Comparing Drivers of Spatial Variability in U.S. Lake and Stream Phosphorus Concentrations

Area of Science:

• Environmental Science
• Water Quality
• Ecology

Background:

• Surface water phosphorus (P) concentrations are critical for freshwater ecosystem health.
• Identifying drivers of P loading and pollution sources is essential for effective water quality restoration.
• Environmental factors mediate P transport and retention in aquatic systems.

Purpose of the Study:

• To identify key drivers of surface water phosphorus concentrations in streams and lakes across the conterminous United States.
• To determine how environmental factors and pollution sources co-locate to influence P loading.
• To inform watershed restoration strategies by understanding P dynamics.

Main Methods:

• Utilized publicly available spatial data sets of P pollution sources and environmental variables (temperature, precipitation, soil erodibility).
• Matched spatial data with over 7,000 stream and lake total P observations.
• Employed correlation, regression, and machine learning techniques to analyze P drivers.

Main Results:

• Stream P concentrations were strongly correlated with annual fertilizer/manure inputs and agricultural legacy sources.
• Lake P concentrations showed associations with agricultural inputs but were more influenced by historic erosion and internal recycling.
• Both stream and lake P concentrations are projected to increase due to warming temperatures and forest recovery.

Conclusions:

• Streams may respond more rapidly to agricultural nutrient management improvements than lakes.
• Lake P dynamics are complex, influenced by long-term factors, suggesting slower responses to management.
• Climate change and land use recovery will exacerbate P loading challenges, necessitating adaptive restoration strategies.