| A detailed trend analysis
of 12 years of data (1988-2000) for 22 surface waters in acid-sensitive regions
of the United Kingdom, in which individual site data have
been combined to identify national-scale trends, has shown strong common
patterns of temporal variation. Results suggest a
widespread reduction in sulphate concentrations, hydrogen ion and inorganic
aluminium species, and increases in acid neutralising capacity.
Many chemical changes have not been linear. However, the first five years were
characterised by high concentrations of marine ions and
relatively stable pollutant sulphate concentrations and the remaining period by
lower concentrations of marine ions and declining sulphate. Genuine
"recovery", in terms of declining acidity in response to reduced
anthropogenic sulphur deposition is only apparent, therefore, for the latter
part of the monitoring period. Reductions in calcium concentrations appear to
have partially offset the influence of sulphate reductions on
acidity, as have increases in organic acidity associated with strong and
widespread rising trends in dissolved organic carbon. Fluctuations in
a number of climatic factors over the monitoring period have led to significant
inter-annual variability in nitrate, which exhibits little long-term trend,
marine ions and acidity, emphasising the need for long monitoring periods if
underlying trends are to be correctly identified.
Keywords: acidification, recovery, long-term trends, climate,
Dissolved Organic Carbon, United Kingdom Acid Waters Monitoring Network |