Evaluating Phosphorus Retention in Saturated Riparian Buffers

Issue

A saturated riparian buffer (SRB) is an established edge-of-field conservation practice to reduce nutrient transport from tile-drained agricultural fields to surface waters. In an SRB, a field drainage tile is intercepted, and a fraction of the flow is diverted as shallow groundwater through a riparian buffer. Although SRBs have been shown to be effective for nitrate-nitrogen (N) removal in tile-drained landscapes, their impacts on phosphorus (P) retention remain unclear, hindering inference of the broader benefits of SRBs beyond N reduction.

Objective

The overarching goal of this project is to provide a more comprehensive understanding of the performance of SRBs on P retention beyond their effectiveness in N removal. Specific objectives of this project are to:

1. accurately quantify P loads to SRBs;
2. evaluate P retention within SRBs; and
3. investigate relationships between P retention and N removal in SRBs.

Approach

This research will leverage three already-established SRBs in central Iowa: SH-1 in Boone County in the headwaters of the Big Creek watershed, BCR-2 in Hamilton County on Bear Creek, and LT-5 in Polk County on Alleman Creek. We will conduct high-frequency measurements of drainage flow and the concentrations of total N, nitrate, total P and reactive P in water samples collected from water control structures and monitoring wells at the three SRBs. We will evaluate the co-benefits or trade-offs of SRBs in water pollutant reduction from tile drainage.