Identifying riparian sinks for watershed nitrate using soil surveys

Area of Science:

• Environmental Science
• Soil Science
• Hydrology

Background:

• Riparian zones are vital for controlling watershed nitrogen flux, but their effectiveness varies significantly.
• Lack of stratification for nitrate removal capacity hinders accurate watershed modeling and targeted restoration.

Purpose of the Study:

• To evaluate the Soil Survey Geographic (SSURGO) database's ability to classify riparian zones based on groundwater nitrate removal capacity.
• To identify key SSURGO map classifications for predicting high nitrate removal potential.

Main Methods:

• Examined 100 riparian sites in Rhode Island with varying geomorphic settings (till, outwash, organic/alluvial).
• Defined high nitrate removal capacity by >10m hydric soil width and absence of surface seeps.
• Utilized SSURGO classifications (geomorphology, hydric soil) to stratify sites.

Main Results:

• SSURGO classification combining geomorphology and hydric soil status distinguished riparian sites by nitrate removal potential.
• Over 75% of "organic/alluvium-hydric" and "outwash-hydric" sites showed high removal capacity.
• Over 85% of "till" and "nonhydric outwash" sites exhibited low removal capacity.
• The STATSGO database significantly under-represented critical riparian features compared to SSURGO.

Conclusions:

• SSURGO database classifications, particularly geomorphology and hydric soil data, can reliably stratify riparian zones by groundwater nitrate removal capacity.
• This stratification is essential for improving watershed nitrogen flux models and guiding effective riparian management and restoration.