Fig. 3. Variation of Fe and Ni contents in surface water and
column water of the J. A. Alzate Reservoir. The water selfcleaning
capacity for iron concentration is clearly shown by
the decreasing values from the entrance of the reservoir down
to the dam. The nickel concentration of some sampling sites
were below the detection limit of the evaluation technique.
collected at the beginning of the rainy season,
and the fourth and fifth ones were obtained when
the Alzate Reservoir water level had considerably
increased. The volume enlargement is shown by
the depth data, varying from 0.4 to 8.3 m producing
a total metal dilution.
3.2. Sediment metal concentrations
Table 4 shows the average concentrations of
iron, zinc, chromium, copper, nickel, lead and
cadmium in the Alzate Reservoir sediments for
all sampling sites for all campaigns. In general,
the heavy metal concentrations of the sediments
were found to decrease in the sequence: Fe)Zn
) Cr ) Cu ) Ni ) Pb ) Cd. According to
Kruskal]Wallis proof see Table 4. there are no
statistical differences in the concentration of
chromium, iron and cadmium among the different
sampling zones, suggesting a uniform distribution
of those heavy metals in sediments and a
similar precipitation behaviour Tipping et al.,
1993; Droppo and Stone, 1994; Stone and Walling