Assessment of river health using in situ water quality parameters and miniass protocol in the Marico and Crocodile rivers, North West Province, South Africa

Abstract

Freshwater resources in South Africa are limited and scarce, which is mainly attributed to the country’s varying climate resulting in predominantly desert to semi-desert conditions. Among the freshwater resources, groundwater is by far the most abundant and readily available source of water; followed by lakes, reservoirs and the rivers that provide a vital connection and access to freshwater. The Crocodile and Marico rivers are the two main rivers in the Crocodile (West) Marico Water Management Area (WMA) which primarily lies within the North West Province. Rivers have undergone varying degrees of mild to severe alteration or deterioration due to anthropogenic impacts. Groot Marico River catchment in the North West Province has for centuries been a highly desirable tract of land for human settlement purposes; whereas the Crocodile River is one of the most adversely affected rivers in South Africa. The River Health Programme (RHP) data on both the Marico and Crocodile rivers are outdated and the exclusive use of physic-chemical water quality parameters (which provide direct evidence of water quality) only represents the prevailing water quality at the time of sampling rather than a long-term indication of the river health. The continuous monitoring and associated protection of aquatic ecosystem condition or ‘health’ is important in maintaining rivers ecosystem services. The current study was to determine the current condition of the Marico and Crocodile rivers based on the mini-SASS biomonitoring tool in correlation with the selected water quality parameters in an attempt to provide a holistic assessment of the rivers and to contribute to the continuous river health monitoring. This was achieved by assessing the selected water quality parameters at various sites of the Marico and Crocodile Rivers in North West Province, in conjunction with the use on benthic macroinvertebrates in the mini-SASS biomonitoring tool. The physico-chemical water quality parameters proved effective in differentiating the seasonal temporal conditions of both the Marico and Crocodile rivers. The Marico River’s aquatic habitats are generally in good condition, but are slowly becoming affected by agricultural return flows and the abstraction of water from the main stream. Given that irrigated and dryland agriculture, urban and mining dominate catchment land uses, the DO and temperature levels recorded in this study indicate that the Crocodile river are under severe stress and may potentially be on the verge of collapse. This was evident in the overall mini-SASS scores indicated in this study whereby the Crocodile River can be classified as very poor condition (critically modified – purple) with scores of <4.8 and <5.3 for sandy and rocky aquatic habitats, respectively.