The effects of land cover on soil CO2 flux in a temperate suburban neighborhood

Soil respiration plays an important role in regulating atmospheric carbon dioxide concentration and climate dynamics. Soils contain the largest terrestrial active carbon pool surpassing vegetation or the atmosphere. Soil organic carbon dynamics is related to vegetation cover, thus any manipulation of the soil such as land use change alter source or sink characteristics for atmospheric CO₂ and other green-house gases. The objective of this study was to investigate land cover effects on concentrations of soil carbon dioxide in a suburban neighborhood in Baltimore County, MD. Here the USDA Forest Service operates a CO₂ flux tower. Soil CO₂ concentration, soil temperature, and soil moisture were continuously collected from forest and grass, two common land cover types, in a temperate suburban landscape. Each were replicated three times. VAISALA CO₂ sensors, thermistors and moisture sensors were installed at six depths: soil surface, 2, 5, 10, 20, and 30 cm. The data was collected between May 2011 and February 2012. July was hot and dry and resulted in moderate drought conditions followed by the rainiest August-September of all time (66 cm) in 117 years. CO₂ concentrations at all six depths were consistently higher in the lawn soils compared to the forest soils, with the greatest difference highlighted at the deepest point of 30 cm. After moderate drought conditions in July, rainfall in late August as well as after larger storms of Hurricane Irene and Tropical Storm Lee, caused spikes or the "pulse effect" in soil CO₂ concentrations at all depths. These large storm events seemed to have a lasting effect on the soil CO₂ concentrations. Using the standard chamber method, CO₂ efflux ranged from 3.32 x 10^-9 to 7.28 x 10^-8 m³ m^-2 s^-1 and 6.79 x 10^-9 to 1.45 x 10^-7 m³ m^-2 s^-1 for forest and grass, respectively. Continuous measurements are important to better understand soil CO₂ flux under different land cover and the impact of extreme events that are predicted to increase in frequency and intensity in the future.