Predicting nitrogen and acidity effects on long-term dynamics of dissolved organic matter

Area of Science:

• Environmental Chemistry
• Ecology
• Biogeochemistry

Background:

• Dissolved organic carbon (DOC) fluxes are increasing, potentially linked to sulphur and nitrogen pollution.
• Understanding the drivers of DOC flux is crucial for predicting aquatic ecosystem responses to environmental change.

Purpose of the Study:

• To develop and validate the MADOC model integrating vegetation, soil, and water chemistry processes.
• To investigate the mechanisms behind sustained increases in DOC fluxes.
• To explore the relationships between pH, pollution, and DOC dynamics.

Main Methods:

• Integrated existing models of vegetation growth, soil organic matter turnover, acid-base dynamics, and organic matter mobility into the MADOC model.
• Calibrated model parameters using field experiments with controlled acidifying and alkalising solution additions.
• Validated the model against observed long-term trends in acid waters.

Main Results:

• The MADOC model successfully reproduced observed responses of pH and DOC to experimental treatments.
• Model simulations indicated that sustained DOC increases are best explained by a continuously replenishing carbon pool.
• The model suggests a link between increased plant productivity, pH changes, and DOC increases.

Conclusions:

• The MADOC model provides a robust framework for understanding DOC dynamics in response to environmental changes.
• Sustained DOC increases are likely driven by ongoing carbon replenishment rather than the dissolution of large accumulated stores.
• Nitrogen pollution's impact on DOC will manifest and persist after soil pH stabilization, influenced by plant productivity.