AP Environmental Science

## Learning Outcomes

- Explain how litter from land reaches rivers, lakes, coasts, and oceans
- Distinguish between **point-source pollution** and **nonpoint-source pollution** in litter problems
- Describe how aquatic litter harms organisms through entanglement, ingestion, and ghost fishing
- Understand why plastics create long-term pollution problems, including the formation of microplastics
- Link organism-level harm to environmental-level effects such as habitat damage and biodiversity loss
- Identify human and economic impacts of aquatic trash, including cleanup costs and fishery losses
- Evaluate practical strategies that reduce litter hazards in aquatic systems

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand litter hazards in aquatic systems, with a focus on the following syllabus points:

- Know that much aquatic litter starts on land and is transported into water by wind and especially **stormwater runoff**
- Identify litter carried by runoff as primarily **nonpoint-source pollution**, rather than pollution from a single discharge pipe
- Explain the difference between **entanglement** and **ingestion** as two major hazards to aquatic organisms
- Understand that lost, abandoned, or discarded fishing gear can continue trapping organisms through **ghost fishing**
- Know that plastics are especially harmful because they are persistent and break down into **microplastics**
- Explain how aquatic litter can damage habitats, disrupt food webs, reduce biodiversity, and interfere with human uses of waterways
- Recognise that affected organisms include fish, seabirds, sea turtles, marine mammals, freshwater turtles, and invertebrates
- Understand mitigation approaches, including source reduction, improved waste management, stormwater controls, cleanup, and fishing-gear recovery

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why is litter in aquatic systems usually classed as **nonpoint-source pollution**?
2. What is the difference between entanglement and ingestion?
3. How does lost fishing gear continue to harm organisms after it is abandoned?
4. Why does plastic remain a problem even after it breaks into small pieces?
5. Give one way litter in water harms humans or the economy, not just wildlife.

## Introduction

Litter hazards in aquatic systems are a clear example of how human activity on land affects both freshwater and marine environmentss. For AP Environmental Science, this topic matters because it connects pollution pathways, food webs, habitat damage, biodiversity loss, and environmental management. A common exam trap is thinking that aquatic litter is mainly thrown directly into the ocean. In reality, much of it begins on land and enters water through runoff, storm drains, streams, and rivers.

This topic also shows an important APES pattern: a pollutant can cause harm at more than one scale. A plastic bottle ring can injure one animal directly, but widespread debris can also alter habitats, damage fisheries, and reduce the recreational value of a whole water body.

> **Key Term: aquatic trash**
> Human-made solid waste found in rivers, lakes, streams, wetlands, estuaries, or oceans.

### How litter gets from land to water

A large share of aquatic litter comes from land-based activities. Common starting points include littering, overflowing bins, illegal dumping, poorly contained waste, and trash left on streets, sidewalks, parking lots, or beaches. Once trash is loose in the environment, wind and rainfall can move it.

The most important transport route is **stormwater runoff**. When rain falls on impervious surfaces such as roads and parking lots, the water cannot infiltrate the ground easily. Instead, it flows across the surface, picking up trash along with oil, sediment, fertilizers, and other pollutants. This runoff then enters storm drains, streams, rivers, lakes, and eventually coastal waters or the ocean.

This is why inland litter can become marine pollution. A wrapper dropped far from the coast can still enter a storm drain, move into a creek, then into a river, and finally reach a bay or the open ocean. Freshwater systems are not separate from marine litter problems; they are often the pathway that delivers waste to the sea.

> **Key Term: stormwater runoff**
> Water from rain or snowmelt that flows over land instead of soaking into the ground, carrying pollutants into waterways.
>
> **Key Term: nonpoint-source pollution**
> Pollution that comes from many diffuse sources rather than one single, identifiable discharge point.

A major distinction for the exam is **point source** versus **nonpoint source** pollution. A factory pipe releasing waste into a river is a point source because the discharge location is known. Litter washed from many streets, lawns, and parking lots into drains is mainly nonpoint source pollution because it comes from many scattered places.

Students sometimes pick “point source” because storm drains look like pipes. That is the wrong reasoning. The drain is part of the transport system, but the litter itself usually came from many diffuse land locations.

> **Test Tip:** If an FRQ asks how litter reaches water, build a full cause-and-effect chain: improper disposal on land → wind or runoff transport → storm drain or stream entry → river or lake movement → aquatic harm.

### Direct biological hazards: entanglement, ingestion, and ghost fishing

Aquatic litter harms organisms in several direct ways, but the two most tested are **entanglement** and **ingestion**.

**Entanglement** happens when organisms become caught, wrapped, or snagged in debris. Common examples include fishing line, nets, rope, plastic packing bands, and plastic rings. Once entangled, an organism may have trouble swimming, surfacing, feeding, or escaping predators. The debris can also cut into tissue, causing wounds and infection. In severe cases, the animal drowns or dies from starvation.

Sea turtles, seabirds, fish, and marine mammals are all vulnerable. A seal trapped in netting may be unable to surface properly. A bird entangled in line may lose the ability to fly or feed. A turtle caught in plastic loops may continue growing while the plastic cuts deeper into its body.

> **Key Term: entanglement**
> Harm that occurs when an organism becomes caught or wrapped in debris such as nets, fishing line, rope, or plastic bands.

**Ingestion** happens when organisms swallow litter. Sometimes they mistake it for food. A common example is a sea turtle eating a plastic bag that resembles jellyfish prey. In other cases, organisms accidentally take in small plastic particles while feeding. Once swallowed, debris can block the digestive tract, reduce feeding, cause internal injury, create a false sense of fullness, and lead to starvation.

This is a different mechanism from entanglement. Entanglement stops movement or damages the outside of the body. Ingestion damages feeding and digestion from the inside.

> **Key Term: ingestion**
> Harm that occurs when an organism swallows debris directly or mistakes it for food.

A special case is **ghost fishing**. This refers to continued trapping or capture by lost, abandoned, or discarded fishing gear. A net or trap does not stop being dangerous once fishers lose control of it. It may continue catching fish, crustaceans, turtles, seabirds, or marine mammals for long periods.

This matters because the gear is designed to catch organisms efficiently. So derelict fishing gear is often more dangerous than ordinary litter. It is both persistent waste and an active killing mechanism.

> **Key Term: ghost fishing**
> Continued capture or entanglement of organisms by lost, abandoned, or discarded fishing gear.

Ghost fishing also creates a compounding effect. Organisms trapped in derelict gear may die and attract scavengers or predators, which then become trapped as well. That increases mortality beyond the original catch.

> **Test Tip:** In short-answer questions, separate hazards clearly. Write one sentence for entanglement effects and one for ingestion effects. This avoids vague answers like “plastic harms animals” that often miss available marks.

### Why plastics are especially dangerous

Not all litter behaves the same way. AP Environmental Science puts extra emphasis on plastics because they are persistent. Many natural materials biodegrade relatively quickly, but plastic usually does not fully disappear in a short time. Instead, it breaks into smaller pieces.

Sunlight, heat, and physical abrasion cause larger plastic items to fragment. This process is often called photodegradation. The key point is that fragmentation is not the same as safe removal. A broken plastic bottle does not vanish; it becomes many smaller plastic particles that are harder to remove and easier for organisms to ingest.

> **Key Term: microplastics**
> Very small plastic particles, usually less than 5 mm in size, formed by the breakdown of larger plastics or released directly as small manufactured particles.

Microplastics matter because many more organisms can take them in. Large animals may ingest bags or bottle caps, but smaller organisms such as plankton-feeding species, filter feeders, and benthic invertebrates can ingest microplastics. Once smaller organisms consume them, those particles can move through food webs.

Be careful here. The strongest APES-ready claim is that plastics and microplastics are persistent, can be ingested, and can transport pollutants through food webs. You do not need to claim precise human toxic effects from microplastics unless the question provides evidence.

Plastics can also alter physical conditions in habitats. Floating or accumulated debris may block sunlight from reaching aquatic plants and phytoplankton. Surface debris can reduce visibility for predators and prey. Larger debris can smother or scrape habitats.

### System-wide-level impacts: from individual harm to habitat damage

Students often stop at individual examples, such as a turtle swallowing plastic. That is only part of the story. Aquatic litter also causes environmental-level harm.

First, habitats can be physically damaged. Debris may smother wetland vegetation, scrape coral, bury benthic habitats, or snag on seagrass beds. Lost fishing gear can drag across habitats or remain lodged in them. In freshwater systems, trash can collect along stream banks and in riparian zones, altering habitat structure.

Second, food webs can be disrupted. If primary consumers, filter feeders, or juvenile fish are harmed by ingestion or habitat loss, that affects predators above them. If species die from entanglement or ghost fishing, population sizes can decline. Repeated mortality and reduced reproduction can lower biodiversity.

Third, aquatic litter can interact with other pollution problems. Urban runoff that carries trash often also carries gasoline, heavy metals, fertilizers, and pesticides. So the same pathways that deliver litter may also intensify eutrophication, contamination, or sedimentation.

The Great Pacific Garbage Patch is a useful example of large-scale debris accumulation. It formed as ocean currents concentrated floating litter in the North Pacific Gyre. It is not a solid island of trash, but a region with unusually high concentrations of floating debris, especially plastics. This case shows how ocean circulation can concentrate persistent waste far from where it entered the water.

In freshwater, similar principles apply on a smaller scale. Trash can accumulate in harbors, river mouths, wetlands, or lake shorelines. The exact debris differs by place, but the ecological pattern is the same: persistent litter enters, accumulates, injures organisms, and degrades habitat quality.

### Human and economic impacts of aquatic litter

APES questions often reward answers that move beyond wildlife impacts. Aquatic litter also affects humans directly and economically.

One impact is reduced recreation and tourism. Trash on beaches, riverbanks, and lake shorelines makes these places less attractive and less safe. Sharp debris can injure swimmers or boaters. Dirty shorelines may lower tourism revenue.

Another impact is damage to fishing industries. Ghost fishing kills commercially valuable organisms and reduces harvestable populations. Habitat damage to estuaries, wetlands, or seagrass beds can reduce nursery habitat for fish and shellfish, lowering future fishery productivity.

Boating and shipping can also be affected. Debris may foul propellers, clog intake systems, or create navigation hazards. Cleanup costs for governments and local communities can be substantial as well.

There is also a public health angle. Contaminated waste in waterways may expose people to pathogens or harmful materials. A conservative APES claim is that litter can interfere with water use, recreation, and potentially contaminate seafood pathways through persistent pollutants.

This means aquatic litter is not just a conservation issue. It is also a resource-use and economic issue.

### Reducing litter hazards in aquatic systems

The best management strategies target the problem before litter reaches water. Once debris enters rivers, lakes, or oceans, removal becomes harder and more expensive.

The first priority is **source reduction**. This means producing and using less unnecessary waste, especially single-use plastic items. Reusable containers, better packaging choices, and reduced littering all lower the amount of material available to enter waterways.

Second, **improved waste management** matters. Secure bins, reliable collection systems, and prevention of trash escaping during transport reduce the chance of land-based litter becoming aquatic trash.

Third, **stormwater controls** can interrupt the transport pathway. Because much litter enters water through runoff, reducing polluted runoff is essential. Practical measures include street sweeping, constructed wetlands, retention and infiltration basins, and more permeable urban design that reduces the amount of water rushing into storm drains.

Fourth, **cleanup and removal** remain important. Beach cleanups, river cleanups, harbor trash traps, and debris booms can remove material already in the system, especially in accumulation zones.

Fifth, **fishing-gear recovery programs** directly address ghost fishing. Retrieving derelict nets, traps, and lines removes an especially harmful form of debris. Prevention is also important, such as better gear marking, collection, and disposal systems.

The strongest APES answers usually connect these solutions back to the pathway:
less litter generated on land, less litter transported by runoff, less debris entering aquatic systems, less harm to wildlife and habitats.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Aquatic trash is human-made solid waste found in freshwater and marine systems
- Much aquatic litter starts on land and reaches water through wind and especially stormwater runoff
- Litter transported by runoff is mainly **nonpoint-source pollution**
- Entanglement harms organisms by restricting movement, feeding, and breathing and can cause injury or drowning
- Ingestion harms organisms through blockage, internal injury, false fullness, starvation, and death
- Ghost fishing occurs when lost or discarded fishing gear continues trapping organisms
- Plastics are especially harmful because they persist and fragment into **microplastics** rather than disappearing
- Microplastics can be ingested by small aquatic organisms and can move through food webs
- Aquatic litter damages habitats, disrupts food webs, and can reduce biodiversity
- Human impacts include cleanup costs, reduced recreation and tourism, fishery losses, and boating hazards
- Strong mitigation strategies include source reduction, improved waste management, stormwater controls, cleanup, and fishing-gear recovery
- The Great Pacific Garbage Patch is an example of large-scale debris accumulation caused by ocean currents concentrating floating litter

## Key Terms and Concepts

- aquatic trash
- stormwater runoff
- nonpoint-source pollution
- entanglement
- ingestion
- ghost fishing
- microplastics


Human Impacts on Ecosystems - Litter hazards in aquatic systems