Document Type

Thesis - University Access Only

Award Date

1995

Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

James J. Doolittle

Abstract

Soil samples were collected from the proposed Lake Andes-Wagner (LAW) irrigation project area in Charles Mix iv County, South Dakota and analyzed for selenium (Se) content in order to help evaluate the potential for significant Se discharge with drainage waters. Soil samples were collected along orthogonal transects at four depths (0 to 0.5, 0.5 to 1.0, 1.0 to 2.0, 2.0 to 3.0 m), and analyzed for available Se (Fl-Se), conditionally available Se (F2-Se), and total Se (Tot-Se). Unavailable Se (F3-Se) was calculated from the difference between Tot-Se and the sum of Fl-Se plus F2-Se. Selenium concentrations in the extracts and digests were determined using a continuous-flow hydride generation atomic absorption method. Geostatistical procedures were used to determine the spatial relationships of the Se fractions. The investigation showed that Tot-Se ranged from 159.3 to 9375.1 ppb, Fl-Se from Oto 7495.0 ppb, F2-Se from 0 to 4337.3 ppb, and F3-Se from 0.3 to 5321.9 ppb. Variogram analysis indicated that there were spatial relationships from 810 to 7500 m. Spherical and Gaussian models produced the best fit for all the variograms. Nugget variance for Fl-Se was substantially higher than those for Tot-Se and F2- Se; however, variance increased with depth for all Se fractions. Based on the variogram parameters, kriging was used to interpolate between data points, and generate contour maps of Se concentration in the project area. Mean Se concentration increased with depth for Tot-Se, Fl-Se, and F2-Se, but decreased with depth for F3-Se. Positive correlations between Tot-Se:Fl-Se, Tot-Se:F2-Se, Tot-Se: F3-Se and Fl-Se:F2-Se were all extremely significant (a= 0.0001). The Pearson correlation coefficients for Tot-Se:Fl-Se, Tot-Se:F2-Se and Fl-Se:F2-Se increased with depth, but decreased with depth for Tot-Se:F3-Se. Moreover, a positive correlation between Se fractions and landscape elevation was found. From this investigation, several conclusions can be deduced. Selenium distribution in the proposed project area is quite uneven. Most of Fl-se and F2-Se had moved down to a deeper depth. There were a few sites where the Se concentrations measured (9.4 ppm Tot-Se and 7.5 ppm F1-Se) could present a localized problem; however, it may not have a significant effect after these "hot spots" are diluted by low Se drainage water from surrounding areas of the project.

Library of Congress Subject Headings

Soils -- Selenium content
Soils -- South Dakota -- Lake Andes -- Selenium content
Irrigation -- Research -- South Dakota -- Lake Andes

Format

application/pdf

Publisher

South Dakota State University

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Rights Statement

In Copyright