20 10 D The establishment of ecological and O EPARTMENT environmental reference conditions is needed in the assessment of global change and in lake management at the local scale. In the research of this thesis, I returned to basics in the interpretation of midge palaeolimnology, aiming to refine F the understanding of midge distribution G patterns and taphonomical processes EO for more reliable reconstructions of past S environmental conditions. To do this, I CI examined surface sediment datasets at ENCE different geographical scales, used environ- mental screening, tested the potential of S several calibration models and applied the A developed models to sediment profiles. ND A special focus of this work was on the G climate and environmental variability during EO the time periods of the Medieval Climate Anomaly, the Little Ice Age and the most GRAPHY recent anthropogenic era. a 4 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY a4 t Department of Geosciences and Geography A P. omi ISsN-l 1798-7911 ISsN 1798-7911 (print) ISBN 978-952-10-4281-2 (paperback) l ISBN 978-952-10-4282-9 (PDF) uoto SPATIAL AND TEMPORAL VARIABILITY http://ethesis.helsinki.fi/I IN MIDGE (NEMATOCERA) Helsinki university Print Helsinki 2010 AssEMBLAGES IN SHALLOW FINNISH lakes (60−70 °N): commuNity- BASED MODELLING OF PAST ENVIRONMENTAL CHANGE tomi P. luoto Spatial and temporal variability in midge (Nematocera) assemblages in shallow Finnish lakes (60−70 °N): community-based modelling of past environmental change TOMI P. LUOTO ACADEMIC DISSERTATION To be presented, with the permission of the Faculty of Science of the University of Helsinki, for public examination in the auditorium E204, The Physicum building, on 21 May 2010, at 12 noon. DEPARTMEnt OF GEOSCIENCES And GEOGRAPHY A4 / HELSINKI 2010 © Tomi P. Luoto (synopsis and Paper VI) © John Wiley & Sons Ltd (Paper I) © SAGE publications (Paper II) © The Finnish Environment Institute et al. (Paper III) © Elsevier Ltd (Paper IV) © The Ecological Society of America Cover photo: Newly frozen Lake Pieni-Kauro in October 2009 Author´s address: Tomi P. Luoto Department of Geosciences and Geography P.O. Box 64 00014 University of Helsinki Finland [email protected] Supervised by: Professor Veli-Pekka Salonen Department of Geosciences and Geography University of Helsinki Finland Reviewed by: Dr. Oliver Heiri Institute of Environmental Biology Utrecht University The Netherlands Associate Professor Roberto Quinlan Department of Biology York University Canada Opponent: Dr. Stephen J. Brooks Department of Entomology Natural History Museum UK ISSN 1798-7911 ISBN 978-952-10-4281-2 (pbk.) ISBN 978-952-10-4282-9 (PDF) http://ethesis.helsinki.fi Helsinki University Print Helsinki 2010 Luoto T.P., 2010. Spatial and temporal variability in midge (Nematocera) assemblages in shallow Finnish lakes (60−70 °N): community-based modelling of past environmental change. Helsinki University Print. Helsinki. 62 pages and 20 figures. Abstract Multi- and intralake datasets of fossil midge as- sin were river contribution, water depth and sub- semblages in surface sediments of small shallow merged vegetation patterns. In addition, the re- lakes in Finland were studied to determine the sults of the intralake dataset showed that the fossil most important environmental factors explaining midge assemblages represent fauna that lived in trends in midge distribution and abundance. The close proximity to the sampling sites, thus en- aim was to develop palaeoenvironmental calibra- abling the exploration of within-lake gradients in tion models for the most important environmen- midge assemblages. Importantly, this within-lake tal variables for the purpose of reconstructing heterogeneity in midge assemblages may have past environmental conditions. The developed effects on midge-based temperature estimations, models were applied to three high-resolution fos- because samples taken from the deepest point of sil midge stratigraphies from southern and east- a lake basin may infer considerably colder tem- ern Finland to interpret environmental variability peratures than expected, as shown by the pres- over the past 2000 years, with special focus on the ent test results. Therefore, it is suggested here Medieval Climate Anomaly (MCA), the Little that the samples in fossil midge studies involv- Ice Age (LIA) and recent anthropogenic chang- ing shallow boreal lakes should be taken from es. The midge-based results were compared with the sublittoral, where the assemblages are most physical properties of the sediment, historical ev- representative of the whole lake fauna. idence and environmental reconstructions based Transfer functions between midge assem- on diatoms (Bacillariophyta), cladocerans (Crus- blages and the environmental forcing factors tacea: Cladocera) and tree rings. that were significantly related with the assem- The results showed that the most important blages, including mean air TJul, water depth, hy- environmental factor controlling midge distribu- polimnetic oxygen, stream flow and distance to tion and abundance along a latitudinal gradient littoral vegetation, were developed using weight- in Finland was the mean July air temperature ed averaging (WA) and weighted averaging-par- (TJul). However, when the dataset was environ- tial least squares (WA-PLS) techniques, which mentally screened to include only pristine lakes, outperformed all the other tested numerical ap- water depth at the sampling site became more proaches. Application of the models in downcore important. Furthermore, when the dataset was studies showed mostly consistent trends. Based geographically scaled to southern Finland, hy- on the present results, which agreed with pre- polimnetic oxygen conditions became the domi- vious studies and historical evidence, the Me- nant environmental factor. The results from an dieval Climate Anomaly between ca. 800 and intralake dataset from eastern Finland showed 1300 AD in eastern Finland was characterized that the most important environmental factors by warm temperature conditions and dry sum- controlling midge distribution within a lake ba- mers, but probably humid winters. The Little Ice DEpartmENT OF GEOSCIENCES AND GEographY A Age (LIA) prevailed in southern Finland from ca. 1550 to 1850 AD, with the coldest condi- tions occurring at ca. 1700 AD, whereas in east- ern Finland the cold conditions prevailed over a longer time period, from ca. 1300 until 1900 AD. The recent climatic warming was clearly repre- sented in all of the temperature reconstructions. In the terms of long-term climatology, the pres- ent results provide support for the concept that the North Atlantic Oscillation (NAO) index has a positive correlation with winter precipitation and annual temperature and a negative correla- tion with summer precipitation in eastern Fin- land. In general, the results indicate a relative- ly warm climate with dry summers but snowy winters during the MCA and a cool climate with rainy summers and dry winters during the LIA. The results of the present reconstructions and the forthcoming applications of the models can be used in assessments of long-term environmen- tal dynamics to refine the understanding of past environmental reference conditions and natural variability required by environmental scientists, ecologists and policy makers to make decisions concerning the presently occurring global, re- gional and local changes. The developed midge- based models for temperature, hypolimnetic ox- ygen, water depth, littoral vegetation shift and stream flow, presented in this thesis, are open for scientific use on request. 4 Acknowledgements I am very thankful to the Finnish Graduate School mid palaeoecology. I also wish to acknowledge in Geology, the EPHIPPIUM project (Academy my other research colleagues and collaborators of Finland, grant no. 1107062), the Finnish En- for all the discussions and their valuable advice tomological Society, Nordenskiöld Foundation on my work. Dr Roy Siddall is thanked for im- and the University of Helsinki Fund (Mathemat- proving the english of the synopsis. The help and ics and Science Fund) for their financial support support of coworkers at the department, such concerning this thesis. as Mikko Haaramo MSc, Dr Mia Kotilainen, My supervisor, Prof. Veli-Pekka Salonen, has Frauke Kubischta MSc, Ilona Romu MSc, Eli- given true support in my career and I am very na Sahlstedt MSc, Tuija Vaahtojärvi and Kirsi- grateful for the trust he has shown me. The re- Marja Äyräs, is deeply appreciated. viewers, Dr Oliver Heiri and Dr Roberto Quin- I thank my parents Sirpa and Mauri Luo- lan, provided critical and constructive comments to and my in-laws Riitta and Reijo Nevalainen that improved the value of this thesis. for their support and help when needed. Spe- I express my gratitude to the coauthors, Dr cial thanks go to my hairy friends at home: On- Kaarina Sarmaja-Korjonen, Dr Liisa Nevalain- ni, Helmi and Vilho. I just love you guys! The en, Dr Tommi Kauppila, Prof. Salonen and Dr greatest and most heartwarming thanks belong Samuli Helama, for fruitful collaboration. I spe- to my dearly loved wife, Liisa, who guided, en- cifically want to thank Kaarina for her unself- couraged and kicked me in the buttocks during ish support, guidance and friendship. I thank Dr difficult times, but also provided me such com- Seija Kultti for helping me numerous times and fort at home that it was always easy to forget all Dr Marjut Nyman for introducing me to chirono- about the science. I am among those who think that science has great