Cambridge IGCSE Marine Science Practical Skills 6: Pollution, human impact and data evaluation

Cambridge 0697 does not label a separate set of Topic 6 pollution practicals. This editorial chapter applies the official AO3 contract to unfamiliar human-impact evidence in Paper 2: planning, safe observation, data processing, conclusions, method evaluation and justified improvements. It must not be treated as an invented Cambridge practical unit.

Turn an impact claim into a testable question

Avoid broad questions such as “Does tourism damage reefs?” Define an exposure, outcome, place and comparison: “How does live-coral cover differ between frequently visited and restricted reef sites at matched depth?”

The independent variable may be a controlled treatment in a model, but field studies often compare exposure categories rather than manipulate them. The dependent variable might be litter density, species richness, coral cover, dissolved oxygen, pH or organism abundance. Record likely confounders such as depth, substrate, current, temperature and sampling effort.

Use several independent sites per category. Many quadrats at one tourist site measure local variation but do not replicate the tourist category. Select sites before seeing their outcomes and use the same method, season and tidal window.

Pollution surveys

For shoreline litter, define a belt width and length, classify items using a written scheme and report count or mass per unit area. Use gloves or tools and do not handle sharps, medical waste or unknown chemicals. Record large items separately from fragment counts because one object breaking into pieces can inflate count.

Microplastic investigations require contamination controls. Cover samples, use clean glassware where appropriate, avoid synthetic clothing fibres where feasible and include a procedural blank. Visual identification alone can misclassify sand, shell or organic fragments, so conclusions should say “suspected microplastics” unless material identity is confirmed.

Oil-impact observations may record percentage cover, affected organisms or distance from a source. Do not enter contaminated water or touch oil. Use photographs, authorised datasets or teacher-provided samples when direct sampling is unsafe.

Nutrient and oxygen evidence

Eutrophication evidence may include nutrient concentration, producer abundance, water clarity and dissolved oxygen. A single low oxygen reading does not prove fertiliser caused it. Temperature, mixing, salinity, respiration and time of day also matter.

Plan a spatial sequence from likely input towards reference water, or a time series before and after an event. Measure at the same depth and time window. Calibrate probes, rinse them between sites and allow readings to stabilise. Include field blanks or standards where the method supports them.

Graph each variable against distance or time. The predicted causal sequence is nutrient rise, producer growth, death and decomposition, increased aerobic respiration, oxygen decline and mortality. Observations may capture only part of that sequence, so conclusions must be limited accordingly.