Seasonal measurement of greenhouse gas concentrations and emissions along the longitudinal profile of a small stream

Abstract

In order to find out whether streams might be a major source of greenhouse gases to the atmosphere, our investigation sought to determine the total emissions of CH4, CO2, and N2O from the surface water of a small stream. Over a period of a year we used floating chambers to measure gas emissions along the longitudinal profile of Sitka Stream (Czech Republic). Additionally, we measured gas concentrations of surface and interstitial waters. We found that interstitial and surface waters were supersaturated by all monitored gases – especially by CH4 – and that the stream is a significant emitter of these greenhouse gases. The concentrations and the emission rates of all three gases were higher in the downstream part than upstream. In the case of CH4 the majority of total annual emissions (90%) was released from the most downstream section, representing only 1/5 of the stream’s total surface area (0.18 km2). The majority of CH4 and CO2 emissions were released during warmer periods of the year and the highest N2O emissions from Sitka were recorded during summer and winter. The total annual emissions of CH4, CO2, and N2O into the atmosphere from the water’s surface were estimated to be 0.6 t, 210 t, and 0.2 t, respectively. After conversion of the greenhouse gas emissions to CO2 equivalents using a calculation by IPCC, CO2 accounts for the majority of total annual emissions of greenhouse gases (70.1%), with the second being N2O (22.7%), and the last CH4 (7.2%) for a 100-year time horizon. This work brings worthwhile data of greenhouse gas emissions and concentrations from a small water stream based on seasonal measurements along the longitudinal profile.