A study on the pH and conductivity of rural rainfall employing two collocated samplers

Abstract

A set of about 100 daily rainfall samples were collected over a period of about one year during the 1995-1996 period using two collocated, automated samplers placed ~4 m apart at the rural Kadoorie Agricultural Research Centre (KARC) in Hong Kong. The pH and conductivity of the rainwater were measured immediately after sample collection. There is a strong correlation between the two free hydrogen ion concentrations (R2 ≃ 0.92) and an even stronger one between the conductivities (R2 ≃ 0.99). Statistically, there is no difference at the 0.05 level of significance between the means of either the two free hydrogen ion concentrations or the two conductivities. The conductivity results suggest that the total dissolved solids in the two samplers is probably quite similar in magnitude. No relationship is observed between thee free acid content and daily rainfall Volume in either sampler, a result similar to that obtained in previous studies involving bulk fall at the KARC and wet fall in urban Hong Kong as a whole. A weak hyperbolic relationship exists between the rainfall volume and the conductivity, and their log-log plot indicates only a somewhat weak inverse linear relationship, with correlation coefficients of -0.60 and -0.61 for the two samplers, considered individually. Finally, the unbiased estimates of the product of rainfall volume and conductivity for the collocated samples suggest that the microscale variability (≥4 m) of the mean wet mass flux of total dissolved material in rural Hong Kong rainfall is negligible.