Uncovering Soil and Sediment Properties to Inform Saturated Buffer Design

Issue

Saturated buffers are an edge-of-field practice to reduce nitrate loss from artificial subsurface (tile) drainage by intercepting a tile where it crosses a riparian buffer and diverting a fraction of the flow as shallow groundwater within the buffer. Saturated buffers installed with state or federal cost share are designed according to a USDA-NRCS Conservation Practice Standard, which sets forth the minimum planning criteria that must be met in order for the practice to achieve its intended purpose. Recent analysis of 44 site-years of data from five saturated buffers in Iowa has identified that current design protocols significantly underestimate saturated buffer treated flow. As this parameter directly impacts saturated buffer effectiveness, it is important to understand the relationships among saturated buffer soil and sediment properties and mass nitrate removal.

Objective

The goal of this research is to increase understanding of the important soil and sediment properties that influence nitrate removal capacity within saturated buffers and incorporate these findings into improved saturated buffer design to maximize mass nitrate removal. An improved design worksheet will enhance the effectiveness of batch-and-build efforts to both estimate nitrate removal within established sites and prioritize future installations.

Approach

Recent studies have developed new methods of shallow soil characterization to more accurately and efficiently assess the potential success of conservation practice implementation. This project will conduct electromagnetic terrain conductivity surveys at 20 existing saturated buffer sites. Confirmation borings will be collected at each buffer to confirm the correlation of soil texture and soil organic matter. Observed soil characteristics will be related to ongoing saturated buffer nitrate monitoring at most sites. Outputs from this project will provide a dataset of observed soil and sediment hydraulic properties across a range of already installed saturated buffers that can be incorporated into an improved saturated buffer design worksheet.