Janis Krumins, Maris Klavins, Raimonds Krukovskis, Arturs Viksna, Lauma Busa


Mires are known as consistent environmental archives, but humic acids are the fraction of peat that is most recalcitrant and refractory to organic matter degradation, thus data on environmental changes during mire development can be recorded into them. This work was focused on the studies of stable isotopic ratios delta carbon-13 and delta nitrogen-15, and their distribution in humic acids within fen peat layers of different depths and peat composition. The variations in delta carbon-13 reflect isotopic variations in peat-forming plants over time and can be considered as a function of photosynthetic pathway that is being used to fix carbon dioxide. At the same time, variations in delta nitrogen-15 show nitrogen fixation in peat-forming plants and can be traced along with peat decomposition degree and depth. Properties of humic acids were studied in 2018 at 3 fens located in Latvia and Southern Finland, and comparatively they show properties. The method used for the determination of stable isotopes was the isotope-ratio mass spectrometry that was performed in the Faculty of Chemistry, University of Latvia. Results on delta carbon-13 indicate signal of C3 peat-forming plants, while signal of C4 peat-forming plants is not evident, which can be explained by non-efficient carbon dioxide fixation in fen vegetation. Results on delta nitrogen-15 show variations in nitrogen fixation in fen vegetation. Data show nitrogen fixation in terrestrial plants, however significant shifts in absolute isotope values indicate dependence on variations in peat decomposition degree and botanical composition. Data suggest that differences in peat botanical composition, decomposition degree and site dependent characteristics reflect in differences in delta carbon-13 and delta nitrogen-15 variations


environmental changes; fen peat; humic acids; stable isotopes

Full Text:



C. Zaccone, G. Casiello, F. Longobardi, L. Bragazza, A. Sacco, and T. M. Miano, “Evaluating the ‘conservative’behavior of stable isotopic ratios (δ13C, d15N, and δ18O in humic acids and their reliability as paleoenvironmental proxies along a peat sequence”, Chemical Geology, vol. 285, no. 1-4, p. 124, June 2011.

H. Rydin and J. K. Jeglum,The biology of peatlands. Oxford, OUP, 2013.

T. Sharkey, “Estimating the rate of photorespiration in leaves”, Physiologia Plantarum, vol. 73, no. 1, p. 147, May 1988.

T. Sharkey, “Discovery of the canonical Calvin-Benson cycle”, Photosynthesis Research, vol. 53, p. 835, August 2018.

J. Carter and V. Barwick, Good Practice Guide for Isotope Ratio Mass Spectrometry, FIRMS, 2011.

J. M. McDermott, J. S. Seewald, C. R. German, and S. P. Sylva, “Pathways for abiotic organic synthesis at submarine hydrothermal fields”, Proceedings of the National Academy of Sciences, vol. 112, no. 25, p. 7668, June 2015.

G. J. Retallack, “Cenozoic Expansion of Grasslands and Climatic Cooling”, The Journal of Geology, vol. 109, no. 4, p. 407, July 2001.

M. H. O’Leary, “Carbon Isotopes in Photosynthesis”, BioScience, vol. 38, no. 5, p. 328, May 1988.

D. Robinson, L. Handley, and C. Scrimgeour, “A theory of 15N/14N fractionation in nitrate-grown vascular plants”, Planta, vol. 205, no. 3, p. 397, May 1998.

Z. He, M. Xu, G. Y. Qiu, and J. Zhou, “Use of 15N stable isotope to quantify nitrogen transfer between mycorrhizal plants”, Journal of Plant Ecology, vol. 2, no. 3, p. 107, September 2009.

D. Robinson, “δ15N as an integrator of the nitrogen cycle”, Ecology & Evolution, vol. 16, no. 3, p. 153, March 2001.

I. I. Lishtvan and N. T. Korol, Basic properties of peat and methods for their determination, Nauka I Tehnika, Minsk, 1975.



  • There are currently no refbacks.