Phosphorus Loss from Ephemeral Gully Formation

Gully erosion at Neal Smith National Wildlife Refuge
Nutrient Management

Title:  Phosphorus loss from ephemeral gully formation and sediment transport

Location:  Neal Smith National Wildlife Refuge

Time Period:  2015

Research Team:  Richard Cruse, Eric Hurley, Antonio Mallarino, and Matt Helmers

Project Description:  Project goal was to determine the quantity of phosphorus loss in 12 Iowa watersheds and the proportion of total phosphorus loss from these watersheds that originates from ephemeral gully formation.  In watersheds with 100% rowcrop, approximately 50% of total phosphorus loss was ephemeral gully sourced. The contribution of phosphorus loss from ephemeral gullies is reduced by an average of 50% in watersheds that contain perennial cover in strategic locations reducing ephemeral gully formation. Average loss of water soluble phosphorus from ephemeral gullies was also reduced by 40% when perennial grasses were strategically placed reducing ephemeral gully formation.  

A second task of this grant was to define a mapping procedure to delineate permanent vegetation along streams that represents the riparian zone. Automated methods using imagery, NDVI and proximity to streams generated vegetation polygons far beyond the riparian zone especially in more forested areas of the state. Ancillary data such as alluvial soils and landscape position were tested to see if they improved the riparian designation. Alluvial soils were shown to be helpful but the process still required a staff person to review the preliminary results and make data modifications. This process proved faster than manual digitizing and provided more repeatable and consistent results however, it required good resolution spring CIR imagery.

About a year after this portion of the project was completed, QA/QC conservation practice data was made available for public download as it was reviewed and finalized at The entire statewide dataset was finally completed and online in May 2019.


Funders:  Iowa Nutrient Research Center, NIFA and Iowa State University Department of Agronomy