Comment on ‘the acidity problem — An outline of concepts’ by S. Oden

Conclusions

A numerical study of the 10 yr data does not support the view that the rates of decline of pH in the second 5 yr are the same as in the previous 5 yr as stated by Professor Oden. Neither does it support the view that the pH will continue to decline unless it is asserted that the discontinuity which was postulated to have occurred in 1969/70 will not recur. If the discontinuity does recur it need appear only once in 5 to 20 yr to keep Lake Vättern or Österdalälven near to neutrality and in a period between 1 and oo years for Klaralven, according to which 5 yr period is taken as evidence. The data give no statistically useful evidence of the repetition period but is not inconsistent with a repetition period of 6 yr. If the analysis is not, based on the assumption that a discontinuity is present, it supports an increase in pH with time better than a decrease.

The first 5 yr data could be interpreted as forecasting a continuous decline in pH. The 10 yr data cannot be interpreted as in any way giving cause for alarm. It does in fact give evidence that there can be both slow or rapid increases of pH from year to year so that the postulate of continuing decline in pH cannot be sustained. The variability of the results obtained using the different methods of analysis suggests that no valid extrapolation can be made. The most reasonable postulate at present is that the pH is stationary with considerable statistical fluctuations from year to year.

It is of interest to speculate what would have happened if the present analysis had been available for the Swedish Case Study in 1971.