Renewable Energy, Carbon Cycle, and Environmental Impacts
Renewable Energy and Electricity Production
Geothermal vs. Tidal Power: Pros and Cons
Geothermal Energy: A renewable resource from Earth’s interior, used for space heating or electricity generation. It is inexpensive and reliable. Geothermal energy is environmentally benign, emitting fewer air pollutants than fossil fuels. However, it can release hydrogen sulfide gas and cause land sinking. It can also be expensive for heating buildings.
Tidal Power: A clean, renewable resource for electricity generation. However, only a few locations worldwide have substantial tidal energy. Building tidal power stations is costly, and harnessing tidal energy from estuaries can harm fish and invertebrate species.
Energy Conservation vs. Energy Efficiency
Energy Conservation: Using less energy by reducing energy use and waste.
Energy Efficiency: Using less energy to accomplish a given task.
Thermodynamics and Productivity
Thermodynamics: The study of energy and its transformations.
Gross Primary Productivity (GPP): The rate at which energy is captured during photosynthesis.
Net Primary Productivity (NPP): The amount of biomass exceeding that broken down by a plant during cellular respiration.
The Carbon Cycle
The global movement of carbon between the abiotic environment (atmosphere, ocean) and organisms:
- Atmosphere/ocean → photosynthesis → cellular respiration/combustion/decomposition → atmosphere/ocean
Carbon is essential for organisms’ molecules and the abiotic environment.
The Nitrogen Cycle
Nitrogen is essential for proteins and nucleic acids.
The atmosphere is 78% nitrogen gas.
Five steps in the nitrogen cycle:
- Nitrogen fixation
- Nitrification
- Assimilation
- Ammonification
- Denitrification
Nostoc, a nitrogen-fixing cyanobacterium, grows on a mossy bank.
Ecological Concepts
Niche
The totality of an organism’s adaptations, its use of resources, and its lifestyle. It describes the organism’s place and function within the ecosystem, considering all aspects of its existence—the “way of life of an organism.”
Habitat: Part of an organism’s niche, the place where the organism lives.
Symbiosis
Two species living in close association. Symbiosis is the result of coevolution.
Ecosystems
Freshwater Ecosystems
Include standing-water (lakes and ponds), flowing-water (rivers and streams), and wetlands (marshes and swamps).
Categories of organisms:
- Plankton—phytoplankton and zooplankton
- Nekton—fish and turtles
- Benthos—bottom-dwellers
Estuaries
Coastal bodies of water, partly surrounded by land, with access to the ocean and fresh water from a river.
Salt Marshes and Mangrove Forests
Salt marshes: Shallow wetlands with salt-tolerant grasses.
Mangrove forests: Tropical equivalent of salt marshes.
Environmental Impacts of Resource Extraction
Coal Mining
Surface mining: Within 30 m of the surface. It removes soil, subsoil, and overlying rock strata. 60% of U.S. coal is obtained this way. It is usually safer for miners and less expensive but disrupts the land extensively.
Strip mining: Vegetation, soil, and rock are ‘stripped away.’ A trench is dug to extract coal, and rubble is dumped into nearby valleys.
Subsurface mining: Approximately 40% of coal mined in the U.S.
Surface Mining Control and Reclamation Act
1977—controlled abandoned surface mines and set standards for mines to follow during operation and reclamation.
Clean Air Act Amendments—1990
Provides incentives for utility companies to convert to clean coal technologies.
Petroleum (Crude Oil)
Liquid composed of hundreds of hydrocarbon compounds. Refining separates crude oil into different products based on boiling points (gases, jet fuel, heating oil, diesel, asphalt).
Petrochemicals: Oil is used to produce fertilizers, plastics, paints, pesticides, medicines, and synthetic fibers.
Deepwater Horizon Drilling Platform Explosion—2010
Persian Gulf War—1991
6 million barrels deliberately dumped into the Persian Gulf. Oil wells were set on fire, and lakes of oil spilled into the desert around wells. It may take a century or more for the area to recover.
Nuclear Energy
Nuclear Reactions
Two different types of nuclear reactions:
- Fission: Splitting of a nucleus into two smaller fragments, releasing large amounts of energy (e.g., a neutron crashes into a nucleus of uranium). Used in nuclear power plants.
- Fusion: Two small atoms are combined to form a large atom of a different element (e.g., the process that powers the sun and other stars).
Nuclear Waste Policy Act—1982
The federal government has the burden of developing permanent sites for storage of radioactive waste. Congress identified Yucca Mountain, NV, as the only candidate for a storage facility. In 2009, the Obama administration withdrew support for this site—no new site has been identified. Billions of dollars were spent on feasibility studies. Transportation concerns were a major factor in canceling the project.
Direct Solar Energy
A small portion of the sun’s energy reaches Earth’s surface. It is always available, unlike fossil and nuclear fuels. Solar energy must be collected and transformed into other forms to be useful as an energy source for human use.
Biogas
Biomass can be converted into a mixture of gases, mostly methane. Biogas digesters produce gas for cooking and lighting by microbial decomposition of wastes. Several million are used in China and India. Solid remains can be used as fertilizer. Biogas has the potential to power fuel cells to generate electricity. A Boston pilot project in 1997 provided electricity for 150 homes from sewage sludge.