Chapter 57: The Biosphere and Human Impacts

CHAPTER 57: The Biosphere and Human Impacts

Chapter Contents

  • LO 57.1 Ecosystem Effects of Sun, Wind, and Water

  • LO 57.2 Earth's Biomes

  • LO 57.3 Freshwater Habitats

  • LO 57.4 Marine Habitats

  • LO 57.5 Human Impacts on the Biosphere: Pollution and Resource Depletion

  • LO 57.6 Human Impacts on the Biosphere: Climate Change

Introduction

  • Definition of the Biosphere: The biosphere encompasses all living communities on Earth, including diverse ecosystems ranging from tropical rainforests to marine environments.

  • Distribution of Life: The distribution of life on Earth is influenced by abiotic factors such as temperature and available water, which vary across terrestrial environments.

  • Satellite Imagery: A satellite image of the Americas illustrates chlorophyll abundance, indicating areas of high primary productivity (green areas) versus low productivity (yellow/brown areas like deserts). Coastal areas often possess high productivity due to nutrient-rich upwelling currents.

57.1 Ecosystem Effects of Sun, Wind, and Water

Learning Outcomes

  1. Describe changes in wind and current direction with latitude.

  2. Explain the Coriolis effect.

  3. Describe how temperature changes with altitude and latitude.

Key Concepts

  • Influence of Solar Radiation: The amount of solar radiation received at different Earth locations significantly affects climate patterns. Regions near the equator receive direct solar energy, leading to warmer temperatures, while polar regions receive less concentrated energy, resulting in cooler temperatures.

  • Atmospheric Circulation: The Earth’s rotation and its axial tilt cause seasonal variations affecting global atmospheric and oceanic circulation. This includes:
      - Coriolis Effect: Air currents move in curved paths due to the Earth's rotation. In the Northern Hemisphere, winds deflect to the right, and in the Southern Hemisphere, they deflect to the left.

  • Temperature Dynamics: Temperature varies with latitude (lower near poles) and altitude (decreases by approximately 6°C per 1000 m elevation gain).

Climate Patterns

  • Hot air near the equator rises due to its lower density, cooling down as it ascends, creating precipitation patterns typical in equatorial rainforests. Cooler, descending air patterns contribute to dryer conditions, forming deserts near 30° latitude.

Wind and Ocean Currents

  • Primary Features of Atmospheric Circulation:
      - Air ascends at the equator, condenses to rain, and descends in the subtropics creating damp and dry regions respectively.
      - Ocean currents, influenced by prevailing winds, help in distributing nutrients and affecting climate. For instance, surface winds that blow westward near the equator create gyres in ocean currents, which are circular oceanic currents driven by wind.

  • Gyre Example: North Atlantic Ocean’s gyre flows from North America to Europe, then back.

Impacts of Elevation on Ecosystems

  • The ecological conditions vary drastically between windward and leeward sides of mountains due to rainfall distribution - the rain shadow effect.

57.2 Earth's Biomes

Learning Outcomes

  1. Define biome.

  2. Explain primary factors determining biome locations.

Definition and Classification

  • Biome Definition: Major types of ecosystems characterized by their vegetational structure and distributed over broad areas according to local climatic conditions.

  • Primary Biomes Identified: 8 principal biomes:
      1. Tropical Rainforest
      2. Savanna
      3. Desert
      4. Temperate Grassland
      5. Temperate Deciduous Forest
      6. Temperate Evergreen Forest
      7. Taiga
      8. Tundra

Climatic Influences

  • Temperature & Precipitation: Organisms within these biomes are strongly influenced by average annual temperature and precipitation. Species composition within biomes can vary significantly across regions even if temperature and moisture conditions are similar.

57.3 Freshwater Habitats

Learning Outcomes

  1. Define photic zone.

  2. Explain causes of seasonal turnovers in lakes.

  3. Distinguish between eutrophic and oligotrophic lakes.

Freshwater Ecosystem Characteristics

  • Freshwater habitats cover only 2% of the Earth's surface but are significant for biodiversity and ecological functioning. They include lakes, rivers, and wetlands.

  • Oxygen Dynamics: Oxygen levels vary significantly in freshwater habitats, based on photosynthesis and the decay of organic materials.

Lake Dynamics

  • Photic Zone: The upper layer in lakes where sunlight penetrates for photosynthesis. Below this layer is the aphotic zone where light does not penetrate.

  • Thermal Stratification: In summer, lakes exhibit layers due to temperature differences: epilimnion (top warmer layer), hypolimnion (cold dense bottom layer), and thermocline (transition layer). Seasonal mixing occurs during spring and fall turnovers, cycling nutrients and oxygen.

Lake Types

  • Oligotrophic Lakes: Characterized by clear waters, low nutrients, and high oxygen levels throughout the year.

  • Eutrophic Lakes: High in nutrients leading to algal blooms, often low in oxygen due to decomposition and decay.

57.4 Marine Habitats

Learning Outcomes

  1. Know the different marine habitats.

  2. Explain why El Niño events occur.

Marine Habitat Overview

  • Oceans account for 71% of the Earth’s surface, with diverse habitats including:
      - Intertidal Zones: Areas between high and low tide.
      - Neritic Zones: Well-illuminated waters above the continental shelf.
      - Photic Zones: Regions receiving enough light for phytoplankton productivity.
      - Benthic Zones: Bottom areas of oceans and lakes.
      - Pelagic Zones: Open water areas not associated with the bottom.

Productivity in Marine Systems

  • Primary Producers: Phytoplankton dominate primary production in marine habitats, but nutrient levels in open oceans often limit productivity.

  • Upwelling Areas: Where nutrient-rich deep water rises to the surface, resulting in high productivity.

El Niño Phenomenon

  • El Niño: An abnormal warming of ocean waters near South America, disrupting normal upwelling and reducing marine productivity, affecting global weather patterns.

57.5 Human Impacts on the Biosphere: Pollution and Resource Depletion

Learning Outcomes

  1. Identify major human threats to ecosystems.

  2. Differentiate point-source from diffuse pollution.

Pollution Types

  • Point-Source Pollution: From identifiable locations, such as factories or sewage treatment plants. Example: DDT in freshwater habitats, leading to biomagnification in food webs affecting birds of prey.

  • Diffuse Pollution: Non-point sources contributing excess nutrients (e.g., nitrates and phosphates) into waterways, leading to problems like eutrophication.

Population and Resource Pressure

  • Excessive Water Extraction: High demands on freshwater resources, such as the Colorado River, leading to severe ecological consequences.

  • Deforestation Trends: Significant effects on global carbon cycles and local ecosystems, with widespread biodiversity loss and habitat degradation documented.

Human-Induced Health Issues

  • Increased interactions between humans and wildlife can lead to new zoonotic diseases emerging.

57.6 Human Impacts on the Biosphere: Climate Change

Learning Outcomes

  1. Explain the link between atmospheric carbon dioxide and global warming.

  2. Describe impacts of climate change on ecosystems and human health.

Global Climate Dynamics

  • Carbon Dioxide: An increasing greenhouse gas, primarily due to fossil fuel consumption, significantly alters Earth's temperature balance.

  • Projected Changes: Expected rise in average temperatures and varying global climatic patterns impacting water availability, agriculture, and biodiversity.

Ecosystem and Human Health Effects

  • Impacts on Biodiversity: Species may struggle to adapt fast enough to current rates of warming, putting many at risk of extinction.

  • Rising Sea Levels: Threatening coastal populations and ecosystems due to glacial melting and thermal expansion of seawater.

Implications for Agriculture

  • Varied Agricultural Outcomes: Factors affecting crop yields include changes in temperature and precipitation, with tropical agriculture facing more stress due to its already high temperature limits.

Conclusion

  • Understanding the interconnectivity of these systems is critical for addressing human impacts on the biosphere.

  • Sustainable solutions and awareness of ecological thresholds are necessary to mitigate current and future challenges in biodiversity conservation and climate stability.