Middle Stretch Research Articles

Non-consistent changes and drivers of water-sediment fluxes in the yarlung tsangpo river basin of the Tibetan plateau

Variations in water-sediment fluxes and their driving mechanisms are critical to riverine ecosystems and management. Yet, current estimates of the response of water and sediment flux remain insufficiently quantified, limited by the scarcity of long-term hydrological records in the alpine regions. Here, we leverage decadal observations in the Yarlung Tsangpo River basin, to investigate the dynamic shifts in water-sediment fluxes from 1955 to 2020 and elucidate their linkage to a warming and wetting climate, snowmelt, and environmental greening (including natural- and human-induced greening) in the different spatial and temporal scale. Major drivers of shifts in water-sediment flux are identified by using wavelet coherence and variance partitioning of redundancy analysis. The results highlight that observational data from four gauging stations (i.e., Lhaze, Nugesha, Yangcun, and Nuxia) uncover a substantial decrease in suspended sediment load (SSL) (Nuxia: 12.302 × 104 t/yr, P < 0.05) in the downstream with consistently increasing runoff and precipitation. Especially during the flood season (July to September), the dam/reservoir construction caused a median decrease in SSL. Dropping sediment offsets the slightly rising SSLs in the midstream and upstream (upper Yangcun: 14.8 × 104 t/yr, P > 0.05). Up to 80% of sediment was sourced from the middle stretch between Lhaze and Nugesha despite it supplied with lower regional runoff generation. Nevertheless, the downstream zone experienced the transition from a sediment source to a deposition area around 1998. We further found the negative and positive effects between water-sediment fluxes and revegetation, and demonstrated that employing NDVI to evaluate human-induced vegetation greening might overestimate the impact of ecological restoration programs on water-sediment fluxes. Attribution analysis indicates that precipitation was not the primary contributor to runoff and SSL changes in all stretches of the basin. In the upstream, temperature and associated snowmelt can be more important than precipitation. Compared to before 1998, precipitation is still the primary driver of change in downstream runoff change after 1998, whilst vegetation restoration, rather than precipitation, dominates the reduction in downstream SSL. These findings have far-reaching significance for watershed managers and decision-makers in terms of developing effective strategies for water resources and soil erosion control.

Analysis of Regional Differences in Cadmium Ecological Risk in Surface Waters of the Yangtze River Basin

This study primarily focused on the regional disparities in both water quality criteria and ecological risks attributed to cadmium presence within the surface waters of the Yangtze River Basin. In the initial phase, the long-term water quality criteria for cadmium were recalibrated in accordance with the guidelines outlined in China's "Water Quality Criteria for Freshwater Aquatic Organisms-Cadmium," accounting for the prevalent hardness distribution within the Yangtze River Basin's surface water. Subsequently, a more refined revision was undertaken considering the specific characteristics of the species residing within the Yangtze River Basin. This undertaking led to a comprehensive interpretation of the regional variations in both the distribution of long-term water quality criteria values and the risk quotient distribution of cadmium throughout the Yangtze River Basin. The incorporation of hardness and species-specific attributes resulted in a revised range of long-term water quality criteria for cadmium across different urban locales within the Yangtze River Basin. Notably, the recalibrated values ranged from 0.08 μg·L-1 as the lowest threshold to 0.75 μg·L-1 as the upper limit, signifying a tenfold differentiation. Correspondingly, the urban average annual risk quotient associated with cadmium exposure demonstrated a variation from 0.035 to 1.12, marking a significant 32-fold discrepancy between the lowest and highest values. It is essential to highlight that regions of paramount importance, such as the confluence area connecting the upper and middle stretches of the Yangtze River Basin and the intricate Dongting Lake system, exhibited noteworthy ecological risks attributed to cadmium presence. Consequently, further in-depth investigations into these critical regions are imperative for a comprehensive understanding of the associated risks.

Observations on the Edapho-Microbial Nature of Indian Botanic Garden, Howrah

The edapmo-microbial nature of Indian Botanic Garden was assessed. The activities of Azotobacter were used as an indicator to determine the suitability of edaphic conditions for plant introduction. It was observed that the Hooghly River (Ganga) front had comparatively higher clay content and organic carbon. The water holding capacity, cation exchange ability, pH, porosity and available nutrients such as nitrogen and phosphorus and azotobacter activities of the river site were comparatively superior to the other sites. The middle stretch of the garden area was observed to be more saline than other two stretches. The area towards humaq, settlements was exposed to severe anthropogenic interference. Consequently, the microbial population was diminutive here with relatively inferior edaphic characteristics.

Ichthyofaunal Diversity and Physico-chemical Analysis of Water in the Middle Stretch of Vembanad Lake, Kerala, India

The status of finfish and shellfish diversity and monthly variation in their distribution and abundance were investigated in the middle stretch of Vembanad Lake at 4 selected sites in Kerala. The study was carried out for a period of 7 months from December 2022 to June 2023. In total 31 species of finfishes and shellfishes belongs to 8 orders, 23 families and 29 genera were recorded from the study areas. Calculated values of Biodiversity indices were Shannon Weiner diversity index highest at Vaikom (3.4022), Simpson diversity index highest at Manakunnam (0.9538), Margalef’s richness index highest at Manakunnam (4.346) and Pielou’s evenness index was highest at Thaneermukkom (0.8573). Etroplus suratensis and Villorita cyprinoides were the most abundant species from all four study sites. Three species are under the category of threatened they are Oreochromis mossambicus, Horobagrus brachysoma and Hyporhampus xanthopterus. The result of the present study indicates that the Northern part of Thaneermukkom barrage is endowed with rich edible fish fauna. The physicochemical parameters of water were analyzed during the pre-monsoon and monsoon periods. Salinity was higher on the Northern side of the barrage. During the pre-monsoon period temperature, EC, TDS, alkalinity and salinity were high and during the monsoon period hardness, DO, BOD, Phosphate and Nitrate were high when compared with pre-monsoon but all are within the recommended limit.

Unveiling the Rising Threat of Cadmium Pollution and Alarming Health Risks Associated with the Consumption of 15 Commercially Important Fish Species in the Middle Stretch of River Ganga, at Patna, India.

Among environmental contaminants, the rising level of cadmium in freshwater ecosystems is one of the most significant global concerns. The study addresses the current pollution status of cadmium in the middle stretch of River Ganga and explores the potential hazard associated with the consumption of 15 commercially important fish species by the inhabitants. Together 72 water and sediment samples were analyzed from the four representative sampling sites of River Ganga after the surveillance of major anthropogenic stressors. The concentration of cadmium ranges from 0.003 to 0.011mg/l and 0.2 to 3.48mg/kg in water and sediment respectively in 2022. The average concentration of cadmium was recorded to be the highest in Channa punctatus (1.35mg/kg), followed by Rita rita = Johnius coitor (1.15mg/kg), and the lowest in Labeo bata (0.2mg/kg). The finding highlights greater exposure duration and feeding preferences of fish species have played a significant role in the bioaccumulation of the metal in the riverine system. Notably, the domestic effluents, agricultural runoffs, and pollutants brought along by the tributaries of River Ganga are identified as the main anthropogenic stressors for the moderate to considerably polluted status of the River Ganga. The target hazard quotient (THQ) and target carcinogenic risk (TCR) have revealed a higher susceptibility to cadmium contamination in children followed by females, and males. In addition, hierarchical cluster analysis (HCA) has noted intake of Rita rita, Channa punctata, Puntius sophore, and Johnius coitor could be more detrimental to children's health than adults.

Assessment of Micronucleation and Abnormal Nucleation in the Peripheral Erythrocytes of the Fish Mystus gulio of Hooghly River Downstream as per Seasonal Variation

The aim of the study was to identify the frequencies of micro nucleations (MN) and nuclear abnormalities (NAs) in the peripheral erythrocytes of fish (Mystus gulio Ham. – Buch.) inhabiting downstream at three locations of river Hooghly, West Bengal, India. The study area mainly consists of three sampling sites, viz., Budge Budge (Bg), Batanagar (Bt) and Birlapur (Br), which were selected. The present study is a first-time endeavour to know the environmental status with particular reference to water pollution through genetic biomonitoring in the Hooghly River of a middle stretch from Batanagar to Birlapur near Diamond-Harbour coastal zone in the inhabiting fish (M. julio). The genotoxic effect, especially induction of MN and NAs in the peripheral erythrocytes, was done on the studied fish. In the case of MN frequencies (%), the values for sites Bt1 &amp; Bt2, Bg1 &amp; Bg2 and Br1 &amp; Br2 were observed 1.92±0.10, 1.40±0.24 and 2.00±0.13, respectively were increased during pre-monsoon season compared to post-monsoon season (1.83 ±0.15, 1.36 ±0.04 and 1.91 ±0.12, respectively). The frequencies (%) of NA, such as lobed nuclei (LN), blebbed nuclei (BLN), notch nuclei (NN), bi-nuclei (BN), dumble-shaped nuclei (DSN), retracted nuclei (RN), nuclear caryolysis (NC), and fragmented nuclei (FN) values, were also observed in the fishes of three study sites. In the case of NA frequencies (%), the values for sites Bt1&amp;Bt2, Bg1&amp;Bg2 and Br1&amp;Br2 were observed higher for BLN (1.54±0.09, 1.14±0.07 and 1.77±0.10, respectively), BN (1.09±0.04, 0.85±0.21 and 1.32±0.06, respectively), NN (1.02±0.09, 0.61±0.16 and 1.18±0.06, respectively), LN (1.86±0.08, 1.22±0.07 and 2.12±0.11, respectively), DSN (2.22±0.22, 1.69±0.08 and 2.56±0.11, respectively), RN (2.33±0.15, 1.82±0.13 and 2.73±0.05, respectively), FN (2.20±0.10, 1.72±0.08 and 2.56±0.13, respectively) and NC (3.01±0.06, 2.72±0.11 and 3.32±0.08, respectively) during pre-monsoon season when compared to post-monsoon season (BLN = 1.50 ±0.07, 1.06 ±0.03 and 1.73 ±0.07; BN = 0.83 ±0.11, 0.62 ±0.11 and 1.18 ±0.06; NN = 0.77 ±0.15, 0.43 ±0.11 and 1.05 ±0.03; LN = 1.42 ±0.06, 1.14 ±0.06 and 2.06 ±0.08; DSN = 1.76 ±0.06, 1.34 ±0.05 and 2.36±0.08; RN = 1.68 ±0.08, 1.30 ±0.06 and 2.31 ±0.08; FN = 1.59 ±0.08, 1.18 ±0.04 and 2.46±0.11 and NC = 2.58 ±0.53, 2.37 ±0.43 and 3.18 ±0.09, respectively). This study provides an important impact of mutagenic risk on the fish specimen, which may vanish due to the long-term effect of genotoxins or a combination of other pollutants. This specimen may show an alarming impact of water pollution, and this study is suggested for future study with other fish species to know the risk of vulnerability of mutation.

Quantitative delineation of water sources in the river Ganga using stable water isotopes

AbstractQuantitative delineation of water sources in a large river system is essential for the sustainable use of water. In the present study, we have tested two different methodologies to estimate the contribution from different water sources in the river Ganga. The first model uses stable isotopes and physicochemical parameters of water to delineate the contribution of glacier‐melt, groundwater, and surface runoff in different stretches of the river Ganga. The end member‐based mixing model provides glacier‐melt contribution of ~31.2%, ~5.5%, and ~0.5% in the upper, middle, and lower stretch of the river Ganga. The model showed maximum contribution from groundwater (~66.3%) in the middle stretch and surface runoff (~57.2%) in the lower stretch of the river Ganga. However, the uncertainties in the estimates from the three‐component mixing model were significantly high due to temporal variability in the end member values. To provide estimates with lower uncertainty, an alternate method (discharge dependent budget estimation [DDBE]) has been proposed which delineates the contribution of groundwater and surface runoff in small segments of the river. The DDBE model confines the calculation for budget estimates to smaller segments of the river and hence leads to lower uncertainties in the results, providing improved systematic estimation of water budget for large river systems. In the present study, estimates from the DDBE model suggest that groundwater contributes ~79% of the additional water whereas the contribution from surface runoff is ~21% in the middle and lower stretch of the river Ganga. The DDBE model was successfully applied in 5 small segments along the stretch of the river Ganga and the methodology used shows great potential for systematic delineation of water sources in large river system.

Quaternary alluvial paleosols of the Atbara River, eastern Sudan: description and paleoenvironments

ABSTRACTQuaternary climatic changes in the Nile Basin and their effects on the evolution of African mammals and vegetation are poorly understood, particularly for the last 1 Ma. Pleistocene (~230 to &lt;17 ka) alluvial sediments exposed along the middle stretches of the Atbara River in eastern Sudan are rich in fossil vertebrates and are ideal for paleoenvironmental reconstruction during this time interval. We performed petrographic, mineralogical and geochemical analyses on the middle Atbara paleosols to reconstruct the paleoclimate and paleolandscape. We describe Aridisols/Calcisols characterized by calcretes and containing gypsum and halite, and Vertisols with pedogenic slickensides and a relatively large amount of smectite. The paleosols indicate that the study area transitioned from an arid to semi‐arid climate during Marine Isotope Stage (MIS)7/6, to a more humid climate during MIS5, and then a return to more arid conditions during MIS2. The studied paleosols likely supported a range of grassland and wooded grassland savanna habitats. Our study confirms that the Atbara River Valley provided favorable living conditions for Pleistocene large mammal communities including Homo, potentially facilitating dispersals out of Africa through the Nile corridor.

Analysis and pollution assessment of heavy metals in suspended solids of the middle stretch of river Ganga between Kanpur to Prayagraj, U.P., India

Analysis and pollution assessment of heavy metals in suspended solids of the middle stretch of river Ganga between Kanpur to Prayagraj, U.P., India

Description of a new species of the genus Awaous Valenciennes, 1837 (Gobiiformes: Oxudercidae) from the middle stretch of the Mahanadi River, Odisha, India, with comments on the Awaous species from India.

A new species of the genus Awaous (Oxudercidae), Awaous motla sp. nov., is described based on 18 specimens collected from the Mahanadi River near Sonepur, Subarnapur District, and 3 specimens from the same river near Boudh bridge, Boudh District of Odisha, India. This species is distinct from its congeners by having a combination of characteristics: relatively small eyes, diameter of 6.6-8.4 in head length (LH); robust and long snout, 2.0-2.6 in LH; eye diameter 2.7-4.1 in snout length; cephalic sensory pore system interrupted with eight pores; predorsal scales 13-15; longitudinal scale series 55-58; gill rakers 2 + 1 + (6-7) on the first gill arch; teeth small, conical, and in a single row on the upper jaw and multiserial (2-3) on the lower jaw. This species is also differentiated from some of its congeners in the nucleotide composition of the cytochrome c oxidase I gene by 8.3%-13.8% Kimura two-parameter (K2P) distance and belongs to a separate cluster in the maximum likelihood tree analysis. This finding is also supported by the species delimitation analysis based on Assemble Species by Automatic Partitioning. The new species holds high commercial value in its locality and needs special conservation attention for sustainable utilization.

Abundance, characterization, and removal of microplastics in different technology-based sewage treatment plants discharging into the middle stretch of the Ganga River, India

Sewage treatment plants (STPs) are considered as a prominent source for releasing microplastics (MPs) into the riverine systems. Though MPs abundance and removal efficacy in different secondary treatment technique-based STPs have been extensively studied worldwide, such studies are scarce in Indian conditions. Herein, this study comprehensively assesses MPs abundance, characterization, and their removal in the selected secondary treatment technique-based STPs discharging into the middle stretch of the Ganga River in India. MPs concentration (n/L) in influent and effluent of the STPs varied between 42 ± 10 to 150 ± 19 and 3 ± 1 to 22 ± 5, respectively. Overall, the primary treatment stage was observed to remove MPs by 23–42 %, while the secondary treatment stage removed MPs by 67–90 %. Selected technique-based STPs exhibited varying MPs removal efficacies as follows: SBR (94 %), TF (90 %), AL (88 %), UASB (87 %), ASP (85 %), FAB (84 %), and Bio-tower (77 %). MPs ranging from 50 to 250 μm were the dominant sizes, with PP, PE, and PS being the prevalent polymers. The Ganga River receives about 3 × 108 MPs/day from STP effluents, and an estimated 4.5 × 107 MPs/day are released via the sludge. This comprehensive assessment of MPs abundance and removal from different technology-based Indian STPs will allow the comparison of the generated dataset with similar studies worldwide.

Basin-Scale Geochemical Assessment of Water Quality in the Ganges River during the Dry Season

Identification of sources and transport pathways of heavy metals and major ions is crucial for effective water quality monitoring, particularly in large river systems. The Ganges river basin, the largest and the most populous river basin in India, remains poorly studied in this regard. We conducted a basin-level analysis of major ions, heavy metals, and stable isotopes of nitrate in the Ganges during the pre-monsoon season to constrain the sources and quantify the inorganic chemical composition of the river during its lean flow. Bedrock weathering, anthropogenic interferences, water contribution through tributaries, and surface water-groundwater interaction were identified as the major driver of metal and ion variability in the river. Heavy metals showed the highest concentrations in the upper section of the river, whereas ionic loads were the most variable in the middle. We find a significant impact of tributaries on the metal and ion concentrations of the Ganges in its lower reaches. Isotopic analysis of dissolved nitrate suggested synthetic fertilizers and industrial wastes as the main sources. We find that the otherwise clean waters of the Ganges can show high ionic/metallic concentrations at isolated stretches (As: up to 36 µg/L), suggesting frequent monitoring in the source region to maintain water quality. Except for water collected from the Yamuna and Kannauj in the middle stretch and the Alaknanda and Rishikesh in the upper stretch, the WQI showed acceptable water quality for the sampled stations. These findings provide an insight into the modifications of dissolved inorganic chemical loads and their sources in different sections of the basin, needed for mitigating site-specific pollution in the river, and a roadmap for evaluating chemical loads in other rivers of the world.

Upstream River Erosion vis-a-vis Sediments Variability in Hugli Estuary, India: A Geospatial Approach

Satellite data shows that the Bhagirathi-Hugli River’s riverbank has faced severe erosion during the last decades (1990 to 2020), with the middle stretch of the river being more prone to erosion. This huge sediment load derived from upstream erosion is coming to the estuary. The suspended sediment concentration dynamics of the Hugli estuary were calculated using in-situ data and remote sensing reflectance by establishing a linear regression. A continuous huge sediment load is found in the estuarine water. The sediment concentration was higher pre-monsoon than post-monsoon as the region is highly influenced by monsoonal rainfall and runoff. The sediment concentration was also higher in the estuary’s southwestern section than in the northern part. The impact of this high sediment load contributes to the deposition. This depositional area assessment was performed using an object-based classification approach called Support Vector Machine utilizing Grey Level Co-occurrence Matrix to create cluster textural indices. Despite the impact of continuous sea level rise in the estuary, the result shows that effective island and Chars areas have increased in the past decade due to the upstream erosion-driven sediments.

Diurnal oscillation in dissolved oxygen at sediment-water interface fuels denitrification-driven N removal in Ganga River

Human activities have substantially enhanced riverine nitrogen loads in many parts of the world. The processes such as denitrification remove a large fraction of N added to the system, and thus, are very helpful in mitigating the effects of increasing human N loads in aquatic ecosystems. No systematic studies, so far, are available on current magnitude and factors regulating efficiency of N removal by the Ganga River. Using three sub-sets of studies- main river course, two tributary confluence trajectories and two point source trajectories along 520 km middle stretch, we generated high spatio-temporal resolution data to show that spatially targeted river reaches with higher nitrate concentrations are acting as ‘hotspots’ of N removal in the Ganga River. The static core method was used to measure the rate of denitrification. Intact sediment core samples were incubated in the laboratory condition and efficiency adjusted. Pollution-impacted point sources showed higher rates of denitrification (0.40 mg N/m2/hr to 2.48 mg N/m2/hr) relative to main stream sites (0.32 mg N/m2/hr to 2.09 mg N/m2/hr). Our results indicate that increased level of carbon (C) and phosphorus (P), which often accompany nitrogen (N) inputs from human activities, have enhanced N removal by the river. Periodic oxic-hypoxic cycle at sediment-water interface (DOsw), which might link nitrification with denitrification, has stimulated N removal at study sites in an opportunistic manner. These results suggest that data on this natural process of N removal (denitrification), and factors thereof, especially those accounting for interactive effects at spatially targeted locations, should be taken into account to formulate policies for the management of nutrient and organic pollution.

Distribution and risk assessment of pesticide residues in sediment samples from river Ganga, India.

Indiscriminate use of pesticides leads to their entry in to the bottom sediments, where they are absorbed in the sediment's particle and thus, may become the consistent source of aquatic pollution. The present work was carried out to evaluate pesticide residues in the sediment samples and associated human health risk of commonly used pesticides along the basin of river Ganga. Total of 16 pesticides were analyzed along three stretches of river Ganga. The concentration of pesticides in the upper stretch ranged from ND to 0.103 μg/kg, in the middle stretch ND to 0.112 μg/kg, and in the lower stretch ND to 0.105 μg/kg. Strong positive correlation was found between total organic carbon and total pesticide residues in sediment samples. Carcinogenic and non-carcinogenic values were estimated below the threshold limit suggesting no associated risk. Risks associated with the inhalation route of exposure were found to be higher than the dermal and ingestion routes. Children were found at higher risk at each site from multiple routes of exposure than adult population groups. Toxic unit values were found to be below the threshold value suggesting no risk associated with exposure of pesticides from sediments. However, long term effects on ecological quality due to consistent pesticide exposure must not be ignored. Therefore, the present study focuses on concrete efforts like lowering the irrational used of pesticides, tapping of agricultural and domestic drains, advice to farmers for appropriate use of pesticide doses, to reduce the threat of pesticide pollution in the river system and possible human health risk.

Morphological characteristics of cracks in soil with and without vegetation cover

An assertive understanding of cracks in expansive soils makes their typification a challenge, especially in field conditions. Seeking to overcome such difficulty, digital images have been used to estimate the fractal geometry of surface cracks in soils with and without vegetation in a semi-arid environment. This study was carried out in a cross-section along the main course of a first-order watershed in the Centro Sul region, Ceará State (Brazil). Two treatments comprised soil with and without vegetation cover. Experimental plots were installed to represent the upper, middle, and lower parts of the watershed studied (vegetated and non-vegetated), with an area of 1 m2 and spaced 2 m apart. The following morphometric characteristics of cracks were monitored and evaluated during 38 days, namely: area, weighted average between crack area and its perimeter, weighted average of the fractal dimension area of the cracks, connectivity between cracks and soil moisture. In the soil with and without vegetation, intensity of cracks in the soil had a significant correlation (p ≤ 0.01) with the perimeter, fractal area and crack connection. The intensity of cracks between covered and uncovered plots showed a significant difference (p ≤ 0.01), only in the lower part of the watershed. The middle stretch had higher sand content and differed statistically from the lower stretch for intensity of cracks in the soil. Vegetation influenced the correlation between cracks intensity and their connection, influencing their morphology in the sandy stretch.

Morphometric differentiation of Labeo catla (Hamilton 1822) (Cyprinidae) in rivers: Possible adaptation to hydrology

Morphological differentiation in the Indian major carp, Labeo catla, in the Ganga and Narmada rivers was studied using image-based morphometric and multivariate analytical techniques. Twenty-three truss-network-based distances connecting 11 anatomical landmarks on the fish were measured from the digital images of the specimens collected from seven stations, four of which were set up along the river Ganga, and the other three stations along the river Narmada. For analysis, five stations were considered, as the samples from the three stations on the River Narmada were pooled and treated as a composite sample (Narmada). The multivariate analysis of variance showed evidence for significant morphometric differences between samples collected from the Ganga and those from the Narmada rivers. The subsequent Linear Discriminant Analysis explained 86% of the variability between the stations by two discriminant functions. This fact suggested the existence of three morphometrically different populations of the species along the Ganga. These populations were predominantly distributed in the middle stretch of the river (Ganga_Middle), the Bhagirathi-Hooghly stretch, and the Padma stretch, which are isolated by a barrage that does not allow free bidirectional movement of fish. The important discriminating morphometric characteristics were traits from the head and caudal region as well as the body depth of fish. The relatively narrower angles of snout profiles and lower body depths of the studied fish in populations from the Padma and Bhagirathi-Hooghly stretches of the River Ganga led to more pointed snouts and slenderer bodies. Morphological differentiation can be used as an environmental predictor that, in turn, would be of use in developing effective management strategies for the fish species of stock management concern.

Ecological and human health risk associated with heavy metals in sediments and bioaccumulation in some commercially important fishes in Mahanadi River, Odisha, India

Disposal of untreated municipality sewage, industrial wastes and agricultural runoff into the Mahanadi river causes increased heavy metals load in the river basin. The present study assesses the concentrations of heavy metals (Cr, Cd, Hg, Cu, Zn, Pb and As) in sediments and their bioaccumulation in some commercially important fishes. The potential ecological risk of heavy metals in sediments and human health risk associated with the consumption of fish accumulating heavy metals are also evaluated. The concentration of heavy metals measured followed the hierarchy as follows: Mn > Cr > Zn > Cu > Pb > As > Cd > Hg. Potential ecological risk analysis of sediment heavy metal concentrations indicated that four sites in the middle stretch poses moderate ecological risk whereas three sites in the lower stretch posed low ecological risk. Zn showed hyperaccumulation in five different fish species while Cd was observed to be the least bioaccumulative with a hierarchy of Zn > Cu > Pb > Cr > As > Cd. The demersal fish Notepterus notepterus and Clarias batrachus was observed to be the most bio-accumulative to heavy metals. Though potential human health risk assessed using Target Hazard Quotient, Hazard Index and Carcinogenic Risk was found to be within the acceptable threshold, continued disposal of heavy metals could pose a greater carcinogenic as well as non-carcinogenic risk in this region.

What factors affect the fishing resources of the middle stretch of the River Ribeira de Iguape (SP)?

What factors affect the fishing resources of the middle stretch of the River Ribeira de Iguape (SP)?

Deciphering the nitrate sources and processes in the Ganga river using dual isotopes of nitrate and Bayesian mixing model

The dual isotopes of dissolved NO3- (n = 43) has been used to delineate the nitrate sources and N-cycling processes in the Ganga river. The proportional contribution of nitrate from different sources has been estimated using the Bayesian mixing model. The seasonal NO3- concentration in the lower stretch of the river Ganga varied between 4.1 and 64.1 μM with higher concentration during monsoon and post-monsoon season and lower concentration during the pre-monsoon and winter season. The temporal variation in the isotopic values ranged between +0.0 and +9.6‰ for δ15NNO3- and −1.2 to +11.0‰ for δ18ONO3-. The spatial NO3- concentration during the post-monsoon season varied between 23.2 and 57.7 μM, with higher values from the middle and lower values from the lower stretch of the river Ganga. The isotopic ratio during the post-monsoon season varied between −1.0 and +11.3‰ for δ15NNO3- and −4.6 to +5.2‰ for δ18ONO3-. The temporal dataset from the lower stretch of the river Ganga showed the dominance of nitrate derived from the nitrification of soil organic matter (SOM) (average ∼53.4%). The nitrate contribution from synthetic fertilizers was observed to be higher during the post-monsoon season (34.7 ± 23.4%) compared to that in the monsoon (25.5 ± 19.5%) and pre-monsoon (22.2 ± 19.6%) season. No significant seasonal variations were observed in the nitrate input from manure/sewage (∼13.9%). Spatial samples collected during the post-monsoon season showed higher contribution of synthetic fertilizer in the lower stretch (34.6 ± 22.7%) compared to the middle stretch (21.1 ± 18.2%), which indicates greater influence of the agricultural activity in the lower stretch. The dual isotope study of dissolved NO3- established that the nitrate in the Ganga river water is mostly derived from the nitrification of incoming organic compounds and is subsequently removed via assimilatory nitrate uptake. The study also emphasises significant nitrification and assimilatory nitrate removal processes operating in the mixing zone of the Ganga river and Hooghly estuary.