Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence
- 357 Downloads
Semi-labile dissolved organic carbon (DOC) plays an important role in the transport and hypolimnetic remineralization of carbon in large freshwater lakes. However, sources of semi-labile DOC in lakes remain unclear. This study used a carbon stable isotope approach to examine relative contributions of autochthonous and allochthonous sources to semi-labile DOC. Vertical and seasonal variations in the concentration and carbon stable isotope ratio (δ13C) of DOC were determined in large (surface area 674 km2; maximum depth 104 m), monomictic Lake Biwa. A sharp vertical gradient of δ13C of DOC (δ13C-DOC) during the stratification period [mean ± standard error (SE) −25.5 ± 0.1 and −26.0 ± 0.0‰ in the epi- and hypolimnion, respectively] indicated the accumulation of 13C-rich DOC in the epilimnion. Vertical mixing explained the intermediate values of δ13C-DOC (−25.7 ± 0.0‰) measured throughout the water column during the overturn period. Both DOC concentration and δ13C-DOC decreased in the hypolimnion during stratification, indicating selective remineralization of 13C-rich DOC. Using a two-component mixing model, we estimated the δ13C value of semi-labile DOC to be −22.2 ± 0.3‰, which was close to the δ13C of particulate organic carbon collected in the epilimnion during productive seasons (−22.7 ± 0.7‰) but much higher than the δ13C-DOC in river waters (−26.5 ± 0.1‰). Semi-labile DOC appeared to be mainly autochthonous in origin, produced by planktonic communities during productive seasons. The spatiotemporal uncoupling between production and remineralization of semi-labile DOC implies that hypolimnetic oxygen consumption may be affected by pelagic primary production during productive seasons of the preceding year.
KeywordsSemi-labile dissolved organic carbon Autochthony and allochthony Mixing model Carbon stable isotope ratio Large lake
T. Koitabashi, T. Miyano, and Y. Goda assisted with field sampling. This study was supported by the Basic Research Program of the Japan Science and Technology Agency, the Twenty-first Century Center of Excellence Program (Kyoto University), and the Global Environmental Research Fund (Fa-084) by the Ministry of the Environment, Japan. Our experiments comply with the current law of Japan.
- Clark I, Fritz P (1997) Environmental isotopes in hydrogeology. Lewis Publishers, FloridaGoogle Scholar
- Davis J, Benner R (2007) Quantitative estimates of labile and semi-labile dissolved organic carbon in the western Arctic Ocean: a molecular approach. Limnol Oceanogr 52:2434–2444Google Scholar
- Hill WR, Fanta SE, Roberts BJ (2008) 13C dynamics in benthic algae: effects of light, phosphorus, and biomass development. Limnol Oceanogr 53:1217–1226Google Scholar
- McCallister SL, Guillemette F, del Giorgio PA (2006) A system to quantitatively recover bacterioplankton respiratory CO2 for isotopic analysis to trace sources and ages of organic matter consumed in freshwaters. Limnol Oceanogr Methods 4:406–415Google Scholar
- Nagata T (2000) Production mechanisms of dissolved organic matter. In: Kirchman DL (ed) Microbial ecology of the oceans, 1st edn. Wiley, New York, pp 121–152Google Scholar
- Nagata T (2008) Organic matter-bacteria interactions in seawater. In: Kirchman DL (ed) Microbial ecology of the oceans, 2nd edn. Wiley, New York, pp 207–241Google Scholar
- Pace ML, Carpenter SR, Cole JJ, Coloso JJ, Kitchell JF, Hodgson JR, Middelburg JJ (2007) Does terrestrial organic carbon subsidize the planktonic food web in a clear-water lake? Limnol Oceanogr 52:2177–2189Google Scholar
- Somiya I (ed) (2000) Lake Biwa: environment and water quality formation (in Japanese). Gihodoshuppan, TokyoGoogle Scholar
- Tranvik LJ (1998) Degradation of dissolved organic matter in humic waters by bacteria. In: Hessen DO, Tranvik LJ (eds) Aquatic humic substances. Springer, Berlin, pp 259–283Google Scholar
- Wetzel RG (2001) Limnology: lake and river ecosystems, 3rd edn. Academic Press, San DiegoGoogle Scholar