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
0
25
40
40
15
40
5
15
80
10
5
40
20
40
30
60
2
15
15
20
70
60
40
40
15
20
20
60
4
10
80
20
60
5
40
60
15
20
DEPTH (m)
6
40
20
5
60
15
20
8
10
0
10
10
10
5
0
10
5
5
5
0
12
0
JAN FEB MAR APR MAY
JUN JUL AUG SEP
OCT NOV DEC
Phytoplankton production (mg C m-3 d-1) in
Lawrence Lake, MI, in 1968. From Wetzel (2001,
Fig. 15-22).
3
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
4
0
600
10
1000
1000
1000
800
0
600
200
1000
1000
200
400
600
800
1000
600
1
1000
40
100
600
800
200
400
400
600
100
400
200
400
400
2
100
200
20
100
40
200
40
100
200
100
40
100
3
DEPTH (m)
40
100
10
20
40
40
10
20
4
20
10
10
10
0
10
0
0
5
0
JUL AUG SEP OCT NOV DEC
JAN FEB MAR APR MAY JUN
Phytoplankton production (mg C m-3 d-1) in
Wintergreen Lake, MI, in 1971-72. From Wetzel
(2001, Fig. 15-24).
5
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
6
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
7
What is eutrophication? Eutrophic and
oligotrophic originally coined by Weber in 1907
to describe the abundance of nutrients in bogs in
Germany. Naumann (1919), a Swedish limnologist,
adopted these terms to describe the availability
of nutrients for algae. Thienemann (1925),
German, used these terms more broadly to describe
different kinds of lakes.
8
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, Chla Algae blooms
9
What is eutrophication? Eutrophication -- a
natural process Cultural Eutrophication --
acceleration of the natural process due to human
activities.
10
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
11
Fish
Phytoplankton
Zooplankton
NPP100
12
R 7.5
R 1.7
Fish
20
P 2.5
Phytoplankton
Zooplankton
NPP100
A 10
A 1.9
Of 100 g/m2/y of NPP, we have accounted for only
9.2 being respired. Where did the rest go?
13
R 1.7
R 7.5
Fish
20
P 2.5
Phytoplankton
Zooplankton
NPP100
A 10
A 1.9
80
10
0.6
Detritus
R 90.6
It goes to detritus -- dead organic matter.
14
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
15
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