Hydrological Phases Research Articles

Multi-scale characteristics of drought propagation from meteorological to hydrological phases: variability and impact in the Upper Mekong Delta, Vietnam

Multi-scale characteristics of drought propagation from meteorological to hydrological phases: variability and impact in the Upper Mekong Delta, Vietnam

A new approach to estimate total nitrogen concentration in a seasonal lake based on multi-source data methodology

Nitrogen, a key limiter in lake eutrophication, presents serious threats to both human health and ecological balance. Despite its non-optically active nature, this study introduces an advanced retrieval approach for total nitrogen, utilizing a synthesis of multi-source data and sophisticated machine learning algorithms to markedly boost estimation precision. This innovative method integrates environmental variables, such as water temperature, depth, and flow rate with spectral reflectance, significantly enhancing the predictive accuracy of our machine learning models with high stability. The models tested, including Support Vector Machine (SVM), Random Forest (RF), Extreme Gradient Boosting (XGB), Multilayer Perceptron (MLP), and Convolutional Neural Networks (CNN), with XGB outperforming others by achieving robust metrics: an R2 of 0.78, a Mean Absolute Error (MAE) of 0.21 mg/L, and a Mean Absolute Percentage Error (MAPE) of 16.04 %. Applying the optimized XGB model, we documented fluctuations in nitrogen concentrations within Poyang Lake across different hydrological phases in 2021, revealing the lowest nitrogen levels during the flood season and the highest in low water periods, with high concentrations at the inlets of the North Branch of the Ganjiang River and the Raohe River estuaries. Monte Carlo simulations reveal that the model is not much sensitive to input feature errors, validating its stability. The approach proposed in this study may help more precise total nitrogen retrieval in other similar lake waters.

Impact of joint dispatch of reservoir group on water pollution incident in drinking water source area

To reduce the harm of water contamination incidents in drinking water source areas (DWSAs) and explore feasible approaches, the research developed a hydrodynamic water quality model for DWSAs based on two dimensional water quality and quantity equations, Geographic Information System (GIS), and Digital Elevation Model (DEM). The Heshangshan Drinking Water Source Area (HDWSA) in the Three Gorges Reservoir Area (TGRA) was selected as the research area, with total phosphorus (TP) as the representative pollutant in the water. The research investigated the changes in TP content during various hydrological phase under pollution incident, compared the duration and trends of TP concentration exceeding standard value before and after joint reservoir group dispatch. The results showed that the migration speed of TP pollutants varied from slowest to fastest in the following order: dry phase, recession phase, storage phase, and flood phase. Under pollution incident condition, the time demanded for TP content to meet standard value in each water phase was 36 min (dry phase), 33 min (recession phase), 30 min (storage phase), and 27 min (flood phase). The joint dispatch group 1–3 shortened the time required to meet standard value by 6–13 min (dry phase), 5–11 min (recession phase), 4–9 min (storage phase), and 3–7 min (flood phase). The trend of TP concentration before and after joint dispatch showed four stages: significant increase, sharp decrease, rapid decrease, and slow decrease. Joint dispatch of reservoir group can effectively reduced the TP concentration in DWSA under pollution incident.

Groundwater flow regime shapes nitrogen functional traits by affecting microbial community assembly processes in the subsurface

The complex nitrogen (N) cycle in groundwater systems is affected by both biological and environmental factors. The interactions between hydrogeological conditions and the microbial community assembly processes that impact N-cycling processes remain poorly understood. We explored the assembly patterns of N-cycling microbial communities along the groundwater flow path. The environmental heterogeneity in different hydrological phases increased along the flow path (mean Ed: 0.16–0.49), accompanied by different microbial community assembly patterns. The assembly patterns that engaged in dissimilatory nitrate reduction to ammonium (DNRA) and denitrification changed across the water-sediment phases. Nitrifying microorganisms in the discharge area were mainly influenced by heterogeneous selection (41–69 %), and were closely correlated with dissolved oxygen (DO) concentrations. Homogeneity along flow-through increased stochastic assemblies, such as downstream drift of anammox bacterial (AnAOB) communities. Thus, the N removal pathway changed from “nitrification-denitrification” in the recharge area to “partial nitrification-anammox” in the discharge area. The increasing environmental heterogeneity brought more deterministic assembly patterns of N-cycling communities, linked to higher community turnover along the groundwater flow path. This study indicated that groundwater flow regime determined microbial community assembly patterns, providing valuable insight into the response of N transitions to environmental variations in groundwater systems.

Study of the Hydrological Mode of the Volga-Akhtuba Canal Depending on the Hydrograph of the Volzhskaya HPP Operation

The flow rates and water flow rates in the Volga-Akhtuba Canal, which is of critical importance in the watering of Akhtuba river and Volga-Akhtuba bottom land territory, have been determined in various hydrologic phases. Relationships between discharge flows through the Volgograd hydroelectric unit and flows through the Volga-Akhtuba Canal have been established. Graphs of the relationship between the water level in the lower canal pound and water flows through the Volgograd hydroelectric unit in various years are constructed. Recommendations are given for additional watering of the Volga-Akhtuba bottom land.

Influence of the last (de)glaciation on a complex cave system: Grønli-Seter cave system, Northern Norway

Cave studies enable us to unravel valuable information on landscape evolution. In glacial settings, the glacial cycles induced fluctuations in the underground hydraulic regime, sediment availability and base level in adjacent caves. Here, we present our work on the Grønli-Seter cave system in Northern Norway, which comprises >8 km of passage length at an elevation between 250 m and present sea level. By linking cave morphology and deposits to shifting glacier configurations and external base level changes during the last deglaciation and the Early Holocene, we establish how the hydraulic conditions in the cave system shifted in pace with glacier fluctuations. Maze sections and phreatic loops appear in a hydraulic confined setting close to the interface between the calcite marble and the overlying mica schist. Scallops in the cave walls demonstrate slow, ascending water flow, evidence of subglacial speleogenesis under wet-based, topographically constrained glaciers with a gentle surface slope. Moreover, cave morphology and clastic deposits indicate various hydrological phases of descending water flow, stagnant conditions, and excessive flow rates. Our work establishes that the last glaciation and deglaciation had an insignificant effect on the cave system's solutional development. In contrast, the cave sediments reveal diverse hydraulic conditions that may be related to shifting glacier configurations. This research offers valuable insights into glacier ice-contact speleogenesis and landscape development in glacial terrains.

Disentangling responses of aquatic and terrestrial invertebrates to drying in saline streams and shallow lakes

In inland aquatic ecosystems, drying and salinity can co-occur as natural stressors, affecting aquatic invertebrate communities. Despite recent appreciation of the importance of temporary waterbodies for terrestrial invertebrates, knowledge about the effects of drying on dynamics of aquatic and terrestrial invertebrate communities is scarce, especially in saline ecosystems. This study analyzed structural and compositional responses of both communities to the coupled effects of drying and salinity in two streams and two shallow lakes in Spain, during three hydrological phases: wet, contraction, and dry. In the two studied saline streams, the contraction phase presented the highest aquatic and terrestrial abundance and richness, and the main compositional changes were mainly due, to an increase in aquatic lentic taxa (e.g., Coleoptera), and Araneae and Formicidae as terrestrial taxa. In shallow lakes, which presented highly variable salinity conditions, the highest abundance and diversity values were found at the wet phase for aquatic invertebrates and at the dry phase for terrestrial invertebrates. Compositional invertebrate community changes were due to a decrease in Rotifera and Anostraca (aquatic taxa) in the contraction phase for aquatic communities, and to an increase of Araneae, Coleoptera, and Formicidae (terrestrial taxa) at the dry phase for the terrestrial. Our study evidences the significant effect of drying on both aquatic and terrestrial invertebrates communities in natural inland saline waters and the need to integrate aquatic and terrestrial perspectives to study temporary inland waters.

Integrating spatiotemporal hydrological connectivity into conservation planning to protect temporary rivers

Abstract Temporary rivers (TRs) have been largely overlooked in conservation assessments. Because TRs are such dynamic ecosystems, spatial and temporal aspects of their hydrology and ecology need to be taken into account when designing conservation plans. The aim of this paper is to propose a set of recommendations that could be useful for managers to do this, using seasonal diatom and macroinvertebrate data from north‐eastern Spain as a case study. Beta diversity was partitioned into local and species contributions to beta diversity (LCBD and SCBD). Additionally, priority conservation sites covering the spatial distribution of all species were identified using Marxan and the selection frequency (MSF) of the sites served as a measure of the relative irreplaceability of each site. Using both approaches (beta diversity and Marxan), the effects of changing spatiotemporal connectivity and habitat heterogeneity on the selection and prioritization of sites to be conserved were assessed. It was found that LCBD and MSF ranged widely both in space and time. However, LCBD and MSF were weakly related. Marxan adequately represented all taxa by selecting a few sites, while LCBD selected communities with higher differentiation but not necessarily those with rare species. In addition, SCBDs assigned low values to rare taxa, thus care must be taken when using this index for conservation planning. Spatiotemporal connectivity and local habitat heterogeneity played a critical role at the regional and local scales, driving site prioritization. Overall, we recommend: 1) monitoring multiple hydrological phases to encompass the different community types and capturing total diversity; 2) using Marxan and LCBD in combination, to benefit from their complementary insights; and 3) integrating spatiotemporal isolation and habitat heterogeneity into conservation plans, since they are the main drivers of community variation over space and time in TRs.

Effect of local and regional factors on the structure of the fish communities associated with aquatic macrophyte stands in oxbow lakes on the Amazon floodplain.

The Amazon floodplain is home to an extremely high diversity of fish, with lakes playing an important role in the establishment of this biological richness. These lacustrine environments are subject to constant fluctuations caused by the annual flood pulse, with local factors and other regional patterns also contributing to the variation in fish community structure. The present study verified how local (depth and transparency of the water, the size and species composition of the macrophyte stands) and regional factors (spatial distribution of the stands and the hydrological phase) influence the structure of the fish community of the floodplain lakes of the Môa River, in northern Brazil. Fish species richness was influenced by the depth of the water and the spatial distribution of the macrophyte stands. Fish species composition was influenced by local environmental variables, spatial structure, and the hydrological phase. However, variation partitioning indicated that only the hydrological phase explained the variation in fish composition. These findings indicate that the local environment, the spatial structure, and the hydrological phase drive changes in the structure of the fish communities associated with aquatic macrophytes in the floodplain lakes of the Amazon basin.

Food consumption of the urban population in a municipality in the Legal Amazon, during climate events of flood and drought: a comparative study

The aim of this study was to compare the food consumption of the population of Coari, Amazonas State, Brazil, according to the NOVA Classification, during the hydrological phases of drought and flooding of the Amazon rivers. An epidemiological, population-based, cross-sectional study was carried out. The sample consisted of 457 adult individuals. Data were collected in two stages using a sociodemographic instrument, a 24-hour food recall and a food frequency questionnaire adapted to local habits. The data were analyzed using the statistical program R version 4.2.4, using Pearson's chi-square, Fischer's exact and Bhapkar's tests. The sample was predominantly female (drought = 70%/flood = 71.2%) and brown (drought = 65.4%/flood = 66.2%). Most of the interviewees ate meals (breakfast, lunch and dinner). Afternoon snacks were the most common intermediate meal, especially during flooding (274/70.2%). In natura or minimally processed foods predominated at the three main meals (95%). Ultra-processed foods were consumed little or not at all and were mentioned especially during the drought (152/33.3%; p = 0.007). On the other hand, consumption of regional foods (tucumã, beiju, tapioca flour and açaí) increased during the flood (p < 0.001). Consumption of in natura or minimally processed foods continues to be the mainstay of the diet in the interior of Amazonas, with a predominance of regional foods during the flood and processed and ultra-processed foods during the drought, demonstrating the influence, albeit subtle, of the hydrological phases on the food consumption of this population.

ДИНАМИКА КОНЦЕНТРАЦИЙ РАСТВОРЕННЫХ ФОРМ ТЯЖЕЛЫХ МЕТАЛЛОВ В ВОДЕ РЕКИ МОСКВЫ ПО ДАННЫМ МОНИТОРИНГОВЫХ ИССЛЕДОВАНИЙ В 2021-2023 ГОДА

Background. The Moskva River is a prime example of a natural urban watercourse subjected to strong and varied anthropogenic pressure. For many years, this river has been characterized by increased content of heavy metals. The exceedance of the maximum allowable concentrations of harmful substances in the waters of water bodies used for fishery can result in disruption of the normal functioning of aquatic ecosystems. Relevance. The summarized data collected over the course of monitoring surveys of the Moskva River for three years will be indicative of the relative contribution of natural and anthropogenic sources into its pollution. The aim of this work is to identify the dynamics of spatial and temporal distribution of heavy metals in the Moskva River water and its relation to hydrological seasons, as well as to assess the anthropogenic pressure exerted by the city of Moscow on the river. Methods. Water samples were collected in 2021-2023 during four hydrological seasons. Identification of heavy metals in the collected samples has been carried out using the atomic absorption method. Results. The analysis of the content of dissolved heavy metals (iron, cadmium, cobalt, manganese, copper, nickel, lead, and chrome) in the Moskva River water in various seasons of 2021-2023 has been conducted, and the same was done for zinc in 2023. The dynamics of the spatial and temporal distribution of these heavy metals has been identified, as well as its dependence on the hydrological phases. The influence of the urban infrastructure on the composition of the Moskva River water has been elucidated. Within the investigated area, the exceedance of the values prescribed by the water quality standards for the water bodies used for fishery (MACfish) has been recorded. Conclusion. The waters of the Moskva River have been characterized as polluted, mainly with iron, manganese, copper, and zinc. For lead, chrome, cobalt, nickel, and cadmium, no exceedance of the MACfish has been recorded. It has been found that the majority of the investigated elements were exceeding the values prescribed by the established standards in the spring season, but their concentrations decreased in summer.

A multiproxy approach to reconstruct the Late Holocene environmental dynamics of the semiarid Andes of central Chile (29°S)

Mountain ecosystems located in the Andes cordillera of central Chile (29–35°S) have been strongly affected by the ongoing Mega Drought since 2010, impacting the snow cover, the surficial water resources (and thereby water storage), as well as the mountain biota and ecosystem services. Paleoenvironmental records in this part of the semiarid Andes are key to estimating the effects of past climate changes on local communities helping to forecast the ecological and biological responses under the aridification trend projected during the 21st century. Here we present a 2400-year multiproxy paleoenvironmental reconstruction based on pollen, diatoms, chironomids, sedimentological and geochemical data (XRF and ICP-MS data) of Laguna El Calvario (29°S; 3994 m a.s.l), a small and shallow Andean lake. Four main hydrological phases were established based on changes in the lithogenic and geochemical results associated with allochthonous runoff input and the subsequent response of the biological proxies. Between 2400 and 1400 cal yrs BP, wetter than present conditions occurred based on the intense weathering of the lake basin and the dominance of upper Andean vegetation. A decrease in moisture along with sub-centennial discrete wet pulses and lake-level changes occurred until ~800 cal yrs BP followed long-term stable climate conditions between 1850 and 1950 AD as suggested by a drop in vegetation productivity and low lake levels. From 1950 AD to the present, a decline in moisture with a severe trend to drier conditions occurring in the last decades occurred as reflected by an upward vegetation belt displacement around Laguna El Calvario along with a turnover of diatom assemblages and high productivity in the water column.

Influence of seasonality on the physical-chemical properties of water for human consumption by residents of floating villages in the interior of the Amazon

Abstract The aim of this study was to evaluate the physicochemical properties of the water consumed by residents of floating houses and the influence of the hydrological cycles of flood and drought on these parameters. The sample consisted of 44 floating domestic units per hydrological cycle, located on the edges of the cities of Codajás, Coari and Tefé. Sociodemographic data and data related to water consumption and storage habits were collected using a semi-structured questionnaire. Water samples were collected and analyzed in accordance with the Standard Methods for the Examination of Water and Wastewater. Data were analyzed in the dry and flood hydrological phases and compared to the maximum values allowed by Ordinance GM/MS No. 888/2021. The results showed that the nitrite, manganese and free residual chlorine parameters were not in accordance with the legislation. Manganese (p = .035) and aluminum (p &amp;lt; .001) showed significant differences between the hydrological phases. The considerable increase in aluminum content during the flood period, even though it was within the limits of the ordinance, was also highlighted. Accordingly, even with periodic control by the supply companies, it is important to monitor the water at the point of consumption of the population.

An improved method for paleoflood reconstruction from core sediments in the upper Yellow River

Fluvial deposits represent a sedimentary archive of paleohydrological information, which can be utilized to reconstruct unrecorded floods. A multi-index (grain size, end-member model, and geochemistry elements) approach of core sediments from the upper Yellow River was used to reconstruct its flood history. A high-resolution geochemical profile of the 20.71-m-deep core was obtained by an XRF core scanner. A comparison of sediment grain size with geochemical element ratios indicated that ln(Zr/Ti) can be used as a grain size proxy for the core sediment. Combined with the end-member modeling analysis, the flood energy index (FEI) was constructed to highlight the flood signals and their similar trends with sediment ln(Zr/Ti). Coarsened grain size and increased ln(Zr/Ti) suggested that a high-frequency flood phase appeared to occur in the early Holocene (11–6.5 ka) and late Holocene (3.5–0 ka), while low-frequency floods occurred in the middle Holocene (6.5–3.5 ka). An extreme hydrological phase occurred during 5.8 ka–5.9 ka, which coincided with a sharp increase in sedimentation rates from 0.14 mm/yr to 0.48 mm/yr. The flood activities at the upper reach of the Yellow River are considered to respond to climate variability with the monsoonal shift.

Seasonal patterns in the structure of the fish larvae assemblages in the lower Amazon River

Abstract This study assessed the phenology and functional structure of parental stocks of fish larvae, and evaluated how the species modulate their reproductive activities as a function of natural hydrological regimes in the lower Amazon River, Brazil. Larvae were collected using conical plankton nets monthly over two hydrological cycles between January and December 2013, and between May 2017 and April 2018. The collections were conducted around an alluvial island located near the municipality of Santarém, Pará, Brazil. After identification, individuals were classified into four functional groups (e.g., life‐history strategy, feeding habits, type of migration, and swimming‐performance/microhabitat‐use in the water column) based on species traits. The relationships between seasonal hydrology, environmental variables and larval assemblage structure were evaluated using multivariate analyses. A total of 31,347 fish larvae were collected, from nine taxonomic orders, 26 families, 40 genera and 53 species. The larval assemblages showed highly variable taxonomic and functional composition between different phases of the hydrological cycle (rising water, high water, receding water and low water) and were strongly influenced by environmental variables. Fish reproductive phenology in the lower Amazon is complex and distributed among the hydrological phases. The different ecological characteristics allow the species to withstand specific environmental conditions during each phase. Changes in the structure of larval assemblages indicate that hydrological variability is a key ecological factor influencing the reproductive dynamics of fish and reflects adaptive strategies used to reduce interspecific competition for space and food, maximising recruitment. The variation of fish reproduction across the hydrological cycle that we observed is a result of different ecological characteristics enabling species and functional groups to adapt to environmental conditions of each phase.

Intermittent rivers and ephemeral streams are pivotal corridors for aquatic and terrestrial animals

Abstract Rivers are efficient corridors for aquatic animals, primarily under the assumption of perennial flow. However, the recognition that river drying is a common and widespread phenomenon requires reexamining animal movement through river networks. Intermittent rivers and ephemeral streams have been overlooked when studying animal movement, even though approximately 60% of the global river network dries. In the present article, we extend the current focus of river ecology by integrating the effects of drying on the movement of aquatic and terrestrial animals. Moreover, we introduce a conceptual model that challenges the current bias, which is focused on perennial waterways, by encompassing animal movement across hydrologic phases (nonflowing, flowing, dry, rewetting) and habitats (aquatic, terrestrial). We discuss their corridor function in conservation and restoration planning and identify emerging research questions. We contend that a more comprehensive and inclusive view of animal movement in dry channels will advance ecological understanding of river networks and respective conservation efforts.

Quantifying the impacts of a proposed hydraulic dam on groundwater flow behaviors and its eco-environmental implications in the large Poyang Lake-floodplain system

Dam-induced hydrological alterations and eco-environmental impacts have significant implications, however, these concern issues in large floodplain systems are less well understood. The present study shows a first attempt to adopt a quasi-three-dimensional groundwater flow modeling FEFLOW (Finite Element subsurface FLOW system) to investigate the influences of a proposed hydraulic dam on groundwater dynamics in the largest floodplain lake of the Yangtze River basin (Poyang Lake, China). The FEFLOW model was successfully constructed and has the ability to represent the hydrodynamics of floodplain groundwater flow. Model simulations indicate that, in general, the dam is likely to increase the groundwater levels across the floodplain during different hydrological phases. The responses of floodplain groundwater levels to the dam during the dry and recession phases are stronger (∼2–3 m) than the rising and flooding phases (<2 m). Under the natural condition, the floodplain groundwater may recharge the lake during the dry and recession phases, and discharge the lake during the rising and flooding phases. However, the dam regulation may alter the natural recharge-discharge patterns, forming a generally gaining condition of the floodplain groundwater. The proposed dam is most likely to reduce the groundwater flow velocity (∼<1 m/d) relative to the natural condition (up to 2 m/d) during different hydrological phases, and it may also alter the floodplain groundwater flow direction during the dry and recession phases. Additionally, the floodplain groundwater system is mainly characterized by losing state (−4.5 × 106 m3/yr) under the natural condition, while the dam-induced groundwater system exhibits an overall gaining state (9.8 × 106 m3/yr). The current research findings contribute to future water resources assessment and management by providing a foundation for assessing associated eco-environmental changes of the large lake-floodplain system.

Ichthyoplankton and plastic waste drift in a river in the Amazon Basin, Brazil

Egg and larvae drift is a key mechanism for early fish stages to colonize nursery and growth areas and provides insights into ichthyofauna spawning times and spawning locations—crucial information for understanding fish biology. In the Tapajós River, Amazon Basin, no study has investigated the drift of ichthyoplankton along the hydrological phases nor the occurrence and dispersion of plastic waste associated with plankton. Thus, we aimed to present an overview of the spatio-temporal drift of ichthyoplankton and plastic waste in this river. Temporal sampling was carried out along a spatial gradient of approximately 300 km, covering different sectors of the river. Ichthyoplankton and plastic waste were captured through horizontal trawls on the subsurface of the water column for 10 min. Fish larvae belonging to 10 taxonomic orders and with an average size of 4.98 mm ± 3.14 mm were captured. Clupeiformes larvae occurred in all hydrological phases and reproductive peaks for other orders were recorded. Plastic waste was classified into 20 types according to color and shape and an average size of 1.55 mm ± 1.27 mm. Green fragments and blue filaments were the most abundant. We found the highest density of fish eggs and larvae drifting during the drought phase in stretches with greater environmental structure, whereas plastics were more abundant during the receding water phase in more turbulent stretches that have impacts from illegal mining. Simultaneous drift of ichthyoplankton and plastic waste was recorded in all hydrological phases and sampled sectors. This is worrying because, although we did not analyze the ingestion of plastics by fish larvae, plastic waste can enter the nursery areas of the Tapajós River and reduce the function of these areas for fish. Here we discover through the high densities of fish eggs and larvae deriving that the Tapajós River is an important reproduction site for ichthyofauna and that the presence of different landscape configurations prove to be a key factor in the dispersion, retention and development of ichthyoplankton and plastic waste.

Effect of drying dynamics on the functional structure of a fish assemblage from an intermittent river network

We are living in a fast-changing world promoted by anthropogenic actions and ecosystems’ functioning has been constantly changed. One example is the globally reduction of river flow that can lead to more than 50% of the rivers and streams around the world becoming intermittent. However, the relationship between environmental changes and biological communities has been limited to taxonomic approach, rather than the functional approach. Functional structure determines how individuals interact with the environment and evaluating the effects of hydrological changes in functional variation can elucidate the responses of aquatic biota under climate changes. Thus, we hypothesized that hydrological phases (dry, re-wetting and wet) would influence both environmental conditions and fish composition (i.e., taxonomic richness and functional structure) in one intermittent river. In addition, we expected that: 1) fish assemblages will have higher values of species richness and Functional Diversity indexes—Richness (FRic), Dispersion (FDis), Specialization (FSpe), and Originality (FOri) in drier phases (dry and re-wetting); and 2) higher values of Functional Diversity indexes related to evenness (FEve) and divergence (FDiv) in the wet phase, due to the predominance of species with high dispersal capacity when sites are connected. Sampling was conducted in the Cruxati river during the three hydrological phases along four sites (250 m each). Functional diversity analysis, involving traits of dispersion, life history and trophic ecology were used to apply Functional Diversity indexes. Indexes were compared from null models and all species were ordered in a multidimensional functional space using principal coordinate analysis (PCoA). In the dry phase, taxonomic richness and FRic between communities is higher, as well as FSpe and FOri, showing that each assemblage has unique characteristics with different strategies allowing the establishment in this hydrological phase. However, communities are less functionally dispersed. In the wet phase, when the river is connected, FDis between communities is higher and species abundances are more equitable with regular distribution in the functional space. Therefore, we conclude that local ecological processes (i.e., dynamics of hydrology) may promote the establishment of species according to their functional traits and thereby the functional structure of local assemblages.

PHYTOPLANKTON BIOMASS INCREASES IN A SILT-IMPACTED AREA IN AN AMAZONIAN FLOOD-PLAIN LAKE OVER 15 YEARS

Tailings from bauxite mining in Porto Trombetas (Pará state, Central Amazonia, Brazil) was discharged (1979–1989) into Batata Lake affecting about 30% of its area. The lake belongs to a clear-water flood-plain system along the Trombetas River, a tributary of the Amazon River. Siltation is the main perceived factor impacting aquatic and flooded communities. Besides natural regeneration, a program to restore a section of igapó forest in the impacted area (IA) has been conducted since 1991. Decreased light is the main factor reducing total phytoplankton biomass (PhyBM) in IA. We hypothesized that PhyBM in IA increases over time because of the improvement of the underwater light conditions due to the natural regeneration and restoration. We sampled quarterly PhyBM and limnological variables (depth, transparency, temperature, pH, conductivity, dissolved oxygen, turbidity, suspended solids, total Kjeldahl nitrogen, and total phosphorus), over 15 years (2005–2019) at eight sampling sites in the two areas (N = 349). We also obtained daily climatic and hydrologic data. PhyBM was higher in NIA than in IA. The temporal trend in the annual mean of PhyBM increased significantly over time only in the IA, approximating the NIA values, confirming our general hypothesis. The increase of PhyBM in the IA was negatively related to the residual light attenuation caused by non-phytoplankton turbidity and to total phosphorus, and positively to air temperature and site depth (p &lt; 0.05; Marginal r2 = 0.18; Conditional r2 = 0.29). Instead, in NIA, PhyBM was explained only by the increase in air temperature (p &lt; 0.05; Marginal r2 = 0.15; Conditional r2 = 0.34). We concluded that the PhyBM in the IA positively responds to the synergy between increasing light availability, air temperature, and site depth, and decreasing total phosphorus concentrations, regardless of hydrologic phase.