The effect of illegal dumping on surface water quality using diatoms as a bioindicator

Abstract

Aquatic ecosystems are vital for all life on earth as, without water, there would be no life. It is therefore important that this vital resource is protected, properly managed and that all measures are taken to ensure that it is used in a sustainable manner. As water moves through towns and cities of a region, the water resources are impacted by the anthropogenic activities within these regions. Poor waste management is one such example of an impact that pollutes water resources all over the world. The poor municipal waste management services and the challenges and gaps identified within the waste management legislation, has led to events of illegal dumping. Illegal dumping has been identified as a global problem and not only a local environmental problem in South Africa. The effects caused by illegal dumping are not only limited to where the location of the dumping site is but extends rather to a much greater footprint. Some of the effects caused by illegal dumping include health, social, environmental and economic impacts. Studies have indicated that illegal dumping is more common in the rural communities where there is very limited access to basic services such as potable water, sanitation services and municipal waste collection. This study aimed to assess the impact that illegal dumping has on water quality, through the use of diatoms as a bioindicator of the health of the aquatic ecosystem. Diatoms are known as primary producers that play a significant ecological role in the aquatic ecosystems with their dynamic position at the bottom of the trophic food web. Their specific environmental requirements make them sensitive to any changes within their environment and therefore they are regularly used in aquatic ecosystem studies to assess the anthropogenic impacts and the ecosystem health of aquatic ecosystems. The study was conducted at several surface water bodies within the Ikageng and Promosa suburbs of Potchefstroom in the North-West Province of South Africa. These water bodies form part of a larger drainage system which drains into the Mooi River. The Mooi River is a very important water resource as it is the only source supplying water to the Potchefstroom city. Eight sampling sites were selected for the study at which once-off water and diatom samples were collected during the late summer rainfall month between 15 to 16 February 2019. These sites are located along the drainage lines/streams and dams which all eventually feed into the Mooi River system. The sites were selected as they were representative of the area and the water resources of the area during the time of sampling. Site 8 was used as a reference site to determine the anthropogenic impacts at the other sites and the effect of the illegal dumping on the water quality of those sites. In situ water quality variables were measured at each sampling site and water samples were collected to The effect of illegal dumping on surface water quality using diatoms as a bioindicator measure the physicochemical variables of the water at each site. The samples were analysed for nitrites, nitrates, ammonium, phosphate, sulphate and chloride. The water quality results determined for each site was then compared to the South African water quality guidelines volume 7 specified for aquatic ecosystems to determine if the anthropogenic impacts such as illegal dumping affected the water quality at the different sites. During the diatom sampling, two sets of diatom samples were collected for the live and fixed diatom analysis. Diatoms were sampled from submerged aquatic vegetation stems at each site and prepared and analysed according to the prescribed method of Taylor et al. (2004). The water quality results analysed for the sites raised concern as some of the variables far exceeded the specified concentration range within the water quality guidelines specified for aquatic ecosystems. The inorganic nitrogen (nitrate, ammonium and phosphate) concentrations measured for the sites were very high and indicated the sites to be of a eutrophic/hypertrophic ecological state. These eutrophic conditions at the sites are problematic as it can cause excessive growth of aquatic plants and blue-green algae blooms of which some species could be toxic and harmful to the livestock, humans and wildlife within the area. The chloride concentrations for all sites far exceeded the chronic and the acute effect value. The pH level measured at Site 3 was extremely low and indicated that the system was very acidic, with pH values within the recommended range measured for all the other sites. From the diatom results analysed for the study area, a total of 56 diatom species were identified over the eight sampling sites. The dominant species identified at the sampling sites indicated that all the sites (except sites 1 and 8) are eutrophic as these are species that prefer nutrient-enriched waters and are commonly identified in waters known to be eutrophic and heavily to extremely polluted. The diatom results corresponded with the measured physicochemical water variables which also indicated these sites as nutrients enriched and affected by some sort of pollution. The diatom indices calculated (Specific Pollution sensitivity Index and Generic Diatom Index) also indicated that the sites had poor to bad water quality and was classified as eutrophic ecological state. The Percentage Pollutant Tolerant Valves scores for sites 2 and 3 (fixed) indicated that these sites were heavily contaminated with organic pollution which could be as a result of wastewater discharge from the surrounding areas causing organic pollution. The fixed and live diatom samples had a similar trend for some of the index scores for most of the sites while Site 3 had little resemblance in the index trend for the live and fixed samples. The effect of illegal dumping on surface water quality using diatoms as a bioindicator These results, therefore, indicate that the ecosystem is enriched with nutrients which correlates with the water quality and dominant diatom species. The presence of the illegal dumping at these sites definitely contributed to the elevated nutrient concentrations as previous studies have indicated illegal dumping to be a contributing factor in certain elevated water quality variables such as nutrients. The hypothesis of the study is therefore supported as it can be concluded that the illegal dumping of waste near water sources does negatively influence the water quality of these water resources by altering the water quality parameters which has led to eutrophic polluted conditions. It was concluded that illegal dumping together with various other sources (such as waste water and agricultural runoff) does have an impact on the quality of the selected water resources within the Ikangeng and Promosa area.