Utilisation of satellite data in identification of geomorphic landform and its role in arsenic release in groundwater
The present study was conducted to explore the influence of geomorphic features of the area on the mobilization of arsenic in groundwater. In this study, remote sensing and GIS techniques were used to prepare the geomorphic and slope map of the area. Different geomorphic features were identified on the basis of spectral signature on the LISS III and Landsat satellite image and field survey. Groundwater samples were collected from each representative geomorphic feature to inspect the arsenic contamination in the area. The study area is drained by the Brahmaputra river and its tributaries and contain mainly fluvial geomorphic units especially older flood plain, palaeochannels, oxbow lakes, channel islands; and hilly areas at some of the places. In this study it was observed that enrichment of arsenic in groundwater varies along the geomorphic units in following trends Paleochannel> Younger alluvial plain> Active flood plain> channel island > dissected hills. The above trend shows that a higher concentration of arsenic is found in the groundwater samples collected from the fluvial landforms as compared to those collected from structural landforms. Brahmaputra River and its tributaries carry the sediment load from the Himalayan foothills, which get deposited in these features during the lateral shift of the river’s courses. Arsenic bearing minerals may get transported through river and deposit in the geomorphological features along with organic matter. The flat terrain of the area as seen from the slope map provides more residence time to water to infiltrate into the aquifer. The microbial degradation of organic matter generates the reducing environment and facilitates the dissolution of iron hydroxide thus releasing the adsorbed arsenic into the groundwater.