1. Environmental Systems: Matter, Energy, and Ecosystems
Chapter 2
College Environmental Science

2. Central Case Study: Vanishing Oysters of the Chesapeake Bay
Chesapeake Bay was the world’s largest oyster fishery
Overharvesting, pollution, and habitat destruction ruined it
The economy lost $4 billion from to 2010
Strict pollution standards and oyster restoration efforts give reason for hope

3. The Earth’s systems
Understanding human impacts on the environment requires understanding complex environmental systems
Many issues are multifaceted and interconnected
System: a network of relationships among components that interact with and influence one another
Exchange of energy, matter, or information
Receives inputs of energy, matter, or information; processes these inputs; and produces outputs
Feedback loop: a circular process in which a system’s output serves as input to that same system

4. Negative feedback loop
Negative feedback loop: output resulting from a system moving in one direction acts as an input that moves the system in the other direction
Input and output neutralize one another
Stabilizes the system
Example: if we get hot, we sweat and cool down
Most systems in nature involve negative feedback loops

5. Positive feedback loop
Positive feedback loop: instead of stabilizing a system, it drives it further toward an extreme
Example: white glaciers reflect sunlight and keep surfaces cool
Melting ice exposes dark soil, which absorbs sunlight
Causes further warming and melting of more ice
Runaway cycles of positive feedback are rare in nature
But are common in natural systems altered by humans

6. Environmental systems interact
Natural systems are divided into structural spheres
Lithosphere: rock and sediment
Atmosphere: the air surrounding the planet
Hydrosphere: all water on Earth
Biosphere: the planet’s living organisms
Plus the abiotic (nonliving) parts they interact with
Categorizing systems allows humans to understand Earth’s complexity
Most systems overlap

7. The Chesapeake Bay: a systems perspective
The Chesapeake Bay and rivers that empty into it are an interacting system:
It receives very high levels of nitrogen and phosphorus from agriculture from 6 states, and air pollution from 15 states

8. Sources of nitrogen and phosphorus entering the Chesapeake Bay

9. Eutrophication in the Chesapeake Bay
Nitrogen and phosphorus enter the Chesapeake watershed (the land area that drains water into a river), causing….
Phytoplankton (microscopic algae and bacteria) to grow, then…
Bacteria eat dead phytoplankton and wastes and deplete oxygen, causing…
Fish and other aquatic organisms to flee or suffocate
Eutrophication: the process of
Nutrient overenrichment, blooms of algae, increased production of organic matter, and ecosystem degradation

10. Eutrophication in aquatic systems

11. Global hypoxic dead zones
Nutrient pollution from farms, cities, and industries has led to more than 400 hypoxic (oxygen-depleted) dead zones

12. People are changing the chemistry of Earth’s systems
Chemistry is crucial for understanding how:
Chemicals affect the health of wildlife and people
Pollutants cause acid precipitation
Synthetic chemicals thin the ozone layer
How gases contribute to global climate change

13. Ecosystems
Ecosystem: all organisms and nonliving entities occurring and interacting in a particular area
Animals, plants, water, soil, nutrients, etc.
Biological entities are tightly intertwined with the chemical and physical aspects of their environment
For example, in the Chesapeake Bay estuary (a water body where fresh river water flows into salt ocean water):
Organisms are affected by water, sediment, and nutrients from the water and land
The chemical composition of the water is affected by organism photosynthesis, respiration, and decomposition
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14. Energy and matter flow through ecosystems
Sun energy flows in one direction through ecosystems
Energy is processed and transformed
Matter is recycled within ecosystems
Outputs: heat, water flow, and waste

15. Energy is converted to biomass
Primary production: conversion of solar energy to chemical energy in sugars by autotrophs during photosynthesis
Gross primary production: total amount of chemical energy produced by autotrophs
Most energy is used to power their own metabolism
Net primary production: energy remaining after respiration
Equals gross primary production – cellular respiration
It is used to generate biomass (leaves, stems, roots)
Available for heterotrophs
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16. Primary productivity of ecosystems
Productivity: rate at which autotrophs convert energy to biomass
High net primary productivity: ecosystems whose plants rapidly convert solar energy to biomass

17. A global map of net primary productivity
NPP increases with temperature and precipitation on land, and with light and nutrients in aquatic ecosystems

18. Ecosystems interact across landscapes
Ecosystems vary greatly in size (puddle, forest, bay, etc.)
The term ecosystem is most often applied to self-contained systems of moderate geographic extent
Adjacent ecosystems may interact extensively
Ecotones: transitional zones between two ecosystems in which elements of each ecosystem mix
It may help to view ecosystems on a larger geographic scale
Encompassing multiple ecosystems
Geographic information systems (GIS) use computer software to layer multiple types of data together
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19. Landscape ecology
Landscape ecology: the study of how landscape structure affects the abundance, distribution, and interaction of organisms
Useful for studying migrating birds, fish, mammals
Helpful for planning sustainable regional development
Patches: ecosystems, communities or habitat form the landscape and are distributed in complex patterns (a mosaic)
This landscape consists of a mosaic of patches of 5 ecosystems
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20. Conservation biology
Conservation biologists: study the loss, protection, and restoration of biodiversity
Humans are dividing habitat into small, isolated patches
Corridors of habitat can link patches
Populations of organisms have specific habitat requirements
They occupy suitable patches of habitat in the landscape
If a habitat is highly fragmented and isolated
Organisms in patches may perish
Conservation biologists may use corridors of habitat to link patches to preserve biodiversity

21. Modeling helps us understand ecosystems
Model: a simplified representation of a complicated natural process
Helps us understand processes and make predictions
Ecological modeling: constructs and tests models to explain and predict how ecological systems work
Grounded in actual data and based on hypotheses
Extremely useful in large, intricate systems that are hard to isolate and study
Example: studying the flow of nutrients into the Chesapeake Bay and oyster responses to changing water conditions

22. Ecosystems provide vital services
All life on Earth (including humans) depends on healthy, functioning ecosystems
Ecosystem services: essential services provided by healthy, normally functioning ecosystems
When human activities damage ecosystems, we must devote resources to supply these services ourselves
Example: if we kill off insect predators, farmers must use synthetic pesticides that harm people and wildlife
One of the most important ecosystem services:
Nutrients cycle through the environment in intricate ways