65
5 Eutrophication of Lakes
Fig. 5.7 Spatial distribution
of some of the environmental
variables in the Ibirité reservoir: a total nitrogen (µg l −1 ); b
chlorophyll a (µg l −1 ); c electrical
conductivity (mS cm −1 ); d total
dissolved solids (mg l −1 ); e turbidity (NTU); and f ratio of total
nitrogen to total phosphorus
Environmental variables
Oligotrophic
Mesotrophic
Eutrophic
Secchi disc (m)
2.34 ± 0.86
1.4 ± 0.7
0.47 ± 0.27
Water temperature (°C)
27.98 ± 3.65
25.9 ± 2.57
27.5 ± 3.65
pH
7.69 ± 0.44
8.13 ± 0.50
8.33 ± 0.98
Electrical conductivity (mS cm −1 )
26.34 ± 8.66
135.94 ± 27.36
280.50 ± 114. 46
Total dissolved solids (mg l −1 )
18.45 ± 5.21
91.68 ± 27.33
197.43 ± 70.64
Turbidity (NTU)
5.05 ± 10.29
15.48 ± 28.06
55.78 ± 66.71
Dissolved oxygen (mg l −1 )
7.72 ± 0.81
7.63 ± 1.16
7.00 ± 0.21
Chlorophyll a (µg l −1 )
2.05 ± 3.44
2.34 ± 2.21
53.65 ± 78.66
Total nitrogen (µg l −1 )
0.05 ± 0.04
0.22 ± 0.25
0.29 ± 0.21
Total phosphorus (mg l −1 )
23.16 ± 20.39
23.19 ± 20.41
171.71 ± 260.64
Orthophosphates (µg l −1 )
7.21 ± 5.12
7.90 ± 5.82
22.62 ± 86.78
The values represent the mean (±SD) of the 2-year sampling period
Table 5.1 Environmental
variables sampled in the
oligotrophic, mesotrophic,
and eutrophic reservoirs