TEMPORAL CONTROLS ON CARBON CYCLING IN A SMALL URBANIZED CATCHMENT, INDIANAPOLIS, IN

In this study, a small stream in an urban catchment was sampled at the mouth weekly for a period of eighteen months. In addition, samples were collected daily for one month and every four hours during a single day in the summer, fall, winter and spring seasons. The study objective was to investigate short to long-term controls on carbon cycling in streams in urbanized catchments. Dissolved inorganic carbon (DIC) ranged from 82 to 15 mg C/L, alkalinity ranged from 66 to 347 mg/L and the isotope ratio of DIC (ä13CDIC) ranged from –13.9 to –9.4 0/00 relative to VPDB. Over the short term, hourly and daily water samples showed that increase in stream discharge caused a decrease in DIC and alkalinity and an increase in the ä13CDIC. Over the long-term, weekly water samples showed no distinct seasonal patterns in DIC, alkalinity or ä13CDIC. Temporal control in carbon input, output and biogeochemical cycling and short-term runoff events to the streams affect DIC and ä13CDIC. The results of this study, suggest that the time scale for hydrologic and biogeochemical processes that affect carbon cycling in this small-urbanized watershed is most evident over time periods of hours to months.