Chapter 6 – Aquatic Environments - Objectives

1. Be able to describe the four types of aquatic habitats for microbes 2. Be able to describe the microbial loop3. 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 hypolimnion8. Understand the ranges of numbers of microbes in oligotrophic and

eutrophic water bodies9. Understand the driving force behind the vertical stratification of primary

producers in the water column10. Understand how microbes adapt to extreme temperatures11. 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, aquifersMarine (oceans, estuaries)

Primary producers zooplankton filter feeders/fish

Habitats

1. Planktonic – microbes suspended in the water column2. Benthic3. Mats4. Biofilms

Grazing food chain:

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.

Responsible for most of the primary production in aquatic environments.

Major food supply in aquatic environments.

Support a complex food web.

Phytoplankton are photosynthetic microbes (primarily cyanobacteria and algae).

1. Planktonic – Microbes suspended in the water column

Grazing

GrazingMineralization

Gra

zin

g

Upt

ake

Exc

retio

n

and

lysi

s

Up

take

Excretion

and lysis

Excretion

and lysis

Excre

tion

and

lysi

s

Phytoplankton Zooplankton

BactivorouszooplanktonBacteria

Dissolved organiccompounds

CO 2

primary production

Microbial Loopsecondary production

50% of fixed carbon is released as DOM

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.

2. Benthic habitat

NH /NH3 4+

NO -

3

NO assim ilation-3

NH /NH assim ilation3 4 +

Nitrification

Denitrification

SO assim ilation- 4 2

SO reduction2

-4

Aerobic respiration (m ineralization)

Anaerobic respiration (m ineralization)

CH oxidation4

CH 4

CO 2

Fermentation andmethanogenesis

NO -2

O 2

O 2SO 4

-2

H S2

S 0

S oxidation-2

S assimilation-2

O 2

Surface

Inner (core region)

Inner (core region)

Inner (core region)

Surface

Surface

Biogeochemicaltransformations

Nitr

oge

nS

ulfu

rC

arb

on

M Icrobialtransformations

Biogeochemicaltransformations

Microbialtransformations

Carbon

Aerobic respiration (mineralization)

Anaerobic respiration (mineralization)

CH oxidation4

CH 4

CO2

Fermentation andmethanogenesis

O2

Inner (core region)

Surface

Car

bon

NH /NH3 4+

NO -3

NO assim ilation-3

NH /NH assim ilation3 4 +

Nitrification

DenitrificationNO -2

O 2

Surface

Inner (core region)

Biogeochemicaltransformations

Nitr

oge

n

M icrobialtransformations

Nitrogen

A microbial mat

Sand layer

Cyanobacteria

Oxidized iron

Purple sulfur bacteria

Precipitated iron sulfide

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

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.

3. Mats

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.

Mats form in extreme environments.

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.

4. Biofilms

Organic molecule

M icroorganism

1) the surface is modified by attachment of organic molecules

Biofilm development proceeds in three phases:

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

Freshwater • Lentic (standing) vs. lotic (running)• Springs• Lakes

oligotrophic – deep, low biomasseutrophic – shallow, high biomass

• Groundwater

Marine • Estuaries• Oceans

Aquatic environments

Littoralzone

Limneticzone

Neuston layer

Profundalzone

Benthiczone

Freshwater - A typical lake has several regions of interest.

Neuston layer

Water lipid layer

Air

Protein-polysaccharide layer

Bacterioneuston layer

0

10 nm

0.1 um

1.0 um

Lower neuston

Up to 10 um

The neuston layer occurs at the air-water interface.

Nutrients and microbes aggregate at the neuston.

Littoralzone

Limneticzone

Neuston layer

Profundalzone

Benthiczone

The limnetic zone which is the surface layer of open water where light can penetrate

0 5 10 15 20 25 Temp Co

0 2 4 6 8 10 O mg/l2

Dep

th (

m)

Sediment zone

Water surface

Temperature

Dissolved oxygenThermocline

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.

Epilimnion > 4oC

Hypolimnion < 4oC

Summer

0 2 4 6 8 10 O2 mg/l

Sediment zone

0 5 10 15 20 25 Temp oC

Water surface

Thermocline

Tem

peratu

re

Winter

Epilimnion 0 – 4oC

Hypolimnion > 4oC

Dep

th (

m)

0

-4

-8

-12

-16

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.

Marine water

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.

Microbes in the aquatic environment

Cyanobacteria

Chlorobacteria

Colorless sulfur bacteria andsulfate reducing organism s

Heterotrophic bacteria

Hypolim nion

Epilim nion

Neuston

Benthos

0

4

8R

ela

tiv

e d

ep

th (

m)

3 4 5 6 7 8Log CFU/l

Therm ocline

O 2

H S2

Cyanobacteria

Chlorobacteria

Colorless sulfur bacteria and sulfate reducing organisms

Heterotrophic bacteria

Hypolim nion

Epilim nion

Neuston

Benthos

0

10

20

Re

lati

ve d

ep

th (

m)

1 2 3 4 5 6 7Log CFU/l

Therm ocline

O 2

H S2

Oligotrophic Lake Eutrophic Lake

Heterotrophic counts

Chlorophyll a concentration

400 600 800 1000

Wavelength (nm)

( )Chlorophycophyta

Porphyridium(Rhodophycophyta)

Synechococcus(Cyanobacteria)

Rhodopseudomonas (nonsulfur purple bacteria)

Re

lativ

e ab

sorp

tion

Stratification of primary producers