Abstract
Due to the global increase in the human population, an increase in waste-polluting freshwater ecosystems has been observed. In this study, three freshwater impoundments (Emmarentia Dam, Westdene Dam and Orlando Dam) were sampled over two seasons. Three main objectives were established for this study. The first objective was to identify the types of water pollution at each site by measuring physicochemical parameters and conducting chemical and toxicity analyses on samples collected from each site. The second objective was to identify the leech specimens present at each site and determine their ecology. Lastly, the third objective was to determine if there was a relationship between the identified pollutants and leech distribution.
For objective one, water samples were collected to identify possible toxicants, if any, present in the systems. These samples were sent to WaterLab where standard inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled mass spectroscopy (ICP-Ms) metal scans were conducted on the samples. The results indicated low levels of metal pollution with five elements of the 72 analysed for that surpassed guideline values. These are discussed. Acute toxicity analysis using Daphnia pulex and Poecilia reticulata was conducted at the University of Johannesburg to test and classify the toxicity levels of the impoundments. The acute toxicity analysis from the first season indicates that Westdene Dam was classified as a Class I category, expressing no acute hazard to the exposed aquatic organisms. In contrast, Orlando Dam and Emmarentia Dam were classified as a Class II category, expressing a slight acute hazard. As for the second season all three sites were classified as a Class I category, expressing no acute hazard. The physical parameters measured showed elevated levels of electrical conductivity (EC) which correlated to the elements identified in the chemical analysis.
The leech species identification revealed four species across the three sites, although Orlando Dam only has one of the four species (Helobdella cf' stagnalis (Linnaeus, 1758)). At Westdene Dam three Helobdella species were identified (H. cf'. stagnalis, H. cf'.conifera (Moore, 1933) and H. cf'. modesta (Verril, 1872)) and one Alboglossiphonia cf. sp. in season 1 and season 2. At Emmarentia Dam, the same three Helobdella species were identified (H. cf'. stagnalis, H. cf'. conifera and H. cf'.
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modesta) during season 1; however, in season 2, no Helobdella cf'. conifera species were recorded.
This supported the hypothesis that Orlando Dam would be more polluted because it forms part of the Diepkloof Spruit, while Westdene Dam and Emmarentia Dam form part of the Braamfontein Spruit and were considered to be on a less polluted system. However, the RDA analysis indicated that the distribution of leeches is influenced mainly by temperature, pH and depth in season 1; while pH and depth are driving factors in season 2.
The information gathered in this study provides a baseline that could possibly be used to motivate the use of leeches as bioindicator species, as this information could give a more clear picture of the preferred environmental conditions and the driving forces of the distribution of leeches.