CHANGES TN PHYTOPLANKTON PRTMARY PRODUCTIVÏTY AND BTOI,IASS rN LAKE vrcroRrA rüeñõÅl A Thesi.s Subnitted to the Faculty of Graduate Studi.es The University of Manitoba by Rose Mugidde fn Parti_al Fulfilnent of the Requirernents for the Degree of Master of Science Department of Botany (c) December I Lgg2 \{onatt-iorarv Bibliothèque nationale E*! du Canada Acquisitions and Direction des acquisitions et Bibliographic Services Branch dès services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa, Ontario Ottawa (Ontario) K1A ON4 K1A ON4 Your l¡le Votrc èlércnce Our lile Nolre élérence The author has granted an L'auteur a accordé une licence irrevocable non-exclusive licence irrévocable et non exclusive allowing the National Library of permettant à la Bibliothèque Canada to reproduce, loan, nationale du Canada de distribute or sell cop¡es of reprodu¡re, prêter, distribuer ou his/her thesis by any means and vendre des copies de sa thèse in any form or format, making de quelque manière et sous this thesis available to interested quelque forme que ce soit pour persons. mettre des exemplaires de cette thèse à la disposition des personnes intéressées. The author retains ownership of L'auteur conserve la propriété du the copyr¡ght ¡n his/her thesis. droit d'auteur qu¡ protège sa Neither the thesis nor substantial thèse. Ni la thèse ni des extraits extracts from it may be printed or substantiels de celle-ci ne otherwise reproduced without doivent être imprimés ou his/her permission. autrement reproduits sans son autorisation. ISBN Ø-315-81ê33-6 Canadä CHANGES IN PHYTOPLANKTON PRIMARY PRODUCTIVITY AND BToMASS rN LAKE vrcroRrA (ucerqpe) BY ROSE MUGIDDE A Thesis submitted to the Faorlty of Graduate StudÍes of the Universify of Manitoba in partial fuIlillment of ihe requirements fo¡ the degree of I{ASTER OF SCIENCE @ !992 Pernission has been granted to the LIBRâRY OF TI{E UNTVERSITY OF I4ÄNTTOBA to lend or sell copies of this thesis, to the NATIONAL LIBR.{,RY OF CAIrÍADA to mic¡ofilm this thesis a¡rd to lend o¡ sell copies of the film, and IIÀ¡TITERSITY MICROffiMS þ publish an abstract of this thesis. lhe aul*ror teselses other pubücation rights, and neither the thesis nor extensive exEacts Êom it may be printed or othq¡vise reproduced without the autho/s pennission- ii ABSTRI\CT Mugidde, Rosemary. M. Sc., The university of Manitoba, L992. chanqes in phytoplankton primarv productivity and biomass in Lake Victoria (Ugandaì. Major Supervisor; Dr. R.E. Hecky. Phytoplankton primary productivity and biomass of Lake Victoria, Uganda !,¡ere studied during 1989-91-. The daily integral production (rPD) was between B-2o g oz.m-2.d-l offshore and 8-43 g oz.m-z.d-l inshore, which is about a two ford increase over varues obtained in a study conducted 30 years ago. The mod.ern, maximum producÈivity per unit chlorophyll (p.o) is l-ower than historic but still high when compared. to literature values. chlorophyll-a (chr) ranged from g-40 mg.m-3 offshore and 2o-7o mg.m-3 inshore, and this high argar biomass causes rapid extinction of light. rntegral photosynthesis is nor,/ light linited by self shading whÍch iauses row mean light int,ensities in the water column Gù of (2-3 mEin.m-2.min-1¡. The increases in productivity and biomass have been accompanied by phytoprankton taxonomic changes from diatoms to predominantly cyanobacteria, especially the filarnentous heterocystous cyanobacteria which no!,r seem to have a biological advantage in Lake Victoria. The increases in photosynthesis over the historic values rnight be due to reduced herbivory because of fish community changes or increased nutrient roading. However, further increases in daily integrar production wirr not be possibte because of self-shading effects. iii FORWARD Chapter II v¡as formatted, submitted and accepted for publication in the vern. rnternat. Verein. Limnol. journal. The authorship is Mugidde. R. I\/ ÀCKNOWLEDGMENTS Sincere thanks to my supervisor, Dr.R.E.Hecky for providing invaluable support and guidance in all aspects, keeping the end in sight. r thank the members of my advisory committee, Drs. Gordon Robinson and F.J. Ward. This work would not have been possible without the assistance of various people at the uganda Freshwater Fisheries Research orgianisation and the Freshwater Institute of the Department of Fisheries and oceans (canada). r thank arr the people working on the Lake productivity and Nire perch Projects (u) who assisted in various vrays. rn particular, F. w-8. Bugenyi, c. ogwang-otet and alt the technical staff especially M. Magumba and F.Mugumwe for chemical analysis. r thank A. Katende who was a first rate driver, A. Kibirige and J. l{ere who were expert coxswains. r am particuÌarIy indebted to Dr.E. Fee of the Fl'Ir who taught. me how to use prirnary productivity computer progranmes, read and commented on severar manuscripts and with whom r had rousing discussions. r express my appreciation to Hedy Kling for phytoprankton counts and extensive help in phytoplankton identification. susan Kasian introduced me to sAS progranmes. Mike stainton and other staff at Fwr provided expert laboratory assistance and analyses. r am grateful to the staff of the Freshwater institute who made me feel at home. r thank my corleagues at Fv[r especially H. Bootsma for herpfur discussions and moral v support. Thanks to my farnily for a good deal of support and encouragement. Thank you. Research was funded by the International Development Research centre (canada). r am gratefuÌ to rDRC for funding my studies at the University of Manitoba. vl_ TABLE OF CONTENTS Page LIST oF TABLES... ....viii LIST OF FIGIIRES.. ......ix LTST OF APPENDTCES .....xii LIST OF ABBREVIATIONS .xiv GENERAL INTRODUCTTON ....1 CHAPTER I. SEASON, SPATIAL AND INTER-LÄKE VARIABTLITY TN PHYTOPLANKTON PHOTOSYNTHESIS IN LAKES VTCTORIA, KYOGA AND ALBERT (UGANDA) ....6 TNTRODUCTION .......6 MATERIALS AND METHODS ...8 Study areas ......9 Sample collection treatment and analysis ......1_1 Light and temperature measurements ..1-3 RESULTS AND DISCUSSIONS .....16 Phytoplankton photosynthesis and biornass offshore ..L6 Phytoplankton photosynthesis and biomass inshore ...23 Variation of light characteristics of Lake Victoria.....29 Photosynthesis and biomass'in läkes Kyoga and Arbert....3o Discussion.. ....34 CHAPTER TI. THE INCREASES IN PHYTOPLANKTON PRTMARY PRODUCTIVITY AND BTOMASS TN LAKE VICTORTA (UGANDA): A COMPARTSON OF HISTORIC AND MODERN PHOTOSYNTHETTC PARÄMETERS.. ......38 TNTRODUCTTON ......38 vl_1 MATERIALS AND METHODS ..4O Sample collection, treatment and analysis .....40 RESULTS AND DTSCUSSION ......41. Comparison of inshore and offshore stations ...4L Present and Past .....46 DISCUSSION.. ......47 GENERAL DISCUSSTON.. ...48 coNcLusIoNS. ......53 LITERATITRE CITED . .55 APPENDTCES.. ......64 vrLl- LIST OF TABLES Table Page 1. Means and standard deviation of photosynthetic parameters and integral productivity per unit area of Lake Victoria during 1989 18 2. Light characteristics of Lake Victoria d.uring l_989-9r_ 25 3. Average photosynthetic and light parameters of Lakes Kyoga and Albert during 1989-91-.. 3l_ 4. The past (l-960-6i-) and present (t-989-91) photosynthetic characteristics of Lake Victoria. 43 5. Summary of light and photosynthetic characteristics of Lake Victoria during l_989-91_. 45 l-x LTST OF FIGTIRES Figure page 1. Map of Uganda showing the location of Lakes Victoria, Kyoga and A1bert sampled during the study... 5 2. Map of the Northern Lake Victoria near its out flow at Jinja, showing the sampJ_ed areas 9 3. Map of Lake Kyoga showing the main sampted areas 10 4. Map of Lake ÀIbert showing the main sampled areas L2 5. Photosynthesis vs PAR. 15 6. The depth distribution of photosynthetic rates per unit volume offshore Lake Victoria during L7 7 Seasonal (a) chlorophyll concentrations and (b) maximum specific productivity per unit x chlorophyll (P-*) offshore Lake Victoria during L99O-91.... 19 I Seasonality of daily integral, production (fPD), Secchi disk transparency (SD) and Victoria during l-990-91- 2T . 9 Correlation between chlorophytl-a (ChI) concentration and the inverse Secchi transparency (l_/SD) offshore, during l-990-91_.... 22 l-0 Selected profiles of depth distribution of photosynthetic rates per unit water volume at ínshore stations: pilkington Bay, Buvuma Channel and Napoleon GuIf 24 1-l- Variation of chlorophyll-a (ChI) and maximum specific productivity (p.*) inshore 26 L2 The correlatj-on between chlorophyll-a concentrations and the inverse Secchi transparency inshore during i-999-91- 27 xL 1_3 Variation of the hourly integral production (shown as histograms) with the light extinction coefficient (k) and Secchi depth (SD) at three stations: (a) Pilkington Bay (b) Buvuma Channel and (c) Napoleon Gulf 28 L4 SeasonaÌ variation in 1990-91- of (a) Chlorophyll (ChI) and maximum specific productivity at Bugaia; (b) seasonality of the present and past daily integral productivity offshore 42 xrt LIST OF APPENDTCES Appendix Page i- The in situ phytoplankton parameters of Lake Victoria during 1989-9i_ 64 2 The fight and photosynthetic data of Lake Victoria during l-989-91. 67 3 The Secchi transparency, euphotic depths and light extinction coefficients of Lake Victoria during 1989-91- 70 4 Integral production and photosynthetic data of Lake Kyoga during 73 5 The light and photosynthetic parameters of Lake Kyoga during 1989-9L 75 6 The Secchi transparency, euphotic depths and light extinction coefficients of Lake Kyoga during 1999-91 77 7 The photosynthetic parameters and integral production of Lake Albert during 1989-9L... 79 I The light and photosynthetic data of Lake Albert during 1989-9L 8L xl- l_l_ g The Secchi transparency, euphotic depths and fight, extinction coefficients of Lake Kyoga during 1989-91- 83 xiv LIST OF ABBREVIATIONS Chl chlorophyll-a concentrations (mg.rnr) P the rate of photosynthesis IPH hourly integral product,ion per unit area (g oz.m-2.h-l) IPD daily integral production per unit area (g Or.m-2.d-t) DP.o maximum photosynthesis per unit volume m9 Oz.m-'.h-1) as in Talting (196s) P-o maximum rate of photosynthesis per unit of chlorophyll-a observed as in Talling (l_965) (mg Or.mg chl_-1 .