Transport of Trace Metals by the Rainwater Runoff in the Urban Catchment of Guwahati, India - Management of Natural Resources in a Changing Environment - page 219

In location N, the pH spread from 5.4 to 7.5 with a mean value of 6.3. The fi rst
two events at this location showed decreasing diurnal trend while the third event
showed no distinct trend. All the runoff samples, excepting N8, had pH >5.6 i.e. pH
of natural rainwater. It indicates that the rainwater after falling on soil received some
alkaline contamination from the soil.
Similar unpredictable behaviour in diurnal variations in pH was also seen in the
location K where the values were in the range of 5.7-7.8 with a mean 6.95. All the
samples had pH greater than that of natural rainwater (5.6).
Location R had pH from 6.4-7.6 with a mean value 6.98. The pH showed a con-
tinuous increase with time in the third event, the fi rst event showed no specifi c trend
and the second event showed a decreasing trend. All the events in this location had
alkaline contamination after the rainwater fl owed over the land surfaces. This area
is covered with high traffi c volume and the alkaline contaminants might be related
to vehicular emissions and other traffi c wastes that might contain calcium or mag-
nesium (positive correlation) carbonate/bicarbonate.
For the location M and U, all the events showed decreasing diurnal trend in
pH. The decrease in pH of the runoff with time might be due to leaching of
acidic elements such as Al and Fe from the soil that replaced Ca and Mg in the
runoff.
Location Z had the pH value spread in a small range from 7.0 to 7.9. Here the two
events showed no general trend for pH values. This location had the highest mean
pH (7.4) attributable to the alkaline contamination from vehicular emission, human
wastes and other anthropogenic activities.
The basic statistics of pH for the seven locations are shown in Fig. 3 . The pH of
water affects the solubility of many toxic and nutritive chemicals and the availability

Min Max Mean

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

J N K MR U Z

Sampling Site

Fig. 3 Basic statistics in pH of the seven runoff locations