Phytoremediation for mitigating soil heavy metal contamination: A strategic approach to enhance groundwater resilience in vulnerable shallow aquifer systems

Groundwater, as the predominant freshwater resource globally, faces a growing scarcity challenge amid the rising global population, making it a critical resource in developing nations. Understanding the key factors influencing groundwater availability under current climatic and human-driven conditions is vital for achieving the sustainable development goals (SDGs). In regions like Assam's shallow alluvial aquifers, located in northeastern India along the flood-prone Brahmaputra River and the Himalayan foothills, the quality of groundwater is of paramount concern for managing its extraction and recharge. Despite its huge water potential, the region accounts for some of the most water-stressed pockets of the country, emphasising the need for thorough groundwater resource assessment for effective protection and management. The present study delves into the high vulnerability of groundwater in Assam due to both natural hydrogeological conditions and human-induced factors using geospatial models. Utilising DRASTIC and Risk Index (RI) models, we discovered that shallow groundwater tables and alluvial deposits are particularly susceptible to adverse effects from unplanned changes in land use and land cover (LULC). The findings indicate a significant correlation between urban-induced LULC changes and groundwater quality deterioration. This highlights the likelihood of industrial and domestic pollutants seeping from the soil into the underground aquifers, thus elevating the vulnerability of groundwater. To remediate the non-biodegradable and persistent heavy metal contaminants exposed to the soil from LULC activities, we propose a Nature-based Solution (NbS): phytoremediation using Chrysopogon zizanioides (vetiver grass). Laboratory-controlled experiments were conducted for two months with initial metal concentrations of lead (Pb), cadmium (Cd), and zinc (Zn) at 500 mg/kg. Results from the atomic absorption spectrometer showed selective metal absorption by the plants. The highest extraction capacity observed was 43% for Zn in the plant shoots, likely due to its role in plant metabolism, while 31% Cd and 35% Pb were removed. The study notes phytotoxicity signs, such as leaf chlorosis and shedding, indicating the plant's response to metal stress. However, with survival rates over 50%, the vetiver grass demonstrates significant metal tolerance. By integrating geospatial vulnerability assessment with the ecological technique of phytoremediation, this research presents a comprehensive strategy to enhance groundwater resilience. It showcases the efficacy of vetiver grass in developing green infrastructure solutions, offering a scalable and eco-friendly approach to mitigate soil and groundwater contamination. This study provides valuable insights for environmental policymakers and advocates, promoting sustainable NbS practices for regions facing similar challenges in groundwater management.

Keywords: Groundwater, LULC, Vulnerability, Phytoremediation, Heavy Metals, Vetiver Grass