Physical Characteristics of Streams

1
Energy Dynamics in Lakes
Primary production -- The rate at which plants
(usually phytoplankton) convert solar energy to
organic matter by the process of
photosynthesis CO2 H2O ? OM O2 Measure
by 1. Light-dark bottle method 2. 14C
modification
2
Phytoplankton production (mg C m-3 d-1) in
Lawrence Lake, MI, in 1968. From Wetzel (2001,
Fig. 15-22).
Phytoplankton production in Lawrence Lake Low
in winter, pulse just before ice melt Spring
turnover April peak -- probably diatoms Low in
May Series of summer peaks -- greens then
blue-greens MOM in June and July Decline in
fall, no fall peak (often BG peak in
fall) Depth of photic zone -- 10 m ?
Average over 14 years 99.3 mg C/m2/d
3
Phytoplankton production (mg C m-3 d-1) in
Wintergreen Lake, MI, in 1971-72. From Wetzel
(2001, Fig. 15-24).
Phytoplankton production in Wintergreen Lake
Shallower photic zone 4-5 m Irregular seasonal
fluctions Some very high values Fairly high
under ice
Average over 14 years 1012 mg C/m2/d
4
Net Primary Production in Lakes (from Wetzel
2001, Table 15-13) mg C/m2/d
Ultra-oligotrophic lt50 Oligotrophic
50-300 Mesotrophic 250-1000 Eutrophic
gt1000
Note -- the units are different than in the table
from Rohde (1969)
5
What is eutrophication? Weber in 1907. Naumann
(1919 Thienemann (1925)
6
What is eutrophication? Oligotrophic Eutrophic
Low nutrients High nutrients
(load!) Deep Shallow Orthograde
O2 Clinograde O2 Characteristic PP BGs,
pennate diatoms Characteristic zoop Low
NPP High NPP Deep light penetration Shallow
photic zone Few algae, low Chla Algae blooms
7
What happens to the organic matter produced by
primary production? It gets passed up the food
chain and used in respiration. Lets follow 100
g/m2/y of NPP
Of 100 g/m2/y of NPP, we have accounted for only
9.2 being respired. Where did the rest go?
8
Old limnological paradigm (accepted body of
knowledge) Phytoplankton ? zooplankton ? fish
New limnological paradigm The trophic
structure above the producer-decomposer level,
with all its complexities of population
fluctuation, metabolism, and behavior, has a
relatively minor impact on the total carbon
i.e., energy flux in the system Wetzel 1975
9
New limnological paradigm 1. Detritus is the
central pool of energy 2. Sources of
detritus phytoplankton littoral production
(macrophytes and periphyton) allochthonous 3.
Much detrital metabolism (OM ?CO2) takes place
in the sediments