Faculty of Sciences Department of Geology and Soil Science Research Unit Palaeontology Academic year 2009‐2010 Changes in surface waters: a malacological analysis of a Late Glacial and early Holocene palaeolake in the Moervaartdepression (Belgium). by Lynn Serbruyns Thesis submitted to obtain the degree of Master in Biology. Promotor: Prof. Dr. Jacques Verniers Co‐promotor: Prof. Dr. Dirk Van Damme Faculty of Sciences Department of Geology and Soil Science Research Unit Palaeontology Academic year 2009‐2010 Changes in surface waters: a malacological analysis of a Late Glacial and early Holocene palaeolake in the Moervaartdepression (Belgium). by Lynn Serbruyns Thesis submitted to obtain the degree of Master in Biology. Promotor: Prof. Dr. Jacques Verniers Co‐promotor: Prof. Dr. Dirk Van Damme Acknowledgements0 First of all, I would like to thank my promoter Prof. Jacques Verniers and Prof. Philippe Crombé for providing me with this interesting subject and for giving me the freedom to further extend the analysis beyond the original boundaries. Thanks to my co-promoter Prof. Dirk Van Damme who I could always contact with questions and who provided me with many articles on the subject. I also want to thank Prof. Keppens for giving me the opportunity to perform the isotope analysis at the VUB, even though technology let us down in the end. I would like to thank Koen Verhoeven for sacrificing part of his office and for aiding me with the sampling from the trench. Thanks to Mona Court-Picon for the numerous ways in which she helped me during the making of this thesis and for the nice talks. Thanks to Thomas Verleye and Bert Van Bocxlaer for aiding me with the statistical analysis and for explaining to me how Photoshop and Illustrator work. Without you two it would have taken me much longer and as you both know time is precious when writing a Master thesis. I also want to thank Prof. Achilles Gautier for correcting my English writing. Special thanks goes toward Elena Dierick and Pieter-Jan Vandermeeren which gave up several days of their weekends and/or holiday to help me collect the samples for the evaluation of the recent malacofauna. Thanks to my family, boyfriend and friends for tolerating the neglect and the numerous conversations about snail over the past year. Finally, I would like to thank everyone involved in the GOA project and everyone from the Research Unit Palaeontology for their kindness, constructive comments and the several slices of cake and other sweets. Contents 0 ACKNOWLEDGEMENTS EXTENDED ABSTRACT 1 CHAPTER 1: INTRODUCTION 4 CHAPTER 2: GEOARCHAEOLOGICAL FRAMEWORK 6 2.1 LOCATION AND DEMARCATION OF THE STUDY AREA 6 2.2 GEOLOGICAL TIME FRAME AND CLIMATE 7 2.3. THE FLEMISH VALLEY 8 2.4 THE MOERVAARTDEPRESSION: GEOMORPHOLOGICAL AND HYDROLOGICAL EVOLUTION 10 2.5 PRESENT‐DAY HYDROGRAPHY 12 2.6 HUMAN OCCUPATION HISTORY 12 CHAPTER 3: MOLLUSCAN ECOLOGY 14 3.1 ABIOTIC FACTORS 14 3.1.1 OXYGEN 14 3.1.2 PH AND LIME CONTENT 15 3.1.3 SALINITY 15 3.1.4 CURRENTS AND WAVE EXPOSURE 15 3.1.5 TEMPERATURE 16 3.1.6 WATER DEPTH 16 3.1.7 DROUGHT 16 3.1.8 POLLUTION 17 3.2 BIOTIC FACTORS 17 3.2.1 FOOD 17 3.2.2 ENEMIES 18 3.2.3 COMPETITION 18 3.2.4 LOCOMOTION 18 3.2.5 DISPERSAL MECHANISMS 19 3.2.6 REPRODUCTION 19 3.3 WATER TYPES 20 3.4 TAXONOMIC DESCRIPTION OF THE RECOVERED SPECIES 21 CHAPTER 4: MATERIALS AND METHODS 35 4.1 THE RECENT MALACOFAUNA 35 4.2 THE FOSSIL MALACOFAUNA 37 4.3 STABLE CARBON AND OXYGEN ISOTOPES 41 CHAPTER 5: RESULTS 43 PART I: THE RECENT MALACOFAUNA 43 5.1 THE RECENT SPECIES 43 5.2 STATISTICAL ANALYSIS 44 PART II: THE FOSSIL MALACOFAUNA 46 5.3 THE FOSSIL SPECIES 46 5.4 THE S2 SEQUENCE 47 5.4.1 RELATIVE ABUNDANCE AND MOLLUSCAN ZONATION 47 5.4.1.1 Correspondence Analysis 47 5.4.1.2 Molluscan zonation 48 5.4.2 ABSOLUTE ABUNDANCE 51 5.4.3 SPECIES DIVERSITY 54 5.4.4 ENVIRONMENTAL INDICES 54 5.5 THE S4 SEQUENCE 55 5.5.1 RELATIVE ABUNDANCE AND MOLLUSCAN ZONATION 55 5.5.1.1 Correspondence Analysis 55 5.5.1.2 Molluscan zonation 57 5.5.2 ABSOLUTE ABUNDANCE 59 5.5.3 SPECIES DIVERSITY 61 5.5.4 ENVIRONMENTAL INDICES 62 CHAPTER 6: DISCUSSION 64 6.1 THE RECENT MALACOFAUNA 64 6.2 THE FOSSIL MALACOFAUNA 65 6.2.1 HYPOTHETICAL SCENARIOS OF THE MOERVAARTDEPRESSION DEVELOPMENT 65 6.2.2 MALACOLOGICAL/ENVIRONMENTAL PHASES 67 6.3 COMPARISON WITH MOLLUSCAN EVIDENCE OF ELSEWHERE 70 6.4 COMPARISON OF THE FOSSIL AND RECENT MALACOFAUNA 72 CHAPTER 7: CONCLUSIONS 74 PLATE 1 76 PLATE 2 83 REFERENCES 84 APPENDICES 85 Extended abstract 0 The Moervaartdepression is located in the northern part of the province of East Flanders (NW Belgium), not far from the Dutch border. Nowadays it is a lowland area characterised by meadows and agricultural land, but it used to be a large palaeolake. At the beginning of the Late Glacial, the formation of a large aeolian coversand ridge north of the depression blocked the northwards drainage of several rivers and caused indirectly erosion of broad shallow depressions. These depression were filled up with water due to a rise in the water table and created a series of palaeolakes, among which the Moervaart palaeolake was the largest. Lacustrine sediments were deposited during the Late Glacial and the early Holocene. Eventually, the lake dried out due to a lowering of the water table. The Moervaartdepression has a rich archaeological and palaeoecological potential and has been the subject of detailed and systematic research. Numerous Final Palaeolithic sites are present in the lowlands of Flanders (NW Belgium), but often these sites are disturbed making the reconstruction of the Late Glacial human recolonisation difficult. According to the latest data, Flanders was probably not occupied until the Federmesser culture appeared (ca. 12,500‐9,000 BC). Comparison with neighbouring countries points towards a delayed recolonisation of Belgium. In spite of former research efforts, the Late Glacial recolonisation process is still not well understood (Crombé & Verbruggen, 2002). Therefore, the University of Ghent set up a multidisciplinary research project (Geconcerteerde Onderzoeksactie, GOA) in April 2008, funded by the Special Research Fund (BOF) and titled “Prehistoric settlement and land‐use systems in Sandy Flanders (NW Belgium): a diachronic and geo‐archaeological approach”. The Research Unit Palaeontology of Ghent University is responsible for the palaeoecological part of the project. It includes the malacological investigation here presented. None of the past studies paid much attention to the numerous freshwater molluscs present in the sediments. Usually only a list of species is included without any interpretation. Yet, a detailed study of the fossil malacofauna is an important tool to interpret the local environment. Parameters that can be deduced are ambient and water temperature, water depth, size of the water body, hydrographical connections, oxygen content and aquatic vegetation (Davies, 2008). The palaeomalacological investigation aimed at a palaeoenvironment reconstruction and was performed on sediment sequences obtained from a trench in the centre of the Moervaartdepression. The palaeontological study was combined with an investigation of the recent molluscan fauna in the same region. The fossil and recent faunas were compared in order to find out what impact man has had on the fauna since the Late Glacial. Originally the comparison would only include sampling sites of good water quality, according to the Belgian Biotic Index (BBI) calculated by the Vlaamse Milieu 1 Maatschappij (VMM) in 2007, but since some of the selected sites showed signs of habitat deterioration the study was expanded to include intermediate and poor quality sites. Fossil molluscs were also sampled for stable isotope analysis (δ18O and δ13C), but the planned analysis at the Isotope Ratio Mass Spectrometry (IRMS) laboratory of the Vrije Universiteit Brussel (VUB, Prof. Dr. E. Keppens) were not done because of technical problems. Information on the ecological preferences of the studied molluscan species is available since they still live today. Various abiotic and biotic factors determine their presence. The main deterministic abiotic factors are oxygen and lime content, salinity and temperature of the water. Other abiotic factors include pH, water movement, water depth and periodic desiccation of the water body. For the study of the recent fauna, man‐induced pollution can be added to the list of abiotic factors. Biotic factors relate to the living molluscs and their activities. Next to food, predation and competition reproduction, dispersion and locomotion play an important role in their distribution. For the investigation of the recent fauna, rivers and brooks in the catchment of the Moervaart and Zuidlede River were sampled during the summer of 2009. Site selection was based on the “Biologische waterkwaliteit in Vlaanderen 2007” map, created by the VMM. Values of several environmental parameters (e.g. pH, conductivity, nutrients) were also collected from the VMM website. Eleven sites in total were sampled: seven sites of good biological water quality (BBI 7‐8), two of moderate quality (BBI 5‐6) and two of poor quality (BBI 3‐4). The faunal composition of the communities was analysed by means of Correspondence Analysis (CA), followed by environmental fit (envfit) analysis to verify which environmental parameters influence the community composition and whether water quality could be assessed based on molluscs alone. The parameters that demonstrated a significant relation are biological water quality, nitrates, chloride and chemical oxygen demand. For palaeontological analysis, two sequences (S2 and S4) were sampled from a trench in the deepest part of the palaeolake. Sequence S2 consists of 18 samples over a depth of 136 cm, sequence S4 contains 14 samples over a depth of 164 cm.