20.3 Pollution

Effects of untreated sewage and excess fertiliser on aquatic ecosystems (oxygen-collapse pathway via algal bloom + decomposer respiration). Effects of non-biodegradable plastics in aquatic and terrestrial ecosystems (entanglement, ingestion, microplastic accumulation). Sources and effects of methane and carbon dioxide air pollution — enhanced greenhouse effect and climate change. HL extension: the six-step eutrophication mechanism — increased nitrate availability, increased producer growth, increased decomposition after producer death, increased aerobic respiration by decomposers, reduction in dissolved oxygen, and death of oxygen-requiring organisms.