Ecosystems

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8

Winter

Summer

Slide 46

Acid Precipitation

Combustion of fossil fuels is the main cause of acid precipitation.

North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid.

Acid precipitation changes soil pH and causes leaching of calcium and other nutrients.

Environmental regulations and new technologies have allowed many developed countries to reduce sulfur dioxide emissions.

Slide 47

Changes in the pH of precipitation at Hubbard Brook

Year

2000

1995

1990

1985

1980

1975

1970

1965

1960

4.0

4.1

4.2

4.3

4.4

4.5

pH

Slide 48

Toxins in the Environment

Humans release many toxic chemicals, including synthetics previously unknown to nature. In some cases, harmful substances persist for long periods in an ecosystem.

One reason toxins are harmful is that they become more concentrated in successive trophic levels.

Biological magnification concentrates toxins at higher trophic levels.

PCBs and many pesticides such as DDT are subject to biological magnification in ecosystems.

Slide 49

Biological Magnification of PCBs in a Great Lakes food web

Lake trout

4.83 ppm

Concentration of PCBs

Herring

gull eggs

124 ppm

Smelt

1.04 ppm

Phytoplankton

0.025 ppm

Zooplankton

0.123 ppm

Slide 50

Greenhouse Gases and Global Warming

One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide.

Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing.

Slide 51

The Greenhouse Effect and Climate

CO2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth; this is the greenhouse effect.

This effect is important for keeping Earth’s surface at a habitable temperature.

Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change.

Slide 52

Increasing concentration of atmospheric CO2 is linked to increasing global temperature. Northern coniferous forests and tundra show the strongest effects of global warming.

A warming trend would also affect the geographic distribution of precipitation.