1. Response of an Antarctic Lake Ecosystem to Climate Variation: Linkages between Phytoplankton Species Dynamics and Streamflow Diane M. McKnight 1, Erin Von Maytre 1, John C. Priscu 2,W. Berry Lyons 3, and Michael Gooseff 1 1. Institute of Arctic and Alpine Research Boulder, CO 2. Dept. of Biology, Montana State University, Bozeman, MT 3. Byrd Polar Research Institute, Ohio State University, Columbus, OH

3. Background – Ice Covered Lakes Ice cover- 3-5 m thick, moat in summer Source- streamflow from glacial melt Loss- ablation of ice cover Water column- stable w/depth, some lateral circulation Light penetration about 1% or less

5. Main Phytoplankton Species Chlamydomonus intermedia Oscillatoria linenetica Chlamydomonas subcaudata

6. Main Phytoplankton Species Phormidium angustissimum Chroomonas lacustris Starburst protazoa

7. Dominant species occur in depth zones

8. Dry Valleys and Global Climate

9. Interannual variability in phytoplankton

10. Depth-wise Zonation Taxa Size(  m 3 ) Depths (m)% PAR 1987-1991: Oscillatoria sp. 45-7 0.5-1.6 Oscillatoria limnetica 26-8.5 0.2-0.9 Cryptomonas sp. 2767.5-9.5 0.1-0.4 Chroomonas lacustris 1308.5-9 0.16-0.2 Pyramimonas sp. 5839-10 0.16-0.2 Phormidium angustissimum 29.5-10.5 0.16-0.2 Chlamydomonas subcaudata 904various 0.16-0.2

11. Depth-wise Zonation cont’ Taxa Size(  m 3 ) Depths (m)% PAR Ochromonas nannos* 170*4.5-6.5 0.7-1.0** Chlamydomonas sp. 64.5-8.5 0.4-1.0 Cryptomonas sp 3084.5-8.5 0.4-1.0 Chroomonas lacustris 1778.5-9.5 0.2-0.4 Pyramimonas sp. 3358.5-9.5 0.2-0.4 * Vincent, 1981 ** Vincent, 1988

12. stream gauge algal transect

13. NR

15. Chroomonas lacustris Biovolume

16. Chlamydomonas intermediaPhormidium angustissimum Oscillatoria limnetica Chroomonas lacustris Cryptomonas sp. Lake Fryxell 1997-98 Biovolume (  m 3 /mL) Nov. 18Dec. 29

17. Chlamydomonas intermedia Biovolume

18. Oscillatoria limnetica Biovolume

19. Phormidium angustisimum Biovolume

20. Phytoplankton species changes Species1979-1981 Low flow 1989-1992 High flow 1993-99 Low flow Chroomonas lacustris dominantrareabundant Cryptomonas sp. presentdominantpresent Chlamydomona s subcaudata present?abundantrare Chlamydomona s intermedia present?rareabundant Phormidium angustisimum rare?present Oscillatoria limnetica rare?present>> present

21. Potential Factors Controlling Phytoplankton Light regime in summer Nutrients (N)- diffusion from below oxycline and input from streams Mixotrophy and overwinter persistence Microbial loop dynamics

22. Cyanobacterial mats in stream

23. Stream algal mat changes StreamHabitatMats Change from 1994-98 Canada pavementabundantnone Bowles pavementabundantnone Green pavementabundantnew green mats Delta (upper) pavementabundantnew moss Huey sandysparse more orange, new black Delta (lower) sandysparsenew orange Von Guerard sandysparsemore mats Lawson steepsparse more orange & moss

24. NR ND

25. QQ QQ NR ND

26. Summarizing - trends 1987-99 Streamflow- high flow followed by sustained low flow Major ions increased in upper water column Stream mats-recovery followed by decrease Stream nutrient fluxes- variable!!

27. Conclusions Phytoplankton response to changing climate occurs at the species level Patterns for chlorophytes and cryptophytes related to flow regime Increasing cyanobacterial abundance Potential factors include light regime, nutrient fluxes, mixotrophy, and major ion chemistry

28. A few words of Thanks: National Science Foundation Project No. OPP-9211773, McMurdo Dry Valleys LTER. MCMLTER colleagues Antarctic Support Associates staff