Tracking riverine nitrate sources under changing land use pattern and hydrologic regime

Area of Science:

• Environmental Science
• Geochemistry
• Hydrology

Background:

• Identifying nitrate sources in streams is challenging due to anthropogenic inputs and biogeochemical processes.
• Understanding nitrate dynamics is crucial for managing water quality in coastal watersheds.

Purpose of the Study:

• To explore the dynamics of nitrate sources and transformations in headwater watersheds.
• To investigate seasonal variations in nitrate sources influenced by land use in the Jiulong River Watershed.

Main Methods:

• Utilized dual isotopic analysis of nitrate (δ¹⁵N-NO₃).
• Employed a Bayesian isotope mixing model to quantify nitrate sources.
• Analyzed samples across three watershed types and four seasons.

Main Results:

• Nitrogen sources were the primary determinant of nitrate isotopic composition.
• Chemical fertilizer was the largest contributor (36.9% ± 12.3%), followed by soil N (27.2% ± 4.4%), atmospheric deposition (23.9% ± 11.8%), and manure/sewage (12.0% ± 5.9%).
• Nitrate sources showed significant seasonal variations, with nitrification dominant in warmer months and atmospheric deposition in cooler months.

Conclusions:

• Watershed land use patterns and seasonal biogeochemical processes significantly influence riverine nitrate sources.
• This study highlights the seasonality of nitrate sources in a coastal watershed, crucial for effective water resource management.