Transport of Trace Metals by the Rainwater Runoff in the Urban Catchment of Guwahati, India - Management of Natural Resources in a Changing Environment - page 223

experiments (McDowell 2010 ) using simulated rainfall to generate surface runoff
indicated that the major form of Cd lost was dissolved (average 65 %, <0.45 m)

and could be predicted by water extraction of the soil. Cadmium in soil tends to be
more available when the soil pH is low (acidic) (Elinder 1992 ). It has been found
that cadmium concentration in water is inversely related to the pH and the concen-
tration of organic material in the water.

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Cobalt

Co in the rainwater runoff was distributed from 0.020 mg/L (N5 and U1) to
0.895 mg/L (J13). The minimum, maximum and mean Co contents are shown in
Fig. 5 . Location J possessed the maximum value of cobalt (0.895 mg/L) as well as
the highest mean value (0.385) and location N and U had the minimum value
(0.020 mg/L).
The location J had decreasing diurnal trends of Co in I and III events, increasing
trend in II and V events and the other three events had no distinct trends. For loca-
tion N, increasing trend was found for event I, decreasing trend for event II and no
specifi c diurnal trend for event III.
For location K, Co increased diurnally for event I, while the event II had both
increasing and decreasing trends and no specifi c trend for the event III. In location
M, event I had a decreasing trend while no specifi c diurnal trend could be observed
for the events II and III. In location R decreasing trend was found for the event II
and the events I and III had no specifi c trend. In the location U, increasing trend was
shown by event I in straight line and the event II showed the decreasing trend and
the rest event showed no distinct trend. In the location Z, increasing trend was seen
in event I and no distinct trend were seen in the event II.
The cobalt concentration in the runoff was found to be inversely correlated to the
pH for the locations J, N, R, U and Z. Such type of result was also obtained by
Moore ( 1991 ).

Min Max Mean

0.9

0.6

0.3

0

J N K MR U Z

Runoff Sampling Location

Fig. 5 Basic statistics of cobalt for seven runoff locations