Week 4 Lectures November 2001 Microbial Ecology and Geochemical Cycles

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

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

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

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

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

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 { { {

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

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

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 l Soils that retain water tend to be more susceptible to anaerobic conditions l Clays and silts

Microenvironments Using Soil as an Example Distance, mm

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

Carbon Geochemical Cycle

Nitrogen Geochemical Cycle

Sulfur Geochemical Cycle