1. 1. Introduction The Big Darby Creek is categorized as a national scenic river with an array of biological species. Since this is one of the last pristine rivers in Ohio, concern has grown in regards to human disturbances to the system. Its watershed has been mainly used for agricultural purposes since early pioneers settled the area. Recently, the outskirts of Columbus have been expanding westward into the watershed. Changes in the land use from rural to suburban should leave an impression on the chemistry of the stream water. Long-term stream chemistry analysis will show the effect of human activities on the Big Darby Creek. Effects of Development on the Big Darby Creek Watershed: Stream Geochemistry Catherine Maxwell, School of Earth Sciences, The Ohio State University, Columbus, Ohio, 43210-1398 W. Berry Lyons, Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, 43210 Acknowledgements Thank you to Sarah Fortner, Chris Gardner, Kathy Welch, and Rebecca Witherow. 6. Future Goals Look for more historic chemical data Determine SO 4 2- sources Gather discharge rate data Retrieve population data from census records Calculate area of pavement in watershed Collect data of salt application volume Figure 1 4. Seasonal Variation from 2007 F - concentrations are the lowest of all anions, ranging from 16.8  M to 31.6  M in the Little Darby and 17.3  M to 30.9  M in the Big Darby. NO 3 - concentration decreases from 289  M to 9  M in the spring to the summer and then increases to 265  M in autumn in the Big Darby river. In the Little Darby Creek NO 3 - concentrations decrease from 314  M to 10  M. SO 4 2- increases steadily from 365  M to 590  M in the Little Darby, and from 374  M to1063  M in the Big Darby. Cl - concentrations increase overall in the Big Darby Creek from 772  M to 2274  M. In the Little Darby they fluctuate between 671  M and 819  M. References Big Darby Creek Land Use. Ohio EPA Division of Surface Water. http://www.epa.state.oh.us/dsw/permits/GP_ConstructionSiteStormWater_Darby.html, accessed 2 May 2008. Gardner, C. B. and Carey, A. E., Trace Metal and Major Ion Inputs into the Olentangy River from an Urban Storm Sewer. Environ. Sci. Technol. 2004, 38, 5319-5326. Jackson, R. B. and Jobbagy, E. G., 2005 From icy roads to salty streams, Proceedings of the National Academy of Sciences, 102, 12, 487-14, 488. Kaushal, S. S. et al., Increased salinization of freshwater in the northeastern United States, Proceedings of the National Academy of Sciences, 102, 13, 517-13, 520. Kelly, V. R. et al., Long-Term Sodium Chloride Retention in a Rural Watershed: Legacy Effects of Road Salt on Streamwater Concentration. Environ. Sci. Technol. 2008, 42, 410-415. USGS National Water Information System. Water Quality Samples for the Nation. http://nwis.waterdata.usgs.gov/nwis/qwdata? accessed 4 May 2008. 3. Long-Term Time Series Data Cl - concentrations in the Little Darby are in the 400  M range in the late 1960s and early 1970s, then in the 1980s concentrations drastically increase to between 705  M and 1128  M, then remain close to those high values throughout the rest of the study. Cl - concentrations in the Big Darby are between 564  M and 874  M in the late 1960s. The concentrations increase to over 1000  M by 1992 and drastically increase in 2007 up to the highest concentration of 2274  M. F -  m concentrations in the Little Darby stay relatively constant throughout all historical data. NO 3 - concentrations reached a maximum in October of 1965 and have since remained under half of that concentration, in the Big Darby Creek. In the Little Darby Creek, NO 3 - concentrations reached a minimum of 3  M in September of 2000 and a maximum of 815  M in April of 2001. SO 4 2- concentrations are between 5  M and 97  M in the 1980s, then increase to between 335  M and 815  M in 2000-2001. In 2007 the concentrations remain between 348  M and 590  M. 5. Discussion Concentrations of anions in the Darby are similar to other Ohio Rivers that are influenced by agriculture such as the Scioto River. NO 3 - in the stream water is probably from agricultural sources. Seasonal trends are apparent and are related to human activities and flow variations. Increase in SO 4 2- over time. Increase in Cl - since the 1970s. NO 3 - relatively constant, but the seasonal variability is greater than the long term variability. Many different human activities can contribute Cl - and SO 4 2- to aquatic systems, therefore they are good indications either of general human disturbance in the watershed or of population density. Kaushal et al. (2005) have demonstrated that Cl - concentrations have been increasing at high rates in northeast USA streams due to de-icing operations. The application of de-icing salt Cl - in Ohio averages about 310 X 10 3 M km -2 yr -1 (Jackson and Jobbagy, 2005). Gardner and Carey (2004) have demonstrated that in Columbus, winter additions of road salt onto highways are observed influencing Cl - concentrations in the Olentangy River throughout the calendar year. Nowhere in the Darby system, however, does the concentration reach 7000  M L -1, the recommended upper limit for the protection of freshwater life. For comparison in the Scioto River, the Cl - concentrations range from 577 to 2410  M L -1 with the highest concentrations observed in the late summer and the lowest in the spring (Carey and Lyons, unpublished). Nitrate concentrations in the Scioto range from 19-474  M L -1 with the lowest concentrations in the late summer and the highest in the late winter/spring period (Carey and Lyons, unpublished). Kelly et al. (2008) have observed an annual increase of about 40  M L -1 in chloride in rural streams in southeast New York state between 1985-2005 (from about ~340  M to 1125  M L -1 ). These authors estimate that 83% of this increase is due to road de-icing salt. 2. Methods and Analysis Samples collected every two weeks at the Big Darby Creek, and a tributary, the Little Darby (Figure 1) Filtered through 0.4  m Nuclepore membrane filters using prewashed plastic filtration towers Analyzed for major anions using the ion chromatograph(IC) Relative standard deviation for F -, Cl -, NO 3 -, and SO 4 2- were 5%, 2%, 2%, and 1%, respectively Pictures Above is the downstream view of Little Darby Creek in West Jefferson Below is the view downstream of the Big Darby Creek in Darbydale Photographs were taken by Sarah Fortner