Bird and algal dynamics of two small rivers
Algae are widely present in freshwater environments and serve as important primary producers in aquatic ecosystems, where they generate biomass that is transferred to higher trophic levels. Algae respond to environmental variables such as pH, dissolved oxygen, conductivity, temperature, and different inorganic nutrients. The same environmental variables may differ markedly between different river systems, which may have profound effects on the biota of that system. I hypothesised that the algal composition will determine the productivity of a system that will consequently be reflected by the avian composition depending on that system. The effect of algal community composition on the productivity of that system has received much attention; however, the interactions between freshwater phytoplankton and birds have not been well documented. I therefore conducted an in depth study on the avian and algal biodiversity of two small, closely located, rivers water quality factors involved. The hypothesis I tested was that freshwater quality and environmental parameters affect algal community parameters, which, in turn, affect bird community parameters. To investigate this, monthly algae and bird surveys were done and water quality variables were measured monthly over a period of 11 months (July 2016 - May 2017) along the Mooi River (MR) and Wonderfontein Spruit (WFS). Mooi River had four and Wonderfontein Spruit five sites, all within a radius of 15 km of each other. WFS is known to be highly polluted by residential areas and mining activities, while MR has small scale diamond mining and some agricultural influences. I used ANOVA and t-tests (and equivalent non-parametric tests), linear regressions, cluster analyses, PCA - and NMS ordinations, indicator species analyses, ANOSIM, and SIMPER to analyse the data. Comparisons between the rivers showed significant differences for pH, dissolved oxygen, conductivity, phosphorus, sulphate, nitrate, dissolved inorganic nitrogen, and richness and abundance of birds and algae. Although the phosphorus concentrations were significantly higher for MR, nitrogen was much lower than WFS, limiting algal growth potential. Additionally, multivariate results showed that algal and avian composition differed markedly between rivers. Avian biomass and diversity was strongly correlated with algal abundance that was much higher in WFS, most likely due to organic enrichment. I concluded that algal diversity was associated with water quality measurements, and that algal parameters were associated with bird parameters.