Kerala, the southern state of India, was severely hit by a massive flood in August 2018 affecting millions of people causing loss to the state exchequer. The aim of this paper was to study the ...impacts of this flood on mineralogy, geochemistry (grain size, and heavy metal content) and nutrient content (organic carbon, total and available nitrogen, and phosphorus) of sediment of flood affected Pampa river, Kerala. The study indicates that this large-scale flood results in a considerable reduction in the heavy metals and nutrient concentration of sediment. Frequency histograms for most of the sediment particle size showed unimodal distribution curve with the dominance of sand particles which may be due to wash of fine size fraction like silt and clay during flood. FTIR study indicates that Pampa river sediment is dominant with quartz, orthoclase and microcline feldspar, and kaolinite, along with other trace minerals. SEM study also indicates that quartz is the common occurring mineral and its shape varies from highland to downstream due to transportation. Ratio of carbon to nitrogen and phosphorus particularly at downstream stations indicates the considerable influence of macrophyte which leads to accumulation of terrestrial organic matter. The cluster analysis results indicate that there were some similarity in origin and migration behaviour among these metals and nutrients of the sediments.
Reproductive biology of female amphidromous croaker Johnius coitor (Hamilton, 1822) was studied for the first time from various freshwater stretches of Ganga river basin, India in relation to ...climatic variability. The species showed high spatial variation in reproductive phenology and capable of breeding during pre-monsoon, monsoon, post-monsoon and winter. Water temperature is the most crucial environmental parameter influencing gonadal maturation and breeding. Generalized additive model (GAM) models revealed water temperature near 23–25 °C as optimum and threshold GSI above 3 units necessary for breeding. Pre-spawning fitness (Kspawn50) and size at 50% maturity (LM50) benchmarked through Kaplan-Meier survival fit estimates were in the range 1.27–1.37 units and 19–24.5 cm respectively. First maturity of females was encountered at 11.4 cm within the size range 7.2–28.5 cm. Egg parameters in mature-ripe females ranged between 0.29–0.80 mm (diameter), 0.05–0.19 mg (weight) and 5687–121 849 eggs (absolute fecundity). Mapping of climate preferendum through LOESS smoothing technique hinted water temperatures <20 °C and >32 °C to be detrimental for attainment of pre-spawning fitness while no dependence on rainfall was observed. Based on the climato-hydrological influence on breeding and regional trends of changing climate along river Ganga, we infer minimal climate driven changes in breeding phenology of this amphidromous fish species. Results of this study may serve as baseline information for future studies assessing climate driven changes and evolutionary adaptations in croakers from river Ganga.
Anthropogenic alterations have paramount impacts on the alpha and beta diversity of aquatic resources, and fishes are predominantly susceptible to such impacts. Mahanadi River, one of the major ...peninsular rivers of India, has abundant fish resources, which play a significant role in supporting the fishers’ livelihoods. The exploratory study in the river conducted for three consecutive years recorded 148 species under 53 families. Cyprinids dominated the fish diversity with 41 species, followed by Bagrids (9) and Sciaenids (7). One hundred-one species under 29 families were reported from the freshwater stretch. With a total of 111 species reported under 48 families, the estuarine and tidal freshwater stretch was more speciose, due to marine migrant species which advent the estuarine and tidal freshwaters stretch for breeding and feeding purposes. Tikarpara, a conserved site within a sanctuary, was the most species-diverse as well as a species-even site. The study also recorded the extension of the distributional range of 3 fish species and also 4 exotic species from the river. The seasonal variations in diversity indicated that the deviations were not prominent in freshwater sites, whereas in tidal brackish water sites, species richness was relatively higher in post-monsoon, and species evenness was higher during monsoon. Taxonomic distinctness test showed that the average taxonomic distinctness was high for tidal estuarine locations as they harbour taxonomically distant fishes. The hierarchical clustering of sites showed the inordinate effect of river gradient and fragmentation on the fish community structure. Analyzing the key drivers of the assemblage structure of the entire river, salinity was the major deterministic factor, and within the freshwater stretch, the major influences were depth, transparency, and specific conductivity. The study concluded that, despite all of its ecological stresses, Mahanadi still supports rich fish diversity, yet there is a notable shift in the fish community structure. There is a need for integrating molecular and morphological tools for the taxonomic revision of many genera and species for proper in situ and ex situ conservation measures and to formulate future biodiversity management plans addressing to reduce the impacts of the ecological threats.
•Poor reproductive resilience of minnows towards climate change is presumed.•Vulnerability of the common Gangetic pool barb towards climatic variability was evaluated.•Low threshold rainfall and wide ...thermal cue requirement for breeding observed.•Easiness in attainment of pre-spawning fitness and minimal risk of skipped spawning observed.•Results demonstrate – changing climate pose negligible threat to reproduction of minnows.
Information on various aspects of reproductive traits of female pool barbs from various stretches of Ganga River basin, India was generated in relation to climatic variability. The presumptions surrounding – minnows being the first and easily hit by climatic variability, was validated. GAM models revealed low threshold rainfall requirement (>50 mm) within a wide temperature range (20–30 °C) necessary for attainment of breeding GSI (>10.5 units). Pre-spawning fitness (Kspawn50) and size at 50% maturity (LM50) benchmarked through Kaplan-Meier survival estimates were in the range 1.61–1.67 units (Fulton condition factor) and 8.6–9.0 cm respectively. Mapping of climate preferendum through LOESS smoothing hinted both low-mild rainfall (50–150 mm) and high rainfall conditions (400–700 mm) conducive for attaining pre-spawning fitness while no dependence on temperature was observed. First maturity of females was encountered at 4.7 cm within the size range 4.4–12.6 cm. The present study hinted a probable reduction (1.4–1.8 cm) in size at maturity of female pool barbs. We observed pool barbs can breed within a wide thermal regime following slightest of rainfall events. Collating this with the present rates of climatic variability, we infer negligible threat of changing climate on reproduction of Puntius sophore in near future – contrary to the existing presumptions. Owing to the easiness in attainment of pre-spawning fitness under an apparently flexible climate preferendum, ‘skipped spawning’ decisions while facing climatic variability also seem minimum. The recorded breeding thresholds may serve as future references while assessing climate driven changes on reproduction and evolutionary adaptations in Gangetic minnows.
Kerala state (India) experienced a devastating flood event during the month of August 2018 which has brought considerable changes to the environment and ecosystem, especially to rivers. One of the ...worst affected basin was Pampa river which experienced a severe flood. Aims of this investigation were to define the quality of Pampa river water after the flood. The analysis of physico-chemical parameters indicated transitory variations from pre-flood status as reported by former workers. The pre-flood neutral to the acidic property of water shifted towards alkaline conditions throughout the river stretch post flood. Alkalinity and salinity was almost twice the pre-flood scenario, though the values were within the ranges required for fish survival and growth. Decreased conductivity and increased dissolved oxygen were also the major changes observed post flood. The study indicates that this large-scale flood resulted in a considerable reduction in the concentration of heavy metals and nutrients in the water. Based on water quality index, spatially Pampa river water can be categorised from 'Good' to 'Unsuitable' category. The cluster analysis distinctly differentiates the middle stream stations from lower stream stations. PCA/FA loadings indicate that electrical conductivity, alkalinity, total hardness, calcium, and PO
4
3 -
P show strong positive loadings which indicate that salinity factor and natural weathering are the main factors controlling the water quality. This information would be practical to forecast the health of the ecosystem after the flood and also to develop adequate management plans.
Temperature and seasonal rainfall along with other environmental variables are important in regulating the reproductive cycles in teleost fishes. Certain environmental variables may act as cues for ...reproduction and changes in these may affect seasonality and success of reproduction, as fishes are known to integrate their physiological functions with environmental cycles. Wetlands are sensitive to climate change due to their shallow and confined nature. Since wetlands are important spawning and nursery grounds for many fishes, changes in the environmental variables may have direct consequences for the spawning and survival of fish. In the present study, we have assessed climatic and water chemistry variables capable of influencing seasonality in environmental variables as well as gonadal maturation of spotted snakehead
Channa punctata
, to predict threshold values of Gonado Somatic Index in females and a favourable range of identified climatic and water chemistry variables for breeding success. Among the climatic and water chemistry variables studied, seasonal variation in rainfall was found to have the most profound effect on gonadal maturation and breeding in
C. punctata,
followed by water temperature
.
The favourable range of rainfall obtained varied between 800 mm to 1400 mm, corresponding to the water temperature range between 29 °C and 31 °C. An overall significant warming trend with a reduction in total rainfall has been observed with changes in seasonal trends in temperature and rainfall in the study area. The rainfall being the major climatic factors influencing water chemistry in the wetlands during the spawning season, changes in rainfall pattern may influence breeding periodicity of
C. punctata
in wetlands in climate change scenario.
The main objectives of the present study were to quantify the environmental, especially temperature and rainfall, effects on breeding phenology of selected catfish species and to predict changes in ...breeding phenology of the selected species in relation to climatic variability for the Ganga River Basin. The study showed that changes in rainfall pattern may have the most profound effect on gonad maturation and breeding of
Mystus tengara
and
Mystus cavasius
followed by the effect of increased water temperature due to rising air temperature. Indication of region-specific adaptation was noticed in reproductive phenology of
Eutropiichthys vacha
based on local trends of warming climate. The other habitat parameters, such as dissolved oxygen, alkalinity, nitrate, and phosphate, were correlated with gonad maturity and spawning. Climatic variability may bring region-specific changes in breeding phenology of fish species in the Ganga River. Under a warming climate, changes in precipitation pattern manifested into riverine flow pulse may be the key driver in dictating breeding phenology. Our study indicates
E. vacha
as a climate sensitive species that may be selected as a target species for climate change impact studies.
Invasive species pose a severe threat to biodiversity around the world. Managing the consequences of invasion is difficult in aquatic settings, as the rate at which invaders establish typically ...outpaces the resources available to eradicate them. For proactive management measures to be implemented, prior knowledge of the probability of invasion is required. In this study, we created a spatial model of the probability of the Pirarucu (Arapaima gigas) invasion in the Western Ghats. The Western Ghats, one of the world's top biodiversity hotspots, is home to numerous endemic species, many of which are now threatened. An ensemble modelling approach using 10 models, including machine learning techniques such as Artificial Neural Network (ANN), Maximum Entropy (MaxEnt), Random Forest (RF), Generalised Boosted Regression Model (GBM) and Classification Tree Analysis (CTA), was adopted. The model was built using the species' occurrence data and nine climate variables. The findings revealed that southern regions of the Western Ghats have a high risk of Pirarucu invasion. Sri Lanka also has a much greater geographical area with a higher percentage of appropriate habitats for the species. The study becomes vital as this exotic species was repeatedly reported from the rivers since the extensive floods in the region in 2018. The developed model will assist managers in prioritising locations and initiating monitoring and management steps to prevent the spread before they establish in the wild. With earlier Pirarucu invasions in Bolivia, Peru and East Asia and recent climatic vagaries in the Western Ghats, the native biodiversity of the region is in grave danger of being displaced.
India has a vast network of 14 major rivers and their tributaries, covering 83% of the drainage basin and accounting for 85% of the surface flow. Anthropogenic activities like damming, channel ...modification, water abstraction, sewage and effluent disposal, sand mining, unthoughtful exploitation of biotic resources, etc. are the major threats faced by the rivers in the country. Monitoring protocol of Indian rivers lacks an integrated approach based on judicious use of both abiotic and biotic components as well as a total lack of consideration for ecological health. Index of Biotic Integrity is a flexible multimetric index that can be modified and adapted to the various zoogeographic regions of the world. A fish-based multi-metric IBI was developed by modifying and incorporating metrics that are sensitive to the various ecological stressors faced by Indian rivers, fishes being excellent indicators of river health. The adapted IBI was validated and used to assess ecological health of two rivers—Mahanadi, and its distributary Kathajodi-Devi—flowing through central-eastern India. The study indicated that in River Mahanadi, around 25% of the freshwater river stretch was slightly impaired and the remaining 75% stretch was moderately impaired. In Kathajodi-Devi, most of the river stretches were in a moderately impaired condition, except at Italnga stretch where the river was severely impaired. The Index of Biotic Integrity scores estimated could reflect the ecological health of the rivers. The study shows that use of Index of Biotic Integrity is a useful and reliable approach to assess the health conditions of Indian aquatic resources warranting initiatives to be taken to implement and incorporate it into the country's water resource management.
Water quality is a critical environmental issue, because all forms of life depend on water. The present study focused on the spatiotemporal trends of 22 physicochemical parameters of the water in the ...Chaliyar River, which originates from the Western Ghats, Kerala, in India, and drains into the Arabian Sea. Water samples were collected from eight stations located along the river in different seasons (pre-monsoon, monsoon and post-monsoon) during two annual cycles (2017 to 2019). Most of the water quality parameters showed significant seasonal variations with spatial heterogeneity. Water quality index (WQI) and comprehensive pollution index (CPI) were used to analyze the river water for its potability and pollution status, respectively. The WQI showed “good” to “unsuitable” category and the CPI showed “sub-clean” to “severely polluted” status at the various stations of the river. The nutrient enrichment of water, analyzed using the trophic state index, showed “mesotrophic” to “high eutrophic” state at various stations, indicating that the river is tending toward eutrophication particularly along the downstream stations. Pearson’s correlation demonstrated the influence of natural sources on the riverine water composition. The results of factor analysis revealed that the highest factor loadings were on total hardness, Ca, Mg, chlorinity and salinity, suggesting that non-point inorganic pollution, largely due to river basin geology and salinity ingress, was responsible mainly for potable water quality deterioration. Based on the results, the eight stations along the river were grouped into three clusters of “less,” “moderately” and “highly” polluted and recorded a decrease in water quality from upstream to downstream. The study also highlighted the importance of multivariate statistical techniques in identifying the pattern of variability of parameters, besides helping in developing management strategies to improve river water quality by identifying relatively significant parameters causing the maximum water quality degradation.
