GSA Annual Meeting in Denver, Colorado, USA - 2016

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


HARALSON, Elizabeth A., Earth Sciences, University of Arkansas Little Rock, 2801 S University, FH 307, 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,

Fourche Creek watershed covers roughly 108,800 acres in and around Little Rock, AR, including urban wetlands. The creek, wetlands, and watershed areas provide pollution control, water purification, and storage for the city’s runoff water. Water samples were collected on Fourche Creek at various locations upstream and downstream of the wetlands on four separate occasions over a five-month period. One sampling event occurred during a storm event lasting three days in March 2016. Various water parameters were collected including pH, salinity, conductivity, and temperature. Samples were analyzed for anions and cations by IC, alkalinity by titration, and trace metals by ICPMS. Our results show that water quality changed throughout this watershed based on time of year, amount of precipitation, and influence from the Arkansas River. Certain constituents (Zn, Cr, and nitrate) were common in urban areas. Cation concentrations (Ca, Mg, and Na) generally increased as the creek flowed downstream until the wetlands, where their concentration decreased significantly. For example, during February 2016 the Na and Ca concentrations were 6.2 ppm and 9.3ppm, respectively, in the “pre-wetlands” portion of the creek, then after passing through the wetlands the concentrations decreased to 0.4 and 0.5 ppm, respectively. Several miles downstream of the wetlands, the concentrations of Na and Ca increased to 10.0 and 12.6 ppm, respectively, as Fourche Creek approached the Arkansas River. This could be due to inflow to the creek from the Arkansas River. Trace element concentrations showed a similar behavior to cations in this watershed. This indicates that the wetlands reduce the concentration of cations and trace elements in Fourche Creek, while the Arkansas River water mixes with Fourche Creek water near the confluence, increasing the concentration of cations and trace elements. Anion concentrations remain constant or slightly increase throughout the system. This investigation has illustrated the major effect the wetlands have on cleaning up the water draining from the city of Little Rock.