Aquatic Ecosystems

1
Aquatic Ecosystems
Comparative Approach
Colorado Plateau Example
Exam
2
Aquatic Ecosystems

• Governed by same principles as terrestrial
  ecosystems
• Radically different environmental controls

3
Terrestrial and aquatic ecosystems have
fundamentally different physical environment
4
Aquatic plants have No physical support
structures Small size to maximize diffusion
rates Rapid reproduction to cope with water
mixing and grazing
Aquatic
Terrestrial
5
lv K
Reynolds number
Ratio of inertial to viscous forces
Where l length v velocity K viscosity
constant
6
Size determines feeding strategy Small organisms
cant swim Depend on diffusion Large cells can
sink or float Move vertically Medium-sized
organisms can filter-feed Large organisms can
swim Can chase prey
diffusion
Filter feeding, swimming
7
Biomass, productivity, C storage, and C residence
time ? Higher on land than in ocean, absolute and
areal bases
8
There are more species on land than in the
oceans, But
Ocean
P
h
y
l
a
Symbiotic
Terrestrial
Freshwater
benthic
pelagic
T
o
ta
l
(
3
3)
2
7
1
1
1
4
1
5
1
1
E
n
d
e
m
i
c
1
0

1

0

4

1
Metazoan diversity is higher in the oceans than
on land, at higher taxonomic levels (e.g.,
Phylum) - Longer evolutionary history?
9
Some marine ecosystems are just as productive as
the most productive terrestrial ecosystems The
most widespread marine ecosystems are
unproductive
10
What limits marine production?

• Water? (no, except intertidal)
• Strong contrast with terrestrial systems, where
  water is the dominant limiting factor
• CO2? (no, except sometimes intertidal)
• CO2-bicarbonate-carbonate equilibrium supplies
  CO2
• Light? (always at depth)
• Nutrients? (usually)

11
More light penetrates to depth in oceans than on
land Marine production is restricted to top 200m
(Euphotic zone) Light limits production within
and below this zone
12
Light quality differs between marine and
terrestrial Ecosystems 1. Ocean water enriched
in blue (high-energy wavelengths penetrate
deeper) 2. Forests enriched in red (plants
remove high-energy wavelengths for Ps
13
Marine phytoplankton are like terrestrial shade
plants

• Low photosynthetic capacity
• Spend most time in light-limiting environ
• (due to frequent mixing)
• Sensitive to UV radiation
• Some specialized to use blue light
• e.g., kelps
• High diversity of primary producers (algal
  diversity gtgt vascular plant diversity), maybe due
  to variable light environment

14
Ocean currents create radically different
environments Centers of gyres have little
mixing Off-shore currents cause upwelling Warm
oceans have high vertical stability (not much
vertical mixing)
15
Euphotic zone of oceans are frequently nutrient
poor spatial separation of light and
nutrients Terrestrial plants overcome this via
vascular transport
Some phytoplankton swim or alter buoyancy to
reduce nutrient limitation
Nutrient concentrations of euphotic zone are
highest in upwelling currents Always depleted
at surface by algal uptake
16
Latitudinal gradients in productivity

• Polar oceans are most productive
• More effective mixing of nutrients from depth
  because of lower surface T, and weaker vertical T
  gradient
• Polar lands are least productive
• Less rapid nutrient release from SOM
• Consequences
• Bipolar bird, fish and mammal migrations to
  capitalize on spring blooms of phytoplankton
• Polar distribution of anadromous fish (eat
  marine, breed fresh)

17
Major upwelling zones off Peru, Africa Outer
Banks, North Pacific California, North
Africa Wind-mixing off Antarctica
18
Strength of tropical upwelling off Peru depends
on ENSO
19
Carbon and Nutrient Cycling in the Oceans

• 1. Herbivory is 3X greaterin pelagic vs.
  terrestrial
• Phytoplankton are not
• made of wood
• 2. Microbial loop rapidlyrecycles C and
  nutrients- because low CN andhigh quality C
• 3. Biological pump
• transports C to deeper ocean- about 25 is
  carbonatethe rest is dead cells, feces
• 4. Only about 0.01 of NPP
• accumulates in ocean sediments

20
Herbivory is 3X greater in pelagic vs.
terrestrial -- Phytoplankton are not made of wood
21
What are the limiting nutrients in the ocean?

• NP ratio of ocean waters centers on 141 (ratio
  found in algae)
• Phosphorus is the master element
• N fixation adds N, whenever P is available

22
NP ratio in oceans centers around 141 Redfield
ratio
23
Water chemistry conforms to same element ratio
as in algae--141 N fixers always add N,
whenever this ratio drops
24
Some regions of oceans have high N and P conc.

• Common in subtropical gyres and southern ocean
• Two processes contribute to this
• 1. Micronutrient limitation
• Iron addition experiments
• 2. Grazing

25
Coastal oceans and estuaries

• More nutrient-rich
• Closer to terrestrial inputs
• Benthic decomposition more important
• Less time for decomposition to occur in water
• Often nitrogen-limited
• Perhaps due to denitrification in sediments

26
Lakes

• Intermediate between oceans and land
• Pelagic zone functions like ocean
• Littoral zone is like wetland

27
Lakes

• Production is seldom carbon-limited
• Groundwater and lake water is often
  super-saturated with CO2
• Most lakes are net source of carbon to the
  atmosphere
• Land-water interaction, whereby terrestrially
  produced CO2 dissolves in water, flows to lake,
  and degases

28
Tundra vegetation fixes CO2 from the atmosphere,
some of which is respired to produce CO2 and CH4.
These gases then dissolve in groundwater and are
transported to lakes and streams where they are
subsequently released to the atmosphere to
complete the cycle.
George Kling et al.
29
Global significance is small, but not negligible
implications for estimates of local C balance?
30
Lakes

• Vertical mixing is critical
• Occurs in spring and fall, when lake is
  isothermal
• Wind and wave action drive the mixing
• Brings nutrients from deep waters to surface

31
Lakes

• Nutrients are strongest limitation to NPP
• Lakes generally P-limited Why?
• Surrounding terrestrial matrix is N-limited
• Two basic explanations
• 1. P retained more effectively than N on land
• 2. Lakes add N through N fixation whenever P is
  available

32
Lakes

• Lakes are vulnerable to eutrophication
• Runoff from polluted watersheds
• Also atmospheric deposition

33
Streams and rivers

• Directional movement of water in streams and
  rivers greatly influences their functioning
• Phytoplankton unimportant
• Would get swept away
• Periphyton are main producers

34
River continuum concept Transition in
structure/function along length of river
system inputs, organisms, energy flow
35
Nutrient spiraling

• Nu trients spiral horizontally
• Terrestrial systems vertical N cycling
• Nutrients held surprisingly tightly
• Flow downstream mainly in dissolved form
• Hyporrheic zone
• Flow also occurs within river bed

36
Fossil Creek, Arizona
37
The worst of times water extraction and exotic
species
Fossil Creek, Dam built 1908
Cuatro Cienegas Diversions built 1960s
38
The best of times?? ? High-priority
conservation sites ? Restoration Options
? Receptive managers
39
Approaches

• Surveys
• native and exotic species
• Stable Isotopes
• Experiments
• test mechanisms

40
(No Transcript)
41
N
Springs
Flume and Road
Dam
Fossil Creek
Irving Power Generator (station and housing)
Dirt Access Road
Strawberry
Verde River
Aerial image of Fossil Creek, Arizona Courtesy of
USDA Forest Service 07/13/98 Modified by C.
Williamson/ Marks lab Northern Arizona University
42
(No Transcript)
43
Fossil Creek Springs Area
44
(No Transcript)
45
(No Transcript)
46
Stable isotopes show shifts in food web structure
d15N
47
Fossil Creeks Future
48
Hydropower Dams energy with no global warming
costs
?
49
Static chamber to measure terrestrial trace gas
flux
Floating chamber to measure aquatic trace gas flux