Hydrological Seasons Research Articles

Condutores da dinâmica espacial do zooplâncton em um pequeno rio neotropical

Abstract Aim Our objective was to describe the structure and spatial patterns of the zooplankton community in a small Brazilian river system (Paranaíba River sub-basin) and evaluate the role of an oxbow lake in the dynamics of this community. Methods Zooplankton samples were collected from sites located in an oxbow lake and the Aporé River bed during the rainy and dry seasons. We collected these samples from the surface and bottom levels of two different zones (littoral and channel). For each hydrological season, analysis of variance was conducted to determine the differences in species richness and abundance of zooplankton among different sites (longitudinal), zones (lateral), and depths (vertical). Cluster analysis was performed to assess the similarity in species composition. In addition, a canonical correspondence analysis was used to select the environmental variables that best explained the variation in zooplankton abundance data. Results We recorded 152 species: 70 rotifers, 53 testate amoebae, 20 cladocerans, and 9 copepods. We observed changes in the species richness and abundance of zooplankton along the longitudinal axis of the river in both the rainy and dry seasons. However, we did not detect any lateral or vertical changes in these attributes. Cluster analysis also indicated that the greatest differences in species composition were in the longitudinal axis of the river. The longitudinal variability of zooplankton was mainly associated with the influence of an upstream oxbow lake, as well as the changes in water flow velocity, turbidity, and concentrations of suspended solids downstream. Conclusions Our results demonstrate the importance of a heterogeneity of hydrological characteristics as a structuring factor of the zooplankton community in the Aporé River. Thus, we highlight the relevance of actions to protect and maintain the natural characteristics of these environments.

Combination of linear and nonlinear multivariate approaches effectively uncover responses of phytoplankton communities to environmental changes at regional scale

The response of a community to environmental changes is either linear or non-linear, so that they can be investigated approximately by linear or nonlinear models. At community level, redundancy analysis (RDA) and canonical correspondence analysis (CCA), and Mantel test and Generalized Dissimilarity Modelling (GDM) are two pairs of fundamental multivariate approaches. Thus, it is necessary to determine how they are used for a given group of communities or a metacommunity. In the present study, we explored the applications of the two pairs of commonly used multivariate methods for the analysis of tropical phytoplankton communities. Phytoplankton were collected from 60 tropical reservoirs in southern China at two distinct regions and two hydrological seasons. Because of a short environmental gradient, response of phytoplankton communities to the environmental gradients was first explored with linear models: distance-based redundancy analysis (db-RDA) and Mantel test. Then, CCA and GDM were further applied to recognize the nonlinear relationship between phytoplankton community variation and environmental changes, and to detect the significant environmental and/or spatial variables. Our results strongly suggest that the combination of db-RDA and GDM provides a highly effective tool to uncover the linearity and nonlinearity in community responses and the important associated environmental and spatial variables, which were significantly different between flooding and dry seasons.

COMPARATIVE ANALYSIS OF THE CHEMICAL COMPOSITION OF WATERWATER IN THE SLAVSKY DISTRICT OF THE KALININGRAD REGION BY HYDROLOGICAL SEASONS

The aim of the work is to research the chemical composition of surface watercourses in the Slavsky district of the Kaliningrad region in the winter hydrological season, and to compare the results with the data previously obtained by the authors for the autumn hydrological season and partly for the summer hydrological season. Watercourses and monitoring points for research have been identified: r. Zlaya, r. Shluzovaya, r. Nemoninka and r. Osa. In the winter season, water samples were taken, hydrometric characteristics were measured, and primary hydrochemical indicators were determined. On the basis of the obtained hydrochemical data, integral indicators were calculated to assess the quality of water, using combined lists of maximum permissible concentrations of pollutants. When monitoring hydrochemical indicators, it was revealed that the studied watercourses are, to one degree or another, subject to pollution. The water quality class in them varies from "moderately polluted" to "extremely dirty". When comparing the seasons, a tendency was revealed to improve the quality of water, which is associated with the water content of rivers, as well as with the cycles of natural and anthropogenic activity. The work has theoretical and practical significance. The data can participate in the planning of rational use of natural resources and the selection of measures to improve the geoecological state of the river network of the Slavsky region. The research can serve as a supplement to the formation of the general geoecological picture of the Kaliningrad region.

Seasonal dynamics of chromophoric dissolved organic matter in Poyang Lake, the largest freshwater lake in China

Chromophoric dissolved organic matter (CDOM) plays a vital role in the biogeochemical cycles of elements in aquatic ecosystems. Seasonal dynamics of CDOM of the lake are sensitive indicators of the biogeochemical processes and water quality, which are critical to the water security of the lake. Thus, a field investigation of the CDOM and dissolved organic carbon (DOC) properties was conducted during four hydrological seasons in 2016 to track the temporal variability of CDOM and DOC properties and to explore the influence of rivers and wetlands on the quantity and quality of CDOM in Poyang Lake. The results showed that the alternations of flood and dry periods have a different influence on the quantity and quality of CDOM and DOC in the main lake and the river mouths districts. DOC and aromaticity in the main lake district were more influenced by seasonal variations, while CDOM concentrations and molecular weight in the river mouths were more affected. CDOM fluorescent components in both these districts varied obviously across the hydrological seasons. More terrestrial humic-like substances with higher aromaticity and lower DOC in the rising and flood season than in the dry and retreating season. The contributing rate of CDOM and its terrestrial humic-like substances from input rivers to the lake in the rising season can account for more than 50%, which was more than that in the flood season. Flooding causes wetlands to contribute a higher abundance of CDOM and DOC with lower aromaticity to the lake, contrary to the CDOM features in the flood season, highlighting the important role of wetlands in the organic carbon pool. The DOC can be modeled using CDOM fluorescent and optical parameters by the Support Vector Regression (SVR) method, which provides a tool for DOC dynamic monitoring and water quality management.

Understanding drivers of aquatic ecosystem metabolism in freshwater subtropical ridge and slough wetlands

AbstractHow climate and habitat drive variation in aquatic metabolism in wetlands remains uncertain. To quantify differences in seasonal aquatic metabolism among wetlands, we estimated aquatic ecosystem metabolism (gross primary productivity, GPP; ecosystem respiration, ER; net aquatic productivity, NAP) in subtropical ridge and slough wetlands of the Florida Everglades from more than 2 yr of continuously measured water column dissolved oxygen, photosynthetically active radiation (PAR), water temperature, and water depth. Gross primary productivity and ER were modeled from light, temperature, and water depth using non‐linear minimization and maximum likelihood. Reaeration rates were estimated from wind speed. Dissolved oxygen was below saturation at all sites during both wet and dry seasons. Water depth interacted with vegetation to influence PAR, water temperature, and spatiotemporal patterns in aquatic metabolism. Gross primary productivity and ER were highest at the slough with lowest submerged aquatic vegetation (low‐SAV slough), intermediate in the sawgrass (Cladium jamaicense) ridge site, and lowest at the slough with highest submerged aquatic vegetation (high‐SAV slough). Ecosystem respiration was strongly positively correlated with GPP at the sawgrass ridge and low‐SAV slough sites. Gross primary productivity increased with water temperature and PAR across all habitat types, whereas ER decreased (more respiration) with water temperature and PAR. Net aquatic productivity was negatively correlated with water temperature and positively correlated with PAR, suggesting that ER was more sensitive than GPP to water temperature. Aquatic metabolism was largely net heterotrophic in all wetlands, and high‐SAV appeared to buffer seasonal variation in PAR and water temperatures that drive NAP in subtropical wetlands. Our results suggest that aquatic ecosystem metabolism in wetlands with seasonal hydrology is sensitive to changes in water depth and vegetation density that influence temperature and light. Expanding our understanding of how metabolic processes and carbon cycling in wetland ecosystems vary across gradients in hydrology, vegetation, and organic matter could enhance our understanding and protection of conditions that maximize carbon storage.

Оценка экологического состояния поверхностных вод Казани

The study of the influence of technogenesis on the state of surface waters in urbanized areas is one of the most urgent ecological and social problems. For processing and analysis of hydrochemical indicators of surface water bodies of Kazan for the period 2014–2020 the generally accepted stasticial indicators, as well as the methods of multivariate statistics were used. Hydrochemical models were built using the ArcGisMap software package. The data were grouped using the cluster analysis method separately for each hydrological season with the allocation of 6 groups of hydrochemical components in relation to the maximum permissible values. It has been revealed that the minimum technogenic load on the surface waters of the city falls on the spring period. Based on the analysis of the results obtained, an ecological and hydrological assessment of the state of surface waters was carried out. It was showed that the water bodies of Kazan are classified as unfavorable water bodies.

Terrestrial connectivity, upstream aquatic history and seasonality shape bacterial community assembly within a large boreal aquatic network

During transit from soils to the ocean, microbial communities are modified and re-assembled, generating complex patterns of ecological succession. The potential effect of upstream assembly on downstream microbial community composition is seldom considered within aquatic networks. Here, we reconstructed the microbial succession along a land-freshwater-estuary continuum within La Romaine river watershed in Northeastern Canada. We captured hydrological seasonality and differentiated the total and reactive community by sequencing both 16 S rRNA genes and transcripts. By examining how DNA- and RNA-based assemblages diverge and converge along the continuum, we inferred temporal shifts in the relative importance of assembly processes, with mass effects dominant in spring, and species selection becoming stronger in summer. The location of strongest selection within the network differed between seasons, suggesting that selection hotspots shift depending on hydrological conditions. The unreactive fraction (no/minor RNA contribution) was composed of taxa with diverse potential origins along the whole aquatic network, while the majority of the reactive pool (major RNA contribution) could be traced to soil/soilwater-derived taxa, which were distributed along the entire rank-abundance curve. Overall, our findings highlight the importance of considering upstream history, hydrological seasonality and the reactive microbial fraction to fully understand microbial community assembly on a network scale.

Use of GIS based Inverse Distance Weighted interpolation to assess surface water quality: Case of Wadi El Bey, Tunisia

Sustainable management of water resources involves inventory, conservation, efficient utilization, and quality management. Although, activities relating to quantity assessment and management in terms of river discharge and water resources planning are given attention at the pollution level of the watershed, water quality assessment are still being done at specific locations of major concern. The use of Geographical Information System (GIS) based on water quality information system and spatial analysis with Inverse Distance Weighted (IDW) interpolation enabled the mapping of water quality indicators in watershed of Wadi El Bey, Tunisia. Using 13 sampling locations, water quality indicators were monitored from 2012 to 2016; covering full hydrological season. Maps of spatio-temporal variations in some physical parameters (Temperature, pH), chemical (chemical oxygen demand, Biochemical oxygen demand, total suspended solids...) and microbiological ones ( Fecal​ coliform, Escherichia coli, Staphylocoques ...) were used to evaluate the water quality across monitoring stations and analyze the sources of water pollution along the river courses. The production of water quality maps will improve monitoring, enforce the standards and regulations towards better pollution management and control. Patterns were clearly defined; methods were statistically valid and the IDW predictions were made to exhibit high prediction. Thus, the spatial distribution maps show that the agricultural activities, domestic, and industrial discharges are fundamental causes of water pollution in the study area specially the industrial zone of Grombalia. The results of IDW helped us to identify key areas requiring control in the Wadi el Bey River, which pointed the way for further delicacy management of the river. • The present investigation highlights the assessment of Wadi El Bey water quality. • Spatiotemporal variation of pollutants was assessed using GIS and IDW interpolation. • Models were statistically valid and the IDW was observed to exhibit high prediction. • Study area was highly contaminated by the Grombalia industrial discharges. • Water quality maps enforce regulations for better pollution management and control.

Monitoring a critical population of the Bolivian river dolphin, Inia boliviensis, before and after closing the floodgates of a hydroelectric dam in the Amazon Basin, Brazil: A quantitative analysis

Dam constructions threaten aquatic fauna, degrading their habitats and causing population fragmentation. Environmental impact studies were carried out from March 2010 to July 2015 as part of the licensing process concerning the Jirau Hydroelectric Dam construction, located on the Madeira River, Rondônia, Brazil, aiming to assess its impacts on the local fauna. The dam closed its gates in December 2012 and the water level rose from 2013 to 2015, creating a 468 km2 reservoir. Dams may be a source of negative effects to several species, including the Bolivian river dolphin, Inia boliviensis, which have a restricted distribution in northern Bolivian rivers and part of the Madeira River Basin. This study evaluated the presence of I. boliviensis in different sections of the Madeira River before reservoir filling (BRF) and after reservoir filling (ARF) through a quantitative analysis. Dolphins were actively searched along linear transects in four sections of the river: Abunã, Mutum, Caiçara and Canteiro, over 125 km (250 km round trip). A total effort of 986 h was carried out along 210 days during the hydrological seasons (falling, low, rising and high-water level). Twenty-nine (29) groups were recorded BRF in the direct dam influence area (N = 62), while thirty-eight (38) groups were documented ARF (N = 111). The highest number of sightings was recorded in Abunã during both periods: 24 in BRF (N = 50) and 33 in ARF (N = 101). The greatest number of dolphins was detected during the falling and low hydrological seasons: 19 in BRF (N = 48) and 30 in ARF (N = 92). This is expected, since decreasing water levels lead to a higher concentration of prey and, consequently, higher numbers of dolphins can be observed. Standardized methodology and experienced staff are essential to ensure adequate dolphin population estimates, especially in these critical habitats, where the main impacts caused by the dam are population fragmentation, isolation and extirpation, and reproductive segregation.

Hydrological seasonality and nutrient stoichiometry control dissolved organic matter characterization in a headwater stream

Dissolved organic matter (DOM) is a diverse and highly complex mixture of organic macromolecules, and thus plays a central role in aquatic ecosystems. However, responses of components and sources of DOM to hydrological processes and trophic levels (nutrient stoichiometric ratios) are poorly understood, particularly in monsoonal headwater streams of Asia that are vulnerable to catchment physical characteristics. In this study, the excitation - emission matrix florescence spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) was used to explore the DOM characters in a headwater stream, where seasonal rainfalls and nutrient levels vary largely. The EEM-PARAFAC modelling identified one autochthonous protein-like fluorescence substance (C1) and two allochthonous fulvic- and humic-like fluorescence compounds (C2 and C3). The allochthonous compounds dominated the overall DOM signal in the headwaters. The hydrological seasonality coupled with nutrients was key in modulating headwater DOM sources and components. Seasonal rainfall events contributed more allochthonous terrestrial-derived DOM flushing into river waters, resulting in higher fulvic- and humic-like organic matter (C2 + C3) in the wet season. In the dry season, longer water residence time accompanying with higher C:P stoichiometric ratio was responsible for higher autochthonous microbial- and plant-derived DOM (tryptophan and tyrosine fractions), also reflected by higher C1, biological index (BIX) and freshness index (β:α). In-stream microbial metabolism of labile DOM fractions largely contributed to autochthonous DOM and partial pressure CO2 increase in the headwater stream. Our findings indicate that quality and quantity of DOM in headwater streams play a crucial role in downstream carbon cycle. Furthermore, the evidence combined from PARAFAC components, pCO2 and spectral slope clearly highlights the importance of microbial metabolism of carbon in lotic systems, especially during a dry season with increased residence time.

Flow Dynamics Influence Fish Recruitment in Hydrologically Connected River–Reservoir Landscapes

AbstractHydrologic processes are often important determinants of successful recruitment of native fishes. However, water management practices can result in abnormal changes in daily and seasonal hydrology patterns. Rarely has fish recruitment across river–reservoir landscapes been considered in relation to flow management, despite the direct relationship between reservoir water management and the resulting upstream and downstream hydrology. We evaluated the relationships between lotic and lentic hydrology and recruitment of two native broadcast‐spawning fishes, Freshwater Drum Aplodinotus grunniens and Gizzard Shad Dorosoma cepedianum. Four seasonal periods for each species were identified that related to the species’ spawning biology, from which we derived our remaining hydrology variables. Annual hydrology variables were also considered in our analysis. We developed regression models in conjunction with a model‐selection procedure for each species and habitat type based on the catch‐curve residuals from fish populations in hydrologically connected river–reservoir systems in the Ozark Highland and Ouachita Mountain ecoregions, USA. Our results indicated that recruitment of reservoir Freshwater Drum was negatively correlated to annual reservoir retention time. In lotic habitats, Freshwater Drum recruitment was positively correlated with prespawn discharge conditions and negatively correlated with annual flow variability. Similarly, riverine Gizzard Shad recruitment was positively correlated to the frequency of high‐flow pulses during the spawning period. Our results indicate that releasing reservoir water to best mimic relatively natural flow patterns may benefit some broadcast‐spawning species that occupy both lentic and downstream lotic environments, especially during the spring. This information, combined with future efforts on additional spawning guilds, will provide a foundation for developing holistic river–reservoir water‐allocation plans.

Seasonal Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) movements in the Poyang Lake, China: Implications on flexible management for aquatic animals in fluctuating freshwater ecosystems

Identifying seasonal high-use habitats and migration corridors is the basis for migratory species conservation. Previous studies have focused on Marine Protected Areas, while freshwater ecosystems, often accompanied by severe hydrological fluctuations, suggest new perspectives for flexible management. Poyang Lake is an essential habitat for the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP), supporting almost half of their natural population. However, studies on the movement patterns and habitat preferences of YFPs still lack there, preventing potential protected areas’ effectiveness. In this study, we conducted 10 surveys for the YFP population in the main body and tributaries of Poyang Lake from October 2018 to August 2020. We used habitat modeling to analyze their seasonal habitat use and the environmental predictors. YFPs showed a seasonal movement pattern consistent with water level fluctuations. They entered the tributaries from the main lake body in low and medium water levels and returned to the main lake during high water level periods. The water depth was the most important environmental variable in each hydrological season that affects YFPs’ habitat selection. The suitable water depth was about 4-8 m during the low water level, 6-12 m during the medium water level, and 7-20 m during the high water level. YFPs’ 50% core habitats distribution showed noticeable seasonal changes. The proportion of their suitable habitats in the whole lake was relatively low, which was highest during high water level (16.89%), and the weakest during low water level (12.11%). Considering the seasonal movements of the YFPs in the lake, we recommend flexible management measures for their core habitats to alleviate human interference and restore their movement rhythm between the river and the lake, which shed light on protected area management for aquatic animals in such seasonal fluctuating habitats.

Analysis of Seasonal Energy Characteristics of the Marmara Sea Upper Layer Dynamics

Purpose. The aim of the work is to assess the role of the basic forces in formation of the dynamic structures of the upper layer in the Marmara Sea in different hydrological seasons. Methods and Results. The numerical model developed in Marine Hydrophysical Institute, Russian Academy of Sciences, was used to calculate the hydrodynamic and energy characteristics of the sea circulation. The horizontal spatial resolution was 1.22 × 0.83 km, 18 horizons were used vertically, and the time step was 0.5 min. The characteristics of the waters inflowing through the Bosporus and Dardanelles straits corresponded to the available observational data. On the sea surface, the daily average fields of tangential wind stress, heat fluxes, precipitation and evaporation for 2008 were preset; these parameters were calculated using the regional atmospheric model MM5. Spatial distributions of the vortex structures and the corresponding energy flows in the upper sea layer for different seasons were considered. Having been analyzed, the average seasonal spatial distributions of the current velocity fields and the components of the kinetic energy budget showed that during the year, the vortices in the upper sea layer were formed mainly by two mechanisms. In the central part of the sea, generation of a large-scale anticyclone and its seasonal variability are basically conditioned by the wind forcing, whereas formation and evolution of coastal cyclonic eddies are caused by the buoyancy force. In the fields where the buoyancy, pressure and friction forcing takes place, the zones of local extremes are distinguished. Two of them are the areas of water inflow through the Bosphorus and Dardanelles straits. The strongest variability is observed in the Bosporus region that is certainly conditioned by the fact that the inflowing Black Sea waters have a decisive influence on seasonal nature of the Marmara Sea circulation. The extreme values in the other zones are the result of the coastline structure heterogeneities, that leads to formation of the coastal eddies, the energy source for which is the available potential energy. Conclusions. Analysis of the results of the performed numerical experiment makes it possible to conclude that in the upper layer of the Marmara Sea, formation and variability of the central anticyclone are conditioned by the wind forcing, while those of the coastal cyclones – by the buoyancy effect.

Seasonal hydrology influences energy channels in food webs of rivers in the lower Okavango Delta

Floodplain aquatic ecosystems experience temporal changes in basal production sources and inputs from allochthonous sources that influence energy flow. We analyzed stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) from 449 fish muscles representing 18 species to characterize energy pathways in two rivers of the lower Okavango Delta, Botswana. We sampled fish during wet and dry seasons and used mixing models to estimate proportions of major basal production sources assimilated by fishes. We estimated trophic position (TP) for each fish population and assessed the association between TP and the degree that fish biomass was supported by a single production source. During the wet season, fishes in the Boteti River assimilated material through food chains originating mainly from aquatic macrophytes. During the dry season, terrestrial C3 plants and terrestrial C4 grasses assumed greater importance. In the Boro River, terrestrial C3 plants were inferred to be an important production source supporting fishes during the wet season, with aquatic macrophytes becoming more important during the dry season. In both rivers and seasons, the degree of dependence on a single source was negatively related to TP, supporting the hypothesis that organisms positioned higher in the food web tend to be supported by multiple food chains and basal sources, whereas organisms lower in the food web may be supported by many or few food chains. We showed that consumers in river food webs shift foraging habits in response to seasonal patterns of connectivity and habitat availability, thus promoting long-term population and community stability.

Analiz sezonnykh energeticheskikh kharakteristik dinamiki verkhnego sloya vod Mramornogo morya

Purpose. The aim of the work is to assess the role of the basic forces in formation of the dynamic structures of the upper layer in the Marmara Sea in different hydrological seasons. Methods and Results. The numerical model developed in Marine Hydrophysical Institute, Russian Academy of Sciences, was used to calculate the hydrodynamic and energy characteristics of the sea circulation. The horizontal spatial resolution was 1.22 × 0.83 km, 18 horizons were used vertically, and the time step was 0.5 min. The characteristics of the waters inflowing through the Bosporus and Dardanelles straits corresponded to the available observational data. On the sea surface, the daily average fields of tangential wind stress, heat fluxes, precipitation and evaporation for 2008 were preset; these parameters were calculated using the regional atmospheric model MM5. Spatial distributions of the vortex structures and the corresponding energy flows in the upper sea layer for different seasons were considered. Having been analyzed, the average seasonal spatial distributions of the current velocity fields and the components of the kinetic energy budget showed that during the year, the vortices in the upper sea layer were formed mainly by two mechanisms. In the central part of the sea, generation of a large-scale anticyclone and its seasonal variability are basically conditioned by the wind forcing, whereas formation and evolution of coastal cyclonic eddies are caused by the buoyancy force. In the fields where the buoyancy, pressure and friction forcing takes place, the zones of local extremes are distinguished. Two of them are the areas of water inflow through the Bosphorus and Dardanelles straits. The strongest variability is observed in the Bosporus region that is certainly conditioned by the fact that the inflowing Black Sea waters have a decisive influence on seasonal nature of the Marmara Sea circulation. The extreme values in the other zones are the result of the coastline structure heterogeneities, that leads to formation of the coastal eddies, the energy source for which is the available potential energy. Conclusions. Analysis of the results of the performed numerical experiment makes it possible to conclude that in the upper layer of the Marmara Sea, formation and variability of the central anticyclone are conditioned by the wind forcing, while those of the coastal cyclones – by the buoyancy effect

Flow rate regime of the Western Urals’s rivers

The flow rate is one of the most important elements of the river’s water regime. Establishing patterns in river flow rates’ changes within a year and by season is of great importance for the hydrological forecasts for spring floods, rain floods and hydrological calculations. By now, there are few publications on this area, both in Russia and abroad. The initial data were divided into 5 hydrological seasons – winter and summer low water, rise and fall of spring floods and autumn rain floods. For each season, an analysis of river flow rate over a period (1936-2013) was done. The average flow rate in rivers varied greatly depending on the water regime’ phase and the type of terrain in which the river flows. For all seasons, the amplitude of fluctuations in the flow rate on the plain rivers is less than on the mountain ones. So, in mountain rivers, flow rates vary from 0.04 to 2.42 m/s, and on flat rivers from 0.02 to 1.43 m/s. As well the pairwise and multiple correlation coefficients of flow rates for each morphometric and catchment characteristics were calculated. The highest correlation coefficients were obtained for the dependency between the average flow rate and the watershed elevation (0.30-0.75) and the watershed slope (0.42-0.76). The multiple correlation coefficients between the average flow rate and all catchment’s morphometric characteristics varied from 0.97 to 0.99. Results verification on an independent data demonstrated that the relative error was on average 2%.

Hydrology drives variation in spawning phenologies and diversity of larval assemblages of Australian wet–dry tropical fish

Abstract Setting ecologically based water‐extraction rules requires an understanding of the relationships between hydrology and the completion of aquatic organism life cycles. Successful reproduction of riverine fishes has been linked to hydrological variation across diverse climatic regions. However, the reproductive ecology for many species in wet–dry tropical northern Australia is poorly understood, and consequently there is little knowledge on how temporal (seasonal) and spatial hydrological variation influences fish reproduction in this region. This study aimed to quantify the hydrology‐related reproductive ecologies of freshwater fish across the wet–dry seasonal cycle and between differing hydrological classes in a northern Australian river (Daly River, Northern Territory) subject to increasing interest in water extraction. Sampling of larval and juvenile fish was undertaken over 1 year at eight sites classified into perennial and intermittent flow types. Fish spawning phenologies were developed and spatial–temporal dynamics in larval fish assemblages were investigated using model‐based multivariate and univariate analyses. Spawning occurred in all hydrological seasons, with low‐flow dry season periods identified as important for many fish taxa. For a different fish assemblage, spawning mostly occurred during high‐flow wet season periods. Larval assemblages in the wet season were more diverse than in the dry and wet–dry seasons. Perennial sites maintained higher diversity than intermittent sites year‐round; however, larvae were more abundant in intermittent sites for some taxa. Spatial and temporal differences in larval assemblages were largely explained by variation in the occurrence and relative abundance of three aseasonally spawning taxa (Craterocephalus spp., Melanotaenia spp. and Ambassis spp.) and the largely wet‐period spawning of Terapontidae spp. These results add to growing evidence of variation in spawning phenologies among fish species and the use of multiple hydrological phases for aseasonal reproduction. The diverse range of hydrological conditions used for spawning and rearing, and the differences between hydrological river classes among taxa, suggests that water‐extraction and environmental flow rules should aim to maintain hydrological conditions catchment‐wide during both low and high‐flow periods to reduce the risk of impacting fish reproduction. In particular, the results suggest that if perennially flowing sites began to flow intermittently, such as through over‐extraction of water or due to climate change, less diverse fish assemblages may result. This study expands our understanding of the relationships between hydrology and the reproductive ecology of freshwater fish in wet–dry tropical climates and may inform future ecologically based approaches to setting water‐extraction rules.

How trees thrive in a dry climate: diurnal and seasonal hydrology and water relations in a riparian cottonwood grove.

In semi-arid ecoregions, trees are restricted to river valley floodplains where river water supplements the limited precipitation. To characterize the associated diurnal and seasonal dynamics in hydrology and water relations, we studied narrowleaf cottonwoods (Populus angustifolia) along a prairie river in Canada. From June through August, the shallow soil moisture was depleted but moisture remained higher above the alluvial groundwater table, which dropped to 2.3m along with river recession. Throughout the summer, with the daily rise in temperature and insolation, foliar stomatal conductance (gs) and transpiration (E) increased to midday and then fell, thus maintaining the midday leaf water potential (Ψmd) above ~-1.7MPa. This Ψmd approximated the water potential associated with 12% loss of xylem conductivity due to cavitation for branches (P12); the Ψmd and P12 varied independently across eight trees, providing differences in relative hydraulic risk. Sap flux density (Fd) was measured with thermal dissipation probes, and revealed diurnal patterns similar to foliar E. In contrast to our expectation, the daily Fd maxima were consistent through the summer despite the seasonal recession in water supply. Canopy conductances (GS), derived from Fd, sapwood area and canopy area, declined with vapor pressure deficit (D) and fell slightly in late summer along with stomatal sensitivity, which reflects the magnitude of decrease in GS with increasing D. For spatial up-scaling, satellite-derived near-infrared reflectance of vegetation revealed the woodland phenology, with leaf expansion from May through June and gradual decline in photosynthetic productivity through the summer. Thus, the phreatophytic cottonwoods: (i) sustained substantial water use and productivity through the warm and dry summer, by (ii) accessing shallow soil moisture and then deeper alluvial groundwater, and (iii) providing diurnal stomatal regulation, to (iv) avoid xylem cavitation and (v) maintain fairly constant hydraulic conductance.

Spatial and temporal correlation between severe droughts and extreme low flow on rivers in the Russian Plain

Extreme low flow on rivers (when water flow was less than or equal to the value of 75 and 90% exceedance probability), observed in years with severe meteorological and agricultural droughts in the Russian Plain (1972, 1975, 1981, 1995, 1998, 1999, and 2010) were studied. In 1972 and 1975, the exceptional low flow was recorded in the largest area, including the basins of the largest rivers (the Volga, Don, and Dnieper) and even the outlet, as well as in their tributaries. One of the heaviest droughts (2010) accompanied the abnormally low flow only in the Lower Volga and its tributaries in the eastern part of its basin. In other years with severe meteorological and agricultural droughts, their occurrence areas in the Russian Plain were much less. In 1975, extreme low flow was recorded in the rivers of the Volga, Don, and Dnieper basins in the main hydrological seasons (during summer – autumn low-water season and snow-melt flood), as well as all the year round, including their outlet (in their lower reaches in the general case and in the middle reaches in the case of the Dnieper). However, in these seasons in 1972, extreme low flow was recorded in rivers in the basins of the Don and Dnieper (while in the Volga, it took place only during summer – autumn low-water season), and in 2010, it formed only in the Volga basin. Abnormally low flow in years with severe droughts were recorded mostly in rivers of the forest – steppe and steppe zones, as well as the southern part of the forest zone.

Climatic triggers and phenological responses in Isoetes cangae (Isoetaceae), an endemic quillwort from Amazon Iron Rocky Outcrops, Brazil

South America is the center of diversity of the genus Isoetes and several new species have been described in the last decade, especially in Brazil. Isoetes cangae J.B.S. Pereira, Salino & Stützel was first recognized in 2016 as an endemic species of a single lake in Serra dos Carajás, Brazil, in the southeastern Amazon region. The climate of Amazon is warm with a seasonal precipitation regime, which affects aquatic ecosystem properties and regulates plant phenology. Understanding how climatic and hydrological drivers affect I. cangae is fundamental for its conservation because the species is quite vulnerable due to its restricted distribution. In this study, we evaluated the effects of seasonal climatic variations and water level on the phenology of I. cangae over two years. The maximum leaf length, the number of sporophylls (fertile leaves), and the total number of leaves were assessed. Sporophylls were classified into mature and immature, megasporophylls and microsporophylls. The number of leaves, leaf length, and the number of sporophylls changed drastically among the hydrological seasons, but not the ratio between sporophylls and leaves, suggesting that reproductive effort is distributed accordingly over the years. All these factors also varied between years, indicating that inter-annual climatic variations affect the morphology and reproduction of I. cangae. Sporophylls are produced throughout the year, but their maturation and release increase in the rainy and early dry seasons, respectively. Megasporophylls predominate over microsporophylls throughout the year, and the peak of sporophyll maturation occurs during the rainy season, but lasts longer (till early dry season) for megasporophylls. The reproductive traits were associated with lake water level, suggesting that development is stimulated during the driest and hottest periods. Therefore, our results show that environmental factors play an important role in I. cangae phenology and must be considered in the management and conservation efforts to preserve this ancient Amazonian plant.