Transcript Lake Nyos, Cameroon

Role of Microbes in
Aquatic Systems
H2O Structure
Oxygen
-
o
Hydrogen
+
105
Hydrogen
+
Hydrogen Bonding
Water Properties
1. Hydrogen bonding
2. Density anomaly
3. Thermal features
4. Surface effects
5. Viscosity
6. Solvent
Aquatic Biomes
Freshwater
Lakes (lentic)
Wetlands (lentic)
Rivers (lotic)
How are lakes formed?
Lake types
1. Tectonic
2. Volcanic
3. Landslide
4. Solution basins
5. Fluviatile
6. Aeolian
7. Meteorites
8. Animals
9. Glacial
Lake Habitats
Terms
Littoral – near shore area
Pelagic – open water out from littoral
Profundal – deep water area in stratified
water
Aquatic Functional Groups (lentic)
Benthos – living on or in bottom sediments
Plankton – small organisms in pelagic zone,
movement controlled by wind
Phytoplankton – Algae
Zooplankton – Animals
Nekton – large invertebrates and fish capable of
swimming independently
Neuston – organisms associated with top water layer
Macrophytes – Large plants
neuston
zooplankton
macrophyte
phytoplankton
benthos
Food chain example
Big fish
minnows
Four steps
are common
zooplankton
phytoplankton
Lakes can be classified by productivity
Production = biomass (wt)/area (volume)
Lake classification is a continuum ranging
From oligotrophic to eutrophic
ultra-oligotrophic
low productivity
oligotrophic
mesotrophic
eutrophic
high productivity
hypereutrophic
MN Lakes production
Oligotrohphic
Why is it
this way?
Mesotrophic
Eutrophic
General Trends
Oligotrophic
Eutrophic
deep
clear
low production
low nutrients
shallow
not clear
high production
high nutrients
TOO MUCH PRODUCTIVITY A BAD
THING?
High nutrients lead to
high amounts of algae
These algae eventually die
and sink to bottom
Bacteria use oxygen when
decomposing algae
Can lead to fish kills
Remember, high nutrients
levels are natural in rich
soil
The Players
Annie, Fanny, and
Mike
Cyanobacteria
Can produce their own
nitrogen
Anabaena
Microcystis
“drown” out other
algae and plants
Aphanizomenon
Ecosystem: community of different species
and their abiotic environment where energy
flows and matter cycles
What happens in a lake is a
complex interaction of many
variables.
Temperature, wind, soil,
nutrients, biota, etc.
Water temperature and density
o
Water is most dense at 4 C
Ice (solid) is less dense than liquid
Warm water is much lighter than cold water
Water mixing
0
Lake surface
Depth m
When the water
temperature is uniform
the water column will
completely mix with a
little help from the
wind. This is because
the density of the water
is equal throughout the
water column.
Lake bottom
30
Nutrients from bottom
are circulated
throughout lake
0
Temp C
30
Water mixing
At some point the
density difference is
too great for wind to
break
0
Lake surface
Depth m
During the summer the
surface water warms
faster than the rest of
the lake due to poor
transfer of heat in water
Lake bottom
30
0
Called summer
stratification
Temp C
30
Summer temperature stratification zones
0
Epilimnion
Metalimnion
or
Thermocline
Depth m
Hypolimnion
30
0
Temp C
30
Oxygen and temperature cycle in a Dimictic
Oligotrophic lake
surface
ICE
bottom
Winter
0 4 8 12 16
0 4 8 12 16 18
Spring
Summer
Fall
0 4 8 12 16
0 4 8 12 16 0 4 8 12 16
0 4 8 12 16 18
0 4 8 12 16 18
Oxygen concentration mg/L
Temperature, C
0 4 8 12 16 18
Oxygen and temperature cycle in a Dimictic
Eutrophic lake
surface
ICE
bottom
Winter
0 4 8 12 16
0 4 8 12 16 18
Spring
Summer
Fall
0 4 8 12 16
0 4 8 12 16 0 4 8 12 16
0 4 8 12 16 18
0 4 8 12 16 18
Oxygen concentration mg/L
Temperature, C
0 4 8 12 16 18
Winter-Summary
Ice forms barrier to oxygen (no photosynthesis or diffusion)
oligotrophic lake
fewer organisms so low respiration
large body of water so lots of oxygen
eutrophic lake
lots of organisms (especially bacteria on bottom)
so high respiration
smaller volume of water so less oxygen
Summer-Summary
Metalimnion or density gradient prevents oxygen from moving
between epilimnion and hypolimnion
Epilimnion has plenty of oxygen from air and photosynthesis
in both lakes
Hypolimnion-oligotrophic lake
fewer organisms so low respiration
large body of water so lots of oxygen
Hypolimnion- eutrophic lake
lots of organisms (especially bacteria on bottom)
so high respiration
smaller volume of water so less oxygen
Lake Nyos, Cameroon
Meromictic, top 50 m
mixes, bottom 150m loaded
with sodium and carbon
dioxide
Lake Nyos, Cameroon
In 1986 a huge cloud of carbon dioxide
Burped up from the bottom and moved
Down the valley killing 1700 and
livestock
Lake Nyos, Cameroon
Trying to prevent again by
mixing the water
Cultural Eutrophication
Eutrophication
Lakes are basins, and naturally change from
Oligotrophic conditions to Eutrophic ones
Time
Oligotrophic
Eutrophic
deep
clear
low production
low nutrients
High oxygen
shallow
not clear
high production
high nutrients
possible low oxygen
Lake Baikal
Cultural Eutrophication
Artificially fertilizing lakes so eutrophication sets in
sooner
Characteristic is blooms of blue-green algae
Cultural Eutrophication
2 big causes are N and P from:
Municipal waste
Fertilizer runoff (can have many forms)
Cultural Eutrophication
Process is positive feedback
More nutrients leads to more algae
Treated sewage
Lower algae
Die and sink
Cultural Eutrophication
Process is positive feedback
More nutrients leads to more algae
Treated sewage
Bacteria decompose algae using oxygen and releasing nutrients that will
mix into water column again causing more algae growth
Cultural Eutrophication
Effects:
When water not mixing oxygen disappears
Aesthetics
Toxins
Once started very hard to stop due to positive
feedback
Cultural Eutrophication
Some Solutions:
Treat waste
Control runoff from agriculture/livestock
Allow native riparian vegetation
Don’t drain wetlands
Minnesota River carries nutrients down to
Gulf of Mexico, These with other rivers
drain about 1/3 of the continental US
Dead Zone
High nitrogen content of spring
runoff from agricultural land
Less dense fresh water floats on
ocean water and algae bloom
Dead algae and zooplankton sink to
bottom and are decomposed by
heterotrophic bateria
Any animal life that can not move
will die
Dead Zone Solutions
Reduce fertilizer use
Buffers
Reestablish wetlands
Municipal waste
treatment
Will it happen??
Ethanol
Ethanol
Is it a net energy gain???
Ethanol
It apparently is a net energy gain
A study at the U of MN found:
Ethanol from corn produced 25% more energy than inputs
This only uses the sugar from the grain
Future technologies could use cellulose which is found in
many plants that are much more environmentally friendly to
grow than corn
Switch grass
Ethanol
Will it end our dependence on foreign oil?
No way:
If all U.S. corn went into ethanol that would offset 12.3% of gas
Most corn now goes to feed livestock
Significant environmental effects (fertilizers, pesticides, etc.)
Only part of the solution, need to explore cellulose production
BIODIESEL
Diesel fuel made from a blend of biological oil
and diesel fuel
BIODIESEL vs ETHANOL
Energy yield
Green house gas reduction
Dedicated production supply
ETHANOL
BIODIESEL
25%
12%
12%
93%
41%
6%
Synfuel hydrocarbons or cellulosic ethanol, if produced from low-input
biomass grown on agriculturally marginal land or from waste biomass,
could provide much greater supplies and environmental benefits than
food-based biofuels