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

climate, surrounding terrestrial environment ,
prevailing winds, lake circulation dynamics ,
rates of water and inorganic nutrient inflow
and outflow, and chemical precipitation of
essential nutrients control the productivity ,
water quality, and community structure of
aquatic ecosystems ; (2) the dynamics of nutrient
and energy cycling through both biological
and physical processes ; (3) the
mechanisms by which community structure
may inhibit or enhance overall productivity
and water quality ; (4) the response of complex
aquatic ecosystems to a variety of
natural and artificially created disturbances ;
and (5) the mechanisms these systems have
evolved for coping with these disturbances .
The nature of these questions justifies th e
coordinated program which is planned. Some
of the questions this program will bear upo n
and how they intend to be tackled will now
be discussed .
The phytoplankton and bacterial communities
in lakes not only provide the basis fo r
complex food webs, they essentially contro l
the overall water quality and the apparent
state of eutrophication . The sustained abundance
and species composition of the bacterial
and phytoplankton communities depend
to a large extent upon the rate at whic h
they are supplied with essential inorganic
nutrients and energy sources. Most of these
compounds are introduced from the surrounding
terrestrial environment and the
atmosphere through biological fixatio n
processes . The rate at which a lake is supplied
with allochthonous materials may determin e
its productivity structure . Several mechanisms
may be responsible for determining a lake' s
response to allochthonous nutrient input .
These mechanisms relate both to the suppl y
of nutrients to the phytoplankton and bacteria
communities and to the physical an d
biological forces which influence the production
dynamics of these communities .
1 . Dynamics of release of inorganic nutrients
from allochthonous organic material
of varying nutrient richness : The first indication
is that nutrients in nutrient
poor organic material, e .g., wood, are released
slowly. Since the four lakes in thi s
study can be characterized by the nature
and extent of allochthonous input, thi s
mechanism can be studied .
2. Nutrient availability as a function o f
thermal distribution, circulation dynamics,
and cycling dynamics of other chemical
compounds : Vertical density gradients
(determined by vertical therma l
distribution gradients) can control th e
availability of essential nutrients to autotrophic
organisms . The density gradient s
function as a barrier to the mixing o f
nutrients from deeper waters into th e
productive surface waters . Since the
density barrier also inhibits the passag e
of oxygen from the surface into th e
deeper waters the deeper waters some -
times become depleted of oxygen . Thi s
anerobic condition enhances the solubility
of compounds which bind phosphorus
in forms unavailable to phytoplankton
. Thus, the deep waters may be
rich in nutrients which are relatively unavailable
to autotrophic organisms . Th e
four lakes in this study vary greatly i n
the formation of their density gradient s
and thus their capacity to trap nutrients .
This theory is only partially applicabl e
to any particular lake since there exis t
other mechanisms for distributing nutrients.
The shape of the lake basin, direction
and strength of prevailing winds ,
internal circulation currents, disturbanc e
of the bottom sediments by mechanica l
mixing, and dynamics of nutrient trans -
port through the reduced layer of th e
sediment are all mechanisms which ar e
being studied to bear upon the proble m
of nutrient cycling .
3.Biological cycling of nutrients : Since the
communities of phytoplankton and bacteria
in lakes are often limited by the
availability of essential nutrients they
have tended to evolve elaborate mechanisms
for the conservation and recyclin g
of nutrients. In the absence of these
mechanisms, production would mos t
likely be nil. Nutrients cycle through
communities of phytoplankton, zoo -
plankton, bacteria, protozoans, and
littoral aquatic plants. The nature of
these cycles and how they operate with -
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