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Evaluating the Drainage Capacity and Nitrate Loading of Modified Blind Inlets in Row Crop Catchments
Journal article   Open access   Peer reviewed

Evaluating the Drainage Capacity and Nitrate Loading of Modified Blind Inlets in Row Crop Catchments

Matthew T. Streeter and Elliot S. Anderson
Nitrogen (Basel, Switzerland), Vol.7(1), 31
03/20/2026
DOI: 10.3390/nitrogen7010031
url
https://doi.org/10.3390/nitrogen7010031View
Published (Version of record) Open Access

Abstract

Standing tile inlets are commonly used to drain unwanted surface water from croplands but can exacerbate pollution by facilitating the transport of nutrients to waterways. Blind inlets have increasingly been viewed as a beneficial alternative to standing inlets since they control erosion and capture particulate nutrients. However, conventional blind inlets do little to limit dissolved nutrient transport, and modified blind inlet (MBI) designs have been proposed that incorporate woodchips—a medium that facilitates denitrification. While initial investigations have highlighted MBIs’ remediation potential, their ability to meet prescribed drainage standards has not been well-documented. In this study, we designed and installed MBIs composed of pea gravel and woodchips in two eastern Iowa fields under row crop cultivation. Flow and nitrate were continuously monitored using in situ equipment directly downstream of the MBIs (February 2023–June 2025). Observed flows were very ephemeral, consisting of ~25 distinct events at both sites, with no flow recorded in between. During several wet weather events, flow rates exceeded the MBIs’ design requirements, confirming their sufficient drainage capacity to prevent in-field ponding. Nitrate concentrations varied considerably, with long-term averages of 11.6 and 19.1 mg/L and overall loadings of 4.94 and 7.10 kg during our 28-month study. We also measured phosphate and sulfate during select wet weather events, and discrepancies in concentrations between inlets and outlets suggested that groundwater was often present alongside surficial drainage in our monitoring setup. We believe our results argue for increased adoption of MBIs in conservation and further quantification of their remediation capabilities.
 modified blind inlet flow nitrate runoff woodchip bioreactor

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