The Contribution of Occult Precipitation to Nutrient Deposition on the West Coast of South Africa

The Strandveld mediterranean-ecosystem of the west coast of South Africa supports floristically diverse vegetation growing on mostly nutrient-poor aeolian sands and extending from the Atlantic Ocean tens of kilometers inland. The cold Benguela current upwelling interacts with warm onshore southerly winds in summer causing coastal fogs in this region. We hypothesized that fog and other forms of occult precipitation contribute moisture and nutrients to the vegetation. We measured occult precipitation over one year along a transect running inland in the direction of the prevailing wind and compared the nutrient concentrations with those in rainwater. Occult deposition rates of P, N, K, Mg, Ca, Na, Al and Fe all decreased with distance from the ocean. Furthermore, ratios of cations to Na were similar to those of seawater, suggesting a marine origin for these. In contrast, N and P ratios in occult precipitation were higher than in seawater. We speculate that this is due to marine foam contributing to occult precipitation. Nutrient loss in leaf litter from dominant shrub species was measured to indicate nutrient demand. We estimated that occult precipitation could meet the demand of the dominant shrubby species for annual N, P, K and Ca. Of these species, those with small leaves intercepted more moisture and nutrients than those with larger leaves and could take up foliar deposits of glycine, NO3-, NH4 + and Li (as tracer for K) through leaf surfaces. We conclude that occult deposition together with rainfall deposition are potentially important nutrient and moisture sources for the Strandveld vegetation that contribute to this vegetation being floristically distinct from neighbouring nutrient-poor Fynbos vegetation

Chemical characterization of fog and rain water collected at the eastern Andes cordillera

During a three month period in 2003 and 2004, the chemistry of fog and rainwater were studied at the 'El Tiro' site in a tropical mountain forest ecosystem in Ecuador, South America. The fogwater samples were collected using a passive fog collector, and for the rain water, a standard rain sampler was employed. For all samples, electric conductivity, pH, and the concentrations of NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^&minus;, NO₃^&minus;, PO₄^3&minus;, and SO₄^2&minus; were measured. For each fog sample, a 5 day back trajectory was calculated by the use of the HYSPLIT model. Two types of trajectories occurred. One type was characterized by advection of air masses from the East over the Amazonian basin, the other trajectory arrived one from the West after significant travel time over the Pacific Ocean. <P style='line-height: 20px;'> We found considerably higher ion concentrations in fogwater samples than in rain samples. Median pH values are 4.58 for fog water, and 5.26 for the rain samples, respectively. The median electric conductivity was 23 &mu;S cm^&minus;1 for the fog and 6 &mu;S cm^&minus;1 for the rain. The continent samples exhibit higher concentrations of most ions as compared to the pacific samples, but these differences could not be detected statistically

Ion fluxes from fog and rain to an agricultural and a forest ecosystem in Europe

The deposition fluxes of inorganic compounds dissolved in fog and rain were quantified for two different ecosystems in Europe. The fogwater deposition fluxes were measured by employing the eddy covariance method. The site in Switzerland that lies within an agricultural area surrounded by the Jura mountains and the Alps is often exposed to radiation fog. At the German mountain forest ecosystem, on the other hand, advection fog occurs most frequently. At the Swiss site, fogwater deposition fluxes of the dominant components SO 4 # (0.027 mg S m # ), NO 3 # (0.030 mg N m # ) and NH 4 (0.060 mg Nm # ) were estimated to be &lt; 5% of the measured wet deposition (0.85, 0.70 and 1.34 mgm # , respectively). The corresponding fluxes at the forest site (0.62, 0.82 and 1.16 , respectively) were of the same order of magnitude as wet deposition (1.04, 1.01 and 1.36 mg m # ), illustrating the importance of fog (or occult) deposition. Trajectory analyses at the forest site indicate significantly higher fogwater concentrations of all major ions if air originated from the east (i.e. the Czech Republic), which is in close agreement with earlier studies

Vertical Divergence of Fogwater Fluxes

Two almost identical eddy covariance measurement setups were used to measure the fogwater fluxes to a forest ecosystem in the &quot;Fichtelgebirge&quot; mountains (Waldstein research site, 786 m a.s.l.) in Germany. During the first experiment, an intercomparison was carried out with both setups running simultaneously at the same measuring height on a meteorological tower, 12.5 m above the forest canopy. The results confirmed a close agreement of the turbulent fluxes between the two setups, and allowed to intercalibrate liquid water content (LWC) and gravitational fluxes. During the second experiment, the setups were mounted at a height of 12.5 and 3 m above the canopy, respectively. For the 22 fog events, a persistent negative flux divergence was observed with a greater downward flux at the upper level. To extrapolate the turbulent liquid water fluxes measured at height z to the canopy of height h c , a conversion factor 1/[1 + 0.116(z h c )] was determined. For the fluxes of nonvolatile ions, no such correction is necessary since the net evaporation of the fog droplets appears to be the primary cause of the vertical flux divergence. Although the net evaporation reduces the liquid water flux reaching the canopy, it is not expected to change the absolute amount of ions dissolved in fogwater

Analysis of nitrophenols in cloud water with a miniaturized light-phase rotary perforator and HPLC-MS

An all-glass miniaturized light-phase rotary perforator for the enrichment of polar compounds has been modified/miniaturized and applied. Its application is demonstrated here for the analysis of nitrophenols and dinitrophenols from low-concentration/low-volume samples. For the method development of high-performance liquid chromatography-mass spectrometry (MS) four eluents were tested: (1) water-methanol, (2) acetic acid-methanol, (3) trifluoroacetic acid-methanol and (4) water-acetonitrile. The last eluent mentioned was used for the subsequent investigation of samples from field experiments. Detection limits varied between 1 ng and 50 pg. The relative standard deviation in repeated measurements was below 15%, corresponding to a good reproducibility. Recoveries ranged between 31 and 100%, showing a significant dependence on the extraction time and the final volume of the sample after evaporation. Quantification was carried out by using deuterated 4-nitrophenol and 2,4-dinitrophenol as standards and applying previously determined response factors. Structure determination of further substances under atmospheric pressure chemical ionization was performed by a first screening with a source collision-induced dissociation, followed by the definite analysis by MS( n ). The first results are shown for cloud water, fog water and rainwater samples from different locations