Module 2 - Water Quality

AP Environmental Science 2025-26

DO

a measure of how much oxygen is dissolved in the water - the amount of oxygen available to living aquatic organisms.

pH

The number that indicates the relative strength of acids and bases in a substance.

Fecal Coliform

A group of generally harmless microorganisms in human intestines that can serve as an indicator species for potentially harmful microorganisms associated with contaminated sewage.

Biological Oxygen Demand

Biochemical oxygen demand is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.

Nitrates

Nitrate is a polyatomic ion with the chemical formula NO⁻ ₃. Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Nitrates (or nitrites) are natural chemicals that are found in the soil, air and water.

Total Phosphates

Phosphates are chemical compounds containing phosphorus. Phosphorus is a non-metallic element which is necessary for life and is found in rock as inorganic phosphates. As water runs over and through rocks it carries off small amounts of minerals such as calcium, magnesium, and phosphates.

Total Dissolved Solids (TDS)

Dissolved solids "refer to any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts, principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates and some small amounts of organic matter that are dissolved in water.

Turbidity or TSS

Turbidity is caused by particles suspended or dissolved in water that scatter light making the water appear cloudy or murky.

Freshwater biomes

A freshwater biome is a large community of flora and fauna (plants and animals) that live in water bodies with low salt content, usually less than 1%.

Lakes & Ponds

A lake is a body of water that is surrounded by land. Lakes are normally much deeper than ponds and have a larger surface area.

Wetlands

An aquatic biome that is submerged or saturated by water for at least part of each year, but shallow enough to support emergent vegetation.

Streams

A small, narrow river.

Rivers

a natural stream of water of usually considerable volume.

Marine biome

Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content.

Estuaries

An area along the coast where the fresh water of rivers mixes with salt water from the ocean.

Salt marshes

A marsh containing nonwoody emergent vegetation, found along the coast in temperature climates.

Mangrove swamps

A swamp that occurs along tropical and subtropical coasts, and contains salt-tolerant trees with roots submerged in water. 

Intertidal zone

The narrow band of coastline between the levels of high tide and low tide.

Coral reefs

The most diverse marine biome on Earth, found in warm, shallow waters beyond the shoreline.

Open ocean

Deep ocean water, located away from the shoreline where sunlight can no longer reach the ocean bottom

Hydrologic cycle

Movement of water through the biosphere

Urban runoff

Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces are constructed during land development

Watershed

All land in a given landscape that drains into a particular stream, river or wetland

Precipitation

Water that falls to the earth as hail, mist, rain, sleet, or snow.

Percolation

Percolation is the movement of water through the soil itself. Finally, as the water percolates into the deeper layers of the soil, it reaches ground water, which is water below the surface. The upper surface of this underground water is called the "water table".

Groundwater

Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations.

Evaporation

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase.

Transpiration

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers

Surface runoff

Surface runoff is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil.

Thermal pollution

Thermal pollution is when an industry or other human-made organization takes in water from a natural source and either cools it down or heats it up. They then eject that water back into the natural resource, which changes the oxygen levels and can have disastrous effects on local ecosystems and communities.

Persistent organic pollutants (POP)

Synthetic, Carbon-based molecules that break down very slowly in the environment are known as persistent organic pollutants (POPs)

Bioaccumulation

An increased concentration of a chemical within an organism over time.

Biomagnification

The increase in chemical concentration in animal tissues as the chemical moves up the food chain.

Primary treatment

In the primary stage, solids are allowed to settle and removed from wastewater. (physical)

Secondary treatment

The secondary stage uses biological processes to further purify wastewater. (biological)

Tertiary treatment

Tertiary treatment includes removal of nutrients such as phosphorus and nitrogen and practically all suspended and organic matter from wastewater. (chemical)

Eutrophication

A phenomenon in which a body of water becomes rich in nutrients.

Clean Water Act

The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.

Safe Drinking Water Act

The Safe Drinking Water Act (SDWA) was established to protect the quality of drinking water in the U.S. This law focuses on all waters actually or potentially designed for drinking use, whether from above ground or underground sources.

Point Source

A distinct location from which pollution is directly produced.

Nonpoint source

A diffuse area that produces pollution.

Indicator Species

A species that indicates whether or not disease-causing pathogens are likely to be present

Fecal Coliform Bacteria

A group of generally harmless microorganisms in human intestines that can serve as an indicator species for potential harmful microorganisms associated with contaminated sewage.

Septic System

A relatively small and simple sewage treatment system, made up of a septic tank and a leach field often used for homes in rural areas.