1. Lecture 11 Introduction to Environmental Engineering Ecosystems

2. Energy and Materials Flow in Ecosystems Energy and Materials both flow in Ecosystems – Energy only up the trophic levels – Materials flow is cyclical Energy – Photosynthesis  Producers (plants) – Respiration  Consumers (animals) – Decomposers – Energy conversion is highly inefficient

3. Energy and Materials Flow in Ecosystems Producers take energy from the sun [nutrients] +CO 2 + sunlight  O 2 + [high energy molecules] Consumers respire [high-energy molecules] + O 2  CO 2 + [nutrients] Waste formed known as detritus Decomposers break-down detritus from plants and animals

4. Energy and Materials Flow in Ecosystems Energy flow is one way Sun  plants  animals  decomposers

5. Energy and Materials Flow in Ecosystems Materials Flow is cyclical – After all, mass can neither be created or destroyed

6. Energy and Materials Flow in Ecosystems

7. Microbial Decomposers – Aerobic degradation [detritus] + O 2  CO 2 + H 2 O +[nutrients] – Anaerobic degradation [detritus]  CO 2 + CH 4 +H 2 S +NH 3 + … + [nutrients] Both anaerobic and aerobic bacteria are used in wastewater Microbes are obigate aerobes, facultative, or obligate anaerobes.

8. Energy and Materials Flow in Ecosystems Mass Balances can be performed on ecosystems When at steady-state an ecosystem is said to be in homeostasis The food web/food chain is in balance Organisms at various trophic levels are in balance

9. Energy and Materials Flow in Ecosystems If a species can grow with no constraints – No predators, lack of food, lack of space (humans) – Growth is: Where N = # of organisms k = constant t = time

10. Energy and Materials Flow in Ecosystems However growth inhibitors do exist

11. Human Influence on Ecosystems Effect of Pesticides Effect of Nutrients on Lakes Effect of Organic Wastes on Streams