APES Unit 8 Water Pollution: Causes, Pathways, and Ecological Consequences

Water pollution

Any physical, chemical, or biological change in water quality that makes water less suitable for an intended use (e.g., drinking, irrigation, aquatic habitat, recreation).

Watershed (drainage basin)

The area of land where precipitation drains to a common body of water; land use within a watershed strongly predicts downstream water quality.

Surface runoff

Rain or snowmelt flowing over land that picks up and transports pollutants (soil, nutrients, oil, metals, trash) into waterways.

Leaching and infiltration

Downward movement of water through soil that carries dissolved chemicals into groundwater; soil does not automatically remove many dissolved pollutants (e.g., nitrates).

Atmospheric deposition

Pollutants released to the air (e.g., nitrogen compounds, mercury) that settle onto land or water and then enter aquatic systems.

Point source pollution

Pollution from a single, identifiable location (such as a discharge pipe from a wastewater treatment plant or industrial facility); easier to monitor and regulate.

Nonpoint source pollution

Diffuse pollution from many small sources spread across a landscape (e.g., agricultural runoff, urban stormwater, construction sediment); harder to control and weather-dependent.

Nutrient pollution

Addition of nitrogen and phosphorus compounds that stimulate excessive plant and algal growth; commonly from fertilizer, manure, and wastewater/septic systems.

Pathogens

Disease-causing organisms (bacteria, viruses, protozoa) that can make water unsafe for drinking and recreation; often linked to sewage and animal waste.

Combined sewer overflow (CSO)

A release during heavy storms when stormwater and sewage share pipes and the system overflows, sending untreated or partially treated waste into waterways.

Oxygen-demanding wastes

Organic materials (e.g., sewage, food-processing waste) that microbes decompose using dissolved oxygen, which can lower oxygen levels in the water.

Sediment pollution

Excess soil and particles in water, often from construction, plowed fields, overgrazing, deforestation, and streambank erosion; increases cloudiness and disrupts habitats.

Wetlands

Areas where water saturates soil for all or part of the year, producing oxygen-poor (anaerobic) soils and supporting water-tolerant plants; provide filtration, nutrient processing, flood control, and habitat.

Mangroves

Salt-tolerant trees and shrubs in tropical/subtropical coastal intertidal zones; stabilize shorelines, trap sediment, and serve as nursery habitat.

Constructed wetlands

Engineered systems that mimic wetland processes to treat wastewater or stormwater by removing sediment and some nutrients and reducing BOD; require land area and proper design.

Heavy metals

Toxic metals (e.g., mercury, lead, cadmium) that can come from mining, industrial processes, and atmospheric deposition; may cause acute or chronic health/ecosystem effects.

Thermal pollution

Human-caused change in water temperature (often from power plant/industrial cooling water); warmer water holds less dissolved oxygen and can stress temperature-sensitive species.

Eutrophication

Nutrient enrichment of water (especially nitrogen and phosphorus) that increases primary productivity (algae/plant growth); can be natural over long timescales.

Cultural eutrophication

Eutrophication accelerated by human nutrient inputs (fertilizer, manure, sewage), often leading to algal blooms and low-oxygen conditions.

Dissolved oxygen (DO)

Oxygen gas dissolved in water and available to aquatic organisms; tends to be higher in cold, fast-moving water and lower in warm, slow or stagnant water.

Biological oxygen demand (BOD)

A measure of how much oxygen microorganisms will consume while decomposing organic matter in a water sample; higher BOD generally means more decomposable waste is present.

Hypoxia (and anoxia)

Hypoxia is low dissolved oxygen; anoxia is no dissolved oxygen—conditions that can kill or drive away fish and invertebrates.

Bioaccumulation

The buildup of a chemical in an organism’s tissues over time because uptake exceeds the ability to metabolize or excrete it (especially for persistent, fat-soluble chemicals).

Biomagnification

Increasing concentration of a chemical at higher trophic levels in a food chain; most associated with persistent, fat-soluble pollutants.

Endocrine disruptors

Chemicals that interfere with the endocrine (hormone) system by mimicking hormones, blocking receptors, or altering hormone production/transport/breakdown; can cause developmental and reproductive changes at very low concentrations, often via wastewater effluent or runoff.