Groundwater systems of the Indian Sub-Continent

© 2015. The Indian Sub-Continent is one of the most densely populated regions of the world, hosting ~23% of the global population within only ~3% of the world's land area. It encompasses some of the world's largest fluvial systems in the world (River Brahmaputra, Ganges and Indus Basins), which hosts some of the highest yielding aquifers in the world. The distribution of usable groundwater in the region varies considerably and the continued availability of safe water from many of these aquifers (e.g. Bengal Basin) is constrained by the presence of natural contaminants. Further, the trans-boundary nature of the aquifers in the Indian Sub-Continent makes groundwater resource a potentially politically sensitive issue, particularly since this region is the largest user of groundwater resources in the world. Indeed, there is considerable concern regarding dwindling well yield and declining groundwater levels, even for the highly productive aquifers. Though irrigation already accounts for > 85% of the total ground water extraction of the region, there is a mounting pressure on aquifers for food security of the region. Highly variable precipitation, hydrogeological conditions and predicted, impending climate change effects provide substantial challenges to groundwater management. The observed presence of natural groundwater contaminants together with the growing demand for irrigated food production and predicted climate change further complicate the development of strategies for using groundwater resources sustainably. We provide an introduction and overview of 11 articles, collated in this special issue, which describe the current condition of vulnerable groundwater resources across the Indian Sub-Continent

Provenance and fate of trace and rare earth elements in the sediment-aquifers systems of Majuli River Island, India

In this work, we present a completely new dataset of Rare Earth Element (REE) distribution and fractionation in the groundwater and sediments of the world's largest populated river island-Majuli, located in the Brahmaputra River, India. Groundwater (n = 9) and borehole sediments (n = 23) of different depths were collected randomly and analyzed for REEs using inductively coupled plasma mass spectrometry (ICP-MS). Multivariate statistical techniques were applied to determine interrelationships among different REEs. Both water and sediments exhibit a higher content of light rare earth elements (LREEs) than heavy rare earth elements (HREEs), implying that source rock composition primarily controls the REE signatures of these river sediments, largely owing to variations in levels of chlorite and monazite, which are more abundant in bottom river sediments of the Brahmaputra. However, lower LREE/HREE ratios in groundwater samples (8.42–14.48) compared to sediments (8.9–52.6) suggest less dissolved phase mobilization of LREE during weathering and transport. Hierarchical cluster analysis showed more consistent clustering in sediment compared to water and clear demarcations of MREE, HREE and LREE were observed in the sediments. The primitive mantle-normalized REE patterns of borehole sediments were similar to the upper continental crust (UCC) and the compositions of average Himalayan rocks. LREE enrichment compared to HREE suggest dominance of a felsic source. However, a La/V versus Th/Yb plot suggests a small contribution from the mafic source component. The sediments show high Th/Sc (>1 of UCC) and high Zr/Sc. A Eu/Eu* verses GdN/YbN plot suggests that the dominant source with Upper crustal composition has undergone multiple recycling