Introduction

The Western Ghats is a chain of mountains extending from north to south along western peninsular India, harbors diverse and endemic flora and fauna (Ramachandra et al. 2015). It has 37 west flowing and 3 east-flowing rivers and their tributaries (Sreekantha et al. 2007). Lotic ecosystem permit complex interactions as well as mass/energy transfer between all its abiotic and biotic entities and have the capability to recover itself from the minor perturbations (Sharma and Kansal 2013). Western Ghats harbor numerous sacred groves (also known as Devarakadus, Kavu etc.), which are patches of forests having spiritual and religious importance in addition to providing hydrological services, habitat, bio-geochemical cycling, etc. (Ray et al. 2015; Ramachandra et al. 2016a).
Water quality of riverine systems depends on climate, topography, geology, soil properties, atmospheric deposition and catchment hydrology of a region. Variations in river flow affect water quality by increasing or decreasing the effects like dilution, residence time, mixing and erosion (Purnaini et al. 2018). The rate of evapotranspiration, infiltration, interception and percolation changes through modifications of catchment. Health of lotic ecosystems (streams and rivers) reflects a picture of ecosystem functioning as well as the prevailing human interactions including disturbances (Allan 2004). Anthropogenic activities in the catchment can also lead to higher concentrations of suspended solids, salts and nutrients (Lintern et al. 2018). Water bodies loose the capability of self-purification due to the influence of anthropogenic activities near the catchment (Aishvarya et al. 2018). Human activities in the watershed altering the landscape structure drives variability in the duration of flow and water quality (Huang et al. 2014). The alterations in natural flow regime, changes an ecosystem completely causing variations in physical, biological and chemical conditions of streams and its riparian zones, thereby affecting ecosystem biodiversity (Rolls et al. 2012; Bunn and Arthington 2002). Water discharge varies spatially as well as temporally, and increases along a stream network due to inputs from rainfall, tributaries and groundwater. The rate of flow recession affects the habitat preference, growth and survival of aquatic biota (Rolls et al. 2012).
Land cover in the catchment and riparian forests are vital ecological elements supporting diverse flora and fauna and perform a major role in nutrient cycling and maintaining pristine ecosystem (Girardi et al. 2016; Magdaleno and Martinez 2014). Important drivers of diversity include factors – type of the habitat, hydrologic variables, disturbance and stream morphometric, geologic and lithological variables (Tornwall et al. 2015). Precipitation rate, forests and soil characteristics in the Western Ghats decides the amount of water stored in vadose and saturated zones during monsoon, which later get released to stream in post monsoon season (Ramachandra et al. 2016a). Monitoring of hydrological variables with statistical analysis helps in better interpretation of hydrologic regime and quality of an ecosystem (Oketola et al. 2013).
Hydrological changes in forest dominated watershed are due to changes in LULC – land use and land cover altering the structure of the landscape (Cui et al. 2012). Water retention capability of the catchment declines with alterations in the catchment integrity. Forest type and its soil modify precipitation rate, bio-geochemical processes, water yield, water discharge and habitats thus interfering with the quality of water flowing to streams and other hydrological aspects (Neary et al. 2009). Run-off coefficient and water yield reduces due to reduction in total forests, especially, old forest (Singh and Mishra 2012). Conversion of forest lands for agriculture/other land use increases overland flow bringing about a decline in recharge and finally, discharge to streams during non-monsoon seasons. The sub-basins receiving good rainfall, with native species of trees in the catchment (covering to an extent more than 60-65%) have increased stream flow even in lean seasons (Ramachandra 2014). Riparian zone regulates stream water quality and are involved in exchange and transfer of elements from terrestrial to aquatic ecosystems. The seasonal and spatial variations in stream water quality is governed by various abiotic, biotic and hydrological factors like temperature, light availability, turbulence, precipitation, terrain, surface runoff, soil, groundwater flow, vegetation, quantity and composition of litter, other land use practices and aquatic biota. The main objective of the current research is to investigate the changes in the physical, chemical and nutrient parameters in selected streams of Aghanashini river basin, mainly, Chandikaholé sub catchments.