Analyzing Within-County Hydrogeomorphological Characteristics as a Precursor to Phosphorus Index Modifications

Area of Science:

• Environmental Science
• Agricultural Science
• Soil Science

Background:

• Phosphorus (P) site assessment is crucial for managing agricultural runoff and protecting water quality.
• Existing P Index tools require updates to accurately reflect diverse environmental conditions.
• Identifying representative sites is key to improving the P Index's effectiveness.

Purpose of the Study:

• To identify key geographic information system (GIS) parameters for P source area assessment in Pennsylvania.
• To ensure updated P Index modifications cover all feasible parameter combinations.
• To develop a manageable approach for identifying representative near-stream agricultural sites.

Main Methods:

• Compiled soil and topographic variables at 30-m resolution for Pennsylvania.
• Extracted areas within 90 m of permanent streams.
• Utilized k-means clustering and classification trees within counties to define topoedaphic groups.

Main Results:

• Identified 2-5 topoedaphic groups per county, effectively representing near-stream complexity.
• Available water capacity, hydraulic conductivity, and organic matter were the most significant environmental variables.
• County-level clustering proved effective, but discontinuities across soil survey boundaries limited broader application.

Conclusions:

• County-scale topoedaphic groupings offer a practical method for site selection in P assessment.
• The identified representative sites enable comprehensive P Index evaluation across Pennsylvania's hydrogeomorphic diversity.
• Future work will integrate management practices and validate the revised P Index.