Monsoon-driven nutrient pollution assessment and source tracking in tropical mountain headwaters using positive...

Area of Science:

• Environmental Science
• Hydrology
• Ecosystem Ecology

Background:

• Tropical mountain ecosystems are vulnerable to nutrient enrichment due to monsoonal hydrology and land use.
• Nutrient pollution threatens downstream water quality and ecosystem services.
• Understanding nutrient dynamics is crucial for managing these sensitive environments.

Purpose of the Study:

• To investigate the spatiotemporal variability of dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silica (DSi) in surface and groundwater.
• To quantitatively apportion the sources of these nutrients in the Munnar Critical Zone Observatory, Western Ghats, India.
• To assess the eutrophication potential and inform nutrient management strategies.

Main Methods:

• Seasonal monitoring of surface water and groundwater over three monsoon cycles.
• Analysis of dissolved inorganic nitrogen, phosphorus, and silica concentrations.
• Application of the Positive Matrix Factorization (PMF) model for nutrient source apportionment.
• Calculation of nitrogen and phosphorus ratios to infer nutrient limitation and cycling pathways.

Main Results:

• Extremely high DIN/DIP ratios (up to 299:1) indicate severe phosphorus limitation.
• Significant riverine DIN flux (3.79 × 10³ tons/year) dominated by anthropogenic nitrogen inputs.
• Agricultural fertilizer identified as a major source of nitrate and phosphate, while sewage waste contributed significantly to nitrite and ammonium.
• Groundwater nitrate peaked during the monsoon due to agricultural leaching, and dissolved silica was enriched by silicate weathering.

Conclusions:

• The study quantifies significant nitrogen excess and high eutrophication potential exported from this anthropogenically stressed headwater system.
• Urgent management interventions are required, including optimized fertilizer application, riparian buffer restoration, and improved sanitation.
• These actions are crucial to curb nutrient pollution and safeguard downstream ecosystem services in tropical mountain regions.