Atmospheric input of nitrogen to a coastal fynbos ecosystem of the south-western Cape Province, South Africa

Results are presented of nitrogen input via bulk precipitation over a two-year period, to coastal fynbos vegetation occurring on soils of low nutrient status. The annual precipitation recorded during the study periods of 1980 – 81 and 1981 – 82 was 381mm and 466mm respectively which was below the 40-year mean of 577mm recorded for the area. Total nitrogen input during 1980 – 81 was 1,99kg N ha−1 y−1. Of this 1,12kg N ha−1 y−1 was inorganic nitrogen in the form of NO3-N and NH4-N. Inorganic N input occurred predominantly in the winter rainfall months of June to August. Inorganic N input during 1981 – 82 was 1,79kg N ha−1 y−1 with an NH4-N to NO3-N quotient of 1. Logarithmic relationships exist between NO3-N and NH4-N concentrations in bulk precipitation and the volume of precipitation collected at weekly intervals. Bulk precipitation collectors at 1,5m and 4m were not suitable to determine the infuence of local recycling of dust aerosols. It is probable that although atmospheric N deposition may contribute a portion of the extra-system N, it alone is not sufficient to replenish N lost by coastal fynbos ecosystems as a result of recurrent short interval fires. Rather the low input of nitrogen to the Pella site reported gives an indication of the levels of N deposition to be expected in the fynbos region where N is derived mainly from oceanic sources and few anthropogenic activities influence precipitation composition