Assessing the Influence of Hilly Landscape Characteristics on River Water Quality: A Case of Tlawng River

Abstract

Rivers globally are degrading due to pollution, climate change, and unsustainable practices, with anthropogenic stressors like industrial discharge and agricultural runoff dominating research. In India, the Ganges and its tributaries exemplify this crisis, suffering from severe contamination despite large-scale initiatives like Namami Gange. However, studies overwhelmingly focus on human-driven factors, neglecting the role of natural landscape characteristics in shaping water quality. Critical gaps persist in understanding how topography, slope gradients, and hydrological connectivity in low-order streams—vital for local communities—interact with broader river systems. These smaller, ecologically significant streams remain excluded from national assessments, particularly in India’s Northeast Himalayan foothills, where unique hydrological dynamics and fragile ecosystems demand urgent attention. This study aims to analyse how natural landscape characteristics and non-point source pollution interact to influence river water quality. By focusing on hilly terrains, the research emphasizes the role of inherent natural features—such as topography, slope gradients, and catchment hydrology—in shaping water quality dynamics. Hilly regions, often overlooked in favor of large river systems, serve as critical case studies to isolate natural drivers while addressing the understudied role of low-order streams in sustaining local ecosystems and livelihoods. The study’s uniqueness lies in its focus on cause-and-effect mechanisms between landscape attributes and gradual water quality degradation, offering nuanced insights into how terrain-specific processes amplify or mitigate pollution. These findings will advance scientific understanding of natural-environment interactions and provide actionable frameworks for sustainable watershed management in ecologically fragile, data-deficient regions like India’s Northeast Himalayan foothills. The first objective involves a systematic review of existing literature to identify mechanisms linking landscape characteristics to river water quality. This includes analyzing case studies on how natural features and non-point source pollution influence pollutant mobilization, transport, and retention. Key water quality parameters affected by these mechanisms and critical landscape metrics (quantified spatial attributes) are synthesized to define their interdependencies. This phase establishes a conceptual framework for subsequent data collection and analysis. The second objective focuses on selecting a representative hilly river system in India’s Northeast, Tlawng River, in Aizawl, Mizoram, prioritizing low-order streams with limited prior research. Data is collected through field remote sensing, and secondary sources, and based on its availability and relevance, key ecological and water quality parameters are finalized. The third objective involves analyzing temporal and spatial relationships between landscape characteristics and water quality through three steps: (1) mapping land cover changes (2017–2024) and corresponding water quality trends to establish baseline dynamics, (2) conducting correlation tests to determine the influence landscape metrics exert on specific water quality parameters, and (3) applying linear regression to quantify the percentage of water quality variation attributable to measurable changes in landscape metrics (e.g., slope gradients, vegetation cover). This approach isolates the role of natural landscape drivers in shaping river health while identifying dominant mechanisms linking land and terrain features to pollutant dynamics. The study reveals that natural landscape characteristics—particularly slope gradients, topographical connectivity, and catchment hydrology—exert significant influence on river water quality in hilly terrains. Temporal analysis shows a strong correlation between land cover changes and shifts in water quality parameters over 2017–2024. Statistical modelling indicates that steeper slopes amplify pollutant mobilization, while fragmented riparian zones reduce pollutant retention, accelerating degradation. Regression results quantify the degree to which measurable changes in landscape metrics correspond to variations in water quality, highlighting terrain-specific mechanisms driving pollution. These findings underscore the critical role of natural landscape dynamics in mediating water quality, independent of anthropogenic stressors, and provide a foundation for targeted watershed management in ecologically fragile hilly regions. This study establishes that natural landscape characteristics significantly shape river water quality in hilly areas, offering a critical counterpoint to anthropocentric pollution research. By isolating terrain-driven mechanisms—such as slope-induced erosion and hydrological connectivity—it advances understanding of how intrinsic landscape features mediate water quality degradation. Keywords: hill; river; landscape metrics; watershed; cause-effect