Riverine Floodplains Research Articles

Disentangling the Effects of Multiple Impacts of Natural Flooding on a Riverine Floodplain Lake by Applying the Phytoplankton Functional Approach

Riverine floodplains are ecologically remarkable systems that have historically faced strong anthropogenic pressures. The aim of this study was to examine whether the phytoplankton functional approach by Reynolds is a useful tool for disentangling anthropogenic pressure from the impact of natural flooding on a riverine floodplain lake. Lake Sakadaš, part of the large conserved river–floodplain system along the Danube River (Kopački Rit, Croatia), was used as a case study. Historical data on phytoplankton dynamics from the 1970s, when the lake was exposed to direct inflows of agricultural wastewater, were compared with current data from a time when the lake was a strongly protected area. Analysis of the phytoplankton community, based on functional groups and their beta diversities, revealed clear variation between the observed periods. The heavy bloom of species from only one functional group with extremely high biomass indicated a highly impacted environment in the past. Recent data suggest that, with the cessation of direct pollution, near-natural hydrological conditions with flooding as a fundamental environmental driving factor, support algal assemblages characteristic of a naturally eutrophic lake. Assessing multiple pressures on floodplain lakes and disentangling their specific impacts on ecological statuses are crucial for defining the protection and sustainable management of these particularly sensitive and endangered freshwater systems.

Optimized ensemble-based flood hazard mapping in low altitude subtropical riverine terrane

Among various natural hazards, those induced by hydrological and meteorological factors have emerged as the most frequent and damaging. India is at the second from the top, after Bangladesh, of flood hazard-affected countries of the world, causing immense damage to life and property every year. The Middle Ganga Plain in the country is one of the most severely affected regions due to the convergence of Himalayan rivers in the Ganga (Ganges) plain. This study focuses on optimizing novel ensemble models to enhance the mapping of flood hazard susceptibility in specific topoclimatic setting, characterized by a low-altitude-range, sub-tropical monsoonal climate, and a riverine floodplain environment of the tectonically active Middle Ganga Plain. This region forms part of the Ganga Foreland Basin prone to frequent floods. We employ a comprehensive flood inventory and twelve selected flood conditioning factors and is the first study that has developed these ensemble models in low relief riverine floodplain environmental setting with high resolution geomorphology as one of the conditioning factors. Four artificial intelligence ensemble models were employed in this work: Logistic Regression-Evidential Belief Function (LR-EBF), Logistic Regression-Frequency Ratio (LR-FR), Multi-Layer Perceptron-Evidential Belief Function (MLP-EBF), and Multi-Layer Perceptron-Frequency Ratio (MLP-FR). Results showed that LR-based ensembles outperformed MLP-based ensembles in the studied topoclimatic setting, with LR-EBF model achieving 87.2% and 84.7% success and prediction rates respectively. Our results reveal consistent performance differences between LR-based ensembles with FR and EBF models across different environmental settings. MLP-based ensembles, particularly with Frequency Ratio, displayed more significant performance variations. The findings underscore the importance of considering specific topoclimatic and altitudinal range environments when applying flood hazard susceptibility models. Our study also provides valuable insights for planning and policymaking in flood management practices in similar topoclimatic settings worldwide.

Maintenance of High Phytoplankton Diversity in the Danubian Floodplain Lake over the Past Half-Century.

Riverine floodplains are recognized as centers of biodiversity, but due to intense anthropogenic pressures, many active floodplains have disappeared during the last century. This research focuses on the long-term changes in phytoplankton diversity in the floodplain lake situated in the Kopački Rit (Croatia), one of the largest conserved floodplains in the Middle Danube. The recent dataset from 2003 to 2016 and historical data from the 1970s and 1980s indicate high phytoplankton diversity, summarising 680 taxa for nearly half a century. The variability of species richness is driven by specific in-lake variables, particularly water temperature, water depth, total nitrogen, pH, and transparency, determined by a redundancy analysis of the current data. The high phytoplankton diversity levels are sustained regardless of intense pressures on the lake environment, including exposure to strong anthropogenic pollution in the past and extreme hydrological events, both droughts and floods, which have increasingly affected this part of the Danube in the last decades. The conserved hydrological connection between various biotopes along the river-floodplain gradient seems crucial in maintaining high phytoplankton diversity. Accordingly, conserving natural flooding is mandatory to maintain high biodiversity in complex and dynamic river-floodplain systems.

Distribution of the black grouse, capercaillie, and hazel grouse (Tetraonidae) at the northern edge of their species range in the Nenets Autonomous Area

This paper presents data on the distribution of the black grouse Lyrurus tetrix (L., 1758), capercaillie Tetrao urogallus (L., 1758), and hazel grouse Tetrastes bonasia (L., 1758) in the Nenets Autonomous Area (the northeast of the European Russian Federation). The study has revealed trends indicating an expansion of the distribution range of these species to the north. According to our observations, black grouse, capercaillie, and hazel grouse in the Malozemelskaya Tundra are located further north than in the published data – about 40 km for black grouse, 20 km for capercaillie, and 20 km for hazel grouse. In the Malozemelskaya Tundra, the northernmost black grouse and capercaillie were found in spruce forest islands, while the hazel grouse inhabited riverine floodplain forests. In the Bolshezemelskaya Tundra, the capercaillie was the only grouse bird found further north compared to the published data, in the extremely northern islands of the forest within the Shapkina River valley. In the Bolshezemelskaya Tundra, new registrations of the grouse (200 km) and ruffed grouse (100 km) were noted to the east of the known data, indirectly indicating an expansion of the distribution area of these birds to the north in the regions adjacent to the Nenets Autonomous Area. It was noted that the trends of expansion of the range of distribution of black grouse to the north are unidirectional with positive trends in air temperature in the Nenets Autonomous Area and with the processes of gradual overgrowth of woody vegetation in treeless areas located between the forest tundra and northern spruce forest islands.

Attitudes toward moving or staying and buying flood insurance to face varied flood threats in a floodplain community

Demographics and possession of flood insurance are among the factors influencing flood response and recovery actions adopted by individuals, such as deciding to either move out of their homes or stay. It is essential to consider residents' attitudes to help policies prepare for the social and economic impacts of flooding. In some urban areas situated in floodplains, climate change has caused an increase in the severity of flooding. This research project focused on residents living within riverine floodplain areas delimited by FEMA and their attitudes regarding relocation under flood varied threats. A household survey in the United States was conducted in Corvallis, Oregon, which presented participants with different flood threat scenarios involving varying water depths and frequencies. After selecting predictors by applying a collinearity constraint, logistic regression was used to find significant predictors of individuals' attitudes toward moving out of their homes or staying at home and buying or upgrading flood insurance under varied flood threats. The results showed that some low or unknown-magnitude flood scenarios produced statistically significant models to predict mobility, but high-magnitude flooding did not yield statistically significant models. For example, flood insurance possession was the only significant predictor for staying after flooding in various scenarios. A more robust understanding of these interdependencies should increase the effectiveness of growing awareness of environmental threats and participation in risk-reducing behaviors.

Field monitoring of alluvium accumulation in the riverine floodplain of the Oka River, European Russia

Sedimentation traps were used to assess the annual surface renewal dynamics of the low floodplain of the Oka River (a major tributary of the Volga River in central European Russia). Trap-mats and platforms made of crushed bricks were installed in positions near the meandering and relatively straight riverbed, in different sedimentation environments. Stationary research in 2014–2020 covered a section of the bottom of the Oka River valley with a length of more than 400 km along the main channel. The graphical-analytical processing of field data using Ferret's Triangles and sedimentation diagrams showed that transport and deposition of suspended sediment dominated in the accumulation of 87% of alluvium samples. The formation of ripples was not recorded, which was lithologically reflected in the horizontal layering of the new sediment. The determination of the granulometric composition of the removed sediment and their thickness on the traps showed the absence of statistically significant differences according to the Kruskal–Wallis test between the data samples from the trap-mats and trap-platforms. The reference to the daily calendar of synoptic mechanisms according to the classification of Dzerdzeevsky contributed to the identification of meteorological prerequisites for the variation of the hydrograph curve of the Oka River in its middle reaches. Prolonged floods caused by the premature arrival of spring lead to massive deposition of silt and clay particles even on sandbanks. On the other hand, short (15–35 d) March floods and abnormal high water in June, caused by Atlantic cyclone intrusions, can stabilize sand accumulation on the riverine floodplain. The thickest sediment layers on the traps were obtained in 2018 after a very cold March and a powerful April flood, and the overall distribution of alluvium thickness and its particle size distribution also depends on the morphology of the riverine relief. The siltation is caused by the accumulation of silts; the most finely dispersed sediment was deposited in those facies environments for which siltation was also characteristic in historical times.

Prediction of Open Woodland Transpiration Incorporating Sun-Induced Chlorophyll Fluorescence and Vegetation Structure

Transpiration (T) represents plant water use, while sun-induced chlorophyll fluorescence (SIF) emitted during photosynthesis, relates well to gross primary production. SIF can be influenced by vegetation structure, while uncertainties remain on how this might impact the relationship between SIF and T, especially for open and sparse woodlands. In this study, a method was developed to map T in riverine floodplain open woodland environments using satellite data coupled with a radiative transfer model (RTM). Specifically, we used FluorFLiES, a three-dimensional SIF RTM, to simulate the full spectrum of SIF for three open woodland sites with varying fractional vegetation cover. Five specific SIF bands were selected to quantify their correlation with field measured T derived from sap flow sensors. The coefficient of determination of the simulated far-red SIF and field measured T at a monthly scale was 0.93. However, when comparing red SIF from leaf scale to canopy scale to predict T, performance declined by 24%. In addition, varying soil reflectance and understory leaf area index had little effect on the correlation between SIF and T. The method developed can be applied regionally to predict tree water use using remotely sensed SIF datasets in areas of low data availability or accessibility.

Recognition of an extended record of euglenoid cysts: Implications for the end-Triassic mass extinction

The enigmatic non-pollen palynomorph Chomotriletes, occurs consistently within sediments associated with the end-Triassic mass-extinction. Based on a detailed palynological survey and other published records from Europe, Chomotriletes is prevalent within the uppermost Rhaetian Contorta and Triletes Beds and its equivalents elsewhere. Chomotriletes is now a senior synonym for Permian Circulisporites, Meso- to Cenozoic Pseudoschizaea, and Quaternary to Recent Concentricystes. Its widespread occurrence has significance for our understanding of the end-Triassic mass-extinction, but its biological affinity and ecological preference have remained contentious for almost a century. We undertook a TEM examination of a Holocene and a Pliocene example of Concentricystes and found their structure to be a close match to the wall of Jurassic Pseudoschizaea from Italy that has been interpreted to belong to cysts of the Euglenophyceae. Together with a nascent understanding of a deep time record of the euglenoid, Moyeria, Chomotriletes helps document a terrestrial signature of the Euglenophyceae in the fossil record. An extensive literature survey indicates that Chomotriletes is associated with wetlands and riverine floodplain soils, and that it inhabited mainly temperate to tropical latitudes and continues to do so to the present day. Its presence in ancient marine sediments therefore indicates transport via weathering and erosion. The association with wetlands is in line with the ecological preferences of species of the Euglenophyceae. The presence of euglenoid cysts in association with the end-Triassic extinction fits a scenario in which enhanced rainfall followed by strong soil erosion resulted in the release and redeposition of Chomotriletes into shallow marine settings.

Brief floodplain inundation provides growth and survival benefits to a young-of-year fish in an intermittent river threatened by water development

Riverine floodplains are highly productive habitats that often act as nurseries for fish but are threatened by flow regulation. The Fitzroy River in northern Australia is facing development, but uncertainty exists regarding the extent to which floodplain habitats deliver benefits to fish, particularly given the brevity of seasonal floodplain inundation. We investigated the growth rate of young-of-year bony bream (Nematalosa erebi) in main channel and ephemeral floodplain habitats using age derived from otolith daily increments. We also investigated potential mechanisms influencing growth and modelled the consequences of differential growth rate on survival. Our results revealed higher growth occurred exclusively on the floodplain and that zooplankton biomass was the best predictor of growth rate. Modelling indicated that elevated growth rate in high-growth floodplain pools (top 25th percentile) could translate into substantial increases in survivorship. The positive effect of zooplankton biomass on growth was moderated under highly turbid conditions. Temperature had a minor influence on growth, and only in floodplain habitats. Our results indicate ephemeral floodplain habitats can deliver substantial growth and survival benefits to young-of-year fish even when floodplain inundation is brief. This study highlights the need to ensure that water policy safeguards floodplain habitats due to their important ecological role.

Zooplankton size-structure dynamics of a lowland tropical floodplain lake

Floodplains are highly complex ecosystems representing high biodiversity and conservation values, but they are also one of the world’s most threatened ecosystems due to extensive development and anthropogenic activities. Lake Tempe is a lowland riverine floodplain lake in Sulawesi Island, Indonesia, that is subject to multiple stressors such as flow alteration, eutrophication and invasive species. In this study, the dynamics of the zooplankton community size structure was investigated in Lake Tempe. Five size-based metrics, including zooplankton mean body size, total abundance, total, biomass, and normalised biomass size spectra (NBSS) slope and intercept were assessed from net-sampled zooplankton collected monthly from March to December 2016, and the role of environmental variables in shaping these size-based metrics were also examined. Zooplankton community size structure is a useful metric as it is less labour intensive than traditional approaches, provides more data accuracy and does not require highly specialised taxonomic expertise. The zooplankton community in Lake Tempe was characterised by high density of small-sized zooplankton with an average mean body size < 500 µm equivalent spherical diameter. While the zooplankton density was characterised by the dominance of the size class 300–700 µm, there was evidence of a significant contribution of the size > 700 µm towards total biomass. Seasonal hydrological regimes, water temperature and eutrophication parameters, as indicated by total phosphorus and chlorophyll-a concentration, had a significant role in driving the variability of zooplankton community size structure in this system. The results of this study are not only a significant step in providing critical baseline information on the zooplankton assemblage of Lake Tempe, but is also a significant contribution to the overall understanding of zooplankton community structure in tropical lakes, and will aid in improving lake management plans in these regions.

Topographical dynamics based on global and UAV-SfM derived DEM products: a case study of transboundary Teesta River, Bangladesh

ABSTRACT Topographical changes in riverine floodplains need to be measured for assessing geomorphological dynamics and protecting floodplain areas, although topographic evaluation in disaster-prone floodplain in South Asia has been limited due to the lack of multitemporal, high-definition digital elevation models (DEMs) derived from modern techniques including airborne laser scanning, structure-from-motion (SfM) photogrammetry accompanied with Unmanned Aerial Vehicle (UAV, often referred as drone), and field-based mapping approaches. Here we conducted a preliminary study at two locations of Teesta River (Brahmaputra’s tributary) in Bangladesh using the UAV-SfM techniques and generated high-resolution DEMs. The selected locations represent dynamic changes of sediment and water on the floodplain over the years, and the UAV-SfM approach can be an effective method for monitoring those changes, but an archive of the past data has been unavailable. Here we evaluated the topographic changes by comparing the UAV-SfM-derived DEMs of 2022 with global DEM products (NASADEM of 1999), which are often the only available choice of DEMs in this river floodplain. The elevation differences of these two sets of DEMs were in the range of −5.23 to −84.66 m, and volumetric changes of −4.11 ± 0.15 to −86.25 ± 0.20 million m3, likely dominated by erosional processes towards the left side bank where the elevation errors are supposed to be several meters for UAV-DEM and ca. 5–12 m for NASADEM. Although it is not easy to accurately evaluate the absolute values of the changes, these changes may be associated with the upper basin’s morphodynamics.

Interactions of hydrology, geochemistry, and biodiversity in woodland ponds located in riverine floodplains: case study from Scotland

The Gore Glen pond is located in the forested floodplain of the Gore River, in the Mid-Lothian region near Edinburgh, Scotland. This work has considered in detail the hydrology, hydrochemistry, and biodiversity of the pond together with all their interactions and in addition interactions with the adjacent Gore River. It is important as it is one of few studies considering all these issues for a pond located in a riverine floodplain. This work shows the pond is connected to the Gore River for discharge events in the river larger than a 1 in 5-year return period. For these events, the pond acts as an online storage feature and will attenuate the flow, thus contributing towards the mitigation of downstream flooding. These large events are also a potential source of the large amount of sediments, as well as adsorbed chemicals, accumulated in the pond. The open water surface of the pond is covered by duckweed, Lemna minor, for most of the year, and that has profound implications for the hydrobiological community and biogeochemical cycling. The system is characterised by nutrient release from sediments due to the extensive hypolimnion anoxia in the summer/autumn period caused by the decomposition of organic matter. Algae are mostly represented by epiphytic diatoms and the cyanobacterium Microcystis, but their development appears to be constrained by light penetration. The eutrophic conditions are also conducive for the population of Difflugia (Protozoa, Rhizopoda). This work improves our understanding of the ecological relations of testate amoebae—an important group which has recently been used as biological indicators for the analysis of paleoecological relationships and paleogeographical reconstructions.

Decoupling of nitrogen, phosphorus and biogenic silica in floodplain sediments in response to land use change and hydrological alterations

Human activities are altering global biogeochemical cycles of nitrogen (N), phosphorus (P) and biogenic silica (BSi). In order to reveal nutrient dynamics in response to human disturbances, this study explores burial rates and ratios of N, P and BSi in 210Pb-dated sediment cores from eight lakes in the middle Yangtze River floodplain. Mean burial rates of N, P and BSi increased substantially from the early 20th century, except for a hiatus in the 1970s. Before the 1960s, the stable ratios of N:P, N:BSi and P:BSi indicated the nutrient supply from clastic sources, while arable land expansion enhanced nutrient burial in lakes. Although damming increased the retention of N, P and BSi in upstream reservoirs after the 1960s, anthropogenic N and P release to the lakes outpaced the retention by dams, as suggested by continuous increases in N and P burial rates. The concurrent increase in BSi burial rate suggested that nutrient enrichment promoted diatom production at the earlier stage, while rising N:BSi and P:BSi ratios and declining BSi burial rate from the 1990s indicated the Si depletion with further eutrophication. Spatial heterogeneities among the lakes were linked to site-specific factors such as hydrological connectivity and macrophyte growth. Synchronous increases in N, P and BSi burial rates before the 1960s mainly responded to deforestation and arable land expansion; thereafter, the decoupling of N, P and BSi likely resulted from intensive farming (e.g., fertilizer usage) and damming. Given new dam construction and land use change in river basins, the BSi depletion relative to N and P is likely occurring in riverine floodplains worldwide.

Mapping Water Levels across a Region of the Cuvette Centrale Peatland Complex

Inundation dynamics are the primary control on greenhouse gas emissions from peatlands. Situated in the central Congo Basin, the Cuvette Centrale is the largest tropical peatland complex. However, our knowledge of the spatial and temporal variations in its water levels is limited. By addressing this gap, we can quantify the relationship between the Cuvette Centrale’s water levels and greenhouse gas emissions, and further provide a baseline from which deviations caused by climate or land-use change can be observed, and their impacts understood. We present here a novel approach that combines satellite-derived rainfall, evapotranspiration and L-band Synthetic Aperture Radar (SAR) data to estimate spatial and temporal changes in water level across a sub-region of the Cuvette Centrale. Our key outputs are a map showing the spatial distribution of rainfed and flood-prone locations and a daily, 100 m resolution map of peatland water levels. This map is validated using satellite altimetry data and in situ water table data from water loggers. We determine that 50% of peatlands within our study area are largely rainfed, and a further 22.5% are somewhat rainfed, receiving hydrological input mostly from rainfall (directly and via surface/sub-surface inputs in sloped areas). The remaining 27.5% of peatlands are mainly situated in riverine floodplain areas to the east of the Congo River and between the Ubangui and Congo rivers. The mean amplitude of the water level across our study area and over a 20-month period is 22.8 ± 10.1 cm to 1 standard deviation. Maximum temporal variations in water levels occur in the riverine floodplain areas and in the inter-fluvial region between the Ubangui and Congo rivers. Our results show that spatial and temporal changes in water levels can be successfully mapped over tropical peatlands using the pattern of net water input (rainfall minus evapotranspiration, not accounting for run-off) and L-band SAR data.

Settlement suitability analysis of a riverine floodplain in the perspective of GIS-based multicriteria decision analysis

Riverine floodplains are highly dynamic and the most vulnerable space on Earth particularly in flat alluvial plains of major river systems. Suitable site selection for sustainable human settlements in active floodplain areas is a critical task for decision-makers in terms of quality of lithology, ecologically fragile landmass, climate-induced hazards, immense population pressure, and environmental conservation issues. This research introduces a methodology for settlement suitability zone (SSZ) that employs GIS-based multi-criteria decision-making (MCDM) techniques. As a case study, an altered hydrological regime of the lower Ganga riparian zone was chosen to identify the SSZ as these areas are the most susceptible to riverine hazards. Twelve significant variables reflecting on topography, climate, landscape, and environment have been selected in the multi-criteria evaluation platform. The CRiteria Importance Through Intercriteria Correlation (CRITIC) method is adopted to specify the weights of the criteria and utilize an inverse distance-weighted (IDW) spatial interpolation technique to generate an SSZ map in a GIS environment. The study zone is spatially quantified into five categories, from unsuitable to high-suitable with a natural breaks (Jenks) classification method. Subsequently, the final results are validated through a receiver operating characteristics (ROC) curve using randomly selected 56 hazard-exposed location points. The outcome revealed that 8.45% of the riparian area falls under unsuitable, 21.87% under low-suitable, and 33.27% under moderate-suitable for locating human settlements. The generally suitable and high-suitable categories account for 36.40% of the total study zone. A spatial sensitivity analysis is also applied to gauge the influence of each parameter on the MCDM outcomes. The SSZ mapping results from this study can help local authorities to plan for sustainable settlement development in environmentally fragile areas.

Distribution and storage of uranium, and its decay products, in floodplain sediments

Industrialised rivers contain legacy contaminants stored in their sediments and floodplain soils which may inhibit attainment of environmental quality criteria. The River Fal catchment, SW England, is impacted by inputs from uranium mining and clay production and serves as an exemplar for understanding the consequences of medium-term process dynamics in contaminated basins. Radionuclides were determined, by gamma spectroscopy, in six cores from the river floodplain with the aim of quantifying the activities of 238U, and its decay products, and the bomb fallout radionuclides137Cs and 241Am. Activity concentrations of 238U implied inputs from mining, accentuated by flood events and historic industrial accidents, whereas 210Pb activities included a significant input of unsupported 210Pb linked to processed mine spoil. The radionuclide inventories did not decrease systematically downstream revealing evidence of attenuation of particulate radionuclides within the river floodplain sediment column. Storage of legacy contaminants in fluvial systems, at levels in excess of contemporary environmental quality guidelines, emphasises the challenges posed by changing climatic conditions. This scenario raises significant consequences for the management of uranium-contaminated, fertile riverine floodplains within Europe.

Hydrological conditions determine shifts of plankton metacommunity structure in riverine floodplains without affecting patterns of species richness along connectivity gradients

Hydrological conditions determine shifts of plankton metacommunity structure in riverine floodplains without affecting patterns of species richness along connectivity gradients

Integrated assessment of flood risk in Arial Khan floodplain of Bangladesh under changing climate and socioeconomic conditions

AbstractIn the assessment of flood risk, the future flood hazard due to climate change is often tied to the present socioeconomic conditions. This makes an implicit assumption that the drivers of risk, other than the hazard, remain constant with time. Therefore, such risk assessment does not provide a realistic outlook for devising plausible mitigation strategies and plans. In this study, flood risk was assessed from an integrated perspective by considering both physical hazard, and socioeconomic exposure and vulnerability—all changing with time. The flood hazard in the Arial Khan River floodplain in the southcentral Bangladesh was simulated with a two‐dimensional hydrodynamic model, and the exposure and vulnerability were projected using different statistical techniques. Principal component analysis was conducted to assign weights to the indicators of hazard, exposure, sensitivity, and adaptive capacity. The results show that the flood depth, duration, and extent would increase from the baseline to 2080s under regional concentration pathway (RCP) 2.6 and RCP 8.5 scenarios. The sensitivity and vulnerability would decrease, reflecting an improved adaptive capacity. The low‐risk areas could increase from 62% in the baseline to 85%–91% in 2080s depending on the RCPs. The approach followed can be applied elsewhere in developing countries, particularly in riverine floodplain settings.

Hydrological Regime and Fish Predation Regulate the Zooplankton Community Size Structure in a Tropical Floodplain Lake

Floodplain ecosystems are characterised by alternating flood and drought periods that can affect the structure of the aquatic community. Dynamic changes in the hydrological regimes from flooding to dry periods influence the migration and dispersal of aquatic fauna and the exchange of particulate matter and nutrients. Riverine floodplains are among the most productive ecosystems; however, increasing pressure from anthropogenic activities has altered the hydrological regimes, threatening aquatic biodiversity. In this study, we examined the temporal patterns of zooplankton community size structure and fish density during three distinct hydrological events in a tropical floodplain lake, Lake Tempe, Indonesia. We included fish density data and three contrasting hydrological conditions, moderate-, high-, and low-water periods, as the environmental factors regulating zooplankton community structure. In high- and low-water conditions, the ecosystem heterogeneity was characterised by high chlorophyll-a, total nitrogen, and total phosphorus concentrations; high fish density; and high zooplankton abundance and biomass. During the early flood period, the ecosystem was characterised by lower concentrations of trophic indicators and significant decreases in zooplankton abundance and biomass, as well as decreased fish density. While there was no clear association between hydrological conditions and zooplankton size structure, our findings indicate that fish predation probably suppressed zooplankton size diversity in Lake Tempe, shown by the dominant contribution of small-sized zooplankton towards total abundance and biomass under all hydrological conditions. Our results indicate that the patterns of environmental variables, zooplankton community, and fish density are affected by hydrological conditions, highlighting the role of water level fluctuation as the driving factor for zooplankton community structure. Our results also indicated that fish predation led to the development of a small-sized population of zooplankton in Lake Tempe.

Floodplain ecology: A novel wetland community of the Amazon

An expedition to the upper estuarine reaches of the Amazon River reveals intriguing overlap of tropical mangrove wetlands with riverine floodplain forests. This newly discovered type of forested wetland assemblage may provide a uniquely process-rich carbon hotspot.