A multitude of factors determine the health of a river ecosystem: its geomorphological characteristics, hydrological and hydraulic regimes, chemical and physical water quality, and the nature of in-stream and riparian habitats. It is impractical to monitor each of these factors in detail. Therefore, the RHP focuses on selected ecological indicators that are representative of the larger ecosystem and are practical to measure. Since resident aquatic communities reflect the effects of chemical and physical impacts in a time-integrated manner, they are regarded as good indicators of overall ecological integrity.

For the purpose of disseminating results of the RHP, the information resulting from monitoring aquatic community components should be simplified to a point where it can be of use to resource managers, conservationists and the general public. This can be done with a biological index that integrates and summarises biological data within a particular indicator group. Appropriate indicators, for example selected fish community attributes, need to be tested and justified, and linked to measuring units (metrics) that can be used to index ecological condition. In this context, biological indices are used to quantify the condition or health of aquatic ecosystems and the output format is usually numeric.

While biological indicators and indices are the main focus of the RHP, the development and inclusion of indices of physical and chemical indicators are encouraged to increase the information value of the programme.

Aquatic Invertebrate Fauna

A variety of invertebrate organisms (e.g. snails, crabs, worms, insect larvae, mussels, beetles) require specific habitat types and conditions for at least part of their life cycles. Changes in the structure of aquatic invertebrate communities are a sign of changes in overall river conditions. As most invertebrate species are fairly short-lived and remain in one area during their aquatic life phase, they are particularly good indicators of localised conditions in a river over the short term.

The South African Scoring System (SASS) is the biological index used for assessing aquatic invertebrate fauna. This index is based on the presence of families of aquatic invertebrates and their perceived sensitivity to water quality changes (Chutter, 1998). SASS has been tested and is used widely in South Africa as a biological index of water quality (e.g. Dallas, 1997). SASS results are expressed both as an index score (SASS score) and the average score per recorded taxon (ASPT value).

Fish

Fish, being relatively long-lived and mobile, are good indicators of long-term influences on a river reach and the general habitat conditions within the reach. The numbers of species of fish that occur in a specific reach, as well as factors such as different size classes and the presence of parasites on the fish, can be used as indicators of river health.

The Fish Assemblage Integrity Index (FAII) is based on a categorisation of a fish community according to an intolerance rating which takes into account trophic preference and specialisation, requirement for flowing water during different life-stages, and association with habitats with unmodified water quality. Results of the FAII are expressed as a ratio of observed conditions versus conditions that would have been expected in the absence of human impacts. Although this index has been applied and published (Kleynhans, 1999), it is being further developed and refined under leadership of Dr Neels Kleynhans of DWAF: RQS.

The Scoring Guidelines for FAII are the guidelines which were used to rate various attributes of South African freshwater fish species. The tables in the guideline document are the result of the expert knowledge inputs from a range of people that were obtained during 2001.

Riparian Vegetation

Healthy riparian zones maintain channel form and serve as filters for light, nutrients and sediment. Changes in the structure and function of riparian vegetation commonly result from changes in the flow regime of a river, exploitation for firewood, or use of the riparian zone for grazing or ploughing.

Nigel Kemper of IWR Environmental has developed a first prototype of the Riparian Vegetation Index (RVI). The RVI determines the status of riparian vegetation within river segments based on the qualitative assessment of a number of criteria in the riparian zone. These criteria are vegetation removal, cultivation, construction, inundation, erosion/sedimentation and exotic species. The output is expressed as percentage deviation from natural or unmodified riparian conditions.

River Habitats

Loss of habitats is regarded as the single most important factor that has contributed towards the extinction of species in the last century. The destruction of a particular type of habitat will result in the disappearance of certain species. Examples of river habitat types are pools, rapids, sandbanks, stones on the riverbed, and vegetation fringing the water’s edges.
As the availability and diversity of habitat are major determinants of whether a given system is acceptable to a specific suite of biota or not, knowledge of the availability and quality of habitats is very important in an overall assessment of ecosystem health.

Dr Neels Kleynhans of the RQS developed the Index of Habitat Integrity (IHI) (Kleynhans, 1996). The IHI is used to assess the impact of major disturbance factors such as water abstraction, flow regulation, bed and channel modification, removal of indigenous riparian vegetation, and encroachment by exotic vegetation.