Environmental scientists investigated water quality along a river system at four sampling stations: A, B, C, and D, as shown in the map.
State two beneficial substances naturally present in unpolluted river water and state the biological benefit of each.
At Station B, located downstream from intensive agricultural farmland, water analysis reveals high concentrations of nitrate () and phosphate () ions.
State the agricultural source of these nitrate and phosphate ions in river water.
Describe the adverse effect of high nitrate and phosphate concentrations on aquatic organisms in the river.
At Station C, downstream from an untreated municipal sewage outlet, the dissolved oxygen concentration drops to 1.8 mg dm⁻³ and massive fish deaths occur. Explain, in terms of micro-organisms, why sewage discharge causes a severe drop in dissolved oxygen concentration.
A local factory discharges plastic micro-beads and trace lead(II) compounds into the river. State one harmful environmental effect of:
plastics in aquatic habitats
toxic heavy metal compounds (such as lead) in natural water.