Seasonal variations of water and sediment quality parameters in endorheic reed pans on the Mpumalanga Highveld

J Chamier,V Wepener,AR De Klerk,LP De Klerk

doi:10.4314/wsa.v38i5.3

Abstract

The Mpumalanga Lakes District consists of approximately 320 pans, of which less than 3% are classified as reed pans. There is limited information available on reed pans and as a result they are at risk of various anthropogenic activities, for example mining and agriculture. Four reed pans were selected and assessed to determine seasonal trends of a variety of water and sediment quality parameters. The study took place over one seasonal cycle from 2008–2009; samples were collected seasonally to account for various hydrological extremes. Water samples were collected and their nutrient and chlorophyll a concentrations were determined, while various other water quality parameters were measured in situ. Sediment samples were analysed for physical and chemical properties, namely, grain size and organic carbon content. The seasonal changes in concentrations of As, Cr, Cu, Fe, Pb, Mn, Mo, Ni, Se, Sr, U and Zn were also analysed within the surface water and sediment. Increased nutrient concentrations within the water were evident during spring and summer at some of the sites, which influenced other water quality variables, e.g., dissolved oxygen and pH. Seasonal trends in metal concentrations were influenced by the prevailing environmental conditions (e.g., rainfall) experienced at the selected sites as well as physical and chemical properties (e.g., grain size and organic carbon content). This study showed distinct seasonal variability of water and sediment quality parameters in endorheic reed pans on the Mpumalanga Highveld. There is a need for further studies on all of the different types of pans in terms of their water and sediment quality. This type of information will allow for a sound and defensible scientific basis for the assessment of likely impacts (e.g., eutrophication), the evaluation of the significance of these impacts, and the design of remedial and preventative measures.

Highlights

Wetland loss has been estimated to be around 50%, whilst approximately 35 to 50% of wetlands are thought to have already been lost or severely degraded in South Africa (Dini, 2004; DWAF, 2004)
The seasonal trend of nutrient enrichment at the four reed pans is presented as total inorganic nitrogen (TIN), expressed as the sum of NH4+; NO3- and NO2, as well as total inorganic phosphorus (TP), expressed as PO43
Few seasonal trends can be observed with regard to nutrient levels (Fig. 2 A–D), TP concentrations were found to be highest during SUM at all of sites and decreased towards WIN

Summary

Introduction

Wetland loss has been estimated to be around 50%, whilst approximately 35 to 50% of wetlands are thought to have already been lost or severely degraded in South Africa (Dini, 2004; DWAF, 2004). Pans are classified in South Africa as depressional, endorheic wetlands, which are found throughout the world (Goudie and Wells, 1995). These wetlands could otherwise be classified as palustrine or lacustrine, and possess additional features such as having a flat basin floor and no outlet (Dini et al, 1998). The main stressors of concern are usually toxic heavy and/or trace metal contamination, as well as nutrient enrichment (CSIR, 2010) These stressors can have a direct impact on an aquatic environment, including water and sediment quality (Driscoll, 1985; Winterbourne et al, 2000; Dise et al, 2001; CSIR, 2010)

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Discussion

Conclusion