Dominance of in situ produced particulate organic carbon in a subtropical reservoir inferred from carbon stable isotopes

Author(s)

Bueno, Carolina de Castro ^{[1, 2]} ; Frascareli, Daniele ^[2] ; Gontijo, Erik S. J. ^[2] ; van Geldern, Robert ^[1] ; Rosa, Andre H. ^[2] ; Friese, Kurt ^[3] ; Barth, Johannes A. C. ^[1]

Affiliation

^[1] Friedrich Alexander Univ Erlangen Nurnberg, Dept Geog & Geosci, GeoZentrum Nordbayern, Schlossgarten 5, D-91054 Erlangen - Germany

^[2] Sao Paulo State Univ UNESP, Inst Sci & Technol, Ave Tres de Marco, 511 Alto Boa Vista, BR-18087180 Sorocaba, SP - Brazil

^[3] UFZ Helmholtz Ctr Environm Res, Dept Lake Res, Bruckstr 3a, D-39114 Magdeburg - Germany

• Document type: Journal article
• Source: SCIENTIFIC REPORTS; v. 10, n. 1 AUG 6 2020.
• Web of Science Citations: 1

Abstract

Sources of particulate organic carbon (POC) play important roles in aqueous carbon cycling because internal production can provide labile material that can easily be turned into CO2. On the other hand, more recalcitrant external POC inputs can cause increased loads to sedimentary organic matter that may ultimately cause CH4 release. In order to differentiate sources, stable isotopes offer a useful tool. We present a study on the Itupararanga Reservoir (Brazil) where origins of POC were explored by comparing its isotope ratios (delta C-13(POC)) to those of dissolved inorganic carbon (delta C-13(DIC)). The delta C-13(POC) averaged around - 25.1 parts per thousand in near-surface waters, which indicates higher primary production inferred from a fractionation model that takes into account carbon transfer with a combined evaluation of delta C-13(POC), delta C-13(DIC) and aqueous CO2. However, delta C-13(POC) values for water depths from 3 to 15 m decreased to - 35.6% and indicated different carbon sources. Accordingly, the delta C-13(DIC) values of the reservoir averaged around + 0.6 parts per thousand in the top 3 m of the water column. This indicates CO2 degassing and photosynthesis. Below this depth, DIC isotope values of as low as - 10.1 parts per thousand showed stronger influences of respiration. A fractionation model with both isotope parameters revealed that 24% of the POC in the reservoir originated from detritus outside the reservoir and 76% of it was produced internally by aqueous CO2 fixation. (AU)

• FAPESP's process: 16/15397-1 - Organic Carbon cycling in Water Reservoirs of Brazil and Germany: influence of land use and hydrology- ORCWAR
• Grantee: Daniele Frascareli
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/20326-1 - Dissolution and toxicity of silver nanoparticles in the presence of aquatic humic substances and extracellular polymeric substances
• Grantee: André Henrique Rosa
• Support Opportunities: Regular Research Grants