Transcript Chapter 06 water

Chapter 6 – Aquatic Environments - Objectives
1.
2.
3.
Be able to describe the four types of aquatic habitats for microbes
Be able to describe the microbial loop
Understand why activity in the benthos is high and have a basic
understanding of the biogeochemical cycling of carbon and nitrogen in the
benthos.
4. Be able to describe the makeup of a microbial mat including examples of
microorganisms found in a mat.
5. Understand how biofilms develop and the reasons why microbes form
biofilms
6. Be able to define the different regions of a water body: neuston, limnetic,
littoral, and profundal zones
7. Be able to define the thermocline, epilimnion, and hypolimnion
8. Understand the ranges of numbers of microbes in oligotrophic and
eutrophic water bodies
9. Understand the driving force behind the vertical stratification of primary
producers in the water column
10. Understand how microbes adapt to extreme temperatures
11. Be able to describe geothermal vents and their associated community
Aquatic environments
• Cover 70% of the earth’s surface
• Important zone of primary production
• Provides potable water
• Provides water for agriculture and industry
• Provides unique and extreme habitats
• Includes:
Freshwater (rivers, lakes, streams, aquifers
Marine (oceans, estuaries)
Habitats
1.
2.
3.
4.
Planktonic – microbes suspended in the water column
Benthic
Mats
Biofilms
Grazing food chain:
Primary producers
zooplankton
filter feeders/fish
In coastal zones it take 1.5 to 3.5 steps to produce fish because
plants are responsible for some primary production
In the open ocean it takes approximately 5 steps to produce exploitable
fish.
1. Planktonic – Microbes suspended in the water column
Phytoplankton are photosynthetic microbes (primarily cyanobacteria and
algae).
Zooplankton
Dissolved organic
compounds
CO2
Mineralization
E
an xcr
d et i
ly on
si
s
Grazing
Ex
an cret
d l io n
ys
is
E
an xcr
d etio
ly n
si
s
Excretion
and lysis
Major food supply in
aquatic environments.
Support a complex
food web.
Grazing
Uptake
Phytoplankton
Uptake
Responsible for most
of the primary
production in aquatic
environments.
primary production 50% of fixed carbon is released as DOM
Bactivorous
zooplankton
Bacteria
Grazing
Microbial Loop
secondary production
2. Benthic habitat
The benthos is a transition zone between the water column and the
mineral subsurface.
This interface is a diffuse and noncompacted mix of organic matter that has
settled from the surface/mineral particles/water.
Microbial numbers are up to 5 orders of magnitude higher than in the
planktonic environment.
Since activity is high, oxygen is utilized quickly and as a result,
biogeochemical gradients develop that control the types of microbes
and microbial activities found in this region.
Biogeochemical
transformations
+
NH3/NH 4
MIcrobial
transformations
-
NO 3
O2
Surface
Nitrogen
NO-3 assimilation
NH3/NH+4 assimilation
Nitrification
Denitrification
NO-2
Inner (core region)
-2
SO4
O2
Surface
SO-24 assimilation
-4
Sulfur
SO2 reduction
-2
S oxidation
-2
S assimilation
0
S
Inner (core region)
H2S
O2
CO2
Aerobic respiration
(mineralization)
Surface
Carbon
CH4 oxidation
Anaerobic respiration
(mineralization)
Fermentation and
methanogenesis
CH4
Inner (core region)
Carbon
B
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O2
CO2
Aerobic respiration
(mineralization)
Surface
Carbon
CH4oxidation
Anaerobic respiration
(mineralization)
Fermentation and
methanogenesis
CH4
Inner (core region)
Nitrogen
Microbial
transformations
Biogeochemical
transformations
NH3/NH+4
-
NO 3
O2
Surface
-
Nitrogen
NO 3 assimilation
+
NH3/NH 4 assimilation
Nitrification
-
NO 2
Denitrification
Inner (core region)
A microbial mat
3. Mats
Sand layer
Microbial mats are also an
interface in the aquatic
environment in which many
microbial groups are laterally
compressed into a thin mat.
The width of the mat ranges from
several mm to cm
Cyanobacteria
Oxidized iron
Purple sulfur bacteria
Mats are vertically stratified with
an aerobic zone on the top
which is separated from the
bottom anaerobic zone by a
layer of oxidized iron.
Precipitated iron sulfide
Mats form in extreme environments.
Stromatolites are fossilized mats that are 3.5 billion years old and are
among the first indications of life on earth.
Stromatolites were thought to be extinct but were discovered 40 years
ago in Shark Bay, Australia in a hypersaline area. The hypersalinity
prevents marine animals from thriving and grazing on the mat material.
4. Biofilms
Biofilms are a layer of organic matter with attached microbes.
Biofilms form on submerged rock surfaces, plants, skin, ship hulls, pipes,
teeth, catheters and implants, and basically any submerged surface.
Biofilms can be beneficial (wastewater treatment, skin barrier) and can be
harmful (pipeline corrosion, medical implants, tartar).
Benefits (to the microbe) of biofilm growth: Microbes growing in a biofilm
are more resistant to: antibiotics, predation, dessication, changes in
environmental factors (pH, temperature). They also have better
access to solution nutrients because the solution is constantly flowing
over the biofilm.
Organic molecule
Microorganism
Biofilm development proceeds in three phases:
1)
the surface is modified by attachment of organic molecules
2)
reversible attachment of microbes to the organic layer and colonization
3)
irreversible attachment and biofilm formation. In a mature biofilm, the cells are
organized into columns surrounded by large void spaces that form channels to
carry nutrients (O2) deep into the biofilm
Aquatic environments
Freshwater
• Lentic (standing) vs. lotic (running)
• Springs
• Lakes
oligotrophic – deep, low biomass
eutrophic – shallow, high biomass
• Groundwater
Marine
• Estuaries
• Oceans
Freshwater - A typical lake has several regions of interest.
Neuston layer
Neuston
layer
Limnetic
zone
Profundal
zone
Benthic
zone
Littoral
zone
The neuston layer occurs at the air-water interface.
Nutrients and microbes aggregate at the neuston.
Air
0
Water lipid layer
10 nm
Protein-polysaccharide layer
0.1 um
Bacterioneuston layer
1.0 um
Lower neuston
Up to 10 um
The limnetic zone which is the surface layer of open water where light
can penetrate
Neuston layer
Limnetic
zone
Profundal
zone
Benthic
zone
Littoral
zone
The thermocline is a zone defined by a rapid change in temperature. The zone
above the thermocline is the epilimnion and the zone below is the hypolimnion.
The thermocline prevents mixing of lake water through much of the year. Mixing
can only occur in the fall and spring as the water either cools (fall) or warms
(spring) so that the thermocline disappears.
0
2
4
6
Water surface
8
10 O2 mg/l
Depth (m)
Epilimnion > 4oC
Temperature
Thermocline
Dissolved oxygen
Hypolimnion < 4oC
Sediment zone
0
5
10
15
0
2
4
6
Depth (m)
0
Summer
20
o
25 Temp C
8
10 O2 mg/l
Water surface
Epilimnion 0 – 4oC
-4
Thermocline
Winter
-8
-12
Hypolimnion > 4oC
Sediment zone
-16
0
5
10
15
20
25
Temp oC
Marine water
Estuaries are transition areas between freshwater and ocean
environments. Salinities range from 1 to 3.2%. Estuaries harbor unique
ecosystems such as the mangrove swamps and are subject to high
levels of pollution from freshwaters carrying surface runoff that enter the
estuary. Estuaries also serve as environments that can be used to treat
polluted waters before they reach the open ocean.
Oceans have a salinity of 3.5% compared to a salinity of 0.05% in
freshwater environments. Oceans can reach depths of 11,000 m and
are generally divided into two zones, the photic zone (where light
penetrates) which ranges from 1 to 200 meters, and the aphotic zone.
Microbes in the aquatic environment
Numbers vary so much with different water bodies that it is difficult to
provide generalities. However, there are ranges and patterns of microbes
in an oligotrophic and a eutrophic lake environment.
Planktonic numbers are up to 5 orders of magnitude lower than benthic
numbers.
Heterotrophic numbers increase dramatically at the neuston, the
thermocline, and the benthos.
Primary producers arrange themselves in zones according to the
wavelength of light that their chlorophyll-like molecules absorb and
according to availability of H2S.
Eutrophic Lake
Oligotrophic Lake
Neuston 0
0
Cyanobacteria
Neuston
Cyanobacteria
O2
O2
Epilimnion
Epilimnion
10
Relative depth (m)
Relative depth (m)
Chlorobacteria
Thermocline
Thermocline
4
Chlorobacteria
Heterotrophic bacteria
H2S
Heterotrophic bacteria
H2S
Hypolimnion
Hypolimnion
8
20
Colorless sulfur bacteria
and sulfate reducing organisms
1
2
3
4
5
Log CFU/l
Benthos
6
7
Colorless sulfur bacteria and
sulfate reducing organisms
3
4
5
6
7
Log CFU/l
Benthos
8
Chlorophyll a concentration
Heterotrophic counts
(Chlorophycophyta)
Relative absorption
Porphyridium
(Rhodophycophyta)
Synechococcus
(Cyanobacteria)
Rhodopseudomonas
(nonsulfur purple
bacteria)
400
600
800
Wavelength (nm)
1000
Stratification of primary
producers