A nitrogen budget for the Cape Metropolitan area : is nitrogen enrichment occurring in the soils of remnant patches of lowland fynbos?

Anthropogenic activities create nitrogenous pollutants which threaten the existence of lowland fynbos, comprising 92 Red Data Book species and 14 Cape Flats endemics. A regional Nitrogen budget was constructed through the collation of existing data for the Cape Metropolitan Area. An NOx inventory has revealed that vehicles emit 66 % of the total NOx emissions into the atmosphere. The maximum potential N deposition is 184 kg N ha⁻¹ yr⁻¹ for the lowlands. Air quality in an industrial area, Goodwood, has revealed that a large proportion of the emissions remain in the air and have the potential to deposit 33 kg N ha⁻¹ yr⁻¹. Atmospheric N deposited on unimpacted coastal fynbos is 1.99 kg ha⁻¹ yr⁻¹. Thus remnant patches of lowland fynbos are threatened by replacement by grasslands as a result of atmospheric N inputs. Direct measurements of soil N pools are required, since signals of leaching in rivers may be premature as N accumulating in soil pools may not yet have reached saturation point. NH₃ emissions, wet and dry N deposition, and atmospheric transport models are required in order to construct a N budget for the CMA. Thereafter, appropriate preventative strategies can be devised in order to prevent the replacement of remnant patches of lowland fynbos