A HYDROLOGIC COMPARISON OF THE CEDAR RIVER AND WEST OKOBOJI LAKE IN IOWA

This study focused on sampling 4 sites from the Cedar River in Black Hawk County, and 6 sites around West Okoboji Lake in Iowa. Samples in the Cedar River were taken ~10-14 days apart, and 1 per week for 3 weeks in West Okoboji. In the field and lab, each site’s temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), conductivity, turbidity, and total dissolved solids (TDS) were tested. The parameters included in this study are DO, BOD, turbidity, and TDS. These data were used to observe how hydrologic variables changes over time and space, depending on the water’s flow, or lack thereof.

The results show that DO levels are similar in both the Cedar River and West Okoboji Lake. The Cedar River had an average of 8.59 mg/L. Similarly, West Okoboji Lake had a DO average of 8.25 mg/L. The average BOD value for the Cedar River was 0.99 mg/L and 0.61 mg/L for West Okoboji. TDS demonstrated a larger difference; the average for the Cedar River was 342 mg/L, while it was 287 mg/L for West Okoboji Lake. Another parameter with a notable difference between both bodies of water is turbidity. The average for the Cedar River was 15.51 mg/L, while West Okoboji Lake recorded an average of 2.93 mg/L. When compared spatially and temporally, West Okoboji Lake demonstrates consistency of the tested parameters. The Cedar River primarily fluctuates temporally within turbidity and TDS. Spatial fluctuations are observed throughout BOD and turbidity. Despite similar DO levels, the Cedar River’s turbulent flow dissolves surficial materials more actively. Based on low BOD, TDS, and turbidity values, West Okoboji Lake is less biochemically active than the Cedar River. The lower BOD values are somewhat of a surprise. Since West Okoboji Lake is a body of water lacking turbulence, microbiological organisms should complete reactions more effectively than in moving rivers. This trend may be related to the effective best management practices (BMP), such as state regulation or community work.