The Rio Mucajaí in the Homoxi region is a relatively small river, rarely more than 8-10m wide, with abundant meanders. At the time of the survey (at the beginning of the rainy season) it was generally about 1m in depth with a light sediment load. After very heavy rainstorms this rose to a depth of about 2m and the sediment load increased. The river is fed by a network of streams of varying sizes emerging from the surrounding hills. There are a few small natural (oxbow) lakes along its course.
As a result of the gold-mining activities there are now large numbers of man-made lagoons in the valley. These lagoons (whose depth was not determined) vary in size from 10-30m in diameter (in some cases larger), with varying water quality. In some cases these become flooded by adjacent streams or by the Rio Mucajaí itself after heavy rains, suggesting a periodic through-flow of water. In other cases the lagoons are permanently isolated. Some of these isolated lagoons have discoloured water varying from brown to reddish. Most of the lagoons occur among the heavily worked gravel areas in the main Mucajaí valley, but some are in areas of forest alongside the smaller streams. The Yanomami distinguish two types of lagoons: oru pëka uxi (black gold hole) and oru pëka wakë (red gold hole).
According to the Yanomami the behaviour of the river has been altered by the mining activities. Its course has become narrower and straighter in the heavily worked regions, and areas that used to become flooded when it burst its banks during the rainy season (which peaks in July) are now permanently dry.[1] This is primarily due to the gravel banks that have been created along its margins, which can be up to 4m in height.
Table 1: Physical and chemical characteristics of waters in the Homoxi area
|
h |
Location |
pH |
Conductivity |
Alkalinity |
Hardness |
Turbidity |
|
|
|
mS/cm |
mg/L |
NTU |
||
|
|
Lagoons |
|
||||
|
1 |
Behind Tirei maloca |
5.76 |
58.0 |
35.2 |
25.0 |
20.0 |
|
2 |
Beside Mucajaí near Post |
5.40 |
53.6 |
34.1 |
17.5 |
16.0 |
|
3 |
R bank of Mucajaí close to forest |
5.66 |
37.3 |
29.7 |
10.0 |
3.5 |
|
4 |
R bank of Mucajaí close to banana garden |
5.10 |
34.1 |
26.4 |
12.5 |
6.5 |
|
5 |
East end of Homoxi airstrip (left side) |
5.40 |
32.7 |
28.2 |
17.5 |
7.5 |
|
6 |
East end of Homoxi airstrip (right side) |
5.61 |
34.0 |
22.0 |
10.0 |
9.5 |
|
7 |
Mining area close to the river near the Post |
5.23 |
33.8 |
46.2 |
22.5 |
15.0 |
|
8 |
Mining area close to the river near the Post |
5.01 |
59.8 |
31.9 |
22.5 |
1.5 |
|
9 |
Mining area close to the river near the Post |
4.33 |
21.9 |
8.8 |
20.0 |
15.0 |
|
10 |
Mining area close to the river near the Post |
5.64 |
31.2 |
24.2 |
17.5 |
11.0 |
|
11 |
Baiano
Formiga airstrip |
5.92 |
45.4 |
31.9 |
22.5 |
15.0 |
|
12 |
Between Homoxi and Chimarão airstrips |
5.77 |
41.3 |
27.5 |
17.5 |
3.0 |
|
13 |
Between Homoxi and Chimarão airstrips |
5.40 |
27.5 |
19.8 |
30.0 |
9.5 |
|
14 |
Between Homoxi and Chimarão airstrips |
5.78 |
33.1 |
23.1 |
7.5 |
8.0 |
|
|
Rivers |
|
|
|
|
|
|
15 |
Rio Mucajaí |
5.52 |
31.7 |
23.1 |
22.5 |
15.0 |
The above table presents some of the physical and chemical
characteristics of the waters of the man-made lagoons and the Rio Mucajaí at
Homoxi. The alkalinity and hardness
levels show the waters to be slightly hard (containing calcium and magnesium),
which is normal for the water in this region.
The pH values are slightly acidic (4.33 to 5.92) and the conductivity
varies from 21.9 to 59.8 mS/cm. Although the pH values are within the
variation cited by Sioli (1968) for Amazonian waters, the conductivity is much
higher than his – being closer to those found by Ruivo and Sales (1989) in
mining areas in the State of Pará.
[1] During flooding the fish could apparently be found in the flooded forest areas, where there was abundant food for them.