1. Biogeochemical Research At Lake Baikal Beat Müller, Lawrence Och EAWAG Federal Institute of Science and Technology of the Environment, Kastanienbaum, Switzerland Michael Sturm EAWAG Federal Institute of Science and Technology of the Environment, Dübendorf/Switzerland Elena G. Vologina IEC Institute of the Earth‘s Crust, Russ.Acad.Sci., Irkutsk/Russia

2. Focus of Scientific Interest Element budgets and fluxes: How is the lake influenced by changing loads? How do they affect the ecosystem? Quantify the loads in and out of the lake, and quantify the fluxes between reservoirs Sediment formation: Investigation of the biogeochemical processes and rates that determine the formation of the ‘young sediment’ so that the climate signals in the ‘old sediment’ can be interpreted

3. Fluxes between reservoirs and the cycling of elements Import Export Precipitation/Deposition Primary Production Export from Epilimnion (New production) Gross Sedimentation Net Sedimentation Mineralization/ Dissolution Turbulence/ Advection Mineralization BIOLOGY GEOLOGY CHEMISTRY PHYSICS

4. Sediment traps: Export from Hypolimnion Degrad. in water column Gross sedimentation Sinking particle s Particle Fluxes: Sedimentation

5. The Large Moorings

6. current meter (30 min. intervals) Acoustic releaser T-logger (10 min. intervals) sequencing trap (24 cups, 2 weeks interval) integrating trap (2 cups) Mooring Instruments

7. Sediment cores: Net sedimentation Mineralization/Dissolution sediments Particle Fluxes: Sedimentation

10. Mineralization of organic matter Consumption of oxidants Release of nutrients water Processes at the Sediment-Water Interface sediments

11. O 2 concentration profiles Mineralization and Dissolution mm

12. O 2 concentration profiles Mineralization and Dissolution mm In average: 3 mmol O 2 m -2 d -1 => 1.1 mio t O 2 a -1 i.e. Mineralization of => 880 ’ 000 t algae a -1 => 92 km 3 of water (a layer of 3m thickness)

13. Advection: Estimation of annual cold- water intrusions into the deep water of the Lake Turbulent mixing: Determination of vertical diffusivity with temperature microstructure measurements and inertial diffusivity eg. Si bio N P Upwel- ling Cold water intrusion s Fluxes in the water column

14. CDT Probe Temp. logger

15. kt P yr -1 50 10 P flux Water column 40 80 P in Sed. traps 50 25 20 P flux Porewater P in Sediments 25 difference 30 difference P in Sed. traps Fluxes of Phosphorus (South Basin)

16. kt P yr -1 50 Fluxes of Phosphorus (South Basin)

17. Selenga is the main tributary discharging 50 % of the water load 75 % of the particle load 50 % of terrestrial organic carbon Monitoring of Tributaries Reliable monitoring data of hydrology major elements, nutrients suspended particles are essential to estimate element budgets long term changes

18. Sediment Formation Sediment formation: Investigation of the biogeochemical processes and rates that determine the formation of the ‘young sediment’ so that the climate signals in the ‘old sediment’ can be interpreted

19. Formation at the redox interface Upper layer moves up with sedimentation Lower layer stays in place Observed in layers of up to 65’000 years What causes the detachment? Indicators of changes in the catchment (climate?) What happens here? Early diagenetic processes in the sediment

22. Diagenetic Processes of the Fe/Mn layer O2O2 Oxidation of Mn(II) by O 2 Reduction of Mn(IV) by C org, Fe Diffusion CH 4 Methanogenesis Oxidation by Fe-oxide Fe(II) reduces Mn-oxide Diffusion Fe(II) Diffusion of Mn(II) Diffusion of Fe(II) Reduction of Fe(III) by C org

23. Development of Fe/Mn layers Mn Fe

24. Thank you

26. SB NB New Production 20.8 14.6 gC m -2 yr -1 Net Sedimentation 2.6 1.5 gC m -2 yr -1 Fluxes of N, P and Si bio were 30% smaller in the NB than in the SB. Denitrification rates 37 (SB) and 52 (NB) mmol m -2 yr -1. (cf. 57 mmol m -2 yr -1 for oceans (Middleburg et al., 1996)) 10.6 and 6.0 mmol P m -2 yr -1 were transferred to the deep water in the SB and NB where 26% and 42% P were retained in the sediments. Summary Nutrient Budgets

27. Structure of the buried crust: Micro-XRF Profiles

30. Peeper Plate after Exposition

33. O 2 flux Water column 20.8 C org in Sed. traps 14.6 2.6 11.0 O 2 flux Porewate r C org in Sedimens 12.0 difference 6.2 difference 7.2 difference C org in Sed. traps gCm -2 yr -1 13.6 sum Fluxes of Organic Carbon (South Basin)

34. im Sediment- Porenwasser Rücklösung: 0.56 mmol/m 2 d SILIKAT Jährlicher Eintrag aus dem Einzugsgebiet: 250’000 t Si/Jahr bei 31’500 km 2 … 180’000 t Si/Jahr