Paper No. 3
Presentation Time: 9:00 AM-6:00 PM
SEASONAL AND DIURNAL VARIATION OF NITRATE CONCENTRATIONS WITHIN THE HYPORHEIC ZONE OF A LOW-GRADIENT, THIRD ORDER STREAM IN CENTRAL ILLINOIS
HAYDEN, Kelly, Geography-Geology, Illinois State University, Campus Box 4400, Normal, IL 61761, kmhayde@ilstu.edu
Increased nutrient loading of Midwestern streams has generated a demand for research regarding the sources of the nutrients and removal processes that occur once the nutrients have entered a stream system. The purpose of this research is to examine the seasonal and diurnal changes in nitrate concentrations in the hyporheic zone of a third order, low-gradient stream to further understand the ability of a stream system to remove excess nutrients. The study area for this research is located in a meander of Little Kickapoo Creek, 11 kilometers south of Bloomington Illinois. Water samples were collected from five wells at 30, 60, 90, and 150 cm beneath the streambed surface, the stream, and groundwater. All water samples were refrigerated and analyzed for nitrate concentrations using an ion chromatography system. 24-hour tests were also conducted where water samples were collected every hour for 24 hours to observe any diurnal variations.
Seasonal variations in nitrate have been observed from September 2011 to June 2012. Concentrations in nitrate ranged from 0.07 to 0.43 mg/L, with the lowest concentrations occurring January, and the highest in September and May. The data show a steady decrease in nitrate concentrations from September to January, following January, a steady increase was observed until May, and a slight decrease was observed in June. These variations were to be expected because of variations in precipitation, fertilizer application, and amount of organic matter entering the system. Diurnal patterns of increasing and decreasing nitrate concentrations were observed during both 24-hour tests, though more tests are needed to understand the diurnal variations of nitrates. Both the seasonal and diurnal studies of nitrate concentrations provide insight into the ability for the hyporheic zone to remove nutrients from a stream system and the controls of the reduction processes.
