Biological Responses Following Nutrient
Additions to a Small Pond
DONALD L. BROCKWAY, Biologist
PAT C. KERR, Biologist
DORIS F. PARIS, Chemist
JOHN T. BARNETT, Biological Aide
Environmental Protection Agency
Southwest Water Laboratory
Athens, Georgia
INTRODUCTION
Carbon, nitrogen, phosphorus, and other essential nutrients are required for the
growth of all organisms, so there must be competition among the species of mixed
populations for these nutrients (1,2,3,4,5). Because of this competition, nutrient
regulation is very complex and can be understood only by ascertaining which
population is most directly affected by nutrient availability—the population that
requires the most nutrient in the most constant supply. In general, smaller organisms
have faster metabolic rates, shorter cell cycles, and greater nutrient requirements.
Therefore, our working hypothesis is that the heterotrophic bacteria will be the
population most directly affected by addition of nutrients to waters.
Bacteria are generally considered to comprise an insignificant amount of the
plankton standing crop; when only instantaneous crop rather than total production
measurements are considered, this assumption is probably correct. Data cited in
Kuznetsov (6) showed that in some Russian reservoirs the annual production of
bacterial biomass was significantly higher than that of phytoplankton biomass. Odum
(7) indicated that the bacterial biomass estimated at Silver Springs was much smaller
than that of the combined micro- and macrophytes, but he emphasized the very large
role the bacteria play in energy flow of the system.
Phosphorus and nitrogen utilization by growing populations of bacteria has
been documented for at least 35 years (1,4,5,8,9). Stimulation of bacterial growth by
phosphorus has been reported (5,10); also regulation of bacterial growth by the
availability of organic carbon has been demonstrated in both fresh and sea water
(1,5,9). An increase in the availability of organic carbon then increased the nitrogen
and phosphorus requirement so that nitrogen and/or phosphorus could regulate
bacterial growth (1,5,8,9).
Uptake and storage of phosphorus by algae have been demonstrated
(5,11,12,13,14,15), but the absolute amount of phosphorus required to support algal
growth is small. Values for phosphorus incorporation or utilization of 3 x 10"*, 7 x
10"8, and 10~7 /i g phosphorus/cell for three species of algae have been found by
three authors, respectively (5,12,16). Growth of algae in the absence of an external
source of phosphorus has also been well documented (5,11,12,13,14).
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