Climate factors increasing in importance for internal P dynamics in a large eutrophic lake

Area of Science:

• Environmental Science
• Limnology
• Water Quality Management

Background:

• Legacy phosphorus (P) in lake sediments poses a significant challenge to improving water quality through catchment management.
• Understanding the long-term behavior of internal phosphorus reservoirs is crucial for effective lake management and setting realistic recovery targets.

Purpose of the Study:

• To characterize long-term changes in internal phosphorus loading in Lough Neagh.
• To assess the influence of changing lake temperature and catchment inputs on internal phosphorus dynamics.
• To evaluate the impact of internal phosphorus loading on lake water quality over five decades.

Main Methods:

• Utilized steady-state empirical lake models to analyze phosphorus dynamics.
• Compiled and analyzed phosphorus mass balances for Lough Neagh over a five-decade period.
• Investigated the influence of lake water temperature, external phosphorus loading, and pH on sediment phosphorus release.

Main Results:

• Internal phosphorus loading in Lough Neagh increased rapidly in the mid-1990s and has remained elevated.
• Annual mean total phosphorus (TP) concentrations were over 30 μg L⁻¹ higher in the latter half of the study period.
• Net internal phosphorus loading increased from 243 to 577 mg TP m⁻² yr⁻¹, contributing 25% to 47% of the annual mean lake TP concentration.

Conclusions:

• Elevated internal phosphorus loading, driven by temperature, external loading, and pH, will persist, hindering water quality recovery for decades.
• Recycled legacy phosphorus from sediments significantly impedes the achievement of short-to-medium term water quality targets.
• Sustainable lake management requires addressing internal phosphorus sources alongside external load reductions.