Using variations in the stable carbon isotope composition of macrophyte remains to quantify nutrient dynamics in lakes |
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| Authors: | Ulrike Herzschuh Steffen Mischke Hanno Meyer Birgit Plessen Chengjun Zhang |
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| Institution: | 1.Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association,Research Unit Potsdam,Potsdam,Germany;2.Department of Geosciences,University of Potsdam,Potsdam,Germany;3.Institute of Geological Science,Freie Universit?t Berlin,Berlin,Germany;4.Helmholtz Centre Potsdam,German Research Centre for Geosciences (GFZ),Bremerhaven,Germany;5.Center of Arid Environment and Palaeoclimate Research,Lanzhou University,Lanzhou,China |
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| Abstract: | The apparent isotope enrichment factor εmacrophyte of submerged plants (εmacrophyte–DIC = δ13Cmacrophyte − δ13CDIC) is indicative of dissolved inorganic carbon (DIC) supply in neutral to alkaline waters and is related to variations in aquatic
productivity (Papadimitriou et al. in Limnol Oceanogr 50:1084–1095, 2005). This paper aims to evaluate the usage of εmacrophyte inferred from isotopic analyses of submerged plant fossils in addition to analyses of lake carbonate as a palaeolimnological
proxy for former HCO3
− concentrations. Stable carbon isotopic analysis of modern Potamogeton pectinatus leaves and its host water DIC from the Tibetan Plateau and Central Yakutia (Russia) yielded values between −23.3 and +0.4‰
and between +14.0 and +6.5‰, respectively. Values of ε
Potamogeton–DIC (range −15.4 to +1.1‰) from these lakes are significantly correlated with host water HCO3
− concentration (range 78–2,200 mg/l) (r = −0.86; P < 0.001), thus allowing for the development of a transfer function. Palaeo-ε
Potamogeton–ostracods values from Luanhaizi Lake on the NE Tibetan Plateau, as inferred from the stable carbon isotope measurement of fossil Potamogeton pectinatus seeds (range −24 to +2.8‰) and ostracods (range −7.8 to +7.5%) range between −14.8 and 1.6‰. Phases of assumed disequilibrium
between δ13CDIC and δ13Costracods known to occur in charophyte swards (as indicated by the deposition of charophyte fossils) were excluded from the analysis
of palaeo-ε. The application of the ε
Potamogeton–DIC-HCO3
− transfer function yielded a median palaeo-HCO3
− -concentration of 290 mg/l. Variations in the dissolved organic carbon supply compare well with aquatic plant productivity
changes and lake level variability as inferred from a multiproxy study of the same record including analyses of plant macrofossils,
ostracods, carbonate and organic content. |
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