Land use and seasonal effects on dissolved inorganic carbon concentrations of Ohio streams and reservoirs

Recent global and regional carbon budgets have largely ignored freshwater systems, but current research shows that these systems are significant in sequestering organic carbon and venting CO2. In response to this new research, these systems should be examined more closely to determine their importance as carbon sinks or sources. Dissolved inorganic carbon (DIC) plays a significant role as part of the overall carbon budget and should be investigated in depth. For this study, we looked primarily at two Ohio reservoirs to determine how land use and storm events may influence DIC concentrations in these freshwater systems. One reservoir in the study, Acton Lake, has a watershed dominated by agriculture (89% agricultural), while the other, Burr Oak, has a watershed of only 14% agricultural use and 81% forest. We found that DIC concentrations in Acton were at least two times higher than Burr Oak concentrations (~30 versus 15 mgC/L). A comparison of DIC levels in twenty Ohio reservoirs during mid-August showed a positive correlation between percent watershed agriculture and DIC. We also examined the effects of stream discharge at the two study sites and found that as discharge increased, such as during a storm event, the DIC levels decreased. A comparison of DIC to discharge for the three streams that flow into Acton Lake showed a significant negative correlation. We found that in both the streams and reservoirs DIC comprised the largest fraction of carbon during baseflow and minor storm events. Particulate organic carbon became relatively more important during larger storms.