The document discusses ecosystems and trophic levels. It explains that there are four trophic levels: primary producers (plants), primary consumers (herbivores), secondary consumers (carnivores), and decomposers. Between each trophic level, about 10% of energy is transferred. Nutrients cycle through ecosystems with the help of decomposers, which break down organic material and release nutrients back into the soil. The document also discusses nutrient pollution in coastal waters, noting that excess nitrogen and phosphorus can lead to eutrophication and decreased biodiversity.