Ecohydrology and Carbon Cycling in a Headwater Catchment: Identifying the Hydrologic, Biologic and Abiotic Processes Expressed in Terrestrial-Aquatic Connectivity
Dissolved carbon dioxide in headwater streams has been suggested as a tool for assessing whole catchment soil respiration. However, the dynamics of dissolved CO2 in streams are complex, and are driven by many processes, some of which are hydrologically mediated, others are biologically mediated, and still others are mediated by additional abiotic factors. We employed high frequency water quality and hydrometric monitoring in a forested headwater catchment in coastal British Columbia with the goal of elucidating controls over stream water CO2 dynamics at a range of temporal scales. Direct measurements of dissolved CO2 were made in situ using an infrared gas analyzer, while a multiparameter water quality sensor monitored dissolved oxygen, pH, temperature and conductivity. Using these data we went about teasing out the hydrological, biological, and abiotic processes expressed by the concentration dynamics of the dissolved gasses. Dissolved oxygen concentrations in streamwater were inversely related to dissolved CO2 concentrations at diurnal and seasonal scales. However, the behavior of dissolved gasses during rainfall-runoff events varied seasonally, with springtime rainfall events characterized by opposite trends for CO2 and O2, with CO2 concentrations inversely related to storm discharge, while O2 concentrations increased on the rising limbs and decreased on the falling limbs. However, the dissolved gasses were correlated during summer events, with both CO2 and O2 positively related to storm discharge. During the five-month study, the range of observed values was much greater for dissolved CO2 (from 2.7 to 12.0 mg/L for CO2) than for dissolved O2 (7.4 to 10.6 mg/L). The stream was always undersaturated with respect to O2 (flow-weighted mean of 82 percent of oxygen saturation), but supersaturated with CO2. The excess CO2 (EpCO2), which is the amount of dissolved CO2 in streamwater compared to atmospheric equilibrium, ranged from 2.7 to 15.4, with a flow-weighted mean EpCO2 of 6.1. Inputs of CO2 derived from terrestrial soil respiration are clearly evident in the stream chemistry, as seen in the amplitude of diurnal periodicity of CO2, which was greater than that of O2. This research contributes to identifying the terrestrial and aquatic components of stream respiration, which is of fundamental importance to quantifying what is a significant, though poorly constrained, portion of the net ecosystem carbon balance.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1813 Eco-hydrology