Date of Graduation

5-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level

Graduate

Department

Environmental Dynamics

Advisor/Mentor

Miller, David M.

Committee Member

Moore, Philip A. Jr.

Second Committee Member

Owens, Phillip R.

Third Committee Member

Ashworth, Amanda J.

Fourth Committee Member

Hays, Phillip D.

Fifth Committee Member

Evans-White, Michelle A.

Keywords

Watershed dynamics; Surface water dilution

Abstract

The Mulberry River is a 110 km long tributary of the Arkansas River in northwest Arkansas and has been designated as a National Wild and Scenic River since 1992. In 2008, the Mulberry River was added to the 303(d) list of impaired water bodies due to the low pH of a 14.6 km segment of the river which has since increased to 68.7 km. To date, there has been little research performed on the Mulberry River and long-term routinely sampled water quality data is unavailable. The objectives of this dissertation were 1) to evaluate changes in water quality of the Mulberry River and its tributaries over a 4-year period and 2) to evaluate the relationship between forest stand type (i.e., deciduous vs coniferous) and both stream and soil chemistry. Water samples were collected monthly from 11 locations on the Mulberry River and 10 of its tributaries from March 2015 until January 2019. Soil samples were collected from 10 locations throughout the watershed with adjacent deciduous and coniferous stands. Several different tests of soil acidity indicated in no significant differences between soil from beneath the deciduous and coniferous stands. Coniferous forest land use was not correlated with stream pH (P > 0.05) neither was stream pH predicted (P > 0.05; R2 < 0.01) by coniferous forest land use. Trend analyses indicate that there have been significant decreases in specific conductance, total suspended solids, total organic C, total N, SO4, and flow-adjusted soluble Ca and Mg and a significant increase in Cl and total Al, Fe, and Na. Out of the 21 locations sampled, only three had significant decreases in pH suggesting that the watershed has not been acidified during the duration of this study. The decrease in specific conductance and several constituents as well as the increase in streamflow and precipitation throughout Arkansas implies that the watershed has become more dilute with time. The results of this research indicate that conifer growth is not a significant source of acidity and the watershed has not become more acidic over the last 4 years.

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