Elsi Sinikka Kauppinen Trophic state of the Great Masurian Lakes system in the past, present and future - causes, mechanisms and effects of changes Rozprawa doktorska Warszawa 2013 Praca doktorska wykonana pod kierunkiem dr hab.Waldemara Siudy w Zakładzie Ekologii Mikroorganizmów Instytutu Botaniki, Wydziału Biologii Uniwersytetu Warszawskiego ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS My supervisor dr hab. Waldemar Siuda for invaluable support and help, and for possibility to explore the depths of my scientific interests and to develop my abilities to new directions. Prof dr hab. Ryszard Chróst, dr hab Iwona Jasser and dr Bartosz Kiersztyn for their scientific support and help, and also for mental support at rough times, lively company and interesting discussions. PhD and MSc students at the Microbial Ecology Department for their great companionship. My family for everything. 3 FINANCIAL SUPPORT FINANCIAL SUPPORT 1. Project Rates of utilization and mineralization of DOM in situ, Ministry of Science and Higher Education, Poland (BW 2011, University of Warsaw), leader: Elsi S. Kauppinen. 2. Project Detection of internal loading potential in Masurian lakes, Ministry of Science and Higher Education, Poland (BW 2012, University of Warsaw), leader: Elsi S. Kauppinen. 3. Project No N N304 080135, Production, decomposition and respiration of organic matter in the Great Mazurian Lakes. Ministry of Science and Higher Education, Poland, leader: Waldemar Siuda. 4. Project No N304 016 32/0959 Biodiversity and function of the planktonic procaryotic microorganisms in lake ecosystems of the varying trophic states. Ministry of Science and Higher Education, Poland, leader: Ryszard Chróst. 4 TABLE OF CONTENTS TABLE OF CONTENTS Abstract ............................................................................................................................................... 7 In English ......................................................................................................................................... 7 In Polish ............................................................................................................................................ 9 Abbreviations and definitions ......................................................................................................... 12 Abbreviations ................................................................................................................................. 12 Common definitions ....................................................................................................................... 13 Specific definitions ......................................................................................................................... 12 Introduction ...................................................................................................................................... 15 Eutrophication and nutrient cycles in lakes .................................................................................... 16 Eutrophication and nutrient limitation ........................................................................................... 20 Oligotrophication – regulators and effects ..................................................................................... 24 Other factors influencing a lake’s trophic state .............................................................................. 27 Goals of the study ............................................................................................................................. 32 Materials and methods .................................................................................................................... 33 Study area ....................................................................................................................................... 33 In situ measurements and collection of samples ............................................................................ 36 Determination of chemical parameters ........................................................................................... 36 Determination of biological variables ............................................................................................ 37 Determination of physical variables ............................................................................................... 40 External datasets ............................................................................................................................. 41 Analyses based on external datasets ............................................................................................... 42 Statistics .......................................................................................................................................... 42 Results ............................................................................................................................................... 44 Long-term changes in trophic state of the GML-system ................................................................ 44 Present state of the GML-system ................................................................................................... 51 External nutrient inputs .................................................................................................................. 56 Internal nutrient cycles and microbial activity ............................................................................... 61 Nutrient limitation .......................................................................................................................... 66 Climatic influence .......................................................................................................................... 73 Sensitivity to further oligotrophication .......................................................................................... 82 5 TABLE OF CONTENTS Discussion .......................................................................................................................................... 86 Intensive eutrophication phase during 1960-1990 ......................................................................... 86 Oligotrophication and current state of the GML-system ....................................................................... 88 Development of external nutrient inputs ........................................................................................ 93 Regeneration of nutrients and microbial activity ........................................................................... 99 Nutrient limitation during trophic state changes ......................................................................... 101 Climatic influence on the trophic state of the GML-system ........................................................ 106 Where and how can oligotrophication be reached? ...................................................................... 110 Other factors and suggestions for future research ........................................................................ 116 Conclusions .................................................................................................................................. 101 References ....................................................................................................................................... 120 6 ABSTRACT ABSTRACT Background Lakes of the Great Masurian Lakes system (GML-system) have been the topic or model ecosystem in a large amount of studies, but a look at the recent history of ecological changes and evaluation of the present ecological state have not been previously performed in a comprehensive way. For this purpose, I utilised a database of published and unpublished ecological data from 1980-2008 collected by the Microbial Ecology Department. In addition, the present state of the GML-system was investigated during the spring and summer months of 2009, 2010 and 2011. These datasets were combined to evaluate changes in water quality from 1980 onwards. The ecological changes were compared to external input data from a governmental statistical office. The present ecological state of the system was analysed in more detail, and the best strategies to further decrease the trophic state of the lakes and to limit the biomass of phytoplankton and especially cyanobacteria were investigated. Results and conclusions The external nutrient inputs to the GML-system began to decrease in 1990. Signs of oligotrophication became clear after 1995 and continued up to 2005. The highest improvement occurred in Lake Niegocin, owing to highly improved wastewater treatment in the town of Giżyczko. After 2005 the oligotrophication of the GML-system stopped, which corresponds to increasing nutrient inputs from agriculture and tourism and possibly also from internal sources. The differences in trophic state index (TSI) between lakes have decreased significantly. During 2009-2011, mean TSIs ranged from 50 to 63, i.e. all lakes could have been classified as 7 ABSTRACT eutrophic. The trophic state of the GML-system was highly variable and dependent on weather conditions. In 2010, an extreme heat wave caused significant changes in multiple variables (such as limnetic nutrient concentrations and stratification structure) and possibly internal loading of phosphorus from sediments to epilimnion. Main effects of eutrophication of the GML-system were identified to be increased dominance of primary production over respiration (i.e. accumulation of organic