Human Impact: Agriculture and Pollution

This lesson covers the environmental impact of agriculture and pollution, including eutrophication, pesticides, bioaccumulation, deforestation, monoculture, and soil erosion, as required by the Edexcel A-Level Biology specification (9BI0), Topic 10 -- Ecosystems.

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Agriculture and the Environment

Modern agriculture aims to maximise food production, but many farming practices have significant environmental consequences. Understanding these impacts and how to mitigate them is essential for developing sustainable food systems.

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Eutrophication

Eutrophication is the enrichment of a body of water with mineral nutrients (especially nitrates and phosphates), leading to excessive growth of algae and the depletion of dissolved oxygen.

The Process of Eutrophication

flowchart TB
    A["Excess fertiliser\napplied to farmland"] --> B["Nitrates and phosphates\nleach from soil into\nrivers and lakes\n(runoff)"]
    B --> C["Nutrient enrichment\nof water\n(eutrophication)"]
    C --> D["Rapid growth of\nalgae and cyanobacteria\n(algal bloom)"]
    D --> E["Algal bloom blocks\nlight to submerged\naquatic plants"]
    E --> F["Submerged plants\ncannot photosynthesise\nand die"]
    D --> G["Algae eventually\ndie (short lifespan)"]
    F --> H["Large amounts of\ndead organic matter\naccumulate"]
    G --> H
    H --> I["Aerobic decomposers\n(bacteria) multiply\nrapidly, feeding on\ndead matter"]
    I --> J["Decomposers use up\ndissolved oxygen\n(high BOD)"]
    J --> K["Water becomes\nanaerobic (deoxygenated)"]
    K --> L["Fish and other\naerobic organisms\ndie"]

Key Terminology