|
Water is an excellent solvent and transport
medium for particulates, and as such tends to become contaminated by
natural processes such as erosion and dissolution of salts
geologically present in soils, as well as by man-induced processes
and wastes (DWAF, 2002a). Water can become contaminated by a host of
substances,
including:
-
physical soil and clay particles and
organic detritus from storm
runoff;
-
micro-organisms;
-
chemical constituents (inorganic
chemical salts such as sodium, chlorides, ammonia or phosphates or
organic substances such as pesticide residues);
and
-
radioactive
substances.
High nitrate levels in drinking water are
dangerous to human health and cause algal growth and eutrophication
in waterways (CSD, 2001). By monitoring
the ratio of total inorganic nitrogen to
orthophosphate together with the absolute orthophosphate concentration, the potential for
eutrophication can be
determined.
 |
| Assessment of
Data |
In Mpumalanga there are numerous domestic
and industrial land use activities which contribute to surface water
contamination and include human settlements, acid mining and
agriculture. Surface water quality is assessed by measuring the
total inorganic nitrogen and orthophosphate concentrations and by
calculating the ration between them. The table below details the
Nitrogen:Phosphate ratio and orthophosphate concentrations for water
management areas in Mpumalanga in 1996, 2001 and 2002. These values
give a useful indication of the degree of change in the system with
a decrease in the ratio between total inorganic nitrogen and
orthophosphate implying a deterioration of the resource and an
increase indicating an improvement in the system.
|
WMA |
N:P Ratio |
|
|
Orthophosphate Conc
(mg/l) |
|
|
|
|
1996 |
2001 |
2002 |
1996 |
2001 |
2002 |
|
Inkomati |
12.0 |
9.9 |
5.6 |
0.017 |
0.023 |
0.025 |
|
Olifants |
12.8 |
7.5 |
6.4 |
0.015 |
0.019 |
0.022 |
|
Usutu to Mhlatuze |
11.8 |
8.4 |
5.5 |
0.017 |
0.028 |
0.024 |
|
Upper Vaal |
7.0 |
4.9 |
5.1 |
0.026 |
0.057 |
0.072 |
|
|
