Global NEST Journal, Vol 22, No X, pp XX-XX Copyright© 2020 Global NEST Printed in Greece. All rights reserved Isotope hydrology model and stable isotopes in sediment records from Balkan lakes Chantzi P.* and Almpanakis K. Laboratory of Physical Geography, Department of Physical & Environmental Geography, School of Geology, Aristotle University of Thessaloniki (AUTH), GR-541 24 Thessaloniki, Hellas, Greece Received: 02/02/2019, Accepted: 17/03/2020, Available online: 27/05/2020 *to whom all correspondence should be addressed: e-mail: [email protected] https://doi.org/10.30955/gnj.003058 Graphical abstract 1. Introduction Mediterranean area is strongly affected by climate change with a strong impact on the hydrological cycle (Luterbacher et al., 2005; Fletcher and Zielhofer, 2013; Lelieveld et al., 2012). Several climate models end up to interannual variability for both temperature and precipitation (Giorgi, 2006). Moreover, palaeoclimatic reconstructions highlightPROOFS climate and hydrology variation in Mediterranean area during Holocene. In this frame, topography, geomorphological environment, and human activities define how these complex processes balance as regards human societies. Today, it is very important to have in-depth knowledge about past climate variations and modern environment in order to build our future actions with respect to ecological and social impacts. Lakes give the opportunity to assess climate variation as Abstract 1) they are worldwide representing different climate Isotope mass balance in lake systems is strongly conditions (temperature, precipitation, moisture), correlated with several climatic factors such as geographic location (north, south), hydrology systems temperature, evaporation, precipitation and (open, closed, semi-closed), water types (fresh/sea water air moisture. On the other hand, the sedimentary or mixing processes), 2) the response in long-term budget of lake basins driven by climate, tectonic intervals including records of hydrologic extremes, 3) they and/or human impact is an essential pool of are directly linked to climate variations incorporating the environmental records. Precipitation, springs and lake climate-driven episodes of their basins. Isotope mass water δD and δ18O isotope data were used in order to balance in lake systems is strongly correlated with several understand the key factors for the hydrological climatic factors such as temperature, evaporation, balance of Balkan lakes in West Macedonia. In general, it precipitation and air moisture. The well response of is concluded that the open lake Ohrida and isotope hydrology model to different water bodies makes the semi-closed lake Kastoria are more buffered it a reliable tool to assess hydrological studies. Several hydrological as karst systems and less sensitive to studies have been published regarding the estimation of evaporationUNCORRECTED effect, in contrast to the closed water balance parameters such as evaporation (E), inflow lake system of Prespes that present a strong dependence (I) and the corresponding ratio (E/I), the residence time of on climate seasonality. Based on oxygen water in the lake (Turner et al., 2014; Narancic et al., isotopes in bulk sediments, it is concluded that in Kastoria 2017; MacDonald et al., 2017; Gibson et al., 2002; lake basin an increased run-off on the land surface, Petermann et al., 2018), and water yield (Bennett et al., probably under a more humid period, in 2.4 kyr BP 2008; Gibson et al., 2010; 2017). However, isotope mass disturbed the transition to a drier regime from mid/late balance approach using hydrogen (δ2H) and oxygen (δ18O) Holocene to present. stable isotopes overcomes the lack or the limited Keywords: Lake Kastoria, Holocene, Mediterranean, instrumental data concluding in reliable estimations Balkan, palaeoclimate, stable isotopes, sediments. regarding different lake hydrology systems (Haig, et al., 2020). On the other hand, the sedimentary budget of lake Chantzi P. and Almpanakis K. (2020), Isotope hydrology model and stable isotopes in sediment records from Balkan lakes, Global NEST Journal, 22(XX), XX-XX. 2 CHANTZI AND ALMPANAKIS basins driven by climate, tectonic and/or human impact is δ() a*δ h δ ε) /( 1 h ε (3) an essential pool of environmental records. In this study, E L A k we focus on oxygen isotopes 18O/16O as an ideal tracer for where, h: relative humidity normalized to the saturation water cycle and its signature in bulk sediments. Our vapor pressure at the temperature of the air-water interest is focused in the three hydrological different lakes interface, δA: the isotopic value of the air-vapor over the 18 Ohrida, Prespes and Kastoria in south Balkans. Our main lake, εk: kinetic fraction factor, for δ O with εk~14.2(1-h) objectives are (1) to underline the correspondence of ‰ (Gonfiantini, 1986) isotope mass balance model to three well-defined lakes, ** , where 10001 * and (2) to reach a new conclusion about paleoclimatic k conditions in Kastoria lake basin. α*: equilibrium isotopic fractionation factor dependent on 2. Materials and methods the temperature at the evaporating surface 18 2 1 3 2.1. Isotope mass balance model for lake systems O:1/a* exp1137T( – 0.415T –2.0667*10 (4) LL The isotopic mass balance (eq. 2) is based on the water mass balance (eq. 1) for a well-mixed lake with constant 2H:1/a* exp24844T( 2 –76.248T 1 –52.61*10 3 (5) LL water density: TL: temperature of the lake surface water in degrees d V / d t P Q – E Q (1) Kelvin (Majoube, 1971) io Eq. 5 describes an additional equation for δE as proposed dV( δL/dt) Pδ Qδ–Eδ Q δ (2) P i P E o L by Benson and White (1994) based on the same evaporation theory which has been used in other lake where: V and t, are the lake volume and unit time. P and E models (Ricketts and Johnson, 1996). are precipitation and evaporation on lake surface per unit time. Q factor is calculated by the surface and R R/a RHfR / 1RH/a RH1 f (6) e Leq adad kin ad groundwater budget (Qx = Sx + Gx), where o and i markers correspond to outflow and inflow respectively. where, Rad: isotopePROOFS ratio of the free atmospheric water The isotope values of precipitation, evaporation and lake vapor with respect to VSMOW, RH: relative humidity, and water are induced by δP, δE and δL respectively. αeq: fractionation factor dependent on equilibrium The results are expressed in standard delta notation (δ) as isotopic fractionation factor with αeq = (1/α*), αkin: per mil (‰) deviation from the standard V-SMOW as: δ = fractionation factor dependent on wind speed where αkin -1 ((Rsample − Rstandard)/Rstandard) × 1000, where Rsample and = 0.994 for wind speeds less than 6.8 m*s (Merlivat and 2 1 18 16 Rstandard = H/ H or O/ O of sample and standard, Jouzel, 1979), fad: fraction of atmospheric water vapor in respectively. δP and δL are directly measurable on a water the boundary layer over the lake where fad = 0 in case that sample however it is not as easy for δE. Craig and Gordon all the atmospheric water overlying the lake is derived (1965) reported an evaporation model that is used to from evaporation, rather than atmospheric moisture. calculate δE (eq. 3): 18 Table 1. Summary of average annual hydro-climate factors from GNIP (IAEA/WMO, 2017) data and calculated δ OL values for hydrologically closed lakes from Chantzi and Almpanakis, 2018 T (°C) δ18O ‰ VSMOW Altitude (m asl) RH (%) d-excess (1) δ18Ο (2) δ18Ο (3) δ18Ο Mean (1,2) δ18Ο av p L L L L Pedeli Athens 15.2 -7.48 451 71 14.98 -4.65 4.40 -2.89 0.76 Thessaloniki 16 -6.69 93 71 9.03 -3.81 5.16 -2.01 1.57 Patra 18.1 -5.78 112 65 10.99 -2.39 6.23 -0.26 2.99 Edirne, Turkey 15 -8.24 80 71 11.58 -5.4 3.66 -3.63 0.01 aMean SW 20.6 -9.305 0 38 - -2.27 5.64 1.55 3.60 a: Gat et al., 1996; (1): values from Eq3 that corresponds better to the period with high water-table as it cannot render accurately the evaporation process; (2): values from Eq.6 with Fad = 0 that correspond to water vapor of evaporation origin; (3): values from Eq.6 with Fad = 0 that correspond to water vapor of atmospheric moisture origin 3 factor for hydrological closed lakes. Τhe origin of Finally, δE is calculated by δi = (Ri − 1)10 and Ri = UNCORRECTEDatmospheric water vapor in the boundary layer over the (Ri/Rstandard) where R is the isotope ratio and the standard, in this case, is VSMOW. lake plays an important role in the isotopic signature of lake waters (equations of Benson and White, 1994; 2.2. Methodology Ricketts and Johnson, 1996). In fact, the actual mechanism Limnological isotope theory (Leng and Marshall, 2004; is a continuous refresh where the air above the lake Roberts et al., 2008) is based on climatic factors and constantly supplies the evaporation process permitting precipitation-evaporation balance (P/E) for hydrological molecules to pass from the liquid to vapor phase and open and closed lake systems. In the first case, the origin leaving the lake surface. The main incoming air flow of precipitation and temperature oscillations determine pattern in the Mediterranean area is controlled by the 18 the isotopic signature of lake water (δ OLW) instant of the Atlantic Ocean through the Iberian Peninsula or France precipitation-evaporation balance (P/E) that is the key (for the western Mediterranean) or from the European ISOTOPE HYDROLOGY MODEL AND STABLE ISOTOPES IN SEDIMENT RECORDS FROM BALKAN LAKES 3 continent (for the eastern Mediterranean). Table 1 shows loose deposits. Long term water isotope data in the wider IAEA stations with average annual hydro-climate factors area (Figure 3) present a range from -11.1‰ to -8.7‰ for 18 18 from GNIP (IAEA/WMO, 2017) data and calculated δ OL δ Ο and from -69.2‰ to -50.1‰ for δD with respect to values for hydrologically closed lakes.