In the Kruger National Park (KNP) there are five major rivers that historically flowed all year round - the Crocodile, the Sabie, the Olifants, the Letaba and the Luvuvhu. All of these rivers start far outside of the KNP, and as they enter the park they carry with them the pollutants of the developed world that lies beyond Kruger's western boundary.
In the past, due mainly to the demand for irrigation, all the rivers except the Sabie River became seasonal rivers, drying up in winter. About 15 years ago this changed, when the Kruger Rivers Research Program was started to try and save the Park's rivers. The program, together with the new environmentally friendly water act, started the rivers flowing year round again.
The health of Kruger's rivers depends not only on how much water enters the park, but also on what is contained in the water. To keep an eye on this, Kruger works together with the department of water affairs and forestry (Dwaf). Every two weeks Kruger rangers and Dwaf technicians collect water samples from at least two points in each major river, the first usually near where the river enters the park and the second about halfway through the river's course in Kruger.
Although the Shingwedzi River is not a perennial river, it is considered to be one of Kruger's major rivers and is also regularly sampled. Jacques Venter, a bio-technician based at Phalaborwa, is responsible for ensuring all the water samples taken get to the laboratory for analysis and for later compiling the results of the monitoring. The results of the water analyses are compared with Thresholds of Potential Concern (TPCs) that have been established for each river system to help Kruger's management.
From analysis of Kruger's water quality over the last three years, Jacques says that it is clear that the Luvuvhu River is definitely the cleanest in Kruger. "Even the Sabie River, upstream of KNP in the Hazyview area does not even come close to it." The Sabie River is still one of the cleanest rivers in the park, despite the fact that increasing development upstream is having an impact on the water quality. The quality of the Olifants River in terms of chemical pollutants, as opposed to silt, has also improved a lot in recent years.
This is partly due to water affairs clamping down on mines that used to discharge effluent in the river. In the Olifants, silt derived from overgrazing and other bad farming practises is now of more concern. In the Shingwedzi River, the quality of the water is strongly affected by the quality of the groundwater. The soils in the area leach salts into the groundwater, which then interacts with the water in the river, lowering the quality of the water despite the fact that there is little human impact on the river.
The major sources of pollution in the park's rivers are generally agriculture, mining and human habitation. Agriculture uses water, concentrating any pollutants in the water. It also adds pesticides and fertilisers to the water at times. However, some farmers also help river flows by working together with Dwaf and the park to stagger their irrigation times so that the river continues to flow in times of high demand.
Mining pollutants are now being far more strictly controlled through the national water act, and so there has been some improvement in the water quality in recent years. As towns outside of Kruger grow, they also contribute to the pollution of the rivers when for instance sewage is dumped into the river.
In many towns, sewage treatment plants have not kept up with the town's growth, leading to improperly treated sewage being dumped into the rivers. The health of a river is a complex issue, and the ongoing water monitoring allows Kruger's management to identify at what times of the year the rivers are most at risk.
It has also allowed park management to see the improvement in the Olifants River as the mines clean up their water, but the slow degradation of other rivers as increasing human activities outside the park impact the ecosystem.
Thresholds of Potential Concern are a tool that Kruger's managers use to help keep track of how the natural systems in the park are behaving, and whether or not human intervention is necessary to safeguard against harm to the environment. TPCs are part of the park's adaptive management strategy, or 'learning by doing'.
In the case of Kruger's rivers, a set of water quality guidelines has been established for each river, taking into account historical information on the cleanliness of the river and other impacts. Water tests measure things like electrical conductivity, pH, total number of dissolved solids and concentrations of elements such as nitrates, phosphates, calcium, magnesium and other ions.
For each river, the park's river specialists have decided on a specific value that shouldn't be exceeded. For example, pH measures how acid or alkaline the water is on a scale of one to 14, with values below seven showing acidity and values above seven showing alkalinity.
Pure water has a pH of seven, but obviously river water is not pure so the TPCs take this into account. A very acidic river is unlikely under natural conditions, and acidic conditions are more harmful to river life, so the lower threshold of potential concern for all of Kruger's rivers is set at a pH of 6.5.
As the river life is more tolerant of alkaline conditions, the upper threshold of concern is further from seven, and varies in the different rivers from 8.1 in the Sabie to 9.0 in the Olifants. So for the Olifants River, the TPCs for pH are 6.5 to 9.0 and warning bells go off to management if these thresholds are exceeded.
With all the water tests, if the test results produce a value that lies outside the TPCs, then Kruger management meets with the department of water affairs to try and improve the health of the river upstream by looking for sources of pollution. Jacques says that the water quality is strongly affected by the amount of water flowing in the river.
Generally, in dry years and in the winter months when flows are lower, a single pollution event upstream can have major impacts on the water quality readings. Although all of Kruger's rivers have different TPCs, the Sabie River is the shortest but has some of the strictest quality settings.
The Olifants River has some of the loosest water quality guidelines, but this is related to the fact that the Olifants is Kruger's longest and historically most impacted river as it has the most opportunity to gather pollutants upstream in the catchment.
By Melissa Wray and Jacques Venter