[Identify the Nitrate Sources in Different Land Use Areas Based on Multiple Isotopes]

Area of Science:

• Environmental Science
• Geochemistry
• Hydrology

Context:

• Land use patterns critically influence regional water quality.
• Urban and agricultural river systems exhibit distinct nitrogen pollution characteristics.
• Stable isotope analysis is a powerful tool for tracing nutrient sources in aquatic environments.

Purpose:

• To differentiate and quantify nitrate (NO₃⁻) sources in urban (Grand Canal) and agricultural/forest (Yuying River) river systems.
• To assess the impact of land use on nitrogen cycling and pollution dynamics.
• To apply stable isotope analysis (δD-H₂O, δ¹⁸O-H₂O, δ¹⁵N-NO₃⁻, δ¹⁸O-NO₃⁻) and the SIAR model for source apportionment.

Summary:

• Nitrogen pollution levels varied between the Grand Canal and Yuying River.
• Precipitation was the primary water source for both rivers, indicated by hydrogen and oxygen isotopes.
• Nitrification was the dominant nitrogen cycling process, though denitrification occurred in sections of the Grand Canal.
• Nitrate sources differed significantly: urban Grand Canal received more from sewage/manure and soil nitrogen, while agricultural Yuying River was dominated by chemical fertilizer.

Impact:

• Urbanization and associated human activities (sewage, runoff) substantially increase sewage/manure contributions to nitrate pollution.
• Agricultural non-point sources, particularly chemical fertilizers, represent a severe pollution issue in rural river systems.
• Understanding these distinct pollution pathways is crucial for developing targeted water quality management strategies.