REGIONAL DIFFERENCES IN THE RELATION BETWEEN MONTHLY PRECIPITATION AND BULK CONCENTRATION IN FRANCE (RENECOFOR)

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Abstract

Bulk precipitation was sampled weekly from 1993 to 1994 at 27 sites, covering the whole country. In this paper the relations between decreasing concentrations of 4-weekly mean weighted samples with increasing 4-weekly precipitation are studied using two types of equations: (i) y = a + b/x; (ii) y + 1 = axb, where y = concentration of an ion and x = 4-weekly precipitation quantity. Relationships were studied for the major ions. H+ did not show any relationship with the rainfall amount. From the 216 regressions (27 sites × 8 ions) for all the other ions, 55.6% showed a good fit (r equal or above 0.6) and 16.2% a very good fit (r equal or above 0.85). Good fits were found for 85% of the regressions for N-NO3−, 81% for S-SO42−, 63% for Ca2+, 59% for K+, 55% for N-NH4+, 37% for Mg2+, 33% for Cl− and 29% for Na+. The comparison between sites for the same ions showed: (i) the ranking of the sites after the regressions from lower to higher concentration levels does not necessarily correspond to the ranking of the sites bi-annual mean weighted concentrations; (ii) sites showed similar behaviour for certain ions for which an explanation could be found, based on local or regional emission characteristics or air mass influences, and for others this was not possible; (iii) for certain ions and pairs of sites, comparable annual precipitation led to comparable behaviour, for others precipitation was not an explanatory factor at all, (iv) local and regional influences seem to have a much greater impact on decreasing concentrations than the gradient from the Atlantic coast to the eastern French border.

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