Oxbow Lakes Research Articles

Some Cytogenetic Features of <i>Сarassiusgibelio</i> and <i>Сarassius carassius</i>, Populations Living in Hydrologically Diverse Reservoirs of the Tura River Basin

The article presents the results of the analysis of the genetic structure of the populations of Carassius gibelio (Bloch, 1782) and Carassius carassius (Linnaeus, 1758) by the cytometric method by the size of the area of erythrocyte nuclei. The relevance of the work is due to the discussion on the formation of crucian as one species or several ecological forms and the disappearance of crucian as a species in its natural habitat. We compared crucian carp from different types of water bodies: the Tura river, the Niсa river (the left tributary of the Tura), Lake Krivoe (the Tura oxbow lake, periodically communicating with it), Lake Srednee (isolated, not connected with the Tura for more than 70 years). In all studied water bodies, the diploid form of silver crucian dominates. The proportion of triploids in the Nica river and Lake Krivoe did not exceed 5%, in the lake. The average was equal to 20%, and the maximum (30%) was noted in the Tura. The ratio of cytometrically determined diploids and triploids was: in the river Tura - 2: 1, in the river Nica 19:1, in Lake Krivoe 17:1, in Lake Srednee 3:1. At the same time, from 5 to 18% of individuals were not determined by ploidy, their largest number was noted in the sample from Lake Srednee. When comparing the area of erythrocyte nuclei in silver and gold crucian from the lake. The average overlap zone was found at the level of 4554 m2, which suggests natural hybridization of the populations of these species.

High-resolution modeling of meander neck cutoffs: laboratory and field scales

Meandering rivers are distinguished by their characteristic sinuosity, which is subject to modulation through channel cutoff, resulting in the formation of oxbow lakes within the abandoned meander loops. Throughout the evolutionary course of a river, these cutoffs establish a connection between the channel and floodplain systems, both crucial to maintaining the dynamic equilibrium of the river system. Nonetheless, the interactive dynamic between the channel and floodplain and its influence on the transient behavior of the channel’s morphodynamics during a cutoff event are frequently reduced to simplistic representations in computational models. This study introduces a comprehensive numerical model that elucidates the adaptive processes of bed and planform during and subsequent to the inception of cutoff and oxbow lakes. The model is assessed through its application to a laboratory scale cutoff, before being employed to a real-world meandering river, specifically the Ucayali River in Peru, in order to gain understanding into channel development and the intricate patterns of planform dynamics following cutoff events. The model is able to capture the main modes of planform migration, translation and expansion for the case of the bend in the Ucayali River. During the neck cutoff, the model simulates the progression of erosional and depositional waves traveling in upstream and downstream directions respectively, underscoring the importance of incorporating both hydrodynamic and morphodynamic factors in characterizing the river dynamics associated with meander cutoffs.

Discordant spatiotemporal dynamics of functional and phylogenetic diversity of rotiferan communities exposed to aquaculture effluent.

The growth of the human population brought about the global intensification of aquacultural production, and aquaculture became the fastest growing animal husbandry sector. Effluent from aquaculture is an anthropogenic environmental burden, containing organic matter, nutrients and suspended solids that affect water quality especially in the water bodies of high biodiversity and conservation value. Water quality assessment often relies on bioindicators, analysing changes in taxonomic diversity of various freshwater organismal groups. Stepping beyond taxon diversity, we used functional and phylogenetic diversities of rotifers to identify factors affecting their community organization in response to an aquaculture effluent gradient in the largest oxbow lake in the Carpathian Basin, Hungary. Sampling was carried out three times per season at five points along a 3.5 km section of the oxbow lake, including the point of effluent inflow. We used eight traits to evaluate functional diversity: body size, trophi type, feeding mode, protection type, body wall type, corona type, habitat preference and tolerance level. Functional and phylogenetic distances among the 24 species identified indicated trait conservatism. Rotiferan diversity increased with increasing distance from the point of influx in spring and summer. Among the factors affecting community organization in spring and summer, we find examples of environmental filtering, while in autumn the role of biotic interaction is more frequent. Under nutrient-rich conditions in spring and summer, organisms belonging to the same functional group were dominant, whereas under oligotrophic conditions, more diverse but less abundant groups were present. Considering functional and phylogenetic traits allowed us to identify organising forces of rotifer communities in the largest oxbow lake of the Hungarian Lowland.

Four new terrestrial earthworm species from the northeast Thailand (Oligochaeta, Megascolecidae).

Earthworm specimens collected from Sakon Nakhon and Nakhon Phanom, northeast Thailand, were found to contain four new species in the family Megascolecidae, with one species in the genus Metaphire Sims & Easton, 1972, and the other three in the genus Amynthas Kinberg, 1867. These are herein named Metaphiresongkhramensis Chanabun & Panha, sp. nov. in the sexthecal houlleti species group, and Amynthassakonnakhonensis Chanabun & Panha, sp. nov., A.auriculus Chanabun & Panha, sp. nov., and A.bantanensis Chanabun & Panha, sp. nov. in the sexthecal aelianus species group. Metaphiresongkhramensis Chanabun & Panha, sp. nov. occurs in dark clay soil of the oxbow lake of the river, Amynthassakonnakhonensis Chanabun & Panha, sp. nov. occurs in wetland area, A.auriculus Chanabun & Panha, sp. nov. occurs in dark sandy loam habitats of mixed deciduous forest while the following species, A.bantanensis Chanabun & Panha, sp. nov. occurs in sandy loam habitats of paddy fields. Descriptions of the new species, including illustrations of the external and internal morphological characteristics, are provided.

The Bryophyte Flora of Vienna.

The bryophyte flora of Vienna is documented only in parts. Old finds often appeared in publications about Lower Austria; only one study addressed the bryophytes of the inner city. Here, we present a bryophyte flora of Vienna, including historical reports and the results of recent investigations. From 1998 to 2023, we recorded 329 bryophyte taxa in Viennese urban territory. Fifty-six of these were liverworts, and 273 were mosses. Sixty-seven taxa are new for Vienna. Forty-nine taxa, given in historical studies, could no longer be found. If we also count these, 378 taxa occurred in Vienna to date. Of the current occurring bryophytes, 67 species have an endangerment classification. Rich in bryophytes were the dry grasslands of the Lobau, the oxbow lakes of the Lobau and the Prater, and large parts of the Wienerwald. But flat roofs and inner-city areas also showed more than 100 species. Compared to other European cities, Vienna is decidedly species-rich and highly responsible for some species in Austria. Reasons for this are the extensive green spaces and the pronounced climatic gradient from the sub-oceanic west to the sub-continental east of Vienna. Awareness raising for bryophytes we recommend in addition to the existing biotope protection.

WATER AND VEGETATION COVER CHANGE DETECTION USING MULTISPECTRAL SATELLITE IMAGERY: A CASE STUDY ON JHENAIDAH DISTRICT OF BANGLADESH

Water and vegetation are the two most important land cover features of any natural setting. The Jhenaidah District of Bangladesh is known for its remarkable physical geography, featuring diversified vegetation cover and numerous oxbow lakes. Due to several anthropogenic causes, this majestic land cover is degrading rapidly. This study examines the study area's spatiotemporal water and vegetation cover change from 1990 to 2020. Freeware Satellite imageries from the USGS data archive were used as the main secondary data source, ensuring consistency by collecting dry season images. In addition, open discussions with the residents provided valuable insights into the situation. Remote sensing (RS) based Soil Adjusted Vegetation Index (SAVI) was used to detect the water and vegetation cover from the preprocessed satellite imageries. Furthermore, the water and vegetation cover were classified based on a scheme developed by field observation and discussion with the residents. The analysis reveals an overall 84.47% decline in dense vegetation, 63.01% decline in deep water cover, 185.69% increase in shallow water cover, and 16.08% increase in agricultural lands within the mentioned time frame. Almost all the upazila of Jhenauidah district experience the criticality of the land cover change. Among the upazila, Shailkupa faced an unprecedented decline in deep water (95.29%), and Kaliganj faced a heavy decrease in forested vegetation (92.40%). In contrast, shallow water expanded significantly in Sadar Upazila (251.37%), and agricultural land experienced the most increasing trend (32.70%) in Shailakupa Upazila.

Hydrological disturbances enhance stochastic assembly processes and decrease network stability of algae communities in a highland floodplain system

Floodplains are hotspots for biodiversity research and conservation worldwide. Hydrological disturbances can profoundly influence the ecological processes and functions of floodplain systems by altering key biological groups such as algae communities. However, the impacts of flood disturbance on the assembly processes and co-occurrence patterns of algae communities in floodplain ecosystems are still unclear. To ascertain the response patterns of algae communities to flood disturbance, we characterized planktonic and benthic algae communities in 144 water and sediment samples collected from the Tibetan floodplain during non-flood and flood periods based on 23S ribosomal RNA gene sequencing. Results showed that planktonic algae exhibited higher diversity and greater compositional variations compared with benthic communities after flood disturbance. Flooding promoted algae community homogenization at horizontal (rivers vs. oxbow lakes) and vertical levels (water vs. sediment). Stochastic processes governed the assembly of distinct algae communities, and their ecological impacts were enhanced in response to flooding. In the non-flood period, dispersal limitation (81.78 %) was the primary ecological process driving algae community assembly. In the flood period, the relative contribution of ecological drift (72.91 %) to algae community assembly markedly increased, with dispersal limitation (22.61 %) being less important. Flooding reduced the interactions among algae taxa, resulting in lower network complexity and stability. Compared with the planktonic algae subnetworks, the benthic subnetworks showed greater stability in the face of flooding. Findings of this study broaden our understanding of how algae communities respond to hydrological disturbances from an ecological perspective and could be useful for the management of highland floodplain ecosystems.

Linear water column stratification and euphotic depth determine the number of phytoplankton taxa that create biomass peaks in a hypertrophic oxbow lake

The mixing regime, the spatial distribution of nutrients and light determine the distribution of phytoplankton in lakes to a large extent. Linear stratification is a unique phenomenon among the various forms the lakes can stratify, representing a continuous and gradual water temperature decrease with depth. Here, we aimed to understand how mixing, nutrient and light affect the vertical distribution of phytoplankton in the case of linear water column stratification using the taxonomic and functional group approaches. We sampled phytoplankton and physical and chemical variables in the Malom-Tisza oxbow lake (Hungary) monthly from May to September between 2007 and 2009. Our results revealed that multiple biomass peaks of taxa belonging to distinct phytoplankton functional groups could develop in response to the strong linear stratification of the water column. Although several different species represented the functional groups, only one or two species developed the peaks. Light irradiance did not influence the vertical distribution of biomass and taxonomic richness of phytoplankton, but the depth of the euphotic zone determined the number of distinct biomass peaks. We found that diversity indices could not reflect the phytoplankton compositional differences well in the case of linear stratification, but similarity indices calculated among water column layers.

Resolution effects on ox-bow lake mapping and inundation consistency analysis in moribund deltaic flood plain of India.

Research on investigating spatial resolution effect on image-based wetland mapping was done, and reported finer resolution is more appropriate. But is Sentinel image more effective than Landsat image for delineating ox-bow lake, a cut-off channel of a river, and for mapping inundation frequency? Inundation frequency means regularly, water appears in a pixel. In order to obtain these answers, the present study used frequently used spectral indices like normalized difference water index (NDWI), modified NDWI (MNDWI), re-modified NDWI (RmNDWI) and ensemble vegetation inclusive aggregated water index (ViAWI). For obtaining inundation consistency character, the water presence frequency (WPF) approach was adopted. A set of accuracy matrices was applied for validating the resolution effect. Results revealed that among the used indices, MNDWI was found suitable for ox-bow lake mapping. But this index is not able to map vegetated part of the ox-bow lakes. This problem was resolved using ensemble ViAWI. Inundation frequency analysis exhibited that about 70% of the area is consistent with water presence and therefore is hydro-ecologically and economically viable, and no such major differences were recorded between Sentinel and Landsat images. The study further revealed that finer resolution Sentinel images are more effective in ox-bow lake mapping and characterising inundation frequency, but they were not significantly better. Accuracy difference between them was found at the very minimum. Therefore, the study recommended that in a Sentinel image sparse condition, Landsat images could alternatively be used without much accuracy departure, particularly on those water bodies where water appearance is not highly erratic.

Habitat characteristics and biodiversity of nekton in the Alas-Singkil River Basin, Northern Sumatra, Indonesia

Abstract. Muhtadi A, Leidonald R, Fauzia AD. 2023. Habitat characteristics and biodiversity of nekton in the Alas-Singkil River Basin, Northern Sumatra, Indonesia. Biodiversitas 24: 3673-3689. The Alas-Singkil watershed ecosystem is an essential habitat for the diversity of flora and fauna in the North Sumatra region. This study aims to describe the habitat characteristics and distribution of ichthyofauna in the Alas-Singkil watershed. Observations and data collection were carried out in 2021-2022 in all river segments in the Alas-Singkil watershed, including the downstream, swamp, oxbow lake, middle, upstream, and tributaries. Habitat characteristics in the Alas-Singkil watershed are very diverse. Some swamps in the main river's lower to middle reaches allow the ichthyofauna to migrate laterally. In the middle of the main tributaries (sub-watersheds) to the upstream (most) have habitat characteristics dominated by sedimentary rock substrates with relatively moderate-strong currents. The upper reaches of the main river are dominated by rocky substrates with clear, low-medium flowing waters. During observations in the Alas-Singkil watershed, 99 species of fish from 39 families, 9 species of shrimp, 1 species of freshwater crab, 1 species of freshwater turtle, and 1 species of crocodile were collected. Spotted barb (Barbodes binotatus), Blue panchax (Aplocheilus panchax), and Mahseer fish are fishes often found and widely distributed in the Alas-Singkil watershed. The nekton found in the Alas-Singkil watershed is included in the Least Concern (LC) category at 71% and Data Deficient (DD) at 14%. However, there are 2 species (2%) in the Endangered (EN) category and 6 species (5%) in the Vulnerable (VU) category; Ompok brevirictus and Clarias microspilus are species categorized as Endangered Species.

Monitoring hydroecology and climatic variability since ~4.6 ka from palynological, sedimentological and environmental perspectives in an Ox-bow lake, Central Ganga Plain, India

The Ganga-Sai River Interfluve contains several ox-bow lakes in the fertile Central Ganga plains (CGP). A ~2.20-meter deep sedimentary profile obtained near the Chandra Shekhar Azad bird sanctuary (Nawabganj lake-NL) of the CGP was studied to understand the evolution of the ecosystem and climate using pollen/spores, diatoms, testate amoebae, environmental magnetic data,and carbon and nitrogen isotopes. This sedimentary profile is chronologically well-constrained by five radiocarbon (14C) dates. Between 4.6 and 4.4 ka, the sandy sediment and pollen evidence for riparian forest, the absence of aquatic pollen and sponge spicules suggest scant water in the vicinity through the river channel. A semi-closed fluvial ecosystem between 4.4 and 4.2 ka is indicated by testate amoebae, sponge spicules and arboreal pollen. At least two intermittent warm conditions prevailed between 4.6 and 4.2 ka. Between 4.2 and 2.8 ka, high aquatic pollen, diatoms and testate amoebae indicate a lake ecosystem. By ~2.8–0.9 ka the gammoscleres from sponges formed during dry seasons indicate recharging during monsoon as the river shifted. Thereafter, agricultural pollen ( Brassica and Apiaceae) indicates a further shift in the lake boundary exposing land. The highly sandy texture, fluctuating δ13C, δ15N and magnetic mineral values indicate an unstable fluvio-lacustrine deposition inducing hydroecological changes influenced by intermittent about 5–6 humid and dry climatic conditions since ~4.6 ka to present. The calcrete layer in the bottom sediments shows high aridity in CGP between ~5 and 4.6 ka reaching the climax cold-dry event of ~4.2 ka recorded worldwide. The spectral analysis of palynological data from NL and the contemporary Barela Lake, reveals de Vries and Gleissberg cycles of low and high solar irradiance at centennial to multi-centennial scale during the Holocene. The impact on vegetation, sediment depositional dynamics, and shift in river channel was more rapid showing the dominance of ~200 years. periodicity post ~5 ka as compared to ~300 years of dominance prior to this. This centennial timescale is of great speculation for future climate predictions in CGP coupled with the anthropogenic forcings.

Wind of change: selective summer fish kill in an oxbow lake associated with windy weather

Wind of change: selective summer fish kill in an oxbow lake associated with windy weather

Quantification of groundwater-borne greenhouse gases (CH4, CO2, N2O) fluxes to an oxbow lake in a subtropical alluvial-lacustrine plain

Aquatic ecosystems are an important source of greenhouse gases (GHGs) released to the atmosphere. However, studies on GHGs fluxes from lacustrine groundwater discharge (LGD) remain limited, particularly for subtropical alluvial-lacustrine plains. This study used the radon (222Rn) mass balance model to quantify seasonal variations in LGD rates and fluxes of groundwater-borne GHGs (CH4, CO2, N2O) to the Tian-E-Zhou oxbow lake in Jianghan Plain, central Yangtze. The results showed that the LGD rate in winter was 57.67 ± 28.37 mm/d which was higher than that in summer (24.72 ± 12.16 mm/d). The groundwater-borne fluxes of CH4, CO2, and N2O into the lake in winter were 7.84 ± 6.81 mmol m−2 d−1, 1.47 ± 1.07 mmol m−2 d−1, and 3.50 ± 1.90 × 10−5 mmol m−2 d−1, respectively, whereas that in summer were 1.48 ± 2.36 mmol m−2 d−1, 0.72 ± 0.47 mmol m−2 d−1, and 1.53 ± 1.00 × 10−5 mmol m−2 d−1, respectively. High groundwater-borne fluxes of CH4 across both winter and summer could be attributed to abundant buried organic carbon and strong groundwater reducing environment in this subtropical alluvial-lacustrine plain. Seasonally, fluctuations in water levels mainly affected LGD rates, further resulting in greater groundwater-borne GHGs fluxes in winter than in summer. This study can act as an important reference for future studies on the role of groundwater as an emission pathway for GHGs in lakes of subtropical alluvial-lacustrine plains.

Which factors influence spatio–temporal changes in the distribution of invasive and native species of genus Carassius?

Within the genus Carassius Jarocki, 1822 , the crucian carp (C. carassius L., 1758) occurs naturally in the northern part of Middle Danube Basin (Austria, Morava, Slovakia). This species has the least concern status in this region, but observations in the last decades suggest that it is very close to extinction here. The distribution of crucian carp is limited to a small number of vanishing lentic habitats (oxbow lakes, marshlands). These biotopes are in the last stage of succession due to the drying up of the landscape and a reduction in the creation of new natural alluvial habitats. The non-native cyprinid, C. gibelio (Bloch, 1782), known as gibel carp and Prussian carp, has gradually become eudominant in a wide spectrum of habitats/biotopes since the 1960s Several biological adaptations of non-native species are generally considered the strong basis for the mass spreading in the invaded area. The other side of the expansion of non-native C. gibelio is affected by anthropic activities associated with fish farming, translocation and stocking the fish in open water ecosystems. In this study, we analysed historical scientific data on the distribution of Carassius spp. published from the 19th century to the present from the mentioned areas. The results suggest that the number of records of invasive C. gibelio has gradually increase in rivers, regulated channels and creeks, which could be considered as natural pathways of spreading. However, the presence of invasive C. gibelio in artificial biotopes (fishponds, reservoirs) is continuous from the 1960s. In the area mentioned, the artificial biotopes are managed by national fisheries associations and relate to the historical way of farming in Central and Eastern European countries. To show the current state of the fishing grounds of the Slovak Angling Association, we a created the distribution map based on the Carassius spp. catches recorded in last two decades.

The introduced Arapaima gigas in the Bolivian Amazon: Trophic position and isotopic niche overlap with native species

AbstractNon‐native fish species may generate major ecological impacts on native assemblages. This study aims to assess the potential impact of the introduced Arapaima gigas on native fish assemblages in two oxbow lakes of the Bolivian Amazon. Stable isotope data were used to determine trophic position (TP) and isotopic niche overlap, to evaluate potential predation and competition interactions, respectively. Results suggest that A. gigas is more an omnivore than a top predator, as often claimed. Arapaima gigas occupied an intermediate TP between detritivore/herbivore and piscivore fish species and showed broader isotopic niche compared to most native species analysed. The isotopic niche of A. gigas significantly overlapped with most native fish species in one lake (i.e. Lake Mentiroso), while there was low niche overlap in the second (i.e. Lake Miraflores). Given its omnivorous tendencies, the predation impact of A. gigas on other fish species is likely less than currently claimed and likely varies with the food web structure of the ecosystem. More precise data on resource availability and use are necessary to infer whether niche overlap will have negative impacts on native fish species through potential competitive interactions. Increasing our understanding on the processes generating impact of these introductions on resident communities through food web ecology will pave the way for better resource management and conservation efforts.

Non-native fish species expand tacitly but rapidly toward upstream oxbow lakes along the longitudinal gradient

The introduction of non-native fish species poses a threat to native assemblages in floodplain systems. Establishing oxbow lake-based conservation areas has been proposed as a practical approach to mitigate this threat. Previous studies have extensively discussed the effects of lateral connectivity between oxbow lakes and main channels on fish communities but overlooked the spatial longitudinal gradients of oxbow lakes on a broader spatial scale. Over the course of about ten years, the temporal changes in fish community diversity were estimated in 28 oxbow lakes along the Ishikari River in Hokkaido, Japan. The associations between these temporal variations and the locations of the lakes were then explored along a longitudinal spatial gradient. The results showed that upstream oxbow lakes underwent mild alterations to their species composition and maintained a high level of native uniqueness. In contrast, downstream oxbow lakes experienced intense species turnover and increased non-native fish diversity. Additionally, the dominance of non-native fish in downstream areas rapidly expanded upstream to a location 110 km from the source of the Ishikari River over the decade. It is emphasized that the lakes in the upper reaches were the only remaining refuges for native fish and should be prioritized in conservation efforts. Our study proposes the application of location and species contributions to regional community heterogeneity as indicators for highlighting native fish conservation areas.

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

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

Possible mediation of Cladocera species by a researcher's chest wader

Mediation of aquatic species has become an increasing problem for the last few decades. With the increasing commercial import, species’ direct or indirect spread can gain more space. There are several ways for them to land in their new home and spread through the country. Most of the aquatic species are spread by waterways, boats, vehicles, or even with the help of humans. Cladocerans have a good dispersal ability, thanks to their small size, additionally they possess good adaptation, and mechanisms to develop resting eggs. Benthic or littoral species can be mediated much more easily due to their living space, and with the help of human activities (e.g., scientists, anglers and people working in water bodies) they have a higher chance to colonize new habitats. Our goal was to explore if Cladocera species might be mediated by a scientist chest wader, while sampling in similar-sized, close-to-each other lakes, with different utilization. Most of the species were found in abandoned fishing lakes, followed by oxbow lakes (protected), and ultimately in intensively fished lakes. NMDS showed that samples from lakes with the same utilization are similar to each other. Differently utilized lakes can have various Cladocera species, even though they are closely related to each other. Based on the results, scientists can mediate species on their chest wader from lake to lake and may deteriorate the results. We recommend a necessary chest wader cleaning after every sampling process, especially when samples are taken from differently utilized lakes.

First record of Tinodes maculicornis (Pictet, 1834) (Trichoptera: Psychomyiidae) from the Pannonian region in Slovakia

During our study of the caddisfly fauna of the Danube, its branches and oxbow lakes, including the urban and suburban areas of Bratislava (the capital of Slovakia), we made an unexpected record of the species Tinodes maculicornis (Pictet, 1834), which is the first documented occurrence of this species in the Pannonian ecoregion (Hungarian lowlands) and also the easternmost record so far.

Local intensity of artisanal gold mining drives mercury accumulation in neotropical oxbow lake fishes

Driven by surges in global gold prices and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing and driving emissions of significant quantities of mercury (Hg) into the air and freshwater. Hg can be toxic to animal and human populations and exacerbate the degradation of neotropical freshwater ecosystems. We examined drivers of Hg accumulation in fish that inhabit oxbow lakes of Peru's Madre de Dios, a region with high biodiversity value and increasing human populations that depend on ASGM. We hypothesized that fish Hg levels would be driven by local ASGM activities, by environmental Hg exposure, by water quality, and by fish trophic level. We sampled fish in 20 oxbow lakes spanning protected areas and areas subject to ASGM during the dry season. Consistent with previous findings, Hg levels were positively associated with ASGM activities, and were higher in larger, carnivorous fish and where water had lower dissolved oxygen levels. In addition, we found a negative relationship between fish mercury levels associated with ASGM and the occurrence of the piscivorous giant otter. The link between fine-scale quantification of spatial ASGM activity and Hg accumulation, as indicated by the result that in the lotic environment, localized effects of gold mining activities are stronger drivers (77 % model support) of Hg accumulation than environmental exposure (23 %) constitutes a novel contribution to a growing body of literature on Hg contamination. Our findings provide additional evidence of high Hg exposure risks to neotropical human and top carnivore populations subject to the impacts of ASGM, which depend on freshwater ecosystems undergoing gradual degradation. The documented spatial variation in Hg accumulation and increased Hg levels in carnivorous fish should serve as a warning to human communities in Madre de Dios to avoid the proximity of high-intensity gold mining areas and minimize local carnivorous fish consumption.