Aspekte van die ekologiese toestand van die Mvotirivier in die Stanger-omgewing, KwaZulu-Natal

Abstract

Aspects of the ecological state of the Mvoti River in the Stanger area, KwaZulu-Natal Water is a scarce resource and if its quantity and quality are insufficient, it cannot provide the necessary goods and services to the various water consumers. Biomonitoring is used to determine the ecological state of water resources through the use of various biotic indices. The initiation of the River Health Programme (RHP) in South Africa has given sufficient momentum to biomonitoring of rivers in South Africa. The RHP has developed and refined various biomonitoring indices to assess the ecological state of ecosystem components. The Mvoti River, in the vicinity of Stanger, is subjected to extensive water abstraction, which is then utilised for irrigation, industrial use, urban water requirements and various domestic uses by informal settlements. Previous studies on the river indicated that it is in a severely degraded state, especially below the confluences of the Nchaweni and Mbozambo rivers. Thus, this assessment of the current ecological status of the Mvoti River was undertaken to possibly identify the main causes of the degraded state. The study was undertaken during the high (February) and low flow (August) periods in 2005. Selected monitoring sites included sites used in previous studies on the Mvoti River as well as sites on the Nchaweni and Mbozambo tributaries. The RHP methods were implemented in this study to determine the ecological state of the macroinvertebrate and fish communities. Habitat indices and water samples were also used to assess the state of the abiotic components. The habitat indices implemented in this study were the Habitat Quality Index (HQI) and Integrated Habitat Assessment System (IHAS). Physicochemical water analyses were done during each sampling period to assess the water quality. The biotic indices used included the South African Scoring System 5 (SASS5) index to assess the macro-invertebrate community and the Fish Assemblage Integrity Index (FAII) to assess the fish community. The lower Mvoti River contains very little habitat of good quality to support the biotic communities. The habitat is generally degraded due to the destruction of the riparian zone and the dominance of alien vegetation in the form of reeds. This, together with land-use and water abstraction activities, has caused high sediment loads in the lower Mvoti River which are continually moving. The results have shown that site MR1 is in an almost natural state with few modifications. The relative reference site, MR2, was, except for the fish community that showed various modifications, in good condition. The condition of the sites downstream decreased as the various activities around Stanger started to impact on the river. Site MR4 located directly below all activities surrounding Stanger was in a poor ecological state. The results of the Nchaweni and Mbozambo tributaries also indicated that the macroinvertebrate and fish communities are in a degraded condition due to the poor water quality in these systems. The main impact on the Mvoti River and its tributaries is the low habitat diversity together with the altered water quality associated with the multitude of activities in the Stanger area. Overall, the Mvoti River is in a seriously degraded state with even the reference site being subjected to impacts that could potentially be harmful to the ecosystem. The ecological state of the river decreases as it moves past Stanger and is subjected to the impacts from the Nchaweni and Mbozambo rivers in the form of nutrients and salinity concentrations. The impacts on the Mvoti River have a multitude of different sources and if the aquatic ecosystem is to improve, only a collective effort will be of any value