Which of the following is a non-point source of water pollution?
Fertiliser runoff is a non-point source because nutrients leave many dispersed fields through rainfall, overland flow, erosion, and subsurface drainage rather than through one readily identified discharge pipe. Its loading varies with land use, weather, soil, and farm management. A sewage outlet or industrial effluent pipe is a point source whose location can be mapped and monitored directly. Community-level consequences can emerge when physiological injury changes survival, reproduction, species interactions, or the flow of energy through food webs. Aquatic effects depend on chemical form, persistence, solubility, dose, and the capacity of organisms to metabolise or excrete the substance. Catchment processes connect land use with rivers, lakes, estuaries, and coastal waters, so prevention at the source is usually more effective than downstream treatment. Ecological assessment distinguishes hazard from risk: a substance may be intrinsically harmful, but realised impact also requires sufficient environmental exposure. Sensitive developmental stages may respond at concentrations that cause little immediate adult mortality, making reproduction and recruitment essential endpoints.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology