Do Riparian Plants Fix CO₂ Lost by Evasion from Surface Waters? An Investigation Using Carbon Isotopes

Abstract

ABSTRACT. Rivers and streams in many parts of the world contain high concentrations of dissolved carbon dioxide, which is lost to the atmosphere by evasion (outgassing). Recent methodological advances now enable the carbon isotopic composition of this evaded CO 2 to be measured directly, with early results from peatland streams showing it to be depleted in 13 C relative to the atmosphere. The first direct measurements of the radiocarbon age of evaded CO 2 for a stream draining a peatland site in the United Kingdom covered a large range, ranging from modern to >1400 yr BP. We investigated whether a proportion of the carbon fixed by plants growing adjacent to the stream was derived from evasion; this would have implications for the cycling of carbon in such streams, and lead to riparian plants having older, rather than contemporary, 14 C ages.13 C analysis of riparian plants at the site suggested that up to 20% of the carbon they fixed was derived from evasion. Although the 14 C content of the same samples suggested a similar proportion of plant carbon was derived from evaded CO 2 , the uncertainty in these estimates was greater. Fixation of evaded CO 2 was greatest in plants growing within 1 m of the stream. Although the results for this site suggest a small amount of CO 2 lost by evasion from the stream surface is incorporated in plant material, it may be a more important factor at other sites characterized by higher evasion rates, lower wind speeds, and different stream bank morphology.

UK peatland streams release old carbon dioxide to the atmosphere and young dissolved organic carbon to rivers

“…Although streams draining UK peatlands are widely regarded as acidic, organic‐rich systems, they clearly provide a pathway for the potential release of old CO 2 to the atmosphere derived from deep carbonate weathering. Recent work has shown that this old CO 2 can be assimilated by plants growing in the vicinity of peatlands streams [ Garnett and Billett , 2007]. Whilst the presence of old evaded CO 2 derived from peat decomposition cannot be firmly established in this study, it clearly has the potential to contribute to the evasion loss pathway.…”

Radioisotope and stable isotope ratios (Δ14C, δ15N) suggest larval lamprey growth is dependent on both fresh and aged organic matter in streams

“…Terrestrial plant samples were measured for δ 15 N, and the Δ 14 C of FTOM was assumed to match the value of atmospheric CO 2(Garnett & Billett, 2007;Randerson, Enting, Schuur, Caldeira, & Fung, 2002), which was 40 ± 3‰ (zero years old) in the Northern Hemisphere in 2010(Levin, Kromer, & Hammer, 2013). Terrestrial plant samples were measured for δ 15 N, and the Δ 14 C of FTOM was assumed to match the value of atmospheric CO 2(Garnett & Billett, 2007;Randerson, Enting, Schuur, Caldeira, & Fung, 2002), which was 40 ± 3‰ (zero years old) in the Northern Hemisphere in 2010(Levin, Kromer, & Hammer, 2013).…”

RADIOCARBON DATING | 14C of Plant Macrofossils

“…Since, the magmatic CO 2 is 14 C-free, this results of a 14 C dilution in plants of the surrounding areas (Cook et al, 2001;Pasquier-Cardin et al, 1999). Garnett and Billett (2007) follow a similar approach in Tyrrhenian Sea. 14 C activity measurements can then be used as a way to track changes in volcanic activity.…”