Regional and Seasonal Variations of Parameters to Estimate Total Solutes Concentration in Precipitation from pH and Conductivity

In order to expand the applicability of the measurement results of the pH and electrical conductivity of precipitations obtained as a part of environmental education activities, we studied the regional and seasonal variations of the parameters to estimate the dissolved total anions ([An]) and cations ([Cat]) excluding H+, from the pH-values and conductivities. The studied parameters were the concentration-weighted conductivities (λ av-cat) of the major cations (Na+, K+, Ca2+, Mg2+ and NH4+) in precipitation on equivalent bases, and the concentration-weighted conductivities (λ av-an) of major anions (SO42−, NO3− and Cl−). Relatively small regional and seasonal variations were observed in λ av-an; however, remarkable variations were observed in λ av-cat, corresponding to the ionic composition ratios of NH4+ and Na+. Lower λ av-cat values were obtained in the regions and season in which strong influence by sea salt was observed. This may have come from the regional and seasonal fluctuations of the ionic composition ratios of NH4+ and Na+; there is a large difference between these two ion spices in equivalent conductivities. The annual variations of λ av-cat and λ av-an were estimated to be about 3 percent and 0.5 percent, respectively. This method was applied to daily collected precipitations at the Niigata-Maki national monitoring station. We evaluated the estimated errors between the measured and calculated [Cat] and [An] using 3-year averaged λ av-cat and λ av-an for warm and cold seasons separately. Roughly, the monthly, seasonal (warm and cold) and annual average [Cat] and [An] can be estimated within estimation errors of 15 percent from each averaged pH-value and conductivity.