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Acknowledgements This master thesis was a part of a collaborative project with a fellow master student, Sunniva S. Hartman. We conducted the fieldwork together as well as shared fish data and info from the mercury (Hg), selenium (Se) and stable isotopes (N and C) analysis. The project was carried out the Department of Ecology and Natural Resource Management at the Norwegian University of Life Sciences (NMBU). I am grateful to a number of people at NMBU, friends as well as family. I want to thank Sunniva S. Hartman who I worked with and shared thoughts with through this process. My fellow master student Julie Trømborg and Ronny Steen at the Department of Ecology and Natural Resource Management who participated during the fieldwork. Ole-Håkon Heier, Norwegian Hunting- and Angling Association for lending his boat during the fieldwork. Solfrid Lohne at the Department of Environmental Sciences (IMV), NMBU who analysed the Hg and Se samples and Ingar Johansen at the Institute for Energy Technology (IFE) who analysed the stable isotopes. I also want to thank my sister, Åshild Ø. Våge for giving me good advice through the whole writing process. A special and sincere thanks to my supervisors at NUMB: Professor Thrond O. Haugen the eminent R- exspert and Professor Emeritus Bjørn Olav Rosseland who has finances the analysis in this study. You have both been extremely generous with sharing your time and given me constructive feedbacks during the writing process something I’m very grateful for. _________________________________ Kristine Øritsland Våge Ås, May, 2014 ! I! Table of contents Acknowledgements............................................................................................................... -I- Table of contents.................................................................................................................. -II- Abstract ............................................................................................................................... -IV- Samandrag............................................................................................................................ -V- 1. Introduction....................................................................................................................... -1- 2. Materials and methods..................................................................................................... -4- 2.1 Study sites......................................................................................................................... -4- 2.1.1 ”Glomma south of the lake Øyeren”…………………………………………....….. -4- 2.1.2 Djupetjern (UTM32, East 642386, North 6575083)……………………………….. -4- 2.1.3 Holmetjern (UTM 32, East 643106 North 6575690)…………………........………. -5- 2.1.4 Visterflo (UTM32 East 613900 North 6575300)………………………........……... -5- 2.2 Fieldwork.......................................................................................................................... -5- 2.2.1 Fish-sampling……………………………………………………………........……. -5- 2.2.3 Sampling of water, invertebrates and water plants…………………………………. -6- 2.3 Sample preparation, dissection and age determination…................................................. -7- 2.3.1 Sample preparation…………………………………………………………………. -7- 2.3.2 Dissection……………………………………………………............……………... -8- 2.3.3 Age determination………………………………………………........…………….. -8- 2.3.4 Back calculation of growth……………………………………………................…. -9- 2.4 Chemical analyses…………………………………………………........……………... -10- 2.4.1 Total Hg and Se analysis…………................……............................…………….. -10- 2.4.2 Stable isotope analysis…………………………………………........................….. -10- 2.4.3 Estimating the isotopic baseline of δ15N and δ13C.................……...................…. -10- 2.5 Quality assurance…………………………………………...…………….............…… -10- 2.5.1 Hg and Se………………………........................………............…......................... -10- 2.5.2 Stable isotopes (C and N)…………………………………………………………. -11- 2.6 Statistical analysis…………………………….…...…………………………………... -11- 3. Results.............................................................................................................................. -12- 3.1 Water characteristics………........................................................................................... -12- 3.2 Fish characteristics………….......................................................................................... -12- 3.2.1 Degernestjerna (Lake Djupetjern + Lake Holmetjern)........................................…. -12- 3.2.2 Visterflo…………………………………………………………....................…… -13- 3.3 Growth………………….………………………………….………………….….......... -14- 3.3.1 Degernestjerna……………....................................…………………............…….. -14- 3.3.2 Visterflo…………………………………………………………………………… -15- 3.4 Total Hg concentrations in fish………………………………...…………….…...…… -15- 3.4.1 Degernestjerna…………………………………………………………………….. -15- 3.4.2 Visterflo…………………………………………………………………………… -16- 3.5 Total Se concentrations…………………………………………...…………………… -17- 3.5.1 Degernestjerna…………………………………………………………………….. -17- 3.5.2 Visterflo…………………………………………………………………………… -18- 3.6 Molar ratios of Se/THg…………………...……...……………...…………………….. -19- ! II! 3.6.1 Degernestjerna…………………………………………………………………….. -19- 3.6.2 Visterflo…………………………………………………………………………… -21- 3.7 Stable isotopes (∂15N and ∂13C)…………………………………………..………….... -22- 3.7.1 Description of ∂15N and ∂13C signatures in Degernestjerna…............……………. -23- 3.7.2 Description of ∂15N and ∂13C signatures in Visterflo……………………………... -24- 3.8 Relationships between stable isotopes and THg…………………………...………….. -24- 3.8.1 Degernestjerna…………………………………………………………………….. -24- 3.8.2 Visterflo…………………………………………………………………………… -25- 3.9 Selenium, Se/THg ratios and stable isotopes….………………………………………. -26- 3.9.1 Degernestjerna…………………………………………………………………….. -26- 3.9.2 Visterflo.................................................................................................................... -27- 3.10 Multiple regression models…………...…………...…………………………………. -27- 3.10.1 Mercury………………………………………………………………………….. -27- 3.10.2 Selenium…………………………………………........................................……. -30- 4. Discussion and conclusion….………………………………..……..…….…………… -31- 4.1 Biological factors influencing total Hg in perch…………...………………………….. -31- 4.2 Environmental factor influencing THg in perch……………………….……………… -33- 4.3 Factors influencing the Se concentration in perch…………………………...………... -33- 4.4 Molar ratios of Se/THg…………………….……………....................……….............. -34- 4.5 Management implications for recreational fishing.........………...................……...….. -35- 4.6 Suggested improvements and future studies…........................………………….…….. -35- 4.7 Conclusion………………...…………………..………….……………………………. -35- 5. References ....................................................................................................................... -37- Appendices........................................................................................................................... -41- ! III! Abstract ! This study is based on an investigation of Lake Djupetjern, Lake Holmetjern and Lake Visterflo, which are all situated within the Glomma catchment area. The main objectives were to see if European perch (Perca fluviatilis) from the different lakes differ in Hg and Se concentrations and to quantify the contribution from environmental and biological factors to individual variations in THg and Se concentrations. In addition were the molar ratios (Se:Hg) and management implication for recreational fishing of my THg findings assessed. This was conducted by measuring levels of Hg (mg/kg wet weight), Se (mg/kg wet weight) and stable isotopes (C and N) in the muscle tissue of perch. Further were Hg, Se and stable isotopes (15N and 13C) linked to individual characteristics of the collected fish data (length, weight, age). The result showed that 78 % of the analysed perch from Degernestjerna, and 60 % of the analysed perch from Visterflo contained valued above 0.3 mg/kg w.w.. This is an upper level from where consumption advice is given by WHO for groups at risk. The THg concentration ranged from 0.21-2.20 and 0.07-1.50 mg/kg w.w. in Degernestjerna (Djupetjern + Holmetjern) and Visterflo respectively. The one-way ANOVA analysis showed that there were not an all over difference in the THg distribution between the examined lakes, but when adjusted for individual characters (e.g. age) were there clear differences between the lakes. The multiple regression analysis showed there were two supported models (ΔAIC=0.42) fitted to predict THg concentrations in Degernestjerna and Lake Visterflo: Location*Age*∂13C and Location*Age*∂15N.They predicted slightly different outcomes in the examined lakes (1) THg in perch from Degernestjerna increased with increasing age and trophic position combined with foraging in the pelagic area (2) while THg in perch from Visterflo increased with increasing age independent on the trophic level as well as increased THg levels when feeding in the pelagic area. The Se concentrations in the three lakes was lower than detection level (<1µgSe/L), but the one-way ANOVA showed that perch from Degernestjerna had in general higher Se concentrations compared to perch from Lake Visterflo. The most supported model (ΔAIC=0) fitted to predict Se concentrations in Degernestjerna and Lake Visterflo was: Location+weight+∂13C. The model predicted similar outcomes in the examined lakes: high Se concentrations are obtained