The effect of the tropical cloud (fog) forest on the spatial distribution of cesium-137 in soils in the Henri Pittier National Park (Edo. Aragua, Venezuela)

Soils were collected at different elevations (m.a.s.l.) near the two roadways, that pass through the Henri Pittier National Park (Edo. Aragua, Venezuela) in order to determine the distribution of the concentrations of the ¹³⁷Cs fallout and its relation to the tropical cloud forest. Duplicate samples were taken at most elevations between 2–5 cm below the soil surface to confirm that the samples were representative of the area. In many cases, it was difficult or impossible to locate areas that were undisturbed by man or nature. The ¹³⁷Cs (Bq/kg) content was determined by conventional high resolution gamma ray spectroscopy employing a standard comparison method. The background of the ¹³⁷Cs fallout in soils, below the cloud (fog) baseline was calculated to be about 5 Bq/kg on both the south (land) side and north (ocean) side for both roadways. The concentrations of ¹³⁷Cs (Bq/kg) were between 2–3 times higher at the baseline of the cloud (fog) on both sides of the mountain range. The ¹³⁷Cs values at the highest elevations (1105 and 1625 m.a.s.l.) near the roadways were about 5–6 times higher than the determined background levels. Our estimates of the baseline of the cloud (fog) are in good agreement with other visual observations. Finally, we have concluded that the distribution of ¹³⁷Cs in soils in cloud forests can be employed to estimate the baseline and the concentrations of ¹³⁷Cs fallout can be related to the relative density of the cloud (fog) when it was deposited.