224
TEP and attached bacteria (Passow 2002 ). Therefore TEP
constitute a link to higher trophic levels, infl uencing the
fl uxes of matter in lakes.
The importance of TEP in Lake Pavin was assessed dur-
ing the spring diatom bloom in 2000, 2002, 2005 and 2006.
The scopes of these studies were (1) to determine the abun-
dance, the size spectra and the distribution of TEP, (2) to
analyse the bacterial density within TEP, and (3) to test the
potential impact of TEP on the composition and distribution
of both bacteria and protozoa. We reviewed here the main
results of these studies and the roles of these particles in
Lake Pavin, in the general context of freshwater ecology.
13.2 Abundance and Distribution of TEP
Microscopic counts from Lake Pavin revealed that the abun-
dance of TEP ranged from 0.3 × 10^5 particles L −1 to 13.4 × 10^5
particles L −1. Annual means ranged from 3.2 × 10^5 particles
L −1 to 6.7 × 10^5 particles L −1 (Carrias et al. 2002 ; Arnous et al.
2010 ). The abundance of TEP decreased with depth in the
mixolimnion (Fig. 13.2 ) and was related to diatom densities.
TEP are however recorded in high numbers at the oxic-
anoxic boundary (58–60 m depth), where they are probably
produced by the large quantities of dissolved organic carbon
from the monimolimnion. Cumulative surface area of TEP
averaged 35.5 ± 28.7 mm^2 L −1 (Range: 4.6–85.9 mm^2 L −1 ).
Both the abundance and the surface area of TEP were lower
in Lake Pavin than in Lake Aydat (Carrias et al. 2002 ;
Lemarchand et al. 2006 ) and were related to chlorophyll a
concentrations and epilimnetic phytoplankton biomass.
These features indicate that TEP, which originate from dis-
solved organic matter, increase with the productivity of the
environment. The abundances recorded in Lake Pavin are
within the range of those reported from marine environments
of similar trophic status (Passow and Alldredge 1994 ;
Schuster and Herndl 1995 ; Mari and Kiørboe 1996 ).13.3 Size Spectra of TEP
The size spectra of TEP were described by the power rela-
tionship dN/dl = k l −(β +1) where the constant k depends on the
concentration of particles and β describes the size spectra;
the smaller β is, the smaller the fraction of small particles
(Passow and Alldredge 1994 ; Mari and Kiørboe 1996 ). In
practice, for each size interval, the particle concentration
(dN) was normalized to the length of the interval (dl) andFig. 13.1 Double-staining
procedure showing a particle
stained with Alcian Blue ( a )
and the DAPI-stained bacteria
associated to this particle ( b ).
Scale bar represents around 5
μm. See also http://www.aslo.
org/lo/toc/vol_47/
issue_4/1202a1.html
J.-F. Carrias et al.