Index name

Aquatic Toxicity Index

Scientist who Developed Index: Name, Institute; Year; First Reference;

V. Wepener et al.; Research Unit for Aquatic and Terrestrial Ecosystems, Department of Zoology, Rand Afrikaans University; 1992; Wepener, V., et al., 1992. The development of an aquatic toxicity index as a tool in the operational management of water quality in the Olifants River (Kruger National Park). Koedoe 35(2): 1-9.

Abstract (Summary):

The development of an Aquatic Toxicity Index and its application is described. In this index the protection of auatc life is always referred to in terms of toxic effects of different water quality variables to fish, as health indicators of the auatic ecosystem. The final index score is prodeced by means of standard additive techniques as well as by using the water quality variable giving the lowest index score (minimum operator). The minimum operator is employed in order not to conceal important water quality information. The auatic toxicity index development has been linked to toxicological data, internationa water qaulity standards and South African guidelines. The index provides valuable information concerning toxic effects of a specific variable on fish should the threshhold level for normal maintanence of awuatic life be exceeded. This index is intended as an aid in the interpretaion of water quality information in order to facilitate management decisions.

Keywords: Water quality, developmewnt, Aquatic Toxicity Index, environment mangement, Olifants River, Kruger National Park

Introduction

Aquatic Toxicity Index

By Virtue of its position on the eastern border of South Africa, Kruger National Park receives the flow of six main rivers, each of which has different proportions from the specific catchment in the park itself. The Olifants river has the largest catchment area both in size and proportions of catchment area beyond the park boundaries (Walmsley & Davies 1991). The increased competing demand for water by the urban, industrial, mining and agricultural sectors within the catchment boundaries of the Olifants River has focused on the ecological water requirements of the river.

When one considered the demand for water by the Kruger National Park it is evident that water is required for more than one use, i.e. for portable use game watering and ecosystem (equatic and riparian) maintenance (Moore 1990b). In order to facilitate proper water quality management it is necessary to develop a comprehensive water quality management plan for the river. According to vender Merwe & Grobler (1990) the development of such a plan requires a through understanding of the fate and effects of pollutants in the environment. It is further more important to have reliable information on the trends and status of important water quality determinants in these systems.

In the field of water management, scientists, and managers are often confronted with a large array of data which can be totally overwhelming. in order to convey the interpretation of the data in a simplified manner, a set of number or a single number may be devised to integrate the data pool (Smith 1990). This number is known as a water quality index. The use of a water quality index (WQI) would make it possible to bridge the gap between the extremes of water quality index (WQI) monitoring and reporting(House 1989).

Classification and zoning of rivers from an integral part of water pollution control Programmers (Bhargava 1983). A river may be classified into various grades indicating the beneficial use(s) to which it may be put. The grades are based on permissible limits or guidelines of the relevant water quality set by the various authorities. Depending on the quality of water in the river, it can be zoned according to its suitability for specific beneficial use (e.g. maintenance of the aquatic ecosystem).

It is the purpose of this paper to provide the theoretical basis underlying the development of a WQI, or more specially, an aquatic toxicity index intended for the use as a tool in the operational management of the water quality in the Olifants river within the Kruger National Park Boundaries. With the development of such a WQI emphasis was placed on the development an index reflecting the toxicological effects of selected water quality variable on aquatic environment. An aquatic toxicity index (ATI) was therefore develop to reflect the effect of water quality on a specific water use i.e. the aquatic environment.

Uses and Limitation:

It provides valuable information on toxic effects of a specific variables on fish of aquatic body and interpret the water quality in order to facilitate management decisions.

Categorization Table

Table 1 Descriptor word and ATI numerical ranges

Standards Required

No standards required for this index calculation process.

Variables Selection

This index includes 14 variables:

pH
Turbidity
DO
TDS
Pb

PO₄^3-
F^–
NH₄⁺
Ni
Cr

Cu
Zn
Mn
K⁺

Calculation of Aquatic Toxicity Index:

ATI is calculated by the aggregation of sub-index values (q_i)

\(\)

\begin{eqnarray*}
ATI =\frac{1}{100} \Bigg( \sum_{i=1}^{n} \ q^i \Bigg)^2
\end{eqnarray*}

where, q_i is the subindex value of the i^th parameter, n is the number of parameters

Case Studies based on Aquatic Toxicity Index

The ATI method is applied to the data of Olifant River (Kruger National park), South Africa. The was collected at Mambaweir (Department of water affairs sampling site number B7M15) in October 1991 during a bimonthly sampling trip.

References

Wepener, V., et al., 1992. The development of an aquatic toxicity index as a tool in the operational management of water quality in the Olifants River (Kruger National Park). Koedoe 35(2): 1-9.