recorded. The other cladoceran species observed are associated with littoral vegetation, and represented mainly by Alona ossiani , Chydorus pubescens , Ephemeroporus tridentatus and Ilyocryptus spinifer . The zooplankton biomass was very low (the maximum dry weight, observed at the peak of the rainy period in January was 62 ? g.m -3 ). The zooplankton community was dominated by the microzooplankton, with the maximum body length below 900 ? m. This assemblage was very changeable in the short term, both in numerical density and size structure, probably because of the highly variable hydrological regime of the pond. The results from zooplankton composition, including the first record of the rotifer Microcodon clavus to Minas Gerais state and the second in Brazil, highlighted the important role that high-elevation temporary ponds can play as aquatic biodiversity reserves. These unique ecosystems deserve greater efforts of research and monitoring, including studies of their hydrological pat­terns, biological diversity, and adaptive mechanisms of the zooplankton community. Normal 0 21 false false false PT-BR X-NONE X-NONE

Hydrodynamic variability of the Cretan Sea derived from Argo float profiles and multi-parametric buoy measurements during 2010–2012

In this work, we examine the complex hydrology of the Cretan Sea, an important area which affects the dynamics of the Eastern Mediterranean basin. We use T/S profile data derived from the first Argo float deployed in the area during June 2010 within the framework of the Greek Argo program. Temperature and salinity profiles were measured over a 2-year period, analyzed, and combined with time series data recorded from the POSEIDON E1-M3A multi-parametric instrumentation platform operating in the area since 2007. The acquired datasets have been enriched with available CTD profiles taken on the mooring site during cruise maintenance surveys. The combined research activities resulted in a large dataset of physical properties allowing extended geographical coverage and an in-depth analysis of the Cretan Sea dynamics during this 2-year period. Data analysis shows significant variability of water masses of different origin at subsurface and deep layers. This confirms previous findings describing the area as transitional with water masses of different origin meeting and interacting. Furthermore, additional features of the area are described combining information from satellite altimetry. In this study, new circulation systems are identified at intermediate and subsurface layers affecting both the dynamic behavior of the basin’s upper thermocline and the intermediate/deep water mass tempo-spatial variability. We further investigate the physical properties of the water column and suggest an updated mesoscale circulation picture based on the dynamics of the variable hydrological regimes of the Cretan Sea basin.

Water-level fluctuations as a driver of Phragmites australis primary productivity, litter decomposition, and fungal root colonisation in an intermittent wetland

The hypothesis of this study is that the variable hydrological regime of intermittent lakes and wetlands affects the primary productivity, decomposition and root fungal colonisation of Phragmites australis, with effects on the whole ecosystem metabolism. The above-ground biomass of reed stands was monitored in littoral and riparian stands of Lake Cerknica, under different water levels. Leaf and culm litter decomposition was also studied at three locations, from predominantly dry to permanently submerged. Root colonisation by fungi was monitored across two seasons in the littoral reed stand. The primary productivity of the littoral stands was related to a variable degree with water levels and air temperature in July in the current year. In the riparian reeds, only monthly temperatures in October of the previous year were important. The submersion duration of the litter enhanced the decomposition rates. The frequency of fungal colonisation of reed roots was decreasing with the submersion time length. Overall, roots were colonised by arbuscules, hyphae, vesicles, hyphal coils and microsclerotia. The main outcomes of this study deals with the role of intermittent hydrological conditions in determining the structure and functioning of reed-dominated lacustrine wetlands, which are exposed to climate threats.

Sediment transport in two mediterranean regulated rivers

Mediterranean climate is characterized by highly irregular rainfall patterns with marked differences between wet and dry seasons which lead to highly variable hydrological fluvial regimes. As a result, and in order to ensure water availability and reduce its temporal variability, a high number of large dams were built during the 20th century (more than 3500 located in Mediterranean rivers). Dams modify the flow regime but also interrupt the continuity of sediment transfer along the river network, thereby changing its functioning as an ecosystem. Within this context, the present paper aims to assess the suspended sediment loads and dynamics of two climatically contrasting Mediterranean regulated rivers (i.e. the Ésera and Siurana) during a 2-yr period. Key findings indicate that floods were responsible for 92% of the total suspended sediment load in the River Siurana, while this percentage falls to 70% for the Ésera, indicating the importance of baseflows on sediment transport in this river. This fact is related to the high sediment availability, with the Ésera acting as a non-supply-limited catchment due to the high productivity of the sources (i.e. badlands). In contrast, the Siurana can be considered a supply-limited system due to its low geomorphic activity and reduced sediment availability, with suspended sediment concentration remaining low even for high magnitude flood events. Reservoirs in both rivers reduce sediment load up to 90%, although total runoff is only reduced in the case of the River Ésera. A remarkable fact is the change of the hydrological character of the River Ésera downstream for the dam, shifting from a humid mountainous river regime to a quasi-invariable pattern, whereas the Siurana experiences the opposite effect, changing from a flashy Mediterranean river to a more constant flow regime below the dam.