Lake Pavin History, geology, biogeochemistry, and sedimentology of a deep meromictic maar lake

198

the monimolimnion. This hypothesis has been discarded in fur-

ther works, as this deep input should imply a rather strong

advection of water from the monimolimnion toward the mixo-

limnion, inducing for example a strong iron recycling at the

redox interface (i.e. a strong iron rich particles sedimentation

rate). Based on sediment trap data and concentration gradients,

Viollier et al. ( 1997 ) located the sublacustrine inflow within the

mixolimnion, and deduced a fresh water input of 22 Ls−^1.

Aeschbach- Hertig et al. ( 2002 ) concluded the same thanks to

high-resolution CDT profiles and geochemical tracers profiles

analysis and modeling (He,^3 H, CFCs), but with a lower inflow

of 10 Ls−^1. From temperature profiles, these last authors

inferred an intrusion of cold water at about 45 m depth in the

northeast part of the lake (Fig. 11.13).

Works from recent research programs have given new

constrains on the hydrological budget: (i) almost monthly

flow determination of up to 12 streams around the lake from

May 2006 to August 2007, (ii) continuous measurement of

the outlet flow (June 2007–Dec. 2010), (iii) monitoring of

the lake level (Feb. 2009–Dec. 2010); (iv) high resolution

CTD ‐ O 2 profiles and (v) temperature sensors line (precision

0.001 °C; July 2006–Dec. 2006 and April 2007–Dec. 2007).

The lake level is stable within 30 cm of amplitude (level

OTT probe, Feb. 2009–Dec. 2010).

Direct evidences of the sublacustrine input are based on tem-

perature measurements, either from CDT profiles or from the

-25

-20

-15

-10

-5

0

5

0 0,5 1 1,5 2 2,5

13

C

OM oxidation

mixing

1/DIC (mM)-1

0 0.5 1.0 1.5 2.0 2.5

Fig. 11.13 δ^13 C vs.
1/DIC in the
hypolimnion

(^13) C DIC
50
55
60
65
70
75
80
85
90
-10 -5 05
Depth (m)
calc.
meas. May-03
meas.Nov-02
Fig. 11.12 Observed and modeled profiles of δ^13 C of DIC
D. Jézéquel et al.