Total phosphorus reference condition for subalpine lakes: a comparison among traditional methods and a new...

Area of Science:

• Environmental Science
• Limnology
• Water Resource Management

Background:

• Estimating total phosphorus (TP) reference conditions is crucial for lake management and ecological assessments.
• Existing methods like the Morpho-edaphic index (MEI), export coefficients, and diatom/pigment models have limitations in accuracy and applicability.
• A comparative analysis of these methods is needed to identify the most reliable approaches for TP reference condition estimation.

Purpose of the Study:

• To compare the accuracy and uncertainty of frequently used TP reference condition estimation methods for lakes.
• To introduce and validate a novel process-based watershed approach for reconstructing natural or semi-natural TP load scenarios.
• To assess the performance of the new approach against established methods in subalpine lake environments.

Main Methods:

• Evaluated the Morpho-edaphic index (MEI), export coefficient, diatom-inferred, and pigment-inferred TP models using data from 35 subalpine lakes.
• Developed and applied a process-based watershed approach combining space-for-time and space-for-space substitution.
• Trained a hydrological transport model on uncontaminated conditions within or near the watershed to calibrate for the entire area.

Main Results:

• The MEI model showed a root mean square error (RMSE) of 4 μg L⁻¹, but its accuracy decreased with higher alkalinity due to phosphorus solubility.
• The export coefficient model performed similarly to the MEI, while the chlorophyll-inferred TP model had higher uncertainty (RMSE = 8 μg L⁻¹).
• The novel process-based watershed approach demonstrated superior performance with the lowest uncertainty (RMSE = 2 μg L⁻¹), accurately predicting the reference condition.

Conclusions:

• The process-based watershed approach offers a more accurate and less uncertain method for estimating lake TP reference conditions compared to traditional models.
• Limitations of existing methods, such as the MEI's sensitivity to alkalinity, highlight the need for advanced modeling techniques.
• The proposed approach holds significant potential for ecological lake modeling, particularly in studies addressing climate change impacts and eutrophication dynamics related to pristine TP loads.