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Wetland degradation and loss of wetland is one of the emerging challenges against sustaining such worthy environmental capital having plenty of goods and services. In Barind tract of India and Bangladesh, such trend of wetland conversion is highly explicit. Present paper attempted to capture such trend of wetland loss, conversion of wetland and their associated reasons behind. At present total wetlands area of the basin is 220.9 km 2 and which is 35.78% lower than pre-dam wetland coverage. Flow modification triggered by Komardanga dam (34.35% for average flow and 52.24% for peak stream flow have declined) is emerged as one the major reasons behind wetlands loss. It also causes reduction of active flood prone area by 39.72% as well as inconsistent water service to wetlands. De-linking of Punarbhaba river system from Tista river system is another historical cause behind lowering of flow and flood magnitude in Punarbhaba. Loss of tie channels is also responsible for irregular water service to the wetlands. In last 30 years, about 100 km 2 of wetland is transformed into agricultural land, which points out the responsibility of agricultural extension for wetland deterioration. So, periodic monitoring of wetlands, release of ecological flow and stop agricultural encroachment are necessary for sustaining wetland. [ABSTRACT FROM AUTHOR]

Abstract: Sapindus emarginatus is an economically important tropical tree species sparsely distributed in different geographical provinces like Gangetic Plains, Western Ghats, and Deccan Plateau in India. In the present paper estimation of genetic variability within and among 41 accessions representing five populations was carried out using 3 single primer amplification reaction (SPAR) methods viz. RAPD, DAMD and ISSR. The cumulative data analysis was carried out for all three SPAR methods, and showed 82.32% polymorphism across all the accessions of S. emarginatus. Jaccard''s similarity values among 41 accessions ranged from 0.15 to 0.49 with an average value of 0.37. The intra-population genetic diversity revealed highest values of Nei''s genetic diversity (0.19,) Shannon information index (0.29) and polymorphic loci (55.18%), among the accessions of Gujarat (GJ) population, while the corresponding lowest values were (0.10), (0.15) and (26.40%) respectively among the accessions of Rajasthan (RJ) population. The maximum inter-population average genetic distance (0.20) was between Karnataka (KA) and RJ, while the corresponding least genetic distance (0.06) was between Allahabad (AL) and Varanasi (VS) populations. The analysis of molecular variance (AMOVA) revealed maximum percentage of variation among individuals of populations (72%) followed by 16% among regions and 12% among populations. Principal coordinate analysis (PCA) of cumulative data also supported the clustering pattern in the UPGMA dendrogram. These results suggest that genetic diversity is corroborating with the geographical diversity. Mantel''s test was performed which revealed a highly significant correlation between cumulative vs RAPD, and showed the maximum (0.93) correlation coefficient, followed by cumulative vs ISSR (0.78) and cumulative vs DAMD (0.91) respectively, and this clearly indicates that the SPAR methods (RAPD, DAMD and ISSR) are sufficiently informative and are suitable to analyze the genetic variability within and among the populations of S. emarginatus. [Copyright &y& Elsevier]

Abstract: This paper reports a study of the Tista megafan in the foothills of Darjeeling Himalaya. Spread over parts of India and Bangladesh, the megafan is bounded by the Mahananda River to its west and the Tista River to the east. The Atrai and Karatoya Rivers flow through its axial part. The megafan covers an area of ~18,000km2. Near its apex the surface slope is ~0.19°, that declines to 0.01° near the toe. The east–west transverse profile of the megafan is broadly upward convex, with gently sloping (~0.01°) flanks. Maximum width and the length of the megafan are about 145km and 166km respectively. The highest point near the megafan apex is ~150m above the Brahmaputra alluvial plain. The Tista River flanking the megafan has an average annual discharge of 609m3/s with highest average monthly discharge exceeding 2000m3/s during monsoon. Most of the other channels currently traversing the megafan are plains-fed, and compared to Tista and Mahananda Rivers these channels have lesser discharge, higher sinuosity, and decreased widths. A radiating network of abandoned channel belts can be identified in satellite images of the megafan. Each of these major paleochannels is associated with numerous crevasse channels in the distal part of the megafan, forming an intricate network of radial drainage on the megafan surface. Three distinct depositional lobes can be recognised on the Tista megafan. Each of the lobes is identified by a set of ancient and modern radial drainage systems. The lobe boundaries are marked by discordance in drainage network of adjacent lobes. The relative ages of the lobes, as tentatively determined from the drainage discordances, indicate that the megafan first built up the eastern lobe (lobe 1), then shifted to the west to form lobe 2, and finally switched again eastward giving rise to the smallest lobe located close to the mountain front (lobe 3). Although broadly upward convex in cross profiles, subtle reflections of multiple lobes are apparent in some of the cross profiles. Study of the old maps published between 1794 and 1945 reveals that some of the present-day plains-fed rivers, like the Tangon, the Atrai and the Karatoya, were directly connected to the Himalayan catchment basins prior to the late eighteenth century. Archaeological excavations along the banks of these rivers appear to support this paleodrainage configuration. Eight facies and five facies associations were recognised in the uppermost megafan sediments. Facies associations suggest deposition from high-energy sandy streams in the proximal area and deposition from mixed load, sinuous streams and flanking marsh or lake in the distal part of the lobes. Paleocurrent data are consistent with a southwestward spreading paleochannel pattern recognised within the studied part of the megafan. Multiple lobes typify megafans ocurring in different parts of the globe. The existence of the mutiple accretionary lobes in Tista megafan, its radial drainage pattern, its concave-upward longitudinal and convex-upward transverse profile shape make it morphologically comparable with other high-gradient alluvial fans observed in nature and those produced in the laboratory. These morphological features denote the similarities between the small, high-gradient alluvial fans and large, low-gradient megafans, and that in turn may be indicative of the commoness in certain controlling factors between these two depositional systems. [Copyright &y& Elsevier]

The problem of arsenic pollution of groundwater used for domestic water supplies is now well recognised in Bangladesh, India and some other countries of South and South-east Asia. However, it has recently become apparent that arsenic-polluted water used for irrigation is adding sufficient arsenic to soils and rice to pose serious threats to sustainable agricultural production in those countries and to the health and livelihoods of affected people. This paper reviews the nature of those threats, taking into account the natural sources of arsenic pollution, areas affected, factors influencing arsenic uptake by soils and plants, toxicity levels and the dietary risk to people consuming arsenic-contaminated rice. [Copyright &y& Elsevier]

The aim of this paper was to obtain the first screening ecotoxicological risk evaluation in the Sunderban wetlands, the largest prograding delta in the estuarine phase of the River Ganges. The characterization of exposure was conducted by means of an extensive survey of several persistent organic pollutants (PAHs, PCBs, DDTs, PBDEs, HCHs, HCB) measured in seven core sediments from the Sunderban wetlands, obtaining a dataset with more than 2200 analyses. The pollutant effects were assessed by the use of three different sediment quality guidelines (SQGs) previously developed in the literature to evaluate toxicity induced in sediment-dwelling organisms. The three different approaches chosen for risk assessment of the Sunderban were the consensus SQGs obtained by TEC (threshold effect concentration), PEC (probable effect concentration) and EEC (extreme effect concentration), the threshold/probable effect level (TEL/PEL) approach and, finally, the ERL-ERM guidelines, including the m-ERM-Q (mean ERM quotient). The evaluation of the toxicity induced by a mixture of the target pollutants indicated the importance of γ-HCH contamination in the Sunderban sediments despite the very low concentrations measured in core sediments. A different sensitivity for toxicity assessment due to quality guidelines was obtained, as the consensus SQGs based on TEC were less conservative and protective than the TEL and ERL approaches, while the use of m-ERM-Q seems to be the most powerful tool to predict the toxicity related to a contaminant mixture. [Copyright &y& Elsevier]

The Indo-Gangetic plain (IGP; including regions of Pakistan, India, Nepal, and Bangladesh) is generally characterised by fertile soils, favourable climate and an abundant supply of water. Nevertheless, the challenge of increasing food production in the IGP in line with demand grows ever greater; any perturbation in agriculture will considerably affect the food systems of the region and increase the vulnerability of the resource-poor population. Increasing regional production is already complicated by increasing competition for land resources by non-agricultural sectors and by the deterioration of agri-environments and water resources. Global environmental change (GEC), especially changes in climate mean values and variability, will further complicate the agricultural situation and will therefore, have serious implications for food systems of the region. Strategies to reduce the vulnerability of the region''s food systems to GEC need to be based on a combination of technical and policy options, and developed in recognition of the concurrent changes in socioeconomic stresses. Adaptation options need to be assessed with regard to their socioeconomic and environmental efficacy, but a greater understanding of the interactions of food systems with GEC is needed to be able to do this with confidence. This paper discusses information needs relating to resource management and policy support to guide the development of research planning for increasing the robustness of IGP food systems to GEC. Further information is needed to develop a range of adaptation strategies including augmenting production and its sustainability, increasing income from agricultural enterprises, diversification from rice–wheat systems, improving land use and natural resource management, and instigating more flexible policies and institutions. [Copyright &y& Elsevier]

Investigations of changing the flow regime and flow prediction are of vital societal and hydro-ecological importance in a transboundary river like Punarbhaba river between India and Bangladesh. The present paper investigated flow regime though advance periodicity models (Morlet's wavelet transformation) at the seasonal scale. Flow prediction using advanced machine learning techniques like Support vector machine (SVM), Artificial Neural Network (ANN), Hybrid wavelet ANN (W-ANN), Random forest(RF) capturing the periodicity, duration, cyclic or semi-cyclic nature of flow wave or wavelet from the historical time series data (1978–2017) is very crucial for environmental flow management and estimating present and future states of environmental flow. Flow alteration modeling (using heat map) and estimation of environmental flow (using duration curve shifting and RVA methods) are another vital objectives of this work to know the present and future hydro-ecological state. The result of periodicity clearly identified two distinct flow regimes before and after 1992-93 triggered by damming over there in 1992. All the prediction models identified the declining trend of flow in all the seasons, however hybrid wavelet ANN model could be treated as the best suited because of its very high-performance level. The degree of hydrological alteration is identified very high in the post-hydrological alteration (PHA) (post-1992) period and it is likely to be intensified predicted period. The estimated environmental flow state in PHA falls under moderate to critically modified states but if alteration goes on in this way ecological deficit will be the obvious result. For the survival of the river estimated environmental flow could be released primarily. Image 1 • The periodicity analyses for annual and seasonal flow were performed using wavelet. • The flow has been forecasted for 13 years using machine-learning methods. • The hydrological alteration has been estimated. • The present and future environmental flow has been estimated. [ABSTRACT FROM AUTHOR]