Atmospheric nutrient deposition to the west coast of South Africa

- Low rates of N deposition compared to industrial locations.
- Dissolved organic forms of N and P dominate fluxes of these two elements.
- Sodium and Mg fluxes originate from ocean sources and are large.
- Dust inputs of some nutrients, including K, may be important at this site in winter.
- Marine aerosols and mineral dust are important sources of nutrients in deposition.

Atmospheric deposition is an important source of nutrients to many ecosystems, but is of particular importance to plant nutrition in areas where nutrients are scarce. Nutrient containing aerosols enter the atmosphere through industrial and agricultural activities, wildfires, and the production of terrigenous and marine aerosols. In this study, we collected bulk rain precipitation along the Atlantic coast of South Africa in a coastal “strandveld” vegetation region. This region is relatively remote from significant anthropogenic influences and is downwind of a highly productive and stormy portion of the Atlantic. Samples were collected over 12 months at sites along a 17 km downwind transect from the shoreline and analyzed for N, P, Na, Ca, Mg and K. Annual total N and total P fluxes of 4.8 kg ha−1 yr−1 and 0.16 kg ha−1 yr−1 are low compared to global averages. In contrast, fluxes of Na were 88.7 kg ha−1 yr−1, 16.2 kg ha−1 yr−1 for Ca, 12.1 kg ha−1 yr−1 for Mg and 5.2 kg ha−1 yr−1 for K; rates that are higher than most other measurements elsewhere in the world. Dissolved organic N represented ca. 71% of the N flux while 43% of the P flux was in the form of soluble reactive P (SRP). These results combined with the high fluxes of Na and Mg strongly suggest that marine aerosols are important contributors to nutrient deposition at this site.