Environmental Science Study Guide

Unit 1: Ecosystems & Energy Flow

Trophic Level

A feeding position in a food chain (producer, primary consumer, secondary consumer, etc.) defined by the number of energy transfers from the original solar source.

Net Primary Productivity (NPP)

The rate at which producers store chemical energy as biomass, equal to gross primary productivity minus the energy producers use for their own respiration.

10% Rule

The generalization that only about 10% of energy at one trophic level is transferred to the next, with the rest lost mostly as metabolic heat.

Nitrogen Fixation

The conversion of atmospheric nitrogen gas (N2) into ammonia (NH3), performed by bacteria (often symbiotic with legumes) or lightning, making nitrogen usable by plants.

Biogeochemical Cycle

The movement of a chemical element or compound (e.g., carbon, nitrogen, phosphorus, water) through the living and nonliving parts of an ecosystem.

Primary Succession

Ecological succession that begins on bare rock or lifeless substrate with no existing soil, starting with pioneer species like lichens.

Secondary Succession

Ecological succession that begins in a disturbed area where soil already exists, such as after a fire or on abandoned farmland.

Carrying Capacity (K)

The maximum population size of a species that a given environment can sustain indefinitely given available resources.

Keystone Species

A species whose impact on its ecosystem is disproportionately large relative to its abundance.

Eutrophication

The nutrient enrichment of a water body (often from nitrogen/phosphorus runoff) leading to excessive algal growth and subsequent oxygen depletion.

Unit 2: Biodiversity & Populations

Species Richness

The number of different species present in a given community or area.

Biodiversity Hotspot

A region with exceptionally high species endemism that has also experienced significant habitat loss, prioritized for conservation.

r-selected Species

A species that produces many offspring with little parental care, matures quickly, and thrives in unstable or unpredictable environments.

K-selected Species

A species that produces few offspring with high parental investment, matures slowly, and thrives near carrying capacity in stable environments.

Endemic Species

A species found naturally in only one specific geographic location and nowhere else on Earth.

Competitive Exclusion Principle

The ecological principle that two species competing for the exact same limited resource (niche) cannot coexist indefinitely.

Mutualism

A species interaction in which both participating species benefit.

Invasive Species

A non-native species introduced to an ecosystem that causes ecological or economic harm.

Habitat Fragmentation

The breaking up of a large, continuous habitat into smaller, isolated patches, often due to human land use.

Island Biogeography

The theory explaining that species richness on an island increases with island area and decreases with distance from a colonization source.

Unit 3: Water Resources

Watershed

The entire land area that drains surface water into a common river, lake, or other water body.

Point-Source Pollution

Water pollution that originates from a single, identifiable source such as a discharge pipe.

Nonpoint-Source Pollution

Water pollution from diffuse sources such as agricultural or urban runoff, now the leading cause of US water quality impairment.

Biochemical Oxygen Demand (BOD)

A measure of the amount of dissolved oxygen consumed by microorganisms decomposing organic matter in water; high BOD indicates heavy organic pollution.

Dead Zone

An area of water with oxygen levels too low to support most aquatic life (hypoxia), typically caused by nutrient pollution and eutrophication.

Ocean Acidification

The ongoing decrease in ocean pH caused by seawater absorbing excess atmospheric CO2, forming carbonic acid.

Aquifer

An underground layer of permeable rock or sediment that stores and transmits groundwater.

Maximum Sustainable Yield (MSY)

The largest catch or harvest that can theoretically be taken from a renewable resource population indefinitely without depleting it.

Desalination

The process of removing salt from seawater to produce freshwater, typically via reverse osmosis or distillation.

Coral Bleaching

The loss of a coral's symbiotic algae (zooxanthellae) and color, usually caused by heat stress, which can lead to coral death.

Unit 4: Land Use & Agriculture

Soil Horizon

A distinct layer of soil (e.g., O, A, B, C) that differs in composition, texture, and organic content from adjacent layers.

Green Revolution

The mid-20th century transformation of agriculture using high-yield crop varieties, synthetic fertilizers, and irrigation that greatly increased global food production.

Monoculture

The agricultural practice of growing a single crop species over a large area, increasing efficiency but reducing biodiversity and increasing pest vulnerability.

Integrated Pest Management (IPM)

A pest control strategy combining biological, cultural, and minimal targeted chemical methods to reduce reliance on pesticides.

Desertification

The process by which fertile land becomes degraded into desert-like, unproductive land due to overgrazing, deforestation, or drought.

Overgrazing

Livestock consuming vegetation faster than it can regrow, leading to soil exposure and erosion.

Salinization

The buildup of salts in soil, typically from evaporation of irrigation water in dry climates, which reduces soil fertility.

Clear-cutting

A logging method that removes all trees from an area at once, maximizing short-term yield but increasing erosion and habitat loss.

Urban Sprawl

The low-density outward expansion of urban development into surrounding land, increasing car dependence and infrastructure costs.

Aquaculture

The farming of fish and other aquatic organisms, the fastest-growing sector of global food production.

Unit 5: Energy Resources

Nonrenewable Resource

A resource, such as fossil fuels, that forms far slower than it is consumed and is not replenished on human timescales.

Hydraulic Fracturing (Fracking)

A technique injecting high-pressure fluid into shale rock to release trapped natural gas or oil.

Energy Return on Investment (EROI)

The ratio of usable energy gained from a resource to the energy expended to obtain it.

Photovoltaic (PV) Cell

A device that converts sunlight directly into electricity via the photovoltaic effect.

Intermittency

The characteristic of energy sources like solar and wind whose output varies with weather and time of day, requiring storage or backup power.

Cogeneration (CHP)

A system that captures and uses waste heat from electricity generation for additional heating purposes, increasing overall efficiency.

Geothermal Energy

Energy harnessed from heat stored within the Earth, used for electricity generation or direct heating.

Nuclear Fission

The splitting of uranium-235 atoms to release heat energy, used to generate electricity without direct CO2 emissions.

Biofuel

A fuel such as ethanol or biodiesel derived from recently living biomass, used as a substitute for petroleum fuels.

Energy Efficiency

Achieving the same energy service while using less energy, such as through LED lighting or better insulation.

Unit 6: Pollution Types

Primary Pollutant

A pollutant emitted directly into the air from a source, such as carbon monoxide or particulate matter.

Secondary Pollutant

A pollutant formed through chemical reactions in the atmosphere, such as ground-level ozone forming from NOx and VOCs.

Acid Deposition

Precipitation or particles made acidic by atmospheric SO2 and NOx, which damage forests, acidify lakes, and erode structures.

Bioaccumulation

The gradual buildup of a substance within an individual organism over its lifetime.

Biomagnification

The increasing concentration of a persistent toxin at each successive higher trophic level in a food chain.

Persistent Organic Pollutant (POP)

A toxic organic chemical, such as DDT or PCBs, that resists breakdown, travels long distances, and biomagnifies in food webs.

Sanitary Landfill

An engineered waste disposal site using liners and daily soil cover to reduce groundwater contamination from leachate.

Waste Management Hierarchy

The prioritized order of waste strategies: reduce, reuse, recycle/compost, then dispose.

Microplastic

A plastic fragment smaller than 5mm, formed when larger plastic debris photodegrades without fully breaking down.

Thermal Pollution

The discharge of heated water, often from power plant cooling systems, into a natural water body, lowering dissolved oxygen levels.

Unit 7: Climate Systems

Greenhouse Effect

The natural process by which greenhouse gases trap outgoing infrared radiation, warming Earth's lower atmosphere and surface.

Global Warming Potential (GWP)

A measure comparing how much heat a greenhouse gas traps relative to the same mass of CO2 over a set time period.

Positive Feedback Loop

A climate process that amplifies an initial change, such as the ice-albedo feedback, where melting ice increases heat absorption and causes more melting.

Ice-Albedo Feedback

A positive feedback in which melting reflective ice exposes darker surfaces that absorb more solar energy, accelerating further warming.

Tipping Point

A threshold beyond which a change in a system becomes self-sustaining or irreversible, such as ice sheet collapse.

Ocean Acidification

A decrease in ocean pH caused by absorption of excess atmospheric CO2, impairing shell- and coral-forming organisms.

IPCC

The Intergovernmental Panel on Climate Change, the international body that synthesizes and assesses global climate science.

Mitigation

Actions taken to reduce or prevent the emission of greenhouse gases, lessening the severity of future climate change.

Adaptation

Actions taken to adjust human or natural systems to actual or expected impacts of climate change.

Carbon Sequestration

The capture and long-term storage of atmospheric carbon dioxide, through natural processes (forests, soil) or technology (carbon capture and storage).

Unit 8: Policy & Solutions

Externality

A cost or benefit of an economic activity that falls on a third party not involved in the transaction, such as pollution harming nearby residents.

Cap-and-Trade

A market-based policy that sets a total emissions limit and allows firms to buy and sell tradable emissions permits within that cap.

Carbon Tax

A fee imposed on each unit of greenhouse gas emitted, directly pricing the cost of carbon emissions.

Montreal Protocol

The 1987 international treaty that phased out ozone-depleting substances, widely regarded as the most successful global environmental agreement.

Paris Agreement

The 2015 international climate accord in which nearly all countries set voluntary Nationally Determined Contributions to limit global warming.

Precautionary Principle

The principle that lack of full scientific certainty should not be used to postpone action when an activity threatens serious harm.

Sustainable Development

Development that meets present needs without compromising the ability of future generations to meet their own needs.

Environmental Justice

The fair distribution of environmental benefits and burdens across all communities, regardless of income or race.

Environmental Impact Statement (EIS)

A document required under NEPA that assesses the likely environmental consequences of a major proposed federal action.

Life-Cycle Assessment (LCA)

An evaluation of a product's total environmental impact from raw material extraction through manufacturing, use, and disposal.