Date of Award

6-21-2021

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Applied Science

First Advisor

Laura Ruhl

Abstract

The Fourche Creek Watershed is an urban watershed in Central Arkansas, serving as the primary drainage basin for most of metropolitan Little Rock. As land surrounding streams is developed, the risk of negatively impacting water quality through the addition of contaminants like metals, sewage, and pesticides increases. The objective of this project is to introduce a novel method of quantifying the impact of urbanization on streams using a multi-pronged approach including mixing and spatial analyses, dissolved loads, and 87Sr/86Sr ratios throughout the Fourche Creek Watershed to discern specific contributions of baseflow and urban materials into the drainage basin. Generally, Coleman and Rock Creeks (two highly urbanized sub-basins that drain into Fourche Creek) had higher concentrations of major cations and anions than the main channel of Fourche Creek. The main channel also had general increases in concentration downstream for major constituents. Fourche Creek’s confluence is geochemically influenced by the Arkansas River. Redox sensitive elements like Fe and Mn increased as it flowed through the wetlands. Concentrations of Sr increased downstream, and the 87Sr/86Sr became less radiogenic downstream. By assuming a direct relationship exists between land cover percentage and percent contribution of urban materials, we defined the Storm Urban Influence Factor, which allowed for an urban contribution analysis of the entire drainage basin. A mixing analysis of regular conditions found an estimated Cl event flow contribution (estimated minimum urban input) into the watershed of 2.8 - 14.1 mg/L (17.7 – 79.2%). The analysis of 87Sr/86Sr indicated that the mixing of these waters alone cannot be from only baseflow and rainfall, meaning that event flow must be a combination of rainfall with other inputs from urban sources.

Download

Share

COinS