Chapter 2. Science, Matter, Energy and Ecology

Chapter 2. Science, Matter, Energy and Ecosystems: Connections in Nature
[Revised 5/31]

2-1. Science and Environmental Science

What role does science play in understanding environmental issues?
Scientific method: the role of experiments, data, hypotheses, laws and theories. See Figure 2-1.
Science cannot establish absolute truth but this doesn't mean it cannot guide decisions.

Frontier vs. consensus science: who to believe?
Some problems with environmental science:

The issues are very complex and inevitably involve value conflicts, ethics and other social issues.
Often the data we have is inadequate for the decisions that must be made.
For very complex environmental problems (e.g. global warming), it is difficult to apply experimental techniques.

2-2. Matter and Energy

Matter = anything that has mass ("weight") and takes up space. People, atoms, cars, water molecules, cells, calcium atoms, etc. are all example of matter
Matter can change forms in two ways:

Physical change - a change from one physical state to another (e.g. evaporation of water to create water vapor). There is no change in chemical composition.
Chemical change - involves rearrangements of atoms in the molecules during a chemical reaction.
For example, the burning of coal involves chemical and physical change. The solid carbon of the coal combines with gaseous oxygen to produce gaseous carbon dioxide and water vapor. The energy locked up in the coal is released as heat.

Energy = the capacity to do work and transfer heat. Heat, sunlight, electricity, X-rays, etc. are all examples of energy.

Kinetic energy = the energy that matter has because of its mass and velocity (or the velocity of its constituents)
Potential energy = the energy that matter has due to its position or the position/arrangement of its constituents. Chemical bond energy is an important example of potential energy.
Kinetic and potential energy can be interconverted.
Measuring energy: the calorie and kilocalorie (kcal).

Three laws of matter and energy

Conservation of matter: the total amount of matter on earth is constant. The chemical and physical nature of matter changes, but the atoms that make up the matter are neither destroyed nor created. In other words, nothing ever goes away.
Conservation of energy: as matter changes its physical/chemical nature, energy will be converted from one form to another, but the total amount of energy remains the same ("is conserved"). This is the First Law of Thermodynamics.
Second Law of Thermodynamics: when energy is changed from one form to another, some of the useful energy is always degraded to lower-quality, less useful energy. Figure 2.8 illustrates this very clearly. A consequence of the Second Law is that no physical/chemical process can be 100% efficient.

2-3. Introduction to Ecology

Ecology (not the same as environmental science or environmentalism): the science of how organisms interact with each other and with their environment. These interactions are studied at different levels of organization:

Organisms
Populations
Communities and Ecosystems

Earth's life support systems (this is the "spaceship earth" metaphor)

The one way flow of energy through ecosystems: sunlight --> chemical bonds in organisms --> waste heat.
The cycling of nutrients in ecosystems
Earth as the "just right planet": distance from the sun, gravitational field. Also, life on earth has made the earth yet more hospitable for life. (Example - the creation of the protective ozone layer in the upper atmosphere.)
Biodiversity as an ecosystem service.

Ecosystems: abiotic (non-living) components

These are the physical and chemical factors that influence organisms: climate, altitude, soil fertility, precipitation, dissolved oxygen (in water), salinity (e.g. in coastal and marine ecosystems).
Species distributions are limited by these physical factors (the range of tolerance, Fig. 2-16).
Acclimation can help organisms adjust to gradual environmental changes, but threshold effects will occur when limits to acclimation are met.
Limiting factors: often one abiotic factor is of overriding importance in an ecosystem. Examples - soil moisture in deserts, dissolved oxygen in lakes, salinity in estuaries.

Ecosystems: biotic (living) components. Despite the tremendous number of species in most ecosystems, all organisms in an ecosystem can be classified into a small number of categories:

Producers: "make their own food [energy and nutrients] from chemical compounds obtained from their [abiotic] environment" (p. 29). Nearly all are photosynthesizers (plants and some bacteria) which make sugar from carbon dioxide and water, using the energy of sunlight. This includes green plants on land and microscopic algae (phytoplankton) in freshwater and marine ecosystem.
Consumers get their energy and nutrients by feeding on other organisms or their remains.

Herbivores eat plants
Carnivores (primary, secondary, tertiary) eat other animals
Scavengers eat dead organisms
Detritivores eat fragments and wastes of other organisms
Decomposers (mostly some bacteria and fungi) eat dead organic matter, releasing nutrients into soil or sediments.

Respiration (i.e., cellular respiration) is the chemical reaction by which all organisms release the energy contained in food. The reaction combines oxygen with sugar to produce carbon dioxide and water. As this happens some of the energy locked up in the sugar is made available to the organism. The rest is released to the environment as heat.
Biodiversity: "nature's insurance policy against disasters."

Genetic diversity
Species diversity
Ecological (landscape diversity)
Functional diversity

2-4 Connections: Energy Flow in Ecosystems

Some necessary concepts:

Food chain = sequence of organisms, each of which is a source of food for the next. See Figure 2-19
Food web = network of food chains. See Figure 2-20
Trophic levels = producers occupy the first trophic level, herbivores the next, and so on.
Biomass = the mass (usually dry weight) of organic matter in an ecosystem or at a specific trophic level.
Ecological efficiency = the percentage of energy transferred from one trophic level to the next.

The basic ideas of energy flow in ecosystems:

Energy enters ecosystems when sunlight is captured by producers to form chemical bonds in sugar molecules.
The chemical bond energy is transferred from link to link in a food chain/web as consumers consume.
As organisms respire, energy is released to the environment as heat.
In a stable ecosystem, all of the energy captured by photosynthesis is dissipated by respiration.

The "pyramid of energy flow" (Figure 2-21) is triangular rather than rectangular because of respiration within each trophic level. Ecological efficiency is on the order of 10% which means that about 90% is lost between trophic levels. This is a good argument for a vegetarian diet.
Energy flow is ultimately limited by rate of primary production:

Gross primary production (GPP) = rate at which primary producers convert solar energy into chemical bond energy during photosynthesis.
Net primary production (NPP) = what's left after producer respiration (R) is taken into account, so ...
NPP = GPP - R. From the point of view of herbivores and consumers of plant detritus, NPP is the rate (kcal/m2/yr) at which energy being made available.
Primary production on land is limited mostly by climate, in the oceans it is limited mostly by nutrient availability. See Fig. 2-23.
Humans are major consumers of the earth's primary production: we "use, waste or destroy about 40% of the planet's terrestrial primary productivity" (paraphrased quotation from p. 34).

2-5. Connections: Matter Cycling in Ecosystems

Nutrient = any chemical substance needed for life (e.g. carbon, oxygen, calcium, iron, magnesium, ... a list of about two dozen elements). Unlike energy, these substances can be used again and again (i.e. cycled or recycled).
The Carbon cycle (Figure 2-25) includes these pathways and processes:

Terrestrial and aquatic producers remove CO2 from the atmosphere during photosynthesis.
All organisms return CO2 to the atmosphere during respiration.
CO2 can diffuse from the oceans to the atmosphere and from the atmosphere to the oceans.
Burning of wood, fossil fuels and volcanic action add CO2 to the atmosphere.
Carbon can become trapped in organic sediments on land and in the oceans.
Over geological time, uplift can bring carbon-rich sediments to the surface, where weathering returns carbon to the atmosphere as CO2.
For most of Earth's geolgical history, carbon cycle is in balance and CO2 content of atmosphere is constant. Exceptions include period of formation of fossil fuels and the present.
Global warming is resulting from human alteration of the carbon cycle (putting more CO2 in the atmosphere then can be removed by natural processes of photosynthesis and diffusion).

The Phosphorous cycle includes these pathways and processes:

Plants take up Phosphorus from the soil, incorporate it into their biomass.
Phosphorus in plant material passes through food webs, is returned to the soil.
Weathering (breakdown) of rocks with Phosphorus adds Phosphorus to soils.
Erosion and runoff adds Phosphorus to rivers and streams, this ultimately ends up in the oceans.
Over geological time, uplift brings Phosphorus-rich rocks to the surface, where weathering adds it to the soil.

Carbon cycle versus the Phosphorous cycle: the atmosphere is the principal source of carbon, rocks are the principal source of phosphorus.
The water (hydrologic cycle) includes these pathways and processes:

Evaporation and transpiration of water adds water vapor to the atmosphere. (Transpiration = evaporation of water from the pores of leaves).
Condensation of water vapor in the atmosphere produces clouds and fog.
Precipitation of water vapor in the atmosphere returns liquid or solid water to the surface of the earth.
Liquid water infiltrates and percolates through soil to form groundwater.
Runoff (stream and river flow) returns water to the oceans.
Humans can affect this cycle by pumping groundwater, clearing vegetation (reduces transpiration, increases runoff), reducing water quality by adding numerous pollutants.

2-8. Population Dynamics, Evolution and Biodiversity
[Moved to Chapter 3 Outline]