Introduction

The aquatic ecosystem plays a vital role in sustaining ecological processes and the basic needs of society. Ecosystem quality varies due to natural processes (such as climatic factors, precipitation, soil erosion, weathering of rocks, soil quality, and watershed characteristics) and anthropogenic factors such as land-use changes, overexploitation of water resources, and agricultural practices [1,2]. During the twenty-first century, the planning, development, and management of aquatic resources relied on human-centric factors such as population, per capita water demand, agriculture production, and socio-economic activities [3]. Developing countries in the tropics have been facing water stress due to large-scale land cover changes from deforestation [4,5], unplanned developmental activities, and unprecedented and unscientific agriculture practices with extensive water abstraction [6–9]. The overexploitation of freshwater resources to cater to burgeoning societal needs has compromised the health and sustainability of resources in India and across the globe [10,11]. Anthropogenic activities coupled with skewed policies have resulted in the disappearance of pristine forests [12–14] in the catchment, affecting biogeochemical dynamics [4,15–17]. The structural changes in the catchment (landscape) have affected the functional aspects of ecosystems, thereby impairing the assimilative and supportive capacity [18,19] of fragile ecosystems. The impacts are evident with the recurring instances of droughts and floods and with the shortages of quality water affecting the regional economy and people’s livelihoods [20]. The conservation of forests with native species in the catchment has helped sustain the hydrological regime and maintain biodiversity [21].

The integrity of the catchment of aquatic ecosystems decides water sustenance, as vegetation helps in retarding the velocity of water by allowing impoundment and groundwater recharge through infiltration. At the same time, another fraction returns to the atmosphere through evapotranspiration. Forests with native species of plants would aid as sponges, retaining and regulating the transfer of water between land and atmosphere [21]. The mechanism by which vegetation controls the flow regime is dependent on various bio-physiographic characteristics, namely, the type of vegetation, the species composition, maturity, density, structure, aerodynamic and surface resistance, root density and depth, and the hydro-climatic conditions [22]. The roots of diverse terrestrial vegetation provide habitats for diverse microflora and fauna, and with microbial actions, the soil has higher porosity or permeability, thereby enabling efficient infiltration. These functions depend on the diversity and maturity of the forests, and the density of plant species. This necessitates safeguarding and maintaining the existing native forest patches to sustain the hydrological regime, which caters to biotic (ecological and societal) demands. An undisturbed native forest has a consistent hydrologic regime with sustained flows during lean seasons [21,22].

Generally, ecosystems permit complex interactions among abiotic and biotic entities to recover from minor perturbations [21–23]. It is necessary to maintain the quantity, quality, and timing of flow [23,24], which is also known as ecological flow [25–27] across all segments of the riverine systems for the sustainable functioning of freshwater resources. This emphasizes understanding the hydrologic regime and the consumption behavior and transactions of resources among/between ecological and societal activities [28]. The hydrological regime sustaining the biotic components is referred to as an eco-hydrological footprint.

The physical, chemical, and biological characteristics of aquatic ecosystems are determined by water quality assessments [29]. The long-term and continuous monitoring of surface water bodies provides insights into the spatial and temporal variability in water quality [30,31]. Alterations in water quantity and quality govern the species composition, ecosystem productivity, and physiological conditions of aquatic organisms. Altered flows due to changes in ecosystem conditions influence the fish population, bringing about changes in habitat, food availability, community structure, composition, and behavior [32]. Pollutants such as heavy metals cause a severe threat to living organisms and humans as they are toxic and persist for a more extended period in nature, resulting in their bioaccumulation in the food chain [33,34].

Various statistical approaches have been adapted for interpreting water quality variables [35,36]. Furthermore, the computation of water quality indices (WQI) aid in understanding the suitability of water for anthropogenic purposes. Multivariate analysis such as cluster analysis (CA) and principal component analysis (PCA) aid in understanding spatial-temporal variations, a grouping of monitored stations, and identification of important factors that influences the quality of streams [37–40].

The Aghanashini River in the central Western Ghats is a free-flowing river that supports rich biodiversity and sustains people’s livelihoods. The catchment of this river is witnessing land cover changes due to increasing societal demands. This necessitates understanding landscape dynamics with biodiversity, hydrologic regime, and water quality characteristics for the prudent management of fragile aquatic ecosystems.

The eco-hydrological footprint assessment of a river considers water availability, water quality characteristics, and water demand for the sustenance of biotic components. The objective of the current research is to assess the eco-hydrological footprint of the Aghanashini River basin at the sub-catchment level, considering various societal demands, ecological needs, and water availability. This entailed land use analysis; spatio-temporal analyses of annual rainfall data, hydrological and ecological footprint, the computation of eco-hydrological indices (EHI), eco-hydrological footprint, and water quality indices (through water quality assessment).