Paired riparian water table monitoring to quantify hydraulic loading to a saturated buffer

The use of saturated buffers for reducing NO₃-N loads from tile-drained croplands is increasing in the US Midwest and there is a need to develop options for estimating reductions at riparian sites. In this study, we present a paired water table monitoring approach to estimate hydraulic and NO₃-N loading into a saturated buffer in eastern Iowa. One well was located within the saturated buffer (treatment) and a second well was installed in the same section of the riparian buffer but without the saturated buffer (control). Over a season of monitoring, water table depths were remarkably consistent between the two wells but the water table beneath the saturated buffer was consistently 0.22 m higher than the non-saturated buffer control. The increase in water table height increased the amount of water discharged from a 162 m long buffer by 468.2 m³/year and, assuming concentration reduction of 15 mg/l, resulted in a N reduction of approximately 7 kg. Although more work is needed to document this paired monitoring approach elsewhere, the method may hold promise for inexpensively quantifying the performance of conservation practices at landowner-led sites.