Oxbow Lakes Research Articles

The Environmental Impact of Shoreline Changes and Land Use/Land Cover Change Detection in the Niger Delta Region using Geospatial Technology

Managing resources in marine areas necessitates a thorough understanding of coastal processes. This study examines the changes to the shoreline between 1990 and 2021 and assesses how those changes have impacted land use and land cover (LULC). In Yenagoa, Bayelsa State, Nigeria, over a period of 31 years, shoreline changes in the Ikoli River, River Nun, and Oxbow Lake revealed notable oscillations caused by erosion. In particular, band ratios are used to classify LULC maps for each district across the relevant years. The shoreline along the River Nun ranges from 31% to 35%, with 2013 being the highest; along the Ikoli River, it is 33% to 35%, with 2021 being the highest; and along Oxbow Lake, it is 21% to 35%, with 2021 being the highest, according to accurate evaluations of the United States Geological Survey datasets using ArcGIS software. Due to sand mining, boat traffic, heavy rain, fish farming, and oil and gas operations in the area, LULC predicts a sharp decline in vegetation and bare land from 1990 to 2021 and an increase in built-up areas and waterbodies. The socioeconomic risk from environmental stressors and climate change is identified by LULC. Geospatial is useful in coastal defenses and sustainable landuse strategies.

Implications of COVID-19 on oxbow lake (Baors) Fisher's community, Bangladesh: resilience to food security against probable natural calamities

The purpose of studying the consequence of COVID-19 on oxbow lake (Baor) fisher's community is to counteract the negative impacts on livelihoods with food security and figure out diversified resilience options for sustaining basic needs of life. Individual questionnaire interviews, oral history, focus group discussion, and telephonic interviews were among the methodological techniques used to gather primary data. The Baor fisher's community was impaired with income, food and feeding habit, health and marketing. The Baor fishers had to stop harvesting or reducing the amount of fish harvest because of gradual decreasing of consumer demand and prices of fish during the course of COVID-19 pandemic period. The transportation costs were raised up to 50%–80%, while the prices of fish decreased by 15%–30% prior to the onset of COVID-19 pandemic. The frequency of fish consumption was significantly come down to 37.5%. Many households substituted fish to farm reared hens, eggs, domestic hens and ducks, lentils, and vegetables during the period of lockdown across the country. Supply chains of fish and fish culture inputswere disrupted due to inadequacy of transportation facilities. Many school- and college-going students were dropped outduring the ongoing pandemic situation due to their financial problems (10%) and early marriage (7.5%). The secondary sources of income (labor of netting in other aquaculture farms) of Baor fisher's community were also impaired. The resilience options of this study will be helpful to minimize the sudden economic crises, ensure dynamic fish value chains and food security, protect individuals from ongoing health hazards, and promote sustainable food production systems followed by social cohesion and stabilityagainst the prevailing challenges owing to the pandemic and other natural calamities.

Application of Parameterized Grain-Size Endmember Modeling in the Study of Quaternary Oxbow Lake Sedimentation: A Case Study of Tövises Bed Sediments in the Eastern Great Hungarian Plain

Abandoned channels are essential in the Quaternary floodplains, and their infill contains different paleoenvironment recorders. Grain-size distribution (GSD) is one proxy that helps characterize the alluviation and associated sedimentological processes of the abandoned channels. The classic statistical methods of the grain-size analysis provide insufficient information on the whole distribution; this necessitates a more comprehensive approach. Grain-size endmember modeling (EMM) is one approach beyond the traditional procedures that helps unmix the GSDs. This study describes the changes in the depositional process by unmixing the GSDs of a Holocene abandoned channel through parameterized EMM integrated with lithofacies, age–depth model, loss-on-ignition (LOI), and magnetic susceptibility (MS). This approach effectively enabled the quantification and characterization of up to four endmembers (EM1-4); the characteristics of grain-size endmembers imply changes in sedimentary environments since 8000 BP. EM1 is mainly clay and very fine silt, representing the fine component of the distribution corresponding to the background of quiet water sedimentation of the lacustrine phase. EM2 and EM3 are the intermediate components representing the distal overbank deposits of the flood. EM4 is dominated by coarse silt and very fine sand, representing deposition of overbank flow during the flood periods. This paper demonstrates that the parametrized grain-size EMM is reasonable in characterizing abandoned channel infill sedimentary depositional and sedimentation history.

Waterbodies in the Floodplain of the Drava River Host Species-Rich Macrophyte Communities despite Elodea Invasions

The contribution discusses macrophyte communities in natural and man-made waterbodies located on the active floodplain along the Drava river (Slovenia). We presumed that these different types of wetlands host a great number of macrophyte species, but this diversity may be affected by the presence of alien invasive species Elodea canadensis and E. nuttallii. Presence, relative abundance, and growth forms of plant species along with selected environmental parameters were monitored. Correlation analyses and direct gradient analyses were performed to reveal the possible relations between the structure of macrophyte community and environmental parameters. Number of macrophytes in surveyed water bodies varied from 1 to 23. Besides numerous native species we also recorded Elodea canadensis and E. nuttallii, which were present in 19 out of 32 sample sites, with E. nuttallii prevailing. The less invasive E. canadensis was absent from ponds and oxbow lakes but relatively abundant in side-channels, while E. nuttallii was present in all types but dominant in ponds. The most abundant native species were Myriophyllum spicatum and M. verticillatum, Ceratophyllum demersum and Potamogeton natans. Correlation analyses showed no negative effect of the invasive alien Elodea species to the species richness and diversity of native flora. Positive correlation between the abundance of E. nuttallii and temperature of the water was obtained.

Avian species abundance and habitat association in Makurdi metropolis, Benue State, Nigeria

Appraisal of avian species, especially in urban areas, is paramount to determining the health of the environment. The research focused on the abundance, diversity, and habitat association of avian species within and around the new bridge in Makurdi metropolis, Benue State, Nigeria. The habitats selected were: Abattoir (Ab), Oxbow Lake (Ol), and Farmland (Fl). A line transect length of 100 m was laid (1 at Ab, 2 each at Ol and Fl). The line transect method was used to identify and estimate the abundance and diversity of birds (at 06:00–09:00 hrs and 15:00–18:00 hrs) aided with binoculars for 2 consecutive days weekly in June–November 2021. The Textbook on Birds of West Africa was used for the identification of the species. The dataset was analyzed using descriptive statistics and diversity indices. The result revealed a total number of 23 species (4061 individuals) belonging to 15 families. Five species (41 individuals), 19 species (2,804 individuals), and 8 species (1,216 individuals) were recorded at Abattoir, Oxbowlake, and Farmland, respectively. Ploceus cucullatus (55.68%) was the most abundant species, while Accipitridae (12.5%) was the dominant family recorded. Variation in density varies across the habitat, with farmland (723.13) being the densest area. The diversity indices indicated that farmland (D: 0.668, H1: 1.571, and richness (2.267)) had a high value when compared to other habitats. Conservation and management of urban avian species should be encouraged to promote avi-tourism.

Metabarcoding as an effective complement of microscopic studies in revealing the composition of the diatom community – a case study of an oxbow lake of Tisza River (Hungary) with the description of a new Mayamaea species

Diatoms are valuable bioindicators and their traditional classification and identification are mainly based on the morphological characteristics of their frustules. However, in recent years, DNA-based methods have been proposed and are rapidly growing in the scientific literature as a complementary tool to assess the ecological status of freshwaters. Diatom-based ecological status assessment uses indices calculated from sensitivity and tolerance values as well as relative abundance of species. Correct assessment requires an accurate identification of species. In the present study, diatom assemblages of an oxbow lake were investigated using light and scanning electron microscopy as well as metabarcoding using rbcL marker, and the identification results were compared, intending to match barcode sequences of species that are currently missing in the diatom reference database. The investigated oxbow is an important wetland for bird conservation, although it is impacted by land use. Taxon lists based on morphology and metabarcoding considerably differed when bioinformatics analysis involved DADA2 pipeline with Diat.barcode database. Previously unknown sequence variants of four pennate species were found with additional BLAST search. Using phylogeny and p-distance calculations sequences could be matched to three small-celled naviculoid species that were found under a microscope. One of them was found to be a new species of the genus Mayamaea and was described as a new species, Mayamaea ectorii. Additionally, spatial distribution maps for several small-celled naviculoid species are provided for the Hungarian territory.

A tájkép érzékelésének környezetpszichológiai elméletei és egy tiszazugi felmérés tapasztalatai

Several scientific theories have been developed to explain landscape perception by the human. We summarize the evolutionary, that is prospect-refuge, habitat and information processing theories, dealing with social-psychological aspects of the question and also with the ecological aesthetics idea. In 2021 a landscape character survey was carried out among the citizens of the Tiszazug microregion of Hungary. According to the answers of 104 respondants, the character of the landscape in the microregion would change most dramatically by the disappearance of oxbow lakes, floodplain forests and vineyards. They recognize that the decreasing number of the population and aging of the citizens results in decreasing intensity of landuse, the growing extent of areas that are out of crops and an increasing number of abandoned buildings on the level of landscape scenery.

A Detailed Liquefaction Susceptibility Map of Nestos River Delta, Thrace, Greece Based on Surficial Geology and Geomorphology

The existence of high potential onshore and offshore active faults capable to trigger large earthquakes in the broader area of Thrace, Greece in correlation with the critical infrastructures constructed on the recent and Holocene sediments of Nestos river delta plain, was the motivation for this research. The goal of this study is twofold; compilation of a new geomorphological map of the study area and the assessment of the liquefaction susceptibility of the surficial geological units. Liquefaction susceptibility at regional scale is assessed by taking into account information dealing with the depositional environment and age of the surficial geological units. In our case, available geological mapping shows a deficient depiction of Pleistocene and Holocene deposits. Taking into consideration the heterogeneously behavior of active floodplains and deltas in terms of liquefaction, a detailed classification of geological units was mandatory. Using data provided by satellite and aerial imagery, and topographic maps, dated before the 1970’s when extensive modifications and land reclamation occurred in the area, we were able to trace fluvial and coastal geomorphological features like abandoned stream/meanders, estuaries, dunes, lagoons and ox-bow lakes. This geomorphological-oriented approach clearly classified the geological units according to their depositional environment and resulted in a more reliable liquefaction susceptibility map of 4 classes of susceptibility; Low, Moderate, High and Very High. The sediments classified as very high liquefaction susceptibility are related to fluvial landforms, the high to moderate liquefaction susceptibility ones in coastal and floodplain landforms, and low susceptibility in zones of marshes. The sediments classified in the highest group of liquefaction susceptibility cover 85.56 km2 of the study area (16.6%). Particular attention was drawn to critical infrastructure (Kavala International Airport “Alexander the Great”) constructed on the most prone to liquefaction areas.

Fish biodiversity and livelihood of fishermen at an Oxbow lake of South-West Bangladesh

The present study was conducted to know the biodiversity status and assess the existing livelihood conditions of the fishers of Habullah Baor at Bagherpara upazila, Jashore district from November 2017 to April 2018. Sixty fishermen were randomly selected for collecting data through a semi structured questionnaire. The current study discovered that there were 11 different fish species from six orders and seven families in the Habullah baor. All of the sampled fishermen were Hindu. About 25% of the fishermen was young aged, majority was middle aged and 25% was old aged group. A total of 75% of the fishermen had nuclear family and 25% families lived in joint family. Among the fishermen 85% had a few decimal of cultivable land and 15% were truly landless. Annual income of the respondents varied from 30,000 to 70,000 BDT with an average of 42,833 BDT. All fishers had access to drinking water from tube wells. Most of the fishers lived in katcha houses. About 15% of the fishers enjoyed electricity facilities in their home. Among the fishermen investigated, majority had earthen latrine, 20% used tin shed latrine, 8% used concrete latrine and a few of them 10% had no latrine. There were no modern medical facilities in the villages. The respondents had no alternate income sources during the dry season and at the time of ban period. The fishers as a whole are leading measurable life due to great financial hardship. Proper conservation and management measures can be taken to enhance the availability of fish fauna in Habullah baor, so that, the fishermen can harvest ample fish on sustainable basis. Asian J. Med. Biol. Res. 2022, 8 (3), 165-180

Macrophyte habitat architecture and benthic-pelagic coupling: Photic habitat demand to build up large P storage capacity and bio-surface by underwater vegetation

Macrophytes play an important role in shallow lakes if large standing crop can be achieved. Here we stress the role of submerged macrophytes for benthic-pelagic coupling in the shallow oxbow lake Alte Donau (Austria) during restoration triggered by sufficient light availability (12% surface ambient light, photic>12% depth, zoptimum) in both, the benthic and the pelagic habitat. Focusing on zoptimum, rather than on minimum light requirement (euphotic depth), seemed to be more meaningful to follow the macrophyte development. After phosphate precipitation treatment, the photic>12% pelagic habitat accounted for more than half of the total water volume in summer, while the achievement of the same photic>12% conditions for half of the total sediment surface area was delayed by 8 years. A delay of light exposure on the lake bottom area compared to the lake water volume is given by the basin morphometry, but the time span that is required for passing this delay depends on the efficiency of restoration measures. The 8-year delay for Alte Donau means that lake restoration focusing on macrophyte re-establishment was difficult to stimulate due to insufficient light exposure at the lake bottom. A further increase of photic>12% conditions to more than 3/4 size of both pelagic and benthic habitat, however, eventually stimulated sustained macrophyte growth. With the onset of this large macrophyte biomass yield, the phosphorus storage pool of submerged macrophytes exceeded the annual peak concentration of total phosphorus of the whole lake water by about one order of magnitude for the first time. Further, the submerged macrophyte bio-surface exceeded the size of lake bottom surface, also by about one order of magnitude. Our results support that macrophytes can act as a significant sink of phosphorus by retaining this nutrient at least during the growing season. We further see the immensely large macrophyte bio-surface as a vast spatial dimension for an additional habitat for freshwater biota. Therefore, we conclude that mature submerged macrophyte formations need to be considered not only as biomass yield, but create a unique macrophyte habitat architecture as a third main component in the network between benthic (lake bottom) and pelagic (lake water) habitat.

Predictive geospatial model for arsenic accumulation in Holocene aquifers based on interactions of oxbow-lake biogeochemistry and alluvial geomorphology

The identification of arsenic-contamination hotspots in alluvial aquifers is a global-scale challenge. The collection and inventory of arsenic concentration datasets in the shallow-aquifer domain of affected alluvial basins is a tedious and slow process, given the magnitude of the problem. Recent research demonstrates that oxbow-lake biogeochemistry in alluvial plains, mobilization of geogenic arsenic, and accumulation in geomorphologically well-defined areas are interacting processes that determine arsenic-contamination locations. This awareness provides a tool to identify potential arsenic-hotspots based on geomorphological similarity, and thus contribute to a more robust and targeted arsenic mitigation approach. In the present study, a conceptual predictive geospatial model is proposed for the accumulation of dissolved arsenic as a function of interaction of oxbow-lake biogeochemistry and alluvial geomorphology. A comprehensive sampling campaign in and around two oxbow lakes in the Jamuna River Basin, West Bengal (India) provided water samples of the oxbow-lake water column for analysis of dissolved organic matter (DOM) and microbial communities, and groundwater samples from tube wells in point bars and fluvial levees bordering the oxbow lakes for analysis of the geospatial distribution of arsenic in the aquifer. Results show that abundant natural and anthropogenic (faecal-derived) recalcitrant organic matter like coprostanols and sterols in clay-plug sediment favours microbial (heterotrophs, enteric pathogens) metabolism and arsenic mobilization. Arsenic concentrations in the study area are highest (averaging 505 μg/L) in point-bar aquifers geomorphologically enclosed by partially sediment-filled oxbow lakes, and much lower (averaging 121 μg/L) in wells of levee sands beyond the oxbow-lake confinement. The differences reflect variations in groundwater recharge efficiency as result of the porosity and permeability anisotropy in the alluvial geomorphological elements, where arsenic-rich groundwater is trapped in point-bars enclosed by oxbow-lake clays and, by contrast, levee ridges are not confined on all sides, resulting in a more efficient aquifer flushing and decrease of arsenic concentrations.

Plant taphonomy and palaeoecology of Pennsylvanian wetlands from the Erillcastell Basin of the eastern Pyrenees, Catalonia, Spain

The Pennsylvanian flora from the intramontane Erillcastell Basin in the eastern Pyrenees (Catalonia, Spain) is described in a palaeoenvironmental context based on a combined study of sedimentology, plant taphonomy and paleoecology. This basin differs from other Pyrenean basins of this age in comprising a wide array of fluvial channel and floodplain-related facies, with a limited development of peat mire facies. Both late Moscovian and early Ghzelian successions are rich in diverse calamitalean remains (mainly Calamites cistii and C. suckowii, in addition to C. undulatus in the Moscovian) and pecopterid foliage (mainly Polymorphopteris polymorpha) corresponding to marattialean tree ferns. An unusual feature of the fluvial channel assemblages is the common occurrence of arborescent lycopsids, especially Sigillaria brardii, in association with Calamites species, which presumably occupied riparian niches. Palaeotopographic, drainage and climatic constraints of the Erillcastell Basin may explain this unusual ecological distribution of Sigillaria brardii, which is mostly associated with peat mires and oxbow lakes in other coeval intramontane South European basins. Findings improve knowledge of intermontane forest ecosystems during the Middle to Late Pennsylvanian transition.

Landscape Archaeology of Southern Mesopotamia: Identifying Features in the Dried Marshes

The landscape of the Mesopotamian floodplain is mainly structured by channel processes, including the formation of levees, meanders, scrollbars, oxbow lakes, crevasse splays, distributary channels, inter-distributary bays, and marshes. Moreover, several human-made features also form and shape this landscape, such as canals, roads, trenches, farms, and settlement sites ranging in size from villages to cities. A significant part of the Mesopotamian floodplain is covered by marshes, especially the southern region. These marshlands have thrived for thousands of years and are well known for their sustainable biodiversity and ecosystem. However, after the deliberate draining of the marshes in the 1990s, the areas have become dry and only small areas of shallow water and narrow strips of vegetation remain. Several kinds of archaeological landscape features have appeared on the surface and can be clearly identified in both ground surveys and with the use of remote sensing tools. This paper aims to determine the type and nature of the preserved archaeological features that appear in the landscape of the dried marshes and whether they are different from other features elsewhere in the Mesopotamian floodplain. An intensive ground survey was carried out in a selected area of the dried marshland, resulting in the identification of six types of archaeological features: settlement sites, rivers, canals, farms, grooves, and roads (hollow ways). These features used to be covered by bodies of deep water and dense zones of vegetation (reeds and papyrus).

Abundance of Odonata in different microhabitats at an oxbow lake in the Peruvian Amazon

ABSTRACT The relationship between Odonata and vegetation in Amazonia has been studied primarily in streams. In this study, I examined the abundance of adult Odonata in two vegetation types (shrubs and herbs) surrounding an oxbow lake in the Peruvian Amazon. Daytime visual samplings of Odonata were carried out in time blocks along transects in each habitat. Thirteen taxa were identified. Five species were similarly abundant in both habitats, three used mainly herbs, and one mainly shrubs, with no variation among time blocks. The results suggest that most Anisoptera and Zygoptera are adapted to unshaded areas of the lake. Some Odonata also were observed during sunless days with light rainfall, suggesting they are adapted to rainy conditions in tropical climate.

Modeling the Role of Compaction in the Three‐Dimensional Evolution of Depositional Environments

AbstractNatural environments such as coastal wetlands, lowland river floodplains, and deltas are formed by sediment, transported by watercourses and the sea, and deposited over century to millennium timescales. These dynamic environments host vulnerable ecosystems with an essential role for biodiversity conservation, coastal protection and human activities. The body of these landforms consists of unconsolidated sediments with high porosity and compressibility. Consequently, they often experience significant compaction due to their own weight, that is, autocompaction, which creates an important feedback within the geomorphological evolution of the landform. However, this process is generally oversimplified in morphological simulators. We present a novel finite element (FE) simulator that quantifies the impact of natural compaction on landform evolution in a three‐dimensional setting. The model couples a groundwater flow and a compaction module that interact in a time‐evolving domain following landform aggradation. The model input consists of sedimentation varying in time, space and sediment type. A Lagrangian approach underlies the model by means of an adaptive mesh. The number of FEs gradually increases to accommodate newly deposited sediments and each FE changes its shape, that is, becomes compressed, following sediment compaction. We showcase the model capabilities by simulating three long‐term depositional processes at different spatial scales: (a) vertical growth of a tidal marsh, (b) infilling of an oxbow lake, and (c) progradation of a delta lobe. Our simulations show that compaction is the primary process governing the elevation and geomorphological evolution of these landforms. This highlights that autocompaction is an important process that determines the resilience of these low‐lying landforms to climate change.

The Effect of Oxbow Lake Restoration on Breeding Birds in an Agricultural Landscape

The Effect of Oxbow Lake Restoration on Breeding Birds in an Agricultural Landscape

Paleochannel of the Yellow River within the Zoige Basin and its environmental significance on the NE Tibetan Plateau

Paleochannel sedimentary sequences can provide abundant information on regional environmental changes. A typical paleochannel (paleo-oxbow lake type) section of the Yellow River was identified within the Zoige Basin on the NE Tibetan Plateau. A multi-index approach was used to accurately identify sediments of different genetic types, such as riverbed deposits of the Yellow River, paleo-oxbow lake deposits, and overbank flood deposits (OFD) in the section. Based on optically stimulated luminescence (OSL) and AMS 14C dates, we examined the environmental evolution recorded by the section. The results show that: (1) The section is a record of environmental change since 4.17 ± 0.49 ka. During 4.17 ± 0.49 to 3.24 ± 0.26 ka, the ancient Yellow River occupied the channel. At 3.24 ± 0.26 ka, the paleochannel experienced a neck cutoff, and the fluvial environment began to change into the oxbow lake environment. After 2.45 ± 0.11 ka, the paleo-oxbow lake gradually disappeared. Subalpine meadow soil has developed at this site since 1.31 ± 0.05 ka. (2) Paleoenvironmental proxies indicate that the Zoige Basin was warmer and wetter before ~3.00 ka, and became drier and colder after ~3.00 ka, which may be mainly related to the weakening of the East Asian summer monsoon (EASM) and the strengthening of the Westerlies. (3) Two episodes of extreme overbank flooding occurred at 2.96 ± 0.24 to 2.87 ± 0.27 ka and 1.84 ± 0.20 to 1.70 ± 0.16 ka, correlated with climate shift period from the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP), respectively. Due to the relatively cold and dry climate in these periods, glaciers generally advanced on the Tibetan Plateau, and the contribution of snow and ice meltwater weakened. Therefore, the strong rainfall caused by the abnormal atmospheric circulation may be the main cause of these extreme overbank flooding.

Facies development of coal seams in the Knurów deposit (Upper Silesia, Poland)

This paper presents the first attempt to develop the facies model of the entire coal deposit belonging to the Carboniferous productive sequence located in the western part of the Upper Silesian Coal Basin. To achieve this objective, six seams from the Knurów deposit were examined. The deposit belongs to the largest producer of coking coal in Europe, which is Jastrzębska Spółka Węglowa SA (Polish state-run coking coal producer). The maceral composition, vitrinite reflectance, ash yield content, moisture content, gross calorific value, and volatile matter yield were determined. Coals from the Knurów deposit are classified as ortho-bituminous and meta-bituminous coals. Their average degree of coalification, determined by vitrinite reflectance, is RO = 0.79% to RO = 1.09%. Petrographic indices and the analysis of facies diagrams were used to develop the facies model. It was shown that the facies development and sedimentological evolution of the Knurów deposit were determined by the river system extended to the upper delta plain. In accordance with the stratigraphic succession, the oldest deposits are dominated by the reed facies (mainly Calamites) growing in oxbow lakes and dry streambeds. With the passage of time, the importance of the river system for the development of the paleo-environment decreased. Transitional bogs with mixed plant communities were formed. This started the conversion of wetlands into areas occupied by wet forest. At the end of the sedimentation of the documented coal seams in the Knurów deposit, lowland bogs (fens), which were subject to frequent fires, dominated the landscape. Based on a detailed maceral analysis and facies diagram analysis, a strong correlation between fault occurrence and coal facies developed under paleo-river influence was displayed. The aim of the study is to show environmental changes during deposit formation in the context of geological exploration.

Integrated remote sensing and field-based approach to assess the temporal evolution and future projection of meanders: A case study on River Manu in North-Eastern India.

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinuosity index has changed from 2.04 (1932) to 1.90 (2017), and the length of the river has decreased by 7 km in 85 years (1932–2017). The decrease in length is evident from lowering the number of meanders. Uniformity coefficient and coefficient of curvature of the bank soil samples were calculated, indicating that the soil is poorly graded and falls under the cohesionless category. Based on cross-section analysis, sediment discharge, grain-size analysis of the bank material, channel planform change, and radius of curvature, it can be stated that almost all the selected bends have the probability of future cutoff. The highest probabilities were observed in bend 3 (Jalai) and bend 4 (Chhontail). This work is aimed to provide planners with decisions regarding the construction of roads and bridges in areas that show the huge dynamicity of river meandering.

Electrofishing distances for sampling fish assemblages in oxbow lakes of the River Rhine

Assessment of fish assemblage structure depends on representative sampling. In contrast to lotic water bodies, recommendations for a general study design are sparse for lentic water bodies. Therefore, we evaluated the fish assemblages in different littoral structure types (e.g. macrophytes and riprap stone) and the impact of these structure types on the minimum distance required to obtain samples representative of fish species number in oxbow lakes. Boat-based electrofishing was used at 88 sections, each 200-m long within five oxbow lakes connected to the Upper River Rhine in southwest Germany. Submerged macrophytes and riprap stones were important littoral structures for determining fish community structure. Littoral structure was related to species accumulation, which illustrates the importance of littoral structure to define the minimum length of sampling. Our findings suggest that at least 200-m stretches should be sampled to describe fish assemblages in oxbow lakes.