Nitrogen deposition to adjacent grassland and forested areas in the vicinity of Sabie,
Mpumalanga, South Africa was studied. Total deposition amounts to the forested area are
calculated to be 7l.2 kg N ha-1 yr1 and to the grassland area, 25 kg N ha· 1 yr1. The
average deposition amounts are similar to or at least approach nitrogen mineralisation
amounts at nearby sites of 50-70 kg N ha-1 yr1. The deposition amounts are made up of
21.4 kg N ha-1 yr1 dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 42 kg N ha-1 yr1
cloud droplet deposition for the forest. For the grassland, the amounts are 7 kg N ha-1 yr1
dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 10.5 kg N ha-1 yr1 cloud droplet.
deposition. For both wet and cloud droplet deposition, the amount attributable to nitrate
was greater than that attributable to ammonium. For wet deposition, nitrate contributed
4.1 kg N ha-1 yr1 and ammonium contributed 3.7 kg N ha-1 yr1 to both forests and
grasslands. For cloud droplet deposition to forests, the amounts were 28 kg N ha-1 yr1
attributable to nitrate and 14 kg N ha-1 yr1 attributable to ammonium. For grasslands the
amounts were 7 and 3.5 kg N ha-1 yr1. In both forests and grasslands, the component of
dry deposition contributing the most to deposition was ammonia gas, the amounts being
14.2 and 4.3 kg N ha-1 yr1 respectively. Nitric acid contributes 3.7 and 1.9 kg N ha-1 yr1
respectively and is followed by the nitrogen dioxide component that contributes 1.6 and
0.5 kg N ha- I yr1. Ammonium and nitrate particles contribute the least to deposition. For
the forests the amounts are 1 and 0.9 kg N ha-1 yr1 and for the grasslands they are 0.2 and
0.1 kg N ha-1 yr1. A strong seasonal variance in deposition amounts is apparent with
maximum deposition amounts occurring in Summer and minimum amounts in Winter.
Intermediate amounts are deposited in Autumn and Spring, with the latter season having
slightly larger deposition amounts. The seasonal variance is strongly linked to the
seasonal rainfall and cloud droplet deposition patterns. Biomass burning is indicated as a
possible important factor in influencing the chemical composition of rainfall during
Spring. Of the deposition amounts obtained in this study, the deposition from cloud
droplets is high compared to other studies and is probably overestimated. Further
research into this area is needed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/20112 |
| Date | 28 October 2003 |
| Creators | Lowman, Guy Russell Pollock |
| Publisher | University of the Witwatersrand |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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