Identifying Riparian Zones Appropriate for Installation of Saturated Buffers: A Multi-Watershed Assessment.

Saturated riparian buffers are a new type of conservation practice that divert a portion of subsurface tile drainage from discharge to surface water into distribution pipes that discharge tile water into riparian soils. This enables natural processes of biological uptake and denitrification to decrease nutrient loads from drained croplands to surface water, reducing water quality impacts from agriculture. We propose and evaluate criteria to identify riparian zones within a watershed suited to installation of saturated buffers. Soils criteria, applied to soil survey information, include an average of >1% soil organic matter to a 1 m depth; fine-textured subsoils (<50% sand at 0.5-1.5 m depth), and a seasonal high water table <1 m depth. These criteria highlight riparian soil conditions that should enhance nutrient removal. Topographic criteria are also proposed to avoid high streambanks and/or flat riparian topography to avoid bank failure, and inundation of crops above the buffer; which are evaluated using high resolution digital elevation models obtained through LiDAR surveys. The criteria were evaluated in three Midwestern HUC-12 headwater watersheds dominated by fine-grained glacial deposits. Topographic (slope) criteria were generally more restrictive than soils criteria, especially in flat landscapes with increased risk of crop inundation, but >50% of stream banks in all three watersheds were deemed suitable to installation of saturated buffers. The riparian suitability results must be combined with specific information on tile drainage systems to be applied effectively. This effort is facilitating inclusion of a saturated buffer siting tool in the Agricultural Conservation Planning Framework (www.northcentralwater.org/acpf/).