Biogeochemical ResearchAt Lake Baikal

Beat Müller, Lawrence OchEAWAGFederal Institute of Science and Technology of the Environment, Kastanienbaum, Switzerland

Michael SturmEAWAGFederal Institute of Science and Technology of the Environment, Dübendorf/Switzerland

Elena G. VologinaIECInstitute of the Earth‘s Crust, Russ.Acad.Sci., Irkutsk/Russia

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

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/

AdvectionMineralizati

on

BIOLOGY

GEOLOGY

CHEMISTRY

PHYSICS

Sediment traps: • Export from Hypolimnion

• Degrad. in water column

• Gross sedimentation

Sinking

particles

Particle Fluxes: Sedimentation

The Large Moorings

current meter(30 min. intervals)

Acousticreleaser

T-logger(10 min. intervals)

sequencingtrap(24 cups,2 weeks interval)

integratingtrap

(2 cups)

Mooring Instruments

Sediment cores:• Net sedimentation

• Mineralization/Dissolution

sediments

Particle Fluxes: Sedimentation

• Mineralization of organic matter

• Consumption of oxidants• Release of nutrients

water

Processes at the Sediment-Water Interface

sediments

O2 concentration

profiles

Mineralization and Dissolution

mm

O2 concentration

profiles

Mineralization and Dissolution

mm

In average: 3 mmol O2 m-

2d-1 => 1.1 mio t O2 a-1

i.e. Mineralization of => 880’000 t algae a-1

=> 92 km3 of water

(a layer of 3m thickness)

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. Sibio

N P

Upwel- ling

Cold water

intrusions

Fluxes in the water column

Fluxes in the water column

CDT ProbeTemp.logger

kt P yr-1

50 10

P fluxWater column 40 80 P in

Sed. traps

50

25

20P flux

Porewater

P inSediments

25 difference

30 difference

P inSed. traps

Fluxes of Phosphorus (South Basin)

kt P yr-1

50

Fluxes of Phosphorus (South Basin)

Selenga is the main tributary discharging50 % of the water load75 % of the particle load50 % of terrestrial organic carbon

Monitoring of Tributaries

Reliable monitoring data ofhydrologymajor elements, nutrientssuspended particles

are essential to estimateelement budgetslong term changes

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

Formation at the redoxinterface

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

Early diagenetic processes in the sediment

Early diagenetic processes in the sediment

Diagenetic Processes of the Fe/Mn layer

O2

Oxidation of Mn(II) by O2

Reduction of Mn(IV) by Corg, Fe

Diffusion CH4

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 Corg

Development of Fe/Mn layers

Mn

Fe

Thank you

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 Sibio 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

Structure of the buried crust: Micro-XRF Profiles

Peeper Plate after Exposition

O2 fluxWater column

20.8

20.8

Corg inSed.

traps

14.6

2.6

11.0

O2 fluxPorewa

ter Corg inSedimens

12.0

difference

6.2 difference7.2

difference

Corg inSed.

traps

gCm-2yr-

1

13.6

sum

Fluxes of Organic Carbon (South Basin)

im Sediment-Porenwasser

Rücklösung:0.56 mmol/m2 d

SILIKAT

Jährlicher Eintrag aus dem Einzugsgebiet:

250’000 t Si/Jahr

bei 31’500 km2… 180’000 t Si/Jahr