Environmental Systems: Matter, Energy, and
EcosystemsChapter 2
College Environmental Science
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 1980 to 2010
Strict pollution standards and oyster restoration efforts give reason for hope
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
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
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
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
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
Sources of nitrogen and phosphorus entering the Chesapeake Bay
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
Eutrophication in aquatic systems
Global hypoxic dead zones
Nutrient pollution from farms, cities, and industries has led to more than 400 hypoxic (oxygen-depleted) dead zones
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
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
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
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
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
A global map of net primary productivity
NPP increases with temperature and precipitation on land, and with light and nutrients in aquatic ecosystems
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
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)
Landscape ecology
This landscape consists of a mosaic of patches of 5 ecosystems
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
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
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
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