Spatial variability assessment of groundwater quality dispersion with reference to land-use indices

The anthropogenic influences, allied with land-use dynamics, induce the spatial variability of the constituents by overall altering the groundwater qualitative status. It is one of the pertinent linkages, that is seldomly discussed, and in turn, would highlight an insight into the potent pollution sources, pathways, and emergent plumes for accretion or dilution effects in groundwater hydrochemistry. A case study was attempted for assessing the spatial variability of groundwater quality (within shallow aquifers) in the populous Ghaziabad district of western Uttar Pradesh of India. A total number of 26 sampling sites were analyzed for quality parameters such as major cations, anions, and heavy metals for pre-and post-monsoon seasons for two consecutive years (2017&2018). The magnitude of accretion and dilution effects in groundwater were estimated by using a numerical method of Normalized Difference Dispersal Index (NDDI), which targets the site-specific variability of the quality constituents in terms of degree and space. The index value for each constituent parameter was profiled by using geostatistical mapping (ordinary kriging) and further, validated for the spatial pattern through Global Moran’s I. For a plausible comparison, NDDI spatial maps were analyzed with land use indices, namely, Normalized Difference Vegetation Index (NDVI), Normalized Differential Salinity Index (NDSI), Normalized Difference Built-Up Index (NDBI), and Modified Normalized Difference Water Index (MNDWI), to predict the influence sources of accretion or dilution effects of the constituents in the groundwater quality. The obtained results have shown that the NDDI method coupled with land use indices, in the spatial extent, has profoundly estimated the plumes of abundant accretion/dilution of the quality parameters and hotspots were preferably found within the urbanized & highly populated as well as irrigating fields (peri-urban regions) of Ghaziabad district. The study concludes that spatial variations of groundwater quality are easy to comprehend and would pertinently assess the quality control while delivering groundwater monitoring & management strategies for predicting the impacts arising from land-use influences within the regional/localized studies.