Diatoms as an indicator of water quality in the Kuils River, Western Cape South Africa

Abstract

Water is a very important resource that is vital for life. However, this resource is threatened due to anthropogenic activities such as urbanisation, agricultural runoff and industrial activities polluting open freshwater resources such as rivers. Rivers are important systems that play a significant role in nature as they are vibrant ecosystems for various plant and animal species. In addition, rivers may serve as possible sources of drinking water, while certain communities are dependent on rivers as part of their livelihoods, i.e. for fishing and agriculture. It is therefore important to ensure that measures are put in place to manage, monitor and protect open surface water resources. Even though water quality monitoring has previously been conducted using physicochemical analysis strategies, researchers have been challenging and replacing this traditional method with biomonitoring techniques. Biomonitoring techniques allow researchers to get a time-integrated evaluation of the quality of water. In this study, four sites were selected to assess water quality along the Kuils River, Western Cape. Since physicochemical methods have traditionally been used to assess water quality, this study used both physicochemical parameters and diatoms (biomonitoring method) to determine the water quality in the Kuils River. Historical water quality parameters (2019-2021) that were obtained from the Department of Water and Sanitation were used as a reference, to determine whether the results obtained using diatoms as biomonitors correlate with previously documented results obtained from traditionally used methods. The results obtained from the concentrations of the physicochemical parameters measured along the river indicated the presence of pollution, as changes in abundance or composition of diatoms specices were observed. The diatom species collected were counted and the diatom indices were calculated using the Omnidia 6.1 software. Ninety-eight diatom species were identified in this study. Diatom species that are pollution-tollerant, indicators of organic pollution and eutrophication such as Nitzchia palea, Navicula viridula, Eunotia bilunaris and Fragilaria ulna were widely spread. Less-pollution tolerant species such as Gomphonema parvulum and Cyclotella meneghiniana were surpassed in abundance. Thus, both results from diatom indices as well as physicochemical parameters respectively, complimented the fact that water in the Kuils River is of poor quality. It is concluded that diatoms prove to be a valuable biomonitoring tool in determining the water quality of a river. Based on obtained results, it is recommended that future studies on water quality of river systems use diatoms to supplement traditional physicochemical studies to determine water quality of rivers as they have proved to support these traditional studies. As the main aim of this study was to investigate diatoms as indicators of water quality, the index values that were obtained from the study were used to determine the ecological class into which the sampling sites fell. ln addition, these indices indicated diminished water quality within the river system in both high flow and low flow seasons. lncreased nutrient concentrations recorded along the river, indicated poor water quality. Additionally, increased nutrients during high flow seasons can be attributed to high rainfall levels that cause an increase in suspended solids and sediment yields. Runoff from storm water drains, sewage pipes discharging wastewater into rivers could also contribute to increased nutrient concentrations. This study recommends the introduction of green infrastructures to reduce the amount of pollutants entering rivers. Green infrastructure techniques such as rain gardens, pervious pavements and green roofs. These techniques will slow down runoff from storm water drainages. Allowing the runoff to move slowly and be spread out onto more land whereby plants will work as filters and filter out pollutants from runoff, as well as wastewater from treatment works before it infiltrates into the ground and enters water systems.