GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 323-10
Presentation Time: 9:00 AM-6:30 PM


CAREY, Matthew, Department of Earth Sciences, University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72204, RUHL, Laura, Department of Earth Sciences, University of Arkansas at Little Rock, 2801 S University Ave, Little Rock, AR 72204 and POLLOCK, Erik D., University of Arkansas Stable Isotope Laboratory, University of Arkansas, Fayetteville, AR 72701,

The Arkansas River flows through almost 19 miles in the Little Rock Metropolitan area, receiving runoff and discharges from the city of Little Rock and central Arkansas, including discharge from the Fourche Creek watershed. The river is utilized for hydroelectricity, treated wastewater discharges, recreation, and transportation in central Arkansas. Water samples were collected along the river upstream of Murray Lock and Dam, downstream of Little Rock before the Terry Lock and Dam, and within Little Rock on seven separate occasions over an eighteen-month period. One of these occasions includes the sampling of a downstream site over three days during a major storm event. During sampling water parameters were collected, such as pH, salinity, conductivity, temperature, and dissolved oxygen; and water samples were analyzed for anions, cations, alkalinity, and trace metals. Concentrations were compared to water levels in the Arkansas River, upstream activity, and with identified effluent discharges to the river from the Little Rock area to understand the chemical changes in the Arkansas River in the Little Rock area. Each sampling event revealed a gradient from lower to higher concentrations in most constituents as it flowed through Little Rock, such as F, Cl, SO4, Mn, and Fe. Samples from June 2015 were collected during the highest water level during our project (13.22 ft), and had zinc concentrations of 1.52 ppb upstream which increased to 13.64 ppb downstream. Despite having the highest water level, the concentration of chloride almost doubled from the previous sampling events (from 39.2 to 76.7 ppb). The highest concentrations of cations and anions occurred during September 2014 with almost 3 times the concentration of Ca, Na, Cl, and SO4 relative to other sampling periods. These extremely high concentrations coincided with lower water levels and a much drier time of year. The 3-day storm event (March 2016) showed an increase in concentration of constituents shortly after rainfall began, followed by a decrease in concentration as precipitation continued. This investigation revealed the dynamic effect of spatial and temporal changes as well as anthropogenic influences on water quality.