Using a Multi-isotope Approach and Isotope Mixing Models to Trace and Quantify Phosphorus Sources in the Tuojiang...

Area of Science:

• Environmental Chemistry
• Isotope Geochemistry
• Water Quality Management

Background:

• Eutrophication control requires accurate identification of phosphorus (P) sources.
• Phosphate oxygen isotopes (δ18Op) are useful for tracing P, but their application is limited by wide and overlapping source ranges.
• Existing methods need enhancement for precise P source apportionment in aquatic ecosystems.

Purpose of the Study:

• To develop and apply a multi-isotope approach for tracing P sources in the Tuojiang River.
• To assess the effectiveness of combining δ18Op with nitrogen (δ15N), hydrogen (δD), and carbon (δ13C) stable isotopes.
• To quantify the proportional contributions of various P sources using Bayesian and IsoSource models.

Main Methods:

• Analysis of multiple stable isotopes: δ18Op, δ15N, δD, and δ13C.
• Application of Bayesian Stable Isotope Analysis in R (SIAR) model.
• Utilized the IsoSource model for source apportionment.
• Investigated the isotopic equilibrium between δ18Op and ambient water.

Main Results:

• Statistically significant differences in δ18Op values were observed between potential P sources.
• δ15N, δD, and δ13C isotopes effectively assisted δ18Op in identifying main P sources.
• Industrial and domestic sewage were identified as the largest P contributors, followed by phosphate rock/phosphogypsum and agricultural sewage.
• The SIAR model demonstrated lower uncertainty compared to the IsoSource model.

Conclusions:

• A multi-isotope approach combining δ18Op with δ15N, δD, and δ13C is effective for tracing P sources in watersheds.
• Industrial and domestic sewage represent the primary P sources in the Tuojiang River.
• The SIAR model offers a more reliable method for P source apportionment due to lower uncertainty.