Legacy nutrients in the Baltic Sea drainage basin: How past practices affect eutrophication management

Area of Science:

• Environmental Science
• Ecosystem Modeling
• Water Resource Management

Background:

• Anthropogenic nutrient inputs to the Baltic Sea catchment have tripled since 1900, peaking in the 1980s.
• Nutrient storage in land and inland waters creates legacy pools affecting export to the Baltic Sea.
• Terrestrial and aquatic sinks play a dominant role in nutrient removal.

Purpose of the Study:

• To develop a nutrient fate model linking catchment inputs to Baltic Sea loads from 1900 to present.
• To quantify the impact of nutrient storage, time-lags, and legacy effects on riverine nutrient loads.
• To assess the implications for Baltic Sea management plans.

Main Methods:

• Constructed a nutrient fate model for the Baltic Sea catchment.
• Incorporated temporary nutrient storage in land and inland waters (legacy pools).
• Accounted for nutrient removal by terrestrial and aquatic sinks.

Main Results:

• Model indicates response times of ~4 years for nitrogen and 6-18 years for phosphorus riverine loads.
• Mineral fertilizer use dominates inputs; sewage treatment influences load composition.
• Mobilization from legacy pools is the primary source of current anthropogenic riverine nutrient loads.
• Legacy effects of past phosphorus reductions offer unrealized load reduction potential.

Conclusions:

• Nutrient storage and time-lags significantly influence riverine loads to the Baltic Sea.
• Legacy effects of past phosphorus reductions can contribute to meeting management targets.
• Accounting for these factors may reduce the necessity for future mitigation measures.