Karst Springs of Lake Ohrid

Research Collection Master Thesis Karst Springs of Lake Ohrid Author(s): Kunz, Manuel Publication Date: 2006 Permanent Link: https://doi.org/10.3929/ethz-a-005164228 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Diploma Thesis Karst Springs of Lake Ohrid Manuel Kunz 21st March 2006 submitted to the Swiss Federal Institue of Technology (ETH) Zurich Karst Springs of Lake Ohrid Contents Summary 3 Abbreviations 6 1. Introduction 7 1.1. Background . 7 1.2. Study goals and objectives . 10 1.3. Contents of the thesis . 11 2. Study site 12 2.1. Surface springs . 12 2.2. Subaquatic springs . 13 3. Materials and methods 15 3.1. Subaquatic spring search . 15 3.1.1. Littoral zone . 15 3.1.2. Profiling of the water column . 16 3.2. Spring water characteristics . 17 3.2.1. In–situ measurements at surface springs . 17 3.2.2. Water samples . 18 3.2.3. Subaquatic spring sampling . 19 3.2.4. Chemical analysis . 19 3.2.5. Water origin . 20 3.3. Time series of spring water characteristics . 21 3.3.1. Thermistors . 21 3.3.2. Conductivity . 22 3.4. Modeling of steady state concentrations . 22 4. Results and discussion 24 4.1. Localization of subaquatic springs . 24 4.1.1. Subaquatic spring search in the littoral zone . 24 4.1.2. Subaquatic spring search using CTD profiler . 25 4.1.3. Subaquatic spring sampling . 29 4.2. Spring water characteristics . 31 4.2.1. Temperature . 31 4.2.2. Conductivity . 35 4.2.3. pH . 36 4.2.4. Dissolved oxygen . 37 4.2.5. Ionic composition . 37 4.2.6. Isotopic composition . 42 4.3. Modeling of steady state concentrations . 45 4.3.1. Calculation of model inputs . 45 4.3.2. Results and discussion of modeling . 47 1 Karst Springs of Lake Ohrid 5. Synthesis of results 52 5.1. Subaquatic springs . 52 5.2. Temporal stability of spring characteristics . 53 5.3. Spatial heterogeneity of springs . 54 5.4. Subaquatic spring inflow . 55 6. Conclusions 56 List of figures and tables 61 A. Appendix 62 A.1. Positions of CTD profiling . 62 A.2. Background mooring . 64 A.3. Conductivity conversion . 65 A.4. Profiles from Elesec..............................ˇ 66 A.5. Temperature and conductivity at Biljani spring . 67 2 Karst Springs of Lake Ohrid Summary Lake Ohrid in south eastern Europe forms an extraordinary environment. In ad- dition to river inflow and precipitation, Lake Ohrid is fed by groundwater emerging at karstic springs (accounting for ≈ 50 %). Upstream Lake Prespa is discharged by underground flow which feeds certain springs in the Lake Ohrid region. This nutrient and oxygen–rich spring water plays a fundamental role by setting hydro- logic and biologic boundary conditions in Lake Ohrid. It was assumed that half of spring inflow emerges underwater forming potential refugiums for the unique life- forms. Knowledge about subaquatic springs is limited. The goals in this thesis were to develop methods for handling subaquatic springs, to describe physico–chemical characteristics of springs with perspective to assess their importance in the whole ecosystem. Fieldwork was carried out on Lake Ohrid, and at surface springs situated around the lake. A methodology was developed and applied to locate subaquatic springs based on physico–chemical spring water properties. In order to derive water samples from subaquatic springs, a suitable device was constructed. More extended monitor- ing was carried out at surface springs including water sampling and continous measurements. Based on a linear model, mean concentrations of Ca2+ and Cl− in the lake were estimated. Groundwater intruding Lake Ohrid at subaquatic springs was detected at several sites. In the littoral, rather diffusive spring zones than distinct point sources were identified. In the pelagic, clear temperature and conductivity anomalies could be discovered which are likely to be related to emerging spring water. Temperature and conductivity were shown to be adequate tracers to identify subaquatic springs, whereas temperature signals are subject to seasonal changes. The developed device was proved to be suitable to derive water samples from subaquatic springs. In general, physico–chemical parameters of spring water showed only small temporal changes, but large variations comparing different sites. Temporal variability of temperature and conductivity was ± 0.1 ◦C and ± 0.5 µS cm-1, respectively. Tem- perature of spring water ranges from 8.6 to 12.6 ◦C, average conductivity from 227 to 552 µS cm-1, pH from 7.5 to 8.5, and oxygen concetration from 6 to 10 mg l-1. Values of both ionic concentrations and stable isotopes spanned a large range. Using isotopic “fingerprints” of spring water, the referring groundwater sources could be identified, and their relative contribution was quantified. Although based on rough estimations, modeled concentrations in lake water were similar to measured values. Consequentely, the referring water balance is assumed to be adequate. The model was sensitive to spring inputs which points out their relevance for the lake’s hydrology and biology. This study provides a methodology for handling subaquatic springs, quantifica- tions of spring water characteristic, and underlines the importance of subaquatic springs for Lake Ohrid. 3 Karst Springs of Lake Ohrid 4 Karst Springs of Lake Ohrid Acknowledgements The last six months were definitely some of the most intense ones in my entire life. I would never have guessed how many good things can happen in such a short time. I am very greatful that I was given the oppor- tunity to participate in this scientific project which took me to places of breathtaking beauty. I learned so many things and always enjoyed my time. This is all thanks to the many people I got to know in Kastanien- baum and in Ohrid who made everything possible in the first place. My supervisors Johny and Andreas gave me all the support I needed during my thesis project. Your competence and the heartily contact with you always motivated me greatly. Thanks for taking me on board! The entire staff at Eawag Kastanienbaum was of great help. Michi S. introduced me to the world of scientific measuring equipment used in lakes. Together with Christian, we got together all the technical stuff for our fieldwork in the Ohrid region. Without Ruth and Michi M. , I would never have managed to accomplish chemical analysis of my spring wa- ters. Isotopic measurements were made possible by Toni and Carsten. Thanks to Beat who provided helpful hints in geochemistry. All my work in Macedonia was enormously supported by people at the Hydrobiological Institute Ohrid. My fieldtrips on Lake Ohrid and to the adjacent springs are unforgettable. Enormous efforts were done by Borce and Zoran B. , no matter what difficulties arose. The discussions with Zo- ran S. , Dusica, and Trajce always helped to make progress in my project. In the lab, Mare and Beti were always there to make things happen. With- out Goce, all my attempts would have failed in order to organize everything from field work to enter goods for customs clearance. Many thanks to Irene, Angela, Toni, Melanie, and Fabian for your love, and for not forgetting me when I was either far away or my spare time was very limited. This project was financially supported by the Swiss Science Foundation (SNF) in relation to Scientific Co–operation between Eastern Europe and Switzerland (SCOPES). 5 Karst Springs of Lake Ohrid Abbreviations a year, years avg average CTD Conductivity, Temperature, Depth D Deuterium (2H) DO Dissolved oxygen Eawag Swiss Federal Institute of Aquatic Science and Technology, Kastanien- baum HBI Hydrobiological Institute, Ohrid, Macedonia IC Ion chromotography κT Conductivity at temperature T ◦ κ20 Conductivity at 20 C MWL Meteoric water line. Describes the correlation between δ18O and δD of precipitation N Number of measurements O2,sat Oxygen saturation T Temperature Tpot Potential Temperature 6 Karst Springs of Lake Ohrid 1. Introduction Located in south–eastern Europe, Lake Ohrid forms an extraordinary ecosystem. Some of its features were subject to the hereafter presented diploma thesis. This thesis was accomplished as part of the degree in environmental sciences at the Federal In- stitute of Technology (ETH), Zurich, Switzerland. It was written at the Swiss Federal Institute of Aquatic Science and Technology (Eawag), Kastanienbaum, Switzerland, and at the Hydrobiological Institue (HBI), Ohrid, Macedonia. The project was related to a recently finished PhD study which was carried out in corporation with the same institutions (Matzinger et al. 2006a; Matzinger et al. 2006b; Matzinger et al. submitted). It marked also the start of a project in the context of Scientific Co–operation between Eastern Europe and Switzerland (SCOPES) funded by the Swiss National Science Foundation (SNF). This diploma thesis examined karst springs feeding Lake Ohrid. Major focusses were identification of subaquatic springs, characterization of physical and chemical spring water properties, and Lake Ohrid’s sensitivity to spring inflows. In the following introducing sections the outline of this study is described in more details. First, the geographical setting and scientific backgrounds are summarized. Second, based on this review, goals and objectives were developed. Third, the struc- ture of this thesis is explained. 1.1. Geographical and scientific background of the study Lake Ohrid is located in the southern Balkan region (41.1◦ N, 20.7◦ E, 693 m asl; Figure 1). Its surface belongs to both Macedonian and Albanian territory (Figure 2). The Macedonian share accounts for approximately two thirds of the total surface area. The lake is surrounded by mountain ranges. General directions of mountain ridges are roughly north to south.

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