Hydrological Periods Research Articles

Responses of biodiversity to microhabitat heterogeneity in debris flow gullies: Assessing the impact of hydrological disturbance

Rivers play a vital role in the maintenance of the biosphere and human society, since they participate in the global water cycle and provide varied habitats to support biodiversity. Microhabitat heterogeneity is regarded as a key factor driving biodiversity and it plays an active ecological role in different types of mountain rivers. Whether river microhabitat heterogeneity exhibits the same ecological patterns across hydrological periods remains unclear. Here, we analyzed the changes in macroinvertebrate community composition, functional traits, and multi-faceted α-diversity in five debris flow gullies in the Xiaojiang River Basin (southwestern China) between two different hydrological periods. We explored the responses of biodiversity to river microhabitat heterogeneity and its driving factors before and after hydrological disturbance. The results indicated that river microhabitat heterogeneity and three facets of macroinvertebrate α-diversity decreased after hydrological disturbance, with macroinvertebrate state traits becoming more unbalanced. Macroinvertebrate taxonomic diversity increased with increasing river microhabitat heterogeneity across hydrological periods, and this pattern was more prominent before hydrological disturbance. A high correlation emerged between macroinvertebrate phylogenetic diversity and river microhabitat heterogeneity only before hydrological disturbance. Hydrogeomorphic parameters prominently affected macroinvertebrate communities before hydrological disturbance. Water environmental parameters worked together with hydrogeomorphic parameters to shape macroinvertebrate communities in hydrologically disturbed debris flow gullies, indicating a reduced ecological role of river microhabitat heterogeneity. The ecological health of debris flow gullies can be improved by increasing vegetation coverage on river bank slopes to increase slope stability and mitigate hydrological disturbances, as well as placing large rocks into river channels to enhance riverbed stability and create habitats for more biological groups.

Influence of Seasonal Water Level Fluctuations on Food Web Structure of a Large Floodplain Lake in China

Seasonal shifts in hydrology are known to alter the abundance and diversity of basal production resources and habitats and hence strongly influence the structure and function of river ecosystems. However, equivalent knowledge of natural lake ecosystems in floodplain regions is lacking. Here, we used stable isotope ratios of carbon and nitrogen to assess available primary production sources and consumer taxa during the dry and wet seasons in a large floodplain lake connected to the Yangtze River. Fish species showed distinct δ13C values between two hydrological periods but only small changes in δ15N values. Most of the fish species had higher estimated trophic levels in the dry season, likely indicating greater carnivory. Results of Bayesian mixing models revealed that benthic algae and benthic organic matter (BOM), combined with C3 vegetation, were the principal food sources supporting the biomass of most fish species during the low-water period, whereas benthic algae and seston were the most important carbon sources during the flood period. Overall, these findings demonstrate that seasonal hydrological changes, such as water-level fluctuations, can affect the trophic structure and ecosystem functioning of floodplain lake food webs in the subtropical zone.

A Tarso model for studying the level of the Cuiabá river

The Cuiabá River registers cyclical occurrences of floods and droughts over the years, according to the hydrological periods, thus characterizing a non-linear behavior. The prediction of the level of the Cuiabá river is important to help institutions such as the Civil Defense of the state of Mato Grosso and many other institutions that are concerned with the prevention and mitigation of natural disasters. Thus, this study considered the nonlinear Threshold Autoregressive Self-Excking Open-loop (TARSO) model with 2 regimes, with a Bayesian approach. We tested models to which values of the linimetric quota (riverwater level in millimeters) with and without rainfall (mm) were associated. All models were compared using the lowest DIC, MAPE and MSE criterion, and the TARSO (2; 1, 0, 3, 1, 1) model performed best according to these criteria. Finally, the selected model was shown to produce reliable predictions.

Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Water level fluctuations associated with hydrological connectivity consolidate the food web stability of the largest Chinese freshwater lake via mediating trophodynamics and trophic structure

Variation in hydrological connectivity (HC) between rivers and lakes gives rise to periodic large water level fluctuation (WLF) in river-connected lakes (RCL). However, how WLF shapes the material cycling and concomitant trophodynamics of RCL remain unclear. Here we evaluated the resource availability, relative contributions of autochthonous and allochthonous carbon sources (by Bayesian mixing models) and trophic structure (using δ13C and δ15N) of Lake Poyang, the largest freshwater lake in China, during different hydrological periods. Terrestrial C3 plants in the aquatic/terrestrial transition zones (ATTZ) were the main supporter of aquatic consumers all year round. Compared with historical data, the contributions of autochthonous production to aquatic food webs were low. This is primarily ascribed to the influences of hydrological regimes in that the operation of Three Gorges Dam and HC changed the rhythm of WLF in Lake Poyang, restricting the production of aquatic vegetation and epiphytic algae. Most common fish species indicated higher trophic positions (TPs) during the dry than wet season, but only eleven of thirty-six common species showed a statistically significant increase (p < 0.05). Our study reveals a relatively consistent trophic diversity of consumer communities (fish and aquatic invertebrates) during dry and wet seasons, but each trophic guild showed specific trophic response to WLF, as they flexibly adjusted feeding strategies and the degree of trophic niche differentiation. Although WLF triggered fluctuations in the resource availability and species composition of lake food webs, and the TPs and trophic niches of aquatic consumers during different hydrological periods, the resource diversity and habitat complexity driven by HC and WLF reduced the strength of trophic interactions, and thus resulted in overall stability of food web trophodynamics and trophic structure of Lake Poyang. Our findings highlighted the importance of HC and natural WLFs in maintaining the ecosystem stability of large floodplain lakes, and that seasonal WLF patterns should be maintained in future floodplain lake management to conserve biodiversity and the resilience of ecological functions.

Analysis of Spatial and Temporal Variation in Water Coverage in the Sub-Lakes of Poyang Lake Based on Multi-Source Remote Sensing

As the largest freshwater lake in China, Poyang Lake is an internationally important wetland and the largest migratory bird habitat in Asia. Many sub-lakes distributed in the lake basin are seasonal lakes, which have a significant impact on hydro-ecological processes and are susceptible to various changes. In this study, using multi-source remote sensing data, a continuous time-series construction method of water coverage suitable in Poyang Lake was developed. That method combined the downscaling of the MNDWI (modified normalized difference water index) with the ISODATA (iterative self-organizing data analysis technique algorithm), and its accuracy can be up to 97% in the months when Landsat 8 is available or 87% when it is unavailable. Based on that method, the increasing variation in water coverage was observed in the sub-lakes of Poyang Lake during 2013–2020 to be within a range of 200–690 km2 normally. The center of the sub-lakes always remained inundated (&gt;80% inundation frequency), while the surrounding areas were probably kept dry for seven months (except for June to September). The dominant influencing factors of water coverage variations were different in different hydrological periods (wet season and dry–wet season: discharge; dry season: temperature and wind speed; wet–dry season: temperature and precipitation). In addition, “returning farmland to lakes” affected the increase in the water area in the sub-lakes. This study is helpful for the management of water resources and the protection of migratory birds in the Poyang Lake region.

Comparison of artificial neural networks and reservoir models for simulating karst spring discharge on five test sites in the Alpine and Mediterranean regions

Abstract. Hydrological models are widely used to characterize, understand and manage hydrosystems. Lumped parameter models are of particular interest in karst environments given the complexity and heterogeneity of these systems. There is a multitude of lumped parameter modelling approaches, which can make it difficult for a manager or researcher to choose. We therefore conducted a comparison of two lumped parameter modelling approaches: artificial neural networks (ANNs) and reservoir models. We investigate five karst systems in the Mediterranean and Alpine regions with different characteristics in terms of climatic conditions, hydrogeological properties and data availability. We compare the results of ANN and reservoir modelling approaches using several performance criteria over different hydrological periods. The results show that both ANNs and reservoir models can accurately simulate karst spring discharge but also that they have different advantages and drawbacks: (i) ANN models are very flexible regarding the format and amount of input data, (ii) reservoir models can provide good results even with a few years of relevant discharge in the calibration period and (iii) ANN models seem robust for reproducing high-flow conditions, while reservoir models are superior in reproducing low-flow conditions. However, both modelling approaches struggle to reproduce extreme events (droughts, floods), which is a known problem in hydrological modelling. For research purposes, ANN models have been shown to be useful for identifying recharge areas and delineating catchments, based on insights into the input data. Reservoir models are adapted to understand the hydrological functioning of a system by studying model structure and parameters.

First report on the bacterial community composition, diversity, and functions in Ramsar site of Central Himalayas, Nepal.

Wetland bacterial communities are highly sensitive to altered hydrology and the associated change in water physicochemical and biological properties leading to shifts in community composition and diversity, hence affecting the ecological roles. However, relevant studies are lacking in the wetlands of central Himalayas Nepal. Thus, we aimed to explore the variation of bacterial communities, diversity, and ecologic functions in the wet and dry periods of a wetland (designed as Ramsar site, Ramsar no 2257) by using 16S rRNA gene-based Illumina MiSeq sequencing. We reported a pronounced variation in water physicochemical and biological properties (temperature, pH, Chla, DOC, and TN), bacterial diversity, and community composition. Bacterial communities in the dry season harbored significantly higher alpha diversity, while significantly higher richness and abundance were reflected in the wet season. Our results uncovered the effect of nutrients on bacterial abundance, richness, and community composition. Fourteen percent of the total OTUs were shared in two hydrological periods, and the largest portion of unique OTUs (58%) was observed in the dry season. Planctomycetes and Bacteroidetes dominated the wet season exclusive OTUs; meanwhile, Actinobacteria dominated the dry season exclusive OTUs. Bacteria in these wetlands exhibited divergent ecological functions during the dry and wet seasons. By disclosing the variation of water bacterial communities in different hydrologic periods and their relationship with environmental factors, this first-hand work in the Ramsar site of Nepal will develop a baseline dataset for the scientific community that will assist in understanding the wetland's microbial ecology and biogeography.

Toxicological characteristics of drinking water in two large-scale municipal water supply systems of a metropolitan city in Central China.

Drinking water safety is threatened by numerous toxic organic pollutants difficult to chemically monitor. This study aimed to determine the toxicological profiles of organic extracts (OEs) of water samples from source to tap in two drinking water supply systems in a metropolitan city, Central China, during different hydrological periods. Mortality, DNA damage, growth, and development of Caenorhabditis elegans were evaluated following exposure to OEs. The median lethal doses of OEs of drinking water samples (n = 48) ranged from 266 REF (relative enrichment factor) to > 1563 REF. When tested at a dose of 100 REF, 56.25% (27/48) of OEs induced genotoxicity, 4.17% (2/48) inhibited the growth, and 45.83% (22/48) decreased the offspring number in C. elegans. No clear temporal-spatial variation patterns of the OEs toxicity indicators were observed. The correlations among the toxicity indicators were generally poor. The observed toxicities were not closely related to the level of dissolved organic carbon in drinking water. These findings support using multiple endpoint bioassays, such as C. elegans-based approaches, as complementary tools to conventional chemical analysis for drinking water quality monitoring.

Influence and Driving of Environmental Heterogeneity on the Epilithic Diatom Community in Xiangxi River, a Tributary of the Three Gorges Reservoir Area

Environmental heterogeneity can not only increase species diversity to some extent but also affect the stability of terrestrial communities. However, how environmental heterogeneity affects species diversity of epilithic diatom communities in aquatic ecosystems is rarely reported. In this study, therefore, epilithic diatoms and their roles in driving species diversity were explored by quantifying and comparing the environmental heterogeneity in Xiangxi River, a tributary of the Three Gorges Reservoir Area (TGR), on a time scale. The results showed that environmental heterogeneity, taxonomic β-diversity, and functional β-diversity in non-impoundment periods were significantly higher than those in impoundment periods. Moreover, the turnover components in the two hydrological periods showed the highest contribution to β-diversity. However, the taxonomic α-diversity in impoundment periods was significantly higher than that in non-impoundment periods. In addition, functional richness in functional α-diversity was significantly higher in non-impoundment periods than that in impoundment periods, whereas there was no significant difference in other functional α-diversity, i.e., functional dispersion and functional evenness, found between the two periods. Multiple regression on (dis)similarity matrices (MRM) analysis indicated that ammonium nitrogen (NH4+-N) and silicate (SiO32--Si) were the key environmental heterogeneous factors affecting the epilithic diatom community in Xiangxi River during the non-impoundment periods, whereas the key heterogeneous factors were ammonium nitrogen (NH4+-N), silicate (SiO32--Si), and total phosphorus (TP) during the impoundment periods. These results suggested that the environmental heterogeneity during different hydrological periods in TGR can significantly affect the community structure of epilithic diatoms, resulting in the differentiation of species within the community and even affecting the stability of aquatic ecosystems.

Understanding the temporal dynamics of a lowland river fish community at a hazardous intake and floodgate to inform safe operation

Entrainment and mortality of freshwater fish at hazardous pumping station intakes used for Flood Risk Management (FRM) are of global concern. Although upstream and downstream passage of diadromous fish has received considerable attention, the ecological behaviours of river-resident fish at these structures and how to protect these species from entrainment is poorly-understood. At a lowland flood-relief pumping station and floodgate situated off-channel (River Foss) to the main-river Yorkshire Ouse (York, England), multi-beam sonar (Dual-Frequency Identification Sonar: DIDSON) was used over a pluriannual (three years) period to investigate diel movements of river-resident fish in response to the variations in temperature, hydrology and pump and floodgate operation, and to determine fish-friendly management options. Diel lateral movements of thousands of river-resident fish between the main-river, floodgate operated channel (River Foss) and off-channel pump forebay were predominantly during the crepuscular period and daytime, proposing important considerations for when managers should operate pumps and associated flood infrastructure. Seasonal diel movements increased throughout winter during a baseline year (no pump operation) and overwintering behaviour was influenced by cooling river temperatures. A Generalized Linear Mixed Model (GLMM) revealed fish entered the off-channel forebay when river levels were stable and not when they were rising or falling, suggesting hydrological stability was important for the ecological function of this fish community. Two years of impact data (pumps operated) then revealed pump operations severely disrupted the ecological functions of local fish populations, which was also uniquely quantified over two independent 24h periods during which temporal fish counts were reduced by 85%. A trial period where the floodgate was lowered ahead of dawn significantly reduced fish immigration into the hazardous forebay when compared to two different hydrological periods. Modifying when the floodgate and pumps operate, including lowering the floodgate ahead of fish immigration at dawn, and starting pumps during the night (but not day), are therefore promising non-engineered management options to prevent immigration of fish into the hazardous off-channel pump forebay and to reduce entrainment and mortality risk during pump operation.

Seasonal variation of phytoplankton community assembly processes in Tibetan Plateau floodplain.

Uncovering the mechanisms underlying phytoplankton community assembly remains a major challenge in freshwater ecology. The roles of environmental filtering and spatial processes in shaping phytoplankton metacommunity in Tibetan floodplain ecosystems under various hydrological conditions are still unclear. Here, multivariate statistics and a null model approach were used to compare the spatiotemporal patterns and assembly processes of phytoplankton communities in the river-oxbow lake system of Tibetan Plateau floodplain between non-flood and flood periods. The results showed that phytoplankton communities had significant seasonal and habitat variations, with the seasonal variations being more remarkable. Phytoplankton density, biomass, and alpha diversity were distinctly lower in the flood than non-flood period. The habitat differences (rivers vs. oxbow lakes) in phytoplankton community were less pronounced during the flood than non-flood period, most likely due to the increased hydrological connectivity. There was a significant distance-decay relationship only in lotic phytoplankton communities, and such relationship was stronger in the non-flood than flood period. Variation partitioning and PER-SIMPER analysis showed that the relative role of environmental filtering and spatial processes affecting phytoplankton assemblages varied across hydrological periods, with environmental filtering dominating in the non-flood period and spatial processes in the flood period. These results suggest that the flow regime plays a key role in balancing environmental and spatial factors in shaping phytoplankton communities. This study contributes to a deeper understanding of ecological phenomena in highland floodplains and provides a theoretical basis for floodplain ecosystem maintenance and ecological health management.

Sensitivity of river ecological baseflow to climate change in arid areas

River ecological baseflow is key to river ecosystem health and stability and has become particularly important with global climate change aggravation. By considering the Niya River Basin in Xinjiang, based on meteorological data from 1958 to 2021 and hydrological data from 1978 to 2018, the Tennant method was determined to be the best basin ecological baseflow calculation method, the M–K test was used to analyze the abrupt ecological baseflow and climate change characteristics, and the ecological baseflow regression response and sensitivity coefficient models concerning climate change were established. The results showed that 75% of the ecological baseflow in the Niya River Basin ranged from 15 to 31 m3•s−1 in 1978–2018, the average annual temperature increased by 1.6°C at a 0.22°C•(10a)−1 rate, and the annual precipitation increased by 6.3 mm at a 0.98 mm•(10a)−1 rate. The prediction accuracy of the regression model was good, R2 exceeded 0.7, the ecological baseflow response to climate change lagged, and precipitation greatly impacted ecological baseflow. The basin sensitivity coefficient showed a decreasing trend from upstream to downstream, with the annual maximum value in 2010, the minimum value in 1984, the monthly maximum value in April and the monthly minimum value in November. Based on the climate change trend and the social water use of the basin, the ecological baseflow protection targets and measures were proposed according to the season and the hydrological period for actual water resource management and scheduling of the river in this and similar regions.

Temperature and precipitation control the seasonal patterns of discharge and water isotopic signals of the Nyang River on the southeastern Tibetan Plateau

River hydrology on the southeastern Tibetan Plateau (SETP) is particularly sensitive to climate change, through the serious impacts of the decline in Indian summer monsoon (ISM) rainfall and the accelerated melting of snow and glaciers during the recent decades. Investigating the effects of meltwater and rainfall on the seasonality and quantity of river runoff in the region is crucial for improving regional hydrological monitoring and water management, and water stable isotopes can provide an effective method. Based on the event-based data of precipitation and river water isotopes, river discharge and meteorology monitored at a hydrometric station of the Nyang River on the SETP in 2011, we show that river discharge has a strong reliance on temperature and precipitation simultaneously through their controls on the meltwater and rainfall runoff, and river water deuterium excess (d) and δ18O potentially track the meltwater and rainfall effects separately. The seasonal signals of river discharge and isotopic data provide evidence that meltwater is the key factor of river discharge and isotopic changes during the pre-ISM season (low water level period) and ISM rainfall during the early to mid-ISM season (growing and high water level period) but key factors are not clear during the mid to post-ISM season (recession period). These inferred seasonal runoff source relationships are in close agreement with the runoff source contributions estimated using a season-specific δ18O-d mixing model approach. Specifically, the result suggests meltwater contributes ∼28 %, ∼41 % and ∼25 % of the total river runoff, and snowmelt does make a major contribution to the meltwater (compared to glacier melt) during the three individual hydrological periods. This study investigated the event-based river discharge and isotopic responses to temperature and precipitation and the relevance of seasonal meltwater and rainfall effects for a representative basin on the SETP, and we propose that long-term isotopic record of river water in this region may document catchment changes in runoff source relationships (especially snowmelt vs ISM rainfall).

Dietary shift of a pimelodid catfish in response to the flood pulse in the Xingu River

Abstract We assessed the effect of a flood pulse on the diet composition, trophic niche breadth, and feeding intensity of the mandi catfish Pimelodus blochii (Pimelodidae) in the middle Xingu River region, throughout different hydrological periods. Specimens were collected monthly between December 2020 and November 2021, using gillnets. Specimens were measured for standard length (cm) and body weight (g) and then eviscerated to remove the stomach, which was weighed and stored for content identification. In total, we analyzed 93 stomachs of P. blochii, with the species’ diet predominantly composed of fish (86.5%) and terrestrial plants (6.9%). However, this dietary composition varied seasonally, particularly during the flood period when the species exhibited an omnivorous/carnivorous diet, as opposed to other periods when it had a carnivorous/piscivorous diet. Trophic niche breadth also varied, with the species showing a more specialist diet during the filling period. Finally, there was no difference in the amount of food (g) ingested during the hydrological periods. These results highlight the influence of the flood pulse on the feeding ecology of P. blochii, particularly regarding the diet composition. Our findings contribute to advancing the understanding of the relationship between abiotic dynamics and the life history of Amazonian fish species.

Trophic resources use pathways between two coexisting freshwater shrimp (Palaemon argentinus and Macrobrachium borellii)

Context A better understanding of the use of different trophic pathways as a mechanism for adjusting interactions between coexisting omnivorous decapod species may help define the extent of their influence on energy flows in freshwater ecosystems. Aims Analyse the patterns of use of the benthic and littoral pathways by Macrobrachium borellii and Palaemon argentinus during a hydrological cycle in lakes of the middle Paraná River. Methods The study was conducted during one high-water (HW) and one low-water (LW) period in three lakes permanently connected to the middle Paraná River. We calculated the relative contributions of potential basal resources (benthic and littoral) to each species for each lake and hydrological period using mixing models. Key results It was observed that M. borellii feeds more in the littoral pathway and P. argentinus in the benthic pathway, especially in low water where we observed that the partitioning of resources was more pronounced. Conclusion The more aggessive species, M. borelli, during HW period quickly utilises the bioavailable material. Trophic dynamics and resource use are part of the coexistence mechanisms of both decapod species. Implications This may have important consequences in the aquatic trophic webs in which these organisms participate, because when segregating the use of resources, they intervene in different energetic pathways.

Dinâmica espacial da pesca comercial amazônica: uma análise da composição da paisagem e dos desembarques de pescado

Amazonian commercial fishing is artisanal, and landings can be influenced by the flood pulse, the consumer market, the level of exploitation of species, habitat quality and vegetation cover. In this study, landscape variables and the river level were evaluated as possible drivers in the composition of catches landed in three regions of the Solimões-Amazon River. Fish landing data were collected in the upper and lower Solimões River and lower Amazon River. Fishing locations were mapped with information from fishers, civil defense departments and from the literature. Information related to river level and landscape was acquired from databases available online. Maps with the the radius of action of the fishing fleet and the quantification of landscape variables were made for periods of high and low-water, and non-metric multidimensional scaling analysis (nMDS) with catches by species, by region and hydrological period were performed. The largest operating radius of the fishing fleet was of 1,028 km and was identified in the lower Amazon River, which is probably due to the larger size of the consumer market, vessel characteristics and level of exploitation of the species near the landing center. The proportion of vegetation cover was reduced from 87% in the upper stretches of the Solimões River to 46% in the lower stretches. The upper and lower Solimões River regions presented a greater variety of species in the composition of landings. It was identified that the composition of landings between the three analyzed regions possibly varied according to the availability of habitats, indicating the importance of landscape variables for fish landings.

Influence of Pixel Quality, Land Cover, and Hydroclimatic Cycle on Moderate Resolution Imaging Spectroradiometer Inundation Monitoring Performance in the Pantanal, Brazil

Moderate resolution imaging spectroradiometer (MODIS) time series (TS) have been widely applied for flood monitoring in large tropical wetlands. However, little systematic work is available on the influence of pixel quality, vegetation cover, and the annual hydroclimatic cycle on classification performance. In this study, this issue is examined based on a six-year, 250 m resolution MOD13Q1 TS underpinned by extensive in situ measurements. The most parsimonious logistic regression model was obtained for land surface water index (LSWI) and enhanced vegetation index (EVI). The inclusion of the 500 m MCD12Q1 land cover Type 2 product improves accuracy. Performance markedly decreases for subsets that include pixels with a VI quality assurance (QA) level poorer than 0110 and/or a pixel reliability (PR) of three. When a Savitzky-Golay filter was used for TS reconstitution, performance is slightly lower than those obtained in a classification of a VI QA 0001 or PR = 0 level strata; moreover, these have the advantage of gap-free flood monitoring. The overall accuracy (OA) of the PR = 0 subset is better for grasslands, and slightly lower for Savannah, and for woodland and forests. The average OA is highest for the dry season, intermediate for the rainy/flooded season, and lowest for the transitional seasons, when the wetland becomes flooded or dries. Comparisons of internal, k-fold, and external validations indicate that only external validation enables a realistic assessment of flood-mapping performance. The complete substitution of PR = 3 pixels by filled-in values is recommended for operational flood monitoring, and it is concluded that the use of the simplified PR metrics as filtering criteria for gap filling and smoothing is sufficient for flood monitoring in the Pantanal. Classification metrics vary more strongly as a function of the hydrological period than by vegetation cover. MOD13Q1 users should be aware that OA in forest stands during the transition seasons are, on average, 25 p.p. lower than the average OAs obtained for the entire series.

Flood pulse as a driving force of Pb variation in four fish guilds from Puruzinho Lake (western Amazon).

The Brazilian Amazon is heavily impacted by mining activities, especially by gold and cassiterite mining. Pb is a contaminant released during cassiterite extraction, and it stands out for its high toxicity. The present study aimed to evaluate the effect of flood pulse on Pb dynamics in four fish species with different feeding habits (Cichlapleiozona: carnivorous, Mylossomaduriventre: herbivorous, Prochilodus nigricans: detritivorous, and Serrasalmus rhombeus: piscivorous) over four hydrological periods in Puruzinho Lake (Brazilian Amazon), which receives water from the Madeira River. The risk assessment for daily Pb intake through the consumption of these fish by the local riverside population was also carried out. Fish species were sampled during four Amazonian hydrological periods: rising water, high water, falling water, and low water. Pb and stable isotopes (δ15N and δ13C) measurements were carried out on fish muscle. The flood pulse had the same effect on Pb concentrations of all the fish species regardless of their feeding habits, as we found a nonsignificant interaction between these variables. The Pb in fish muscle increased in the flood season (rising and high water) and decreased in the dry season (falling and low water). The Pb concentration in fish increased significantly with their trophic level (δ15N), evidencing the occurrence of biomagnification of the element along the trophic chain (R2 = 0.24). The main food source of the herbivorous fish (δ13C) was very distinct from that of the others, which had a large overlap in their values. Regarding risk assessment, the daily Pb intake through consumption of the herbivorous species during high water (17.82 ± 19.68µg∙day-1) exceeded the limit determined by the Food and Drug Administration (FDA) of 12.5µg∙day-1, representing a health risk to the riverside population of Puruzinho Lake.

Microplastic distribution and migration in soil, water and sediments in Caohai Lake under the different hydrological periods, Southwest China

An increasing number of researchers have focused on microplastics (MPs) pollution in inland freshwater lakes due to its ecotoxicity, while little is known about the effects of hydrological periods on MPs distribution. Therefore, this study aims to investigate MPs distribution, morphological characteristics and physicochemical indices in various environments in dry and wet periods in Caohai Lake. The results exhibited that cultivated soil, water, and sediment in Caohai Lake have been polluted by MPs in dry and wet periods. There were pellets, fragments, film, and fibers of MPs in both dry and wet periods, and MP foam was additionally found in the wet period. MPs with 0 to 0.5 mm possessed the largest proportion in the five environments in dry and wet periods, followed by MPs with 0.5 to 1 mm and 1 to 5 mm. In Caohai Lake, the black, white, green, red, and transparent MPs in dry period, and black, colourful, grey, red and transparent MPs in wet period were found. The developed structural equation model confirmed that MPs in sediment were probably mainly from soil. There are negative effects of the relative abundance of MPs from cultivated soil to lake water in the dry period, whereas the opposite is true in the wet period. Interestingly, the complex and fast water velocity in the estuary in the wet period led to a lower relative abundance of MPs in its sediment in comparison with the dry period. The distribution model of MPs in estuary and lake water in dry and wet periods is not inconsistent. Our results suggest that the related government department should take measures to reduce the MPs pollution in Caohai Lake, especially from the source.