PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Proceedings-Research on Coniferous Forest Ecosystems-A symposium .
Bellingham, Washington-March 23-24, 197 2
Exploring the
aquatic carbon web
Bruce Lighthart and Paul E . Tiegs l
Western Washington State Colleg e
Bellingham, Washington 9822 5
Abstract
An aquatic carbon web containing the six compartments dissolved inorganic carbon (DIC), phytoplank ton,
zooplank ton, dissolved organic carbon (DOC), detritus, and chemoorganotrophic bacteria is discussed . Tentativ e
methods are presented for measuring the pool size and kinetics about each compartment at one depth in the epiand
hypo-limnions during the four seasons in Lake Washington, Lake Sammamish, Lake Chester Morse, an d
Lake Findley.
Introduction
It is a primary concern to man to be able t o
prepare predictive mathematical models of
organic forms in aquatic systems if he is going
to understand and ultimately develop the
tools to wisely manage his water resources . To
prepare such models, it is desirable to evaluate
the pool size (standing stock) and flux (kinetics)
of energy (Lindeman 1942) in all the
fractions or compartments of the system .
Models may be based on measurements o f
energy or of several materials, e .g., carbon ,
phosphorous, and nitrogen ; however, both
approaches are fraught with technical difficulties.
Of the materials named, carbon i s
recommended because it is a major component
of all organic matter and is cycle d
through a relatively well known web in th e
biosphere . In addition, it is possible to follo w
its movement with c" and other simpl e
analytical techniques .
In the aquatic realm, the carbon web ma y
be thought to form a cyclical system made u p
of a series of interrelated compartments . I n
this discussion the carbon web will be limite d
to a consideration of carbon in the followin g
compartments (fig . 1): (1) Dissolved inorgani c
carbon (DIC), (2) Phytoplankton, (3) Zoo -
plankton, (4) Detritus, (5) Dissolved organi c
carbon (DOC), and (6) Chemoorganotrophi c
bacteria (Stonier et al . 1963). The cycle is
initiated when dissolved inorganic carbo n
species such as bicarbonate (or other chemical
species in the aquatic carbonate syste m
(Stumm and Morgan 1970)) are fixed durin g
the photosynthetic process into organic
matter by the photosynthetic organism (primarily
phytoplankton and secondarily photo -
synthetic bacteria) . Phytoplankton form the
first link in the carbon food chain and ar e
either eaten by herbivorous zooplankton, die
and become part of the detritus compartment,
or excrete dissolved organic carbo n
(DOC). As much as 80 percent of the algal
photosynthate may be excreted as glycolic
acid and other compounds into the wate r
(Hutchinson 1957, Fogg 1963, 1965, Hoo d
1970). Subsequently, microorganisms may
take up the DOC transported by the turbulen t
water and metabolize it to inorganic carbo n
forms. Saunders (1957, 1971) and Saunder s
and Storch (1971) have found that th e
h eterotrophic bacteria and phytoplankto n
form a coupled oscillating pair in which th e
bacteria increase in activity during the day in
response to the daylight production and re -
lease of the algal photosynthate into the surrounding
waters . The herbivorous zooplankton
(and carnivorous zooplankton) also
1 Bruce Lighthart is Director, Institute for Fresh- ,
water Studies, and Assistant Professor, Department of
Biology . Paul E . Tiegs is with Institute for Freshwater
Studies .
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