ENVS200-wk5.1-biogeochem

Cycles in ENVS 200

Student Learning Objectives

  • By the end of this class, students will be able to:

    • Explain the main biogeochemical cycles and how materials cycle through Earth’s spheres (Water, Carbon, Nitrogen, Phosphorus).

    • Describe how humans impact each of these cycles.

    • Explain the importance of biodiversity and the different types of diversity.

    • Differentiate between the major biomes on Earth.

Human Population Dynamics

Distribution and Growth

  • Since 1960, the human population growth rate has slowed, but overall population continues to grow.

  • Population is unevenly distributed globally, with developing countries growing 14 times faster than developed countries.

  • Urbanization is increasing; by 2050, two-thirds of the human population will live in cities.

Population Growth Dynamics

  • The global population size continues to increase even with a dropping growth rate due to several factors:

    • Births and immigration increase population size.

    • Deaths and emigration decrease population size.

    • Total fertility rate (TFR) indicates the average number of children born to women in a population:

      • Global TFR decreased from 5 in 1955 to 2.5 in 2013.

      • A TFR of 2.1 indicates stable replacement of parents.

Impact of Life Expectancy

  • Over the past century, population growth has been influenced by reduced death rates and increased life expectancy:

    • Global life expectancy rose from 48 years (1955) to 70 years (2013).

    • Life expectancy in poorer countries was only 55 years in 2013; poverty significantly affects life expectancy.

Age Structure Analysis

  • Population dynamics are also determined by age structure:

    • Age distribution is classified into youth, middle-aged, and older age categories.

    • Age-structure diagrams are utilized to assess whether a population is increasing or decreasing.

Cycling of Matter and Energy

  • Nutrients and energy cycle through ecosystems, but human activities are altering these natural cycles.

Biogeochemical Cycles Overview

  • Biogeochemical cycling integrates biological, geological, and chemical processes and is driven by solar energy and Earth's gravity.

  • It facilitates movement of nutrients and energy through air, water, soils, rocks, and living organisms, supporting sustainability principles.

Main Biogeochemical Cycles

  • The primary biogeochemical cycles include:

    • Hydrologic cycle

    • Carbon cycle

    • Nitrogen cycle

    • Phosphorus cycle

The Water Cycle

Summary of the Hydrologic Cycle

  • The hydrologic cycle is essential for collecting, purifying, and distributing Earth's water; the total amount remains constant.

  • Freshwater constitutes only 3% of Earth's water, with the rest in oceans or as inaccessible ice.

Key Processes

  • Evaporation: Liquid water converts into vapor, primarily through transpiration from plants.

  • Condensation: Water vapor transforms into liquid water, returning to Earth as precipitation.

  • Runoff and Infiltration: Water falls as precipitation and either runs into bodies of water or infiltrates into the ground, replenishing aquifers.

Human Impact on the Water Cycle

  • Major negative impacts of human activities:

    • Over-extraction of freshwater resources.

    • Urbanization leading to increased runoff and reduced transpiration.

    • Draining wetlands, disturbing natural renewal processes, contributing to climate change.

The Carbon Cycle

Overview of the Carbon Cycle

  • The carbon cycle describes the natural cycling of carbon atoms; total carbon amount is balanced in Earth systems.

Key Processes

  • Photosynthesis: Carbon dioxide (CO2) is absorbed by plants and converted into organic carbon.

  • Respiration: Producers, consumers, and decomposers convert organic carbon back into CO2.

Long-term Carbon Storage

  • Some carbon is buried and not decomposed, potentially forming fossil fuels over geological time due to heat and pressure (coal, oil, natural gas).

  • Burning fossil fuels releases CO2, contributing to climate change.

Human Impact on the Carbon Cycle

  • Main negative impacts include:

    • Extracting and burning fossil fuels at rates exceeding natural formation.

    • Deforestation faster than regrowth, reducing carbon absorption.

    • Increased atmospheric CO2 enhances the greenhouse effect, raising temperatures.