The use of periphyton and macro-invertebrates and their susceptibility to changes in river flow characteristics and nutrient composition as an indicator of river health.
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Freshwater systems are a valuable resource under increasing threat due to pollution from activities such as agriculture, industry, mining and domestic use which can pose a risk to human and animal health and may lead to eutrophication. In South Africa, river ecosystem management has shifted from the improvement of water quality to that of the creation of ecological reserves, ecological health and the improvement of biological integrity. This shift has allowed for the increased use of bio-indicators to determine ecosystem health. Macro-invertebrates, riparian vegetation and fish have been used in the suite of bio-monitoring mechanisms and the setting of environmental reserves. However, there is an increasing need to include periphyton as a tool in river ecosystem monitoring due to their absorptive nature and ability to indicate change environmental conditions. In South Africa research suggesting algae as bio-indicators has been primary based on the use of diatoms as a bio- monitoring tool. This study aims to determine patterns and trends in periphyton communities in the summer rainfall region of KwaZulu-Natal, South Africa. This is achieved through five sampling sites aimed at determining the relationship between changes in nutrient and flow regimes on periphyton communities. Two sites on the Msunduzi River are comparable as they have similar flow but different nutrient levels, whilst on the Umgeni River the two sites are comparable as they have differences in flow regimes with similar nutrient conditions. The fifth site on the Hlatikhulu River, Kamberg, is used as a reference site. Sampling occurred over the period June 2014 to June 2015 on a monthly basis to collect algal and invertebrate samples and physico-chemical data. Trends and relationships between physico-chemical and algal biomass were evident. Trends indicated the role rainfall played in increasing river depth and velocity which in turn influenced algal biomass growth and species composition and the effect that seasonality changes had on periphyton communities. Peaks in algal biomass was as a result of increases in nutrients within a particular system while decreases in algal biomass occurred due to an increase in invertebrate grazers. Sloughing events resulted due to increases in flow and velocity. General trends at all five sites showed peaks in algal biomass in early summer and a lesser algal biomass peak in early autumn. This research suggests that if better understanding of periphyton patterns and trends are established, periphyton can be used as an important bio-monitoring tool and aid in the creating and setting of ecological reserves.