Contributions of autochthonous and allochthonous sources to dissolved organic matter in a large, shallow, eutrophic lake with a highly calcareous catchment

• Published in: Limnology and oceanography Vol. 58; no. 4; pp. 1259 - 1270
• Main Authors: Toming, Kaire, Tuvikene, Lea, Vilbaste, Sirje, Agasild, Helen, Viik, Malle, Kisand, Anu, Feldmann, Tõnu, Martma, Tõnu, Jones, Roger I., Nõges, Tiina
• Format: Journal Article
• Language: English
• Published: Waco, TX John Wiley and Sons, Inc 01.07.2013; American Society of Limnology and Oceanography
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Hydrology; Hydrology. Hydrogeology; Isotope geochemistry; Isotope geochemistry. Geochronology; Synecology; Baltic region; Europe; Estonia; stable isotopes; fresh-water environment; C-13/C-12; chlorophyll; concentration; drainage basins; microorganisms; ecosystems; organic materials; pH; phytoplankton; temperature; plankton; lakes
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2013.58.4.1259

We traced the origin of dissolved organic matter (DOM) in the large, shallow, eutrophic Lake Võrtsjärv in Estonia. Allochthonous DOM (Al-DOM) had higher δ13C values than autochthonous DOM (Au-DOM). The δ13C of inflow DOM varied from −28.2‰ to −25.4‰ (mean −26.7‰) and in-lake DOM varied from −28.4‰ to −26.1‰ (mean −27.2‰). Low stable isotope (SI) signatures of Au-DOM were caused by relatively 13C-depleted values of its precursors (mainly phytoplankton) with mean δ13C of −28.9‰. SI signatures of dissolved inorganic carbon (DIC) in the inflows and in the lake were also relatively low (from −15.1‰ to −3.28‰). SI values of DOM were lower during the active growing season from May to September and higher from October to April, with the corresponding estimated average proportions of Al-DOM 68% and 81%. The proportion of Al-DOM decreased with increasing water temperature, chlorophyll a, and pH and increased with increasing water level and concentration of yellow substances and DIC. The high proportion of Al-DOM in Võrtsjärv shows that, even in this highly productive ecosystem, the labile Au-DOM produced is rapidly utilized and degraded by microorganisms and thus makes a relatively small contribution to the instantaneous in-lake DOM pool.