Groundwater Hydrology and its Role in Supporting Aquatic Ecosystems in Semi-Arid Regions

Abstract

Water scarcity in semi-arid regions poses one of the most important environmental issues in the Anthropocene and has become further compounded by climatic variation and increasing anthropocentric demands. Groundwater has traditionally been viewed as a key resource for agricultural and industrial purposes; however, the role of groundwater as a critical yet hidden lifeline for aquatic ecosystem health is often overlooked, resulting in a major gap in both scientific knowledge and policy development. It tackles the "hydro-ecological" divide within a typical semi-arid system, the Lower Bhavani River Basin, characterized by fractured crystalline bedrock lithology. Over the course of 24 months (2024-2026), it quantified the hydrological linkage between groundwater and the Bhavani River using a network of 12 boreholes instrumented with a multi-sensor monitoring network and stable isotope analysis (H and O). Combining these hydrological data with remote sensing-derived riparian vegetation indices (NDVI) and macroinvertebrate diversity within a structural equation model framework, it determines a critical groundwater depth-to-aquifer threshold of 6.5 m below which ecosystem health is critically impaired. It found that current extraction volumes exceed the water balance, creating a "bottleneck effect" where anthropogenic demand during the dry season decouples the essential base flow component. This research emphasizes the dire need for the establishment of an integrated water resources management policy that extends beyond an anthropocentric abstraction regime. The introduction of statutory "Groundwater Environmental Flows" and a system of participatory management are recommended, enabling the balancing of socio-economic demands with the long-term survival of these groundwater-dependent habitats before their irreversible deterioration.