[en] Tritium concentrations in surface waters of river Brahmaputra in the north, Kali river and streams and in ground waters in and around Kaiga, Karnataka in south and in streams and ground water sources around Mumbai lying between these locations have been measured. River waters of Brahmaputra showed concentrations of 1.4 Bq/l (SGM), surface waters of Kali river and nearby streams as well as ground waters around Kaiga showed tritium levels around 0.7 Bq/l (SGM) and ground waters of Mumbai, 0.8 Bq/l (SGM). The values are discussed in the light of similar studies for environmental tritium reported earlier. (author)

[en] The Ganges-Brahmaputra river system supplies more dissolved uranium to the ocean than any other system in the world (Sarin et al., 1990; Sackett et al., 1973). However, there have been no investigations to determine whether riverine supplies of uranium are altered by geochemical reactions in the river-ocean mixing zone. In this study, uranium and salinity data were collected in the Ganges-Brahmaputra mixing zone during a period of low river discharge. The uranium distribution with salinity shows that in waters <12 ppt salinity, uranium activities are significantly lower than predicted from conservative mixing of river and seawater. This suggests that uranium is being removed within the mixing zone. The behavior of uranium in the Ganges-Brahmaputra is in sharp contrast to its behavior in the Amazon mixing zone where McKee et al. (1978) found uranium activities significantly higher than predicted from conservative mixing. The contrasting behaviors for uranium in these systems are due to the different locations where mixing between river and seawater occurs. For the Amazon, mixing takes place on the continental shelf whereas for the Ganges-Brahmaputra, mixing occurs within shoreline sedimentary environments. The physiochemical processes controlling uranium removal to sediment deposits in the Amazon are partly known. The authors discuss mechanisms which may be removing uranium to suspended and mangrove sediments in the Ganges-Brahmaputra

[en] The present study was conducted to measure globally alarming of ten heavy metals (Pb, Cd, Cr, Cu, Hg, Al, Ni, Co, Zn and Mn) in surface water and sediment of the Old Brahmaputra River in Bangladesh. The observed order of heavy metal mean concentration in water and sediments is Al > Mn > Ni > Co > Cu > Pb > Zn > Cr > Cd > Hg in mg/l and Al > Mn > Zn > Ni > Pb > Cr > Cu > Co > Cd > Hg in mg/kg, respectively. The significant variations of Cr, Cu, Al and Ni were found in the water of all seasons (p < 0.05), while sediment showed Pb and Hg exhibited substantial changes in terms of seasons (p < 0.05). Principal component analysis and correlation matrix revealed that significant anthropogenic input of Pb, Cd, Cr, Cu, Hg, Al, Ni, Co, Zn and Mn in water and sediment. In case of water, very strong linear relationships exhibited in Ni versus Cu (0.911), Ni versus Al (0.910), Mn versus Co (0.882), Cr versus Al (0.877), Cu versus Cd (0.853), Ni versus Pb (0.850), Zn versus Cr (0.833), Ni versus Cd (0.828), Cu versus Cr (0.827), Al versus Cd (0.827) and Zn versus Co (0.804) at the significance level 0.05. In sediments, very strong linear relationships were noted in Zn versus Cr (0.889), Al versus Pb (0.848), Co versus Al (0.819) and Mn versus Co (0.806) at the significance level 0.05. The result discovered that water and sediment quality of the Old Brahmaputra River became contaminated due to the anthropogenic sources of industrial, domestic and irrigation discharges. This environmental monitoring and assessment research will be useful for the management and planning for the protection of this river.

[en] Urbanisation and climate change can have adverse effects on the streamflow and water balance components in river basins. This study focuses on the understanding of different hydrologic responses to climate change between urban and rural basins. The comprehensive semi-distributed hydrologic model, SWAT (Soil and Water Assessment Tool), is used to evaluate how the streamflow and water balance components vary under future climate change on Bharalu (urban basin) and Basistha (rural basin) River basins near the Brahmaputra River in India based on precipitation, temperature and geospatial data. Based on data collected in 1990–2012, it is found that 98.78% of the water yield generated for the urban Bharalu River basin is by surface runoff, comparing to 75% of that for the rural Basistha basin. Comparison of various hydrologic processes (e.g. precipitation, discharge, water yield, surface runoff, actual evapotranspiration and potential evapotranspiration) based on predicted climate change scenarios is evaluated. The urban Bharalu basin shows a decrease in streamflow, water yield, surface runoff, actual evapotranspiration in contrast to the rural Basistha basin, for the 2050s and 2090s decades. The average annual discharge will increase a maximum 1.43 and 2.20 m³/s from the base period for representative concentration pathways (RCPs) such as 2.6 and 8.5 pathways in Basistha River and it will decrease a maximum 0.67 and 0.46 m³/s for Bharalu River, respectively. This paper also discusses the influence of sensitive parameters on hydrologic processes, future issues and challenges in the rural and urban basins.

[en] The occurrence of catastrophic events i.e. floods has proven to play a key role in the rapid sediment delivery from the source area to depocenters and in understanding the focused erosion zones in highland areas. Tracking the provenance of these catastrophic flood sediments provides an insight into the linkage between climate-tectonic coupling and earth surface processes. In general, information on sediment sources has been derived through petrographic and mineralogical investigations on distinct grain-sized sediment or on a grain-by-grain basis, zircon U–Pb geochronology. However, information from fractionated sediment investigations has made it impossible to distinguish source areas using different methods. Sr-Nd isotopes on bulk sediment on the other hand, are still uncommon in tracing the sediment provenance. All three methods discuss the provenance based on the geology of the catchment area, cycles of erosion, mineral maturity. The petrographic and mineralogical investigations respond to short-term sedimentary processes, U-Pb zircon chronology responds to long-term sedimentary processes, however, Sr-Nd responds to both the processes. Therefore, it is crucial to critically examine all these methodologies in tracking the origin of sediment. This research gives an integrated mineralogical–geochemical database on sediments carried by the extreme events in the Tsangpo-Siang-Brahmaputra river system. We attempted to compare the above-mentioned fingerprint approaches and determine the optimal strategy by comparing them on the same samples to determine the relative relevance of various sources. The petrographic analysis was done using Gazzi-Dickinsion method and implied that most of the samples were eroded from Higher Himalaya with a minute amount sourced from Tibet Plateau. This was a bit mystifying as the floods were sourced by the bleaching of glacial dammed lakes from the Tibetan Plateau (Panda et al., 2020). In normal conditions, some studies using the zircon U–Pb geochronology have also suggested Higher Himalaya (Namche Barwa massif) as an erosional hotspot in North-Eastern Syntaxis but in case of extreme events, such study are yet to be done. While the Sr-Nd analysis was done and shows the dominancy of sediments derived from the Tibetan Plateau. Thus, the provenance fingerprinting using the two proxies gives dissimilar results. However, the robustness of Sr-Nd systematics allows us to suggest that the megafloods in the Siang River carried a large amount of sediments that were eroded from Tethyan sequences before entering into the George area, adding additional sediment from crystalline material of the higher Himalaya.

[en] South-west monsoon of 2019 advanced towards northern parts of India during the first week of July. Heavy-to-very-heavy rainfall events during July 05–16 resulted in severe flooding over Bihar and Assam and caused huge damage in the form of life and property. More than 90 lakhs people have been affected, and about 100 causalities have been reported in Bihar and Assam due to severe flooding. Results presented in this short communication highlight the importance of space-borne near real-time monitoring of flood events. It is reported that few districts of Assam and Bihar received cumulative rainfall in excess of 1200 mm from multiple heavy rainy events during July 05–16, 2019. Heaviest rainfall events were reported on July 06, 11 and 13. Few districts of Assam and Bihar experienced daily rainfall in excess of 300 to 400 mm during these heavy rainy days with peak hourly rainfall exceeding 50 mm at few synoptic hours. Discharge from Kosi and Brahmaputra rivers combined with heavy cumulative rainfall from multiple rainy episodes during July 05–16 resulted in severe flooding over Assam and Bihar causing losses to life and property.

[en] Distribution of the natural radionuclides ( "2"3"8U, "2"3"2Th, and "4"0K) and their specific activities in sands and sediments of the Brahmaputra (Jamuna) river of Bangladesh together with mineral characteristics has been studied to assess the radiation levels as well as to develop a baseline database for comparison in the future in case of any change in the area under study due to anthropogenic activities. The radiological parameters of natural radioactivity were assessed calculating the radium equivalent activity, hazard index, the absorbed dose rate, and annual effective dose. The average activity concentrations of "2"2"6Ra ("2"3"8U), "2"3"2Th, and "4"0K in sand and sediment were found to be 59 ± 2 and 60 ± 2 Bq/kg, 113 ± 5 and 135 ± 5 Bq/kg, and 983 ± 42 and 1002 ± 43 Bq/kg, respectively. The calculated average absorbed dose rate and annual effective dose were found to be 150 nGy/h and 0.18 mSv/year respectively. These high values are associated with mineral content of the sediment. X-ray diffraction peaks of sand and sediment samples identify quartz, feldspar, rutile, zircon, monazite, uranium fluoride, hematite, kyanite, and uranium arsenide minerals to be present in the samples. (author)

[en] We analyzed changes in the relationship between geo-environment and agricultural land development around the central Jamuna (Brahmaputra) River, central Bangladesh. Based on sedimentary facies analysis and AMS radiocarbon dating, some conclusions are as follows: (1) Natural levees along the Jamuna River formed until ca. 12 to 11 k cal yrs BP; (2) Homesteads (bari-bhiti) were repaired by public works (mati-kata) following some flood events; (3) Paddy fields and homesteads were created since ca. 1.3 k cal yrs BP around central Bangladesh (central Bengal Delta). (author)

[en] The Brahmaputra river system with over hundred tributaries contains one of the biggest single concentration of hydel potential in the world in addition to the tremendous amount of navigable facilities. Ambitious development plans for utilisation of this vast untapped potential of the water resources will also help in solving the perennial problem caused by flood in Assam. A few long term projects for a near permanent solution to the flood problems and also for utilisation of the water resources of the system meaningfully for economic prosperity of the entire region have been suggested. (author). 3 figs., 3 tabs

[en] Highlights: • High levels of dissolved As are observed in YTR system. • Hot springs are main source of dissolved As in the upper reaches of YTR. • Natural attenuation of dissolved As in main channel is mainly due to dilution. • Lowest dissolved As is observed in July and August due to dilution process. • Weathering of As-containing minerals inputs much of As in rivers in wet-season. High levels of dissolved arsenic (As) have been reported in many rivers running though the Tibetan Plateau (TP), the “Water Tower of Asia”. However, the source, spatiotemporal variations, and geochemical behavior of dissolved As in these rivers remain poorly understood. In this study, hot spring, river water, and suspended particulate material samples collected from the Yarlung Tsangpo River (YTR) (upper reaches of the Brahmaputra River) system in 2017 and 2018 were analyzed. Spatial results shown that the upper reaches of YTR (Zone I) have comparatively high levels of dissolved As ([As]_dissolved: mean 31.7 μg/L; 4.7–81.6 μg/L; n = 16), while the tributaries of the lower reaches (Zone II) have relatively low levels (mean 0.54 μg/L; 0.11–1.3 μg/L; n = 7). Seasonal results shown that the high [As]_dissolved (6.1–22.4 μg/L) were found in September to June and low [As]_dissolved (1.4–3.7 μg/L) were observed in July to August. Geothermal water is suspected as the main source of the elevated As levels in YTR due to the extremely high [As]_dissolved in hot springs (1.13–9.76 mg/L) and abundance of geothermal systems throughout TP. However, the seasonal results suggested that weathering of As-containing rocks and minerals is also a key factor affecting the [As]_dissolved in the river water in July to August (wet-season). Natural attenuation of As in main channel is dominated by dilution process due to the lower As concentrations in tributaries, but mostly occurred by both dilution and adsorption (or co-precipitation) processes in tributaries. This work highlights that the weathering process may have an important contribution to the dissolved As in the river waters in wet-season, and the geochemical behavior of As is largely transported conservatively in the main channel and relative non-conservatively in the tributaries in YTR system.