Week 4 LecturesNovember 2001

Microbial Ecology and Geochemical Cycles

This Week’s Lecture

Microbial Ecology

Importance of Oxic/Anoxic Environment

Geochemical Cycles

Applications

Microbial Ecology

Understand the biodiversity of microorganisms and how different metabolically diverse organisms interact

Monitor the activities of microorganisms and their impact on ecosystems

Important Terms

Environment: everything surrounding microorganism including the physical, biological, and chemical factors that act on the organism

Populations of individual microbial species

Guilds are metabolically related populations

The microbial community is made up of guilds

Guilds and Communities

Sediments

Anoxic

Oxic

Community 1 Photic zone

algae cyanobacter

Community 2: Oxic Zone Chemoorganoheterotrophs Chemolithoautotrophs

Guild 1: nitrifiers Guild 2: sulfur oxidizing

bacteria

Community 3: Anoxic Zone Chemoorganoheterotrophs

Guild 3: denitrifiers Guild 4: sulfate reducers Guild 5: fermenters

Chemolithoautotrophs Guild 6: methanogens Guild 7: sulfate reducers

Microbial Habitats and the Oxic/Anoxic Interface

Oxygen clearly plays an important role in determining the range of microbial mediated reactions that occur in any environment

It is important to understand the relationships between these two environments and the factors that lead to the formation of both

Oxygen Relationships in Lake Ecosystems

Sediments

Anoxic

OxicEpilimnion: oxygen concentration relatively uniform and may be as higher as near saturation

Hypolimnion: zone of unmixed water having low oxygen content

Thermocline: zone of sharp temperature gradient that separates the epilimnion and hypolimnion

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Oxygen Relationships in Surface Waters (Streams and Rivers)

Wastewater Discharge

Distance DownstreamDis

solv

ed O

xyge

n m

g/L

Low Dissolved Oxygen

Oxygen Relationships in Groundwater

Groundwater constituents that consume oxygen include: dissolved organic carbon (plant exudates, etc.

methane

inorganics

reduced nitrogen

reduced iron

Typically oxygen concentrations decrease with travel distance

Terrestrial Ecosystems

O horizon: layer of undecomposed plant material

A horizon: surface soil high in organic matter and high microbial activity

B horizon: subsoil; minerals and humus leached from A horizon accumulate, little organic matter

C horizon: soil base with low microbial activity

Interrelationship Between Moisture Content and Oxygenation in Soils

Soils that retain water tend to be more susceptible to anaerobic conditions

Clays and silts

Microenvironments Using Soil as an Example

Distance, mm

Dis

tanc

e, m

m

Geochemical Cycles

oxidation/reduction reactions that describe the changes in an element as it passes through an ecosystem

geochemical cycles then are of interest for elements that undergo oxidation/reduction reactions (C, S, N, Fe, and others)

as shown before, oxygen plays a key role in metabolic reactions and is a major consideration in the description of geochemical cycles

Carbon Geochemical

Cycle

Nitrogen Geochemical Cycle

Sulfur Geochemical Cycle