1. Week 4 Lectures November 2001 Microbial Ecology and Geochemical Cycles

2. This Week’s Lecture l Microbial Ecology l Importance of Oxic/Anoxic Environment l Geochemical Cycles l Applications

3. Microbial Ecology l Understand the biodiversity of microorganisms and how different metabolically diverse organisms interact l Monitor the activities of microorganisms and their impact on ecosystems

4. Important Terms l Environment: everything surrounding microorganism including the physical, biological, and chemical factors that act on the organism l Populations of individual microbial species l Guilds are metabolically related populations l The microbial community is made up of guilds

5. Guilds and Communities Sediments Anoxic Oxic Community 1 l Photic zone l algae l cyanobacter Community 2: Oxic Zone l Chemoorganoheterotrophs l Chemolithoautotrophs l Guild 1: nitrifiers l Guild 2: sulfur oxidizing bacteria Community 3: Anoxic Zone l Chemoorganoheterotrophs l Guild 3: denitrifiers l Guild 4: sulfate reducers l Guild 5: fermenters l Chemolithoautotrophs l Guild 6: methanogens l Guild 7: sulfate reducers

6. Microbial Habitats and the Oxic/Anoxic Interface l Oxygen clearly plays an important role in determining the range of microbial mediated reactions that occur in any environment l It is important to understand the relationships between these two environments and the factors that lead to the formation of both

7. Oxygen Relationships in Lake Ecosystems Sediments Anoxic Oxic Epilimnion: 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 { { {

8. Oxygen Relationships in Surface Waters (Streams and Rivers) Wastewater Discharge Distance Downstream Dissolved Oxygen mg/L Low Dissolved Oxygen

9. Oxygen Relationships in Groundwater l Groundwater constituents that consume oxygen include: l dissolved organic carbon (plant exudates, etc. l methane l inorganics l reduced nitrogen l reduced iron l Typically oxygen concentrations decrease with travel distance

10. 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

11. Interrelationship Between Moisture Content and Oxygenation in Soils l Soils that retain water tend to be more susceptible to anaerobic conditions l Clays and silts

12. Microenvironments Using Soil as an Example Distance, mm

13. Geochemical Cycles l oxidation/reduction reactions that describe the changes in an element as it passes through an ecosystem l geochemical cycles then are of interest for elements that undergo oxidation/reduction reactions (C, S, N, Fe, and others) l as shown before, oxygen plays a key role in metabolic reactions and is a major consideration in the description of geochemical cycles

14. Carbon Geochemical Cycle

15. Nitrogen Geochemical Cycle

16. Sulfur Geochemical Cycle