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 381 mm and 466 mm respectively which was below the 40-year mean of 577 mm recorded for the area. Total nitrogen input during 1980 – 81 was 1,99 kg N ha− 1 y− 1. Of this 1,12 kg 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 1,79 kg 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 1,5 m and 4 m 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. Resultate van stikstoftoevoer deur massa-neerslag oor ’n twee-jaar-tydperk aan kus-fynbos wat voorkom in grond arm aan voedingstowwe, word aangebied. Die jaarlikse neerslag aangeteken gedurende die studie-periodes van 1980 – 81 en 1981 – 82 was 381 mm en 466 mm onderskeidelik en minder as die gemiddelde 577 mm vir die area oor 40 jaar. Die totale stikstoftoevoer gedurende 1980 – 81 was 1,99 kg N ha− 1 j− 1. Hiervan was 1,12 kg N ha− 1 j− 1 organiese stikstof in die vorm van NO3-N en NH4-N. Anorganiese N-toevoer het hoofsaaklik gedurende die nat maande van Junie – Augustus plaasgevind. Anorganiese N-toevoer gedurende 1981 – 82 was 1,79 kg N ha− 1 j− 1 met ’n NH4-N tot NO3-N-kwosiënt van 1. Logaritmiese verhoudings bestaan tussen NO3-N- en NH4-N-konsentrasies in massa-neerslag en die volume van neerslag wat met weeklikse tussenposes versamel is. Massaneerslag-versamelaars by 1,5 m en 4 m was nie geskik om die invloed van plaaslike hergebruik van stof-aerosols te bepaal nie. Alhoewel atmosferiese N-neerslag mag bydra tot die buite-sistemiese N, is dit by sigself onvoldoende om die N wat uit kusfynbos-ekosisteme verlore raak deur die gedurige korttermyn-voorkomste van brande, te vervang. Die redelik lae toevoeging van stikstof in die Pella-gebied gee ’n aanduiding van die stikstofvlakke wat verwag kan word in die fynbos-gebiede waar N hoofsaaklik van oseaan-bronne afhanklik is en min antropogeniese bedrywighede die samestelling van die neerslag beïnvloed.