Phytoplankton yield changes after enrichment in microcosm experiments: Applications for predicting progressive eutrophication in a mesotrophic lake, South Africa

Abstract

Established microcosms containing surface water from the mesotrophic Lake Mokolo were subjected to enrichment of different concentrations with phosphorus. The microcosms were sampled through a 20 day succession period to determine the net effects of increased concentrations of phosphorus in the water column on the phytoplankton community structure during the winter and summer seasons. A significant increase in chlorophyll a (chl-a) was observed when treatments of 30, 40 and 60 µg L -1 P were compared to the controls. On day zero in both the winter and summer microcosm experiments, all four phosphorus treatments had similar species diversity of phytoplankton of the specific seasoned tested (winter: Margalef index = 223; summer: Margalef index = 347). However, 13 days after the addition of 40 and 60 µg L -1 P, the phytoplankton community exhibited a strikingly different species richness (winter: Margalef index = 123; summer: Margalef index = 114). In the winter microcosm experiments, the green alga Scenedesmus armatus dominated the phytoplankton composition at enrichment levels of 40 and 60 µg L -1 P up to day 20. The biovolume of the dinophyceae Ceratium hirundinella declined rapidly after the addition of 40 µg L -1 P in the different summer microcosms. In the summer microcosms, Spondylosium secedens and Microcystis aeruginosa dominated the 40 and 60 µg L -1 P microcosm enrichment experiments.

Effects of elevated CO2 on feeding responses of biological control agents of Pontederia crassipes

“…Hoveka et al (2016) modelled the impact of expected temperature changes as a result of climate change linked to eCO 2 on the invasive potential of P. crassipes in South Africa and showed that under expected rising temperature, the invasive range of P. crassipes is expected to expand into regions that are currently unfavorable to the plant. This coupled with highly eutrophic waters in South Africa (Villiers & Thiart, 2007;Oberholster & Ashton, 2008), suggests that the invasive potential of P. crassipes will be enhanced under future climates, potentially even more by the eCO 2 conditions. In this P. crassipes responses to eCO had effects on insect feeding responses, depending on the insect feeding guild.…”

Time Series Analysis of Water Quality Factors Enhancing Harmful Algal Blooms (HABs): A Study Integrating In-Situ and Satellite Data, Vaal Dam, South Africa

“…The frequency distribution plots (Figure 2) show that most of the Chl−a data are centered near the low-range values, below its average. A similar situation for HN 4 obtained from level−2 generator (l2gen) of NASA SeaDAS v8.3 were used for chlorophylla retrieval. The ratio of (Rrs560/Rrs443) from our previous work [29] is used in this study, it was successfully used to retrieve Chl−a from Landsat-8 data in the Vaal Dam.…”

“…It is indicated that an estimation of more than 83% of land surfaces that are surrounding freshwater systems have been significantly influenced by the footprint of human beings as a response to anthropogenic activities [1,2]. Contaminants from ineffective waste management, pesticides and fertilizers from agricultural areas, pollution from urban, industrial, and domestic wastewater can often be released to ground and surface water [3], and even the landfills or slag heap disposals may release pollutants seeping into nearby water resources [4,5]. The inland freshwater bodies are more vulnerable to such problems of pollution and contamination [6] resulting in the decline of quality and availability.…”

“…Despite such a huge number of dams, South Africa is a water-stressed and scarce country facing critical challenges due to poor water management practices, inadequate infrastructure, and a relentless surge in water demands [14]. Owing to the fact that most South African dams are located downstream of metropolitan and urban areas, they have become more enriched with nutrients [4,15]. The climatic conditions of South Africa associated with nutrient loads resulted in extensive and widespread eutrophication and cyanobacterial blooms in the inland freshwater bodies [16,17].…”

Socio-Economic and Environmental Implications of Bioenergy Crop Cultivation on Marginal African Drylands and Key Principles for a Sustainable Development

“…The decisions that are taken today with regard to a more sustainable future must follow up on this increase, as the extent of water scarcity that is being addressed today is nothing compared to what is to come [93]. Concerning Africa, in 1998 researchers stated that by 2030 freshwater resources in South Africa will have impaired by so much that they will be unable to comply with the needs of the people and the industry [94]. Therefore, while the demand for energy and food in developing countries, such as South Africa for example, is increasing, it is of utmost importance to secure water resources on-site, in an already scarce environment [95].…”