Modeling diffuse phosphorus loads from land to freshwater using the sedimentary record

Area of Science:

• Environmental Science
• Limnology
• Paleolimnology
• Agricultural Science

Background:

• Diffuse phosphorus (P) loading is a major driver of freshwater eutrophication.
• Understanding long-term P load dynamics in agricultural catchments is crucial for effective water management.
• Palaeolimnological models offer a method to reconstruct historical environmental conditions in lakes.

Purpose of the Study:

• To quantify diffuse phosphorus (P) loads to Friary Lough over a 90-year period.
• To validate a palaeolimnological model using contemporary hydrochemical monitoring data.
• To analyze trends in P loads and relate them to agricultural practices and soil P dynamics.

Main Methods:

• Application of a palaeolimnological model to reconstruct lake total phosphorus (TP) loads.
• The model accounts for TP loss to sediments, outflow, and water column storage.
• Verification of reconstructed TP loads (1991-1995) with hydrochemical monitoring data (1997-1998).

Main Results:

• Reconstructed TP loads for 1991-1995 were 2.05-2.53 g m-2 yr-1, consistent with monitoring data.
• A linear increase in TP loads was observed from approximately 1946 to 1995, at a rate of 1.20-1.56 kg km-2 yr-1.
• The rate of TP increase mirrors trends found in a larger catchment, suggesting widespread agricultural impacts.

Conclusions:

• The palaeolimnological model accurately reconstructs historical TP loads, confirming external catchment runoff as the primary source.
• Increasing soil phosphorus concentrations and threshold effects in agricultural soils likely drive the observed rise in diffuse P loss.
• Long-term monitoring and palaeolimnological reconstructions are vital for understanding and mitigating P pollution in lake ecosystems.