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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 , D ü bendorf/ Switzerland

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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 oftheEarth‘sCrust, Russ.Acad.Sci., Irkutsk/Russia


Focus of scientific interest
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

Precipitation/Deposition

Import

Export

BIOLOGY

Primary Production

Export from Epilimnion

(New production)

Turbulence/

Advection

PHYSICS

Mineralization

Gross Sedimentation

Mineralization/

Dissolution

GEOLOGY

CHEMISTRY

Net Sedimentation


Particle Fluxes: Sedimentation

  • Sediment traps:

  • Export from Hypolimnion

  • Degrad. in water column

  • Gross sedimentation

Sinking particles



Mooring Instruments

sequencing

trap

(24 cups,

2 weeks interval)

T-logger

(10 min. intervals)

current

meter

(30 min. intervals)

Acoustic

releaser

integrating

trap

(2 cups)


Particle Fluxes: Sedimentation

  • Sediment cores:

  • Net sedimentation

  • Mineralization/Dissolution

sediments


Processes at the Sediment-Water Interface

  • Mineralization of organic matter

  • Consumption of oxidants

  • Release of nutrients

water

sediments


Mineralization and Dissolution

O2 concentration profiles

mm


Mineralization and Dissolution

In average: 3 mmol O2 m-2d-1

O2 concentration profiles

=> 1.1 mio t O2 a-1

mm

=> 92 km3 of water

(a layer of 3m thickness)

i.e. Mineralization of

=> 880’000 t algae a-1


Fluxes in the water column

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

CDT Probe

Temp.

logger


Fluxes of Phosphorus (South Basin)

50

10

Pin

Sed. traps

80

40

Pflux

Water column

30

difference

Pin

Sed. traps

50

Pflux

Porewater

20

25

difference

Pin

Sediments

25

kt P yr-1



Monitoring of Tributaries

Selengaisthemaintributarydischarging

50 % ofthewaterload

75 % oftheparticleload

50 % ofterrestrialorganiccarbon

Reliablemonitoringdataof

hydrology

majorelements, nutrients

suspendedparticles

are essential toestimate

elementbudgets

longtermchanges


Sediment formation
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


Early diagenetic processes in the sediment
Early diagenetic processes in the sediment

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?




Diagenetic Processes of the Fe/Mn layer

O2

Oxidation of Mn(II) by O2

Reduction of Mn(IV) by Corg, Fe

Reduction of Fe(III) by Corg

Diffusion of Mn(II)

Diffusion of Fe(II)

Fe(II) reduces Mn-oxide

Diffusion Fe(II)

Oxidation by Fe-oxide

Diffusion CH4

Methanogenesis




Summary Nutrient Budgets

  • SB NB

  • New Production20.8 14.6gC m-2 yr-1

  • Net Sedimentation 2.6 1.5gC m-2 yr-1

  • Fluxesof N, P andSibiowere 30% smaller in the NB than in the SB.

    Denitrificationrates 37 (SB) and 52 (NB) mmol m-2 yr-1.

    (cf. 57 mmol m-2 yr-1foroceans (Middleburg et al., 1996))

    10.6 and 6.0 mmol P m-2 yr-1weretransferredtothedeepwater in the SB and NB where 26% and 42% P wereretained in thesediments.




    Fluxes of Organic Carbon (South Basin)

    Corg in

    Sed. traps

    O2 flux

    Water column

    20.8

    20.8

    7.2

    6.2

    difference

    difference

    Corg in

    Sed. traps

    14.6

    13.6

    sum

    O2 flux

    Porewater

    11.0

    12.0

    difference

    Corg in

    Sedimens

    2.6

    gCm-2yr-1


    SILIKAT

    im Sediment-Porenwasser

    Rücklösung:0.56 mmol/m2 d

    bei 31’500 km2…180’000 t Si/Jahr

    Jährlicher Eintrag aus dem Einzugsgebiet:250’000 t Si/Jahr


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