Identifying riparian zones best suited to installation of saturated buffers: a preliminary multiwatershed assessment

Authors: Tomer, Mark; Jaynes, Dan; Porter, Sarah; James, David; ISENHART, THOMAS - Iowa State University

Submitted to: Precision Conservation: Geospatial Techniques for Agricultural and Natural Resources Conservation
Publication Type: Book / Chapter
Publication Acceptance Date: 4/4/2017
Publication Date: 6/16/2017
Citation: Tomer, M.D., Jaynes, D.B., Porter, S.A., James, D.E., Isenhart, T.M. 2017. Identifying riparian zones best suited to installation of saturated buffers: a preliminary multiwatershed assessment. In: Delgado, J., Sassenrath, G., Mueller, T., editors. Precision Conservation: Geospatial Techniques for Agricultural and Natural Resources Conservation. Madison, WI: ASA and CSSA. p. 83-93. https://doi.org/10.2134/agronmonogr59.2013.0018.
DOI: https://doi.org/10.2134/agronmonogr59.2013.0018

Interpretive Summary: Saturated riparian buffers are a new type of conservation practice that divert subsurface tile drainage water from direct discharge to surface water into distribution pipes that discharge the tile water into riparian soils. This enables natural processes of biological uptake and denitrification to decrease nutrient loads that are being lost from croplands via tile drains, reducing water quality impacts from agriculture at relatively little cost. This chapter suggests and evaluates draft criteria that identify riparian zones within a watershed that are suited to installation of saturated buffers. Soils and topographic criteria were used to highlight riparian locations where soil conditions should enhance nutrient removal, but also identify locations where risks of streambank failure and/or inundation of crops adjacent to the buffer may occur. Three Midwestern watersheds were used to demonstrate results. Topographic criteria were more restrictive than soils criteria, especially in flat landscapes, but 30 to 60% of streambank lengths in the test watersheds were deemed suitable to installation of saturated buffers. While this information is useful in planning, on-site investigation is needed to design the saturated buffer practice to fit site-specific conditions. This information is of interest to conservationists and water quality planning agencies in Midwest states where agricultural drainage and water quality issues have become associated with one another.

Technical Abstract: Saturated riparian buffers are a new type of conservation practice that divert subsurface tile drainage water from direct discharge to surface water into distribution pipes that discharge the tile water into riparian soils. This enables natural processes of biological uptake and denitrification to decrease nutrient loads that are being lost from croplands via tile drains, reducing water quality impacts from agriculture at relatively little cost. This chapter suggests and evaluates draft criteria that identify riparian zones within a watershed that are suited to installation of saturated buffers. Soils criteria, evaluated using soil survey information, include subsurface accumulations of soil organic matter (SOM) (> 1% SOM at 0.75–1.2 m depth), relatively fine-textured subsoils (< 50% sand at 0.75–1.2 m depth), and a shallow water table (< 1 m depth) April through June. These criteria highlight riparian locations where soil conditions should enhance nutrient removal. Criteria are also proposed to avoid locations where streambank failure and/or inundation of crops adjacent to the buffer may occur, which are evaluated using high-resolution digital elevation models, now widely available through LiDAR (light detection and ranging) surveys. The criteria were evaluated in three Midwestern HUC-12 watersheds dominated by fine-grained glacial deposits. Results showed topographic criteria were more restrictive than soils criteria, especially in the flattest landscapes, but 30 to 60% of streambank lengths in the test watersheds were deemed suitable to installation of saturated buffers. This evaluation contributed to inclusion of a saturated buffer siting tool in the Agricultural Conservation Planning Framework (ACPF). Local information is needed to design this practice to fit site conditions.