Seasonal Measurement of Greenhouse Gas Concentrations and Emissions Along the Longitudinal Profile of a Small Stream

Abstract

IntroductionIn 2011 the global mean concentration of atmospheric CO 2 was 391 ppm [1], and the average rate of increase in the concentration of atmospheric CO 2 over the period spanning from 1960 to 2005 of 1.4 ppm yr -1 is therefore considered to be the main driver of climate change [2]. The global mean concentrations of CH 4 and N 2 O in 2011 were 1,803 ppb and 324 ppb, respectively [1]. The significant ability of CH 4 and N 2 O molecules to absorb Pol. J. Environ. Stud. Vol. 25, No. 5 (2016), 2047-2056 AbstractIn 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 CH 4 , CO 2 , and N 2 O 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 gasesespecially by CH 4 -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 CH 4 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 km 2 ). The majority of CH 4 and CO 2 emissions were released during warmer periods of the year and the highest N 2 O emissions from Sitka were recorded during summer and winter. The total annual emissions of CH 4 , CO 2 , and N 2 O 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 CO 2 equivalents using a calculation by IPCC, CO 2 accounts for the majority of total annual emissions of greenhouse gases (70.1%), with the second being N 2 O (22.7%), and the last CH 4 (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.

Streambed Organic Matter Controls on Carbon Dioxide and Methane Emissions from Streams

“…It should be noted that such a comparison is not straightforward given the large range. However, a similar pattern is observed when comparing our results with observed ranges of 13−106 mg C m −2 hr −1 in an in situ incubation experiment in an agricultural lowland stream in the Czech Republic, 105 supporting the hypothesis that land use has a strong influence on microbial respiration and associated GHG production in streambeds. We acknowledge that this study ignores any seasonal variations or the absence of water exchange between stream and streambed that was discussed in the section Experimental Limitations, which would likely be found under in situ conditions.…”

“…Our results are comparable to the lower end of the range of 0−1.5 mg C−CH 4 m −2 hr −1 found in an agricultural lowland stream in the Czech Republic. 105 When comparing the mean flux observed here (from Chalk High sediments) with the best estimate of CH 4 emissions from chalk streams in the U.K. of 3.2 × 10 −6 Tg yr −1 , 47 we find that our estimated total of 3.0 × 10 −5 Tg yr −1 are approximately one magnitude higher than estimates based on field observations. A possible explanation for the higher estimates can be found in the absence of macrophytes and associated rhizosphere in the sediments, which are known to promote methane oxidation.…”

“…47 Observed ratios of CH 4 /CO 2 ranged from 0 to 0.011 in Chalk High , which is low compared to earlier findings of 0.22 underneath macrophytes in a U.K. chalk river 17 but similar to a difference of 3 orders of magnitude reported in a survey of a small lowland agricultural stream. 105 However, comparing CH 4 / CO 2 ratios across different landscapes and methods is precarious as little is known about this anaerobic scaling. 33 Fine sediments trapped by vegetated patches are associated with a higher diversity of methanogenic archaea in the streambed.…”

Temporal Patterns of Methane Emissions From Two Streams With Different Riparian Connectivity

“…Although CH 4 production in oxic stream water has been reported (Bogard et al., 2014), in‐stream methanogenesis was probably of minor importance in our case. Internal CH 4 may be produced in organic‐rich sediments and hyporheic biofilm under microscale anaerobic conditions (Mach et al., 2016). However, CH 4 fluxes (12.79 ± 2.40 and 5.04 ± 0.64 g C m −2 yr −1 at H and R, respectively) were high compared with CH 4 production rates in anoxic sediments in the reservoirs fed by our streams (benthic CH 4 flux: 6∼8 g C m −2 yr −1 in the Rappbode and Hassel pre‐dams [Tittel et al., 2019]).…”

“…Temporal variability of CH 4 can be remarkable, typically showing the seasonal pattern with high summer and low winter CH 4 concentrations in temperate regions (Crawford, Stanley, et al., 2014; Dinsmore et al., 2013; Mach et al., 2016; Smith & Böhlke, 2019; L. Yang et al., 2013). The temporal variation is dynamic across a range of timescales.…”