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