AP Environmental Science

## Learning Outcomes

- Understand what peat is and why it is classified carefully on the AP Environmental Science exam
- Explain how peat forms in waterlogged wetlands and why it is a precursor to coal
- Identify the main uses of peat as a fuel and why it is a minor energy source globally
- Describe the environmental impacts of peat combustion and peat extraction
- Apply moisture content and calorific value ideas to simple peat energy calculations
- Compare peat with coal, natural gas, and biomass in terms of renewability, emissions, and environmental effects

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand peat as a fuel source, with a focus on the following syllabus points:

- Know that **peat** is partially decomposed organic matter formed in waterlogged wetlands such as bogs
- Identify peat as a biomass-derived fuel that is generally treated as **nonrenewable on human timescales**
- Explain how peat forms under acidic, low-oxygen conditions and how it can be an early stage in coal formation
- Understand that peat can be dried and burned for heating and, in some places, electricity generation
- Describe combustion impacts, including **carbon dioxide** emissions and particulate pollution
- Explain extraction impacts, including peatland drainage, habitat destruction, and loss of carbon storage
- Understand that peatlands are major **carbon sinks** despite covering a small fraction of Earth’s land area
- Interpret how moisture content affects peat’s energy yield and net usefulness as a fuel

## 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. What is peat, and in what kind of environment does it form?
2. Why is peat usually treated as nonrenewable on human timescales even though it comes from plant material?
3. How does burning peat affect the atmosphere?
4. Why does draining a peatland create environmental damage even before the peat is burned?
5. How does moisture content affect the energy value of peat?

## Introduction

Peat is one of the easiest AP Environmental Science fuels to misclassify. It comes from dead plant material, so students often assume it is simply renewable biomass. But APES cares about **timescale**. Peat forms so slowly that, for practical human energy use, it is treated as effectively nonrenewable.

Peat also matters because its environmental costs come from two separate stages: extracting it from wetlands and burning it as fuel. That makes it a useful exam example for showing that a fuel can be harmful not only during combustion, but also during land disturbance and resource removal.

> **Key Term: peat**
> Partially decomposed organic material, mainly plant matter, that accumulates in waterlogged wetlands such as bogs and can be dried and burned as a fuel.

### What peat is and how it forms

Peat forms where plant material does not fully decompose. In most habitatss, dead leaves, stems, and roots are broken down fairly quickly by decomposers. In peatlands, that breakdown is slowed because the ground is saturated with water and often low in oxygen.

Waterlogging matters because decomposers need oxygen for efficient decay. In bogs and similar wetlands, the conditions are often **anaerobic**, meaning oxygen is absent or very limited. That slows decomposition so much that partially decayed plant material accumulates faster than it is broken down. Over long periods, this builds thick peat deposits.

> **Key Term: anaerobic conditions**
> Low-oxygen or no-oxygen conditions that slow decomposition and change how organic matter breaks down.

Peat is commonly made from wetland plants such as mosses, sedges, and shrubs. It is not yet coal, but it is partway along that path. If buried deeply over geologic time, peat can become coal, especially low-grade coal first.

> **Key Term: coal precursor**
> A material that forms earlier in the process that can eventually become coal over geologic time.

This is an important distinction. Peat is not just “young coal,” and it is not just “wet biomass.” It sits between those ideas. It is recent enough that its plant origins are obvious, but old and slow-forming enough that it should not be treated like wood or crop waste.

A common student mistake is to say “peat is renewable because plants regrow.” That misses the rate issue. Renewable resources are defined by how quickly they are replenished compared with how quickly humans use them. Peat accumulates only very slowly, often around **1 mm per year**, while extraction removes much more than that.

> **Test Tip:** If an FRQ asks whether peat is renewable, do not stop at “it comes from plants.” Add the timescale point: it forms so slowly that APES usually treats it as nonrenewable on human timescales.

### Why peat is a problematic fuel source

Peat has been used as a household fuel and, in some regions, for electricity generation. Its main attraction is local availability. If a region has peatlands nearby, peat may seem like an accessible domestic energy source. That can reduce transport distance compared with importing another fuel.

However, local availability does not make it environmentally sound. Peat has two major categories of impact:

1. **Combustion impacts**
2. **Extraction and drainage impacts**

When peat is burned, it releases **carbon dioxide** and particulate matter. Textbook material also supports soot as a concern, and broader evidence shows other pollutants may be emitted as well. For APES, the safest high-yield answer is to focus on CO₂ and particulates first.

> **Key Term: combustion**
> The process of burning a fuel in oxygen to release energy.

Peat is sometimes wrongly described as cleaner than coal because it is less processed and comes from plants. That is misleading. On an energy basis, peat can produce **very high CO₂ emissions**, comparable to or even higher than some coals. That happens because peat contains much water and has lower energy density, so more mass may be needed to produce the same useful energy.

The second problem is often even more damaging: extracting peat usually requires **draining peatlands**. That changes the wetland from a saturated, oxygen-poor environment into a drier, oxygen-rich one. Once oxygen enters, decomposition speeds up. Carbon that had been stored in the peat begins to be released.

> **Key Term: carbon sink**
> A natural reservoir that stores more carbon than it releases over time.

Peatlands are extremely important carbon sinks. They cover only about **3–4% of global land area**, yet they store roughly **one-third of global soil carbon**. That means disturbing them can release very large amounts of stored carbon relative to their area.

This is why peat is such a strong APES example of system thinking. The fuel is harmful:

- when the peatland is drained
- while the peat is extracted
- when the peat is burned

So even if a question asks only about “using peat as fuel,” a stronger answer includes both stages: habitat damage disturbance and air pollution.

Peat extraction also damages wetland natural system services. Drained peatlands do less flood buffering, less water regulation, less water purification, and provide worse habitat for wetland biodiversity. In some places, drainage also increases subsidence and makes runoff less stable.

> **Test Tip:** For compare questions, split your answer into “before burning” and “during burning.” With peat, this structure helps you score application marks because it shows you understand both extraction and combustion impacts.

### Energy value, moisture content, and worked calculation

Peat’s usefulness as a fuel depends heavily on **moisture content**. This is the most testable quantitative idea in the topic.

Dry peat has a moderate calorific value. A useful figure is about **20 MJ/kg** for oven-dried peat, with broader dry ranges often around **15–22 MJ/kg**. But real peat taken from bogs is often very wet. That water lowers the usable energy sharply, because some of the released energy must go into heating and evaporating the water instead of doing useful work.

At **30–40% moisture**, peat may have a calorific value of only about **10 MJ/kg**. That means wet peat can deliver roughly half the usable energy per kilogram of dry peat.

> **Key Term: calorific value**
> The amount of energy released when a fuel is burned, usually expressed per unit mass.

This matters for net energy yield. A fuel that is bulky, wet, and low in usable energy is less attractive because more has to be harvested, transported, and dried for the same output.

> **Key Term: net energy yield**
> The useful energy obtained from a fuel after subtracting the energy needed to extract, process, and transport it.

Here is a worked example.

A sample of dry peat has a calorific value of **20 MJ/kg**. A wetter peat sample at 35% moisture has a calorific value of **10 MJ/kg**. How much energy would 500 kg of each provide?

Dry peat:

- Energy per kg = **20 MJ**
- Total mass = **500 kg**
- Total energy = **20 MJ/kg × 500 kg = 10,000 MJ**

Wet peat:

- Energy per kg = **10 MJ**
- Total mass = **500 kg**
- Total energy = **10 MJ/kg × 500 kg = 5,000 MJ**

So the same mass of wetter peat provides **5,000 MJ less**, which is half the energy of the dry peat.

Students often miss the implication. The key point is not just that wet peat gives less energy. It also means more peat must be removed and moved to get the same useful output. That increases land disturbance and transport costs.

A second useful calculation uses peat’s carbon dioxide emissions. A broad emission factor is about **106 g CO₂ per MJ** of energy from peat combustion.

If peat provides **10 MJ/kg**, then:

- CO₂ per kg peat = **106 g/MJ × 10 MJ**
- = **1060 g CO₂**
- = **1.06 kg CO₂ per kg peat**

If peat provides **12 MJ/kg**, then:

- CO₂ per kg peat = **106 g/MJ × 12 MJ**
- = **1272 g CO₂**
- = **1.27 kg CO₂ per kg peat**

These figures help explain why peat is not a climate-friendly substitute.

Common errors students make:

- calling peat renewable without mentioning slow formation
- discussing only burning, not peatland drainage
- assuming all biomass fuels have the same carbon impact
- forgetting that wetter fuels often have lower usable energy per kilogram

### Comparing peat with other fuels

Peat is easiest to revise by comparison. It shares features with both biomass and fossil fuels, but is not identical to either.

Peat vs wood

- Both come from plant material
- Wood can be renewable if harvested sustainably over relatively short timescales
- Peat reforms far more slowly, so it is effectively nonrenewable on human timescales
- Both release CO₂ and particulates when burned

Peat vs coal

- Both are solid carbon-rich fuels
- Peat is less transformed and is an earlier stage in coal formation
- Peat usually has lower energy density, especially when wet
- Peatland extraction destroys carbon-storing wetlands, while coal mining disrupts other terrestrial systems

Peat vs natural gas

- Natural gas burns more cleanly in terms of particulates
- Peat generally causes more particulate pollution and high CO₂ emissions per unit energy
- Natural gas is also nonrenewable, but peat has the added issue of destroying peatland carbon sinks during extraction

This is a strong exam comparison because it avoids vague claims. Instead of saying “peat is bad for the environment,” you can explain exactly why it is often worse than students first expect.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Peat is partially decomposed plant material formed in waterlogged wetlands such as bogs
- Peat forms under acidic, low-oxygen, often anaerobic conditions that slow decomposition
- Peat is an early stage in coal formation and can be described as a coal precursor
- AP Environmental Science usually treats peat as nonrenewable on human timescales
- Peat accumulates extremely slowly, often around 1 mm per year
- Peat can be used for heating and, in some regions, electricity generation
- Burning peat releases carbon dioxide and particulate pollution
- Draining and harvesting peatlands damages wetland habitats and releases stored carbon
- Peatlands cover only a small percentage of global land area but store a very large share of soil carbon
- Moisture content strongly lowers peat’s calorific value and usable energy
- Wet peat has lower net energy yield because more energy is lost to heating and evaporating water
- Peat should be evaluated in terms of both combustion impacts and extraction impacts

## Key Terms and Concepts

- peat
- anaerobic conditions
- coal precursor
- combustion
- carbon sink
- calorific value
- net energy yield


Fuel Types and Uses - Peat fuel source