9. Microbial Carbon Cycling in Pelagic Ecosystems: Microbial Methods for Ecosystem Scientists
(14)
~O;IC~--r.~"""~20)
~
2600
Phytoplankton
~
Bacteria
I---"'-"'/~ 1 (100) 30..., 100 h~
......,. _ _ .....
20
/
"''..,.-i o.w.. :X' M.'",~."
0.5
~ 5 ~7~~
(5)
_. __ 1_. ___ . _
j 2
POC Flux
36
A
...... 1 - - - - - ,(10) --~ ....
.... DOC1 ~acteria
B
,
20
,~:'I
POC Flux
>20
30
.
11
Micrograzers
~thonous
? - - . ~30~5
139
FIGURE 9.1. Carbon cycling in marine (A) and freshwater (B) pelagic environments showing the role of planktonic
bacteria. Each box represents a pool; the magnitude (g C m - 2) is shown as the upper number in each box. For some
boxes a rate of production (g C m - 2 yr -1) is also shown as a lower number and in parentheses. The arrows represent
transfers between pools (g C m - 2 yr - 1). Repriartion is shown as a transfer from an organic pool to the pool of
dissolved inorganic C (DIC). Part A represents an open-water marine site with a mixed depth of about 100 m, and
is modified from Peterson (1981) with data from Fasham et al. 1990 and Sarmiento et al. 1993. Part B represents
and oligotrophic lake with an epilimnetic depth of 5 m, and is modified from Cole and Caraco (1993) and Cole et
al. (1989). All numbers should be considered as approximate only.
stantial portion of the demands of zooplankton as
well (see Fig. 9.1). Clearly, the abundance, biomass, production, and respiration of pelagic bacteria are key to understanding C cycling in pelagic
environments.
Abundance and Biomass
Bacteria are the most abundant organisms in the
plankton, and can be the most abundant particles in
some systems. In oligotrophic systems, bacteria can