Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

First Advisor

Laurent Ahiablame

Keywords

Agricultural water management, Dissolved phosphorus, Nitrate-N, Subsurface flow, United States Midwest, Water quality

Abstract

Increased subsurface drainage over the past few decades in eastern South Dakota contributed to agricultural water quality problems. Nutrient losses, primarily nitrate-N and dissolved P, from subsurface drainage, have been identified as major contributors to eutrophication in the Great Lakes and Gulf of Mexico. Denitrifying bioreactors and P adsorption structures are edge-of field practices that can be used to protect water quality in waters downstream of subsurface drainage systems. The objectives of this study were to evaluate the effectiveness of woodchip bioreactors and a P adsorption structure in removing nitrate-N and dissolved P from subsurface drainage water. Four woodchip bioreactors were installed and monitored between 2012 and 2016 near Arlington, Baltic, Hartford and Montrose in eastern South Dakota. One P adsorption structure was designed, installed and monitored for 2016 near Baltic, South Dakota downstream of the Baltic bioreactor. Results showed that nitrate-N reductions ranged from 7% to 100% for the four bioreactors, based on upstream concentrations of 0.79 to 60.9 mg/L during 2014- 2016 study period. Nitrate-N load removal rates varied between 0.01 to 14.6 gm N/m3/day, with upstream and downstream loads of 0.03 to 116 kg/ha/year and 0.0 to 91 kg/ha/year, respectively. The average cost of nitrate removed were estimated to be $11, $20, $13, and $61 kg/N per year for the Arlington, Baltic, Hartford, and Montrose bioreactors, respectively. Dissolved P reduction ranged from 10% to 90 % and the P removal rates varied between 2.2 to 183.7 gm/m3/day during the study period. Average annual cost of dissolved P removed was $209 kg/P. Two regression equations were developed and tested for predicting downstream nitrate-N concentrations in eastern South Dakota. The equations performed with 70% efficiency at the bioreactor sites examined, except at the Baltic site where the equations overestimated downstream nitrate-N concentrations. Based on examination of nitrate removal data of all four bioreactors since installation, their performance appears to decrease over time. The information provided in this study would be useful to increase understanding of the effectiveness of edge-of-field practices for nitrate-N and dissolved P reduction in eastern South Dakota.

Library of Congress Subject Headings

Subsurface drainage.
Bioreactors.
Wood chips.
Phosphorus -- Absorption and adsorption.
Denitrification.
Nitrates.
Water quality management -- South Dakota.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

99

Publisher

South Dakota State University

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Rights Statement

In Copyright