Use of remote sensing and molecular markers to detect toxic cyanobacterial hyperscum crust: A case study on Lake Hartbeespoort, South Africa

In this study, we monitored the formation of cyanobacterial hyperscum and crust formation in Lake Hartbeespoort using satellite images and ground monitoring. The hyperscum that formed near the reservoir wall was characterised by a distinctive white surface layer of crust. Hyperscum is the result of exposure of the cells to high radiation, inflicting irreversible damage to the genetic constitution of the upper layer of Microcystis aeruginosa cells. Under the 3 mm thick layer of crust, dark (<0.93 μmol of photons m-2s-1) anaerobic conditions (0.4 mg/l, 3% saturation) prevailed with high levels of microcystin (12,300 μg/l) in the absence of sunlight irradiation and photolysis by UV light. Real time polymerase chain reaction (PCR) analysis indicated low levels of transcription of the mcyA, mcyB and mcyD genes which are responsible for synthesis of cyanotoxins under these low light intensity conditions. At other sampling sites where cyanobacterial scum occurred and hyperscum crust was absent, only the mcyB and mcyD genes were transcribed. A plausible explanation for the transcription of the mcyA gene in thehyperscum and not at the other sampling sites, was the presence of environmental stress-inducing factors, e.g. low light intensity (0.93 μmol of photon m-2 s-1) and pH 6.1. At the sampling site where no cyanobacterial scum was visible on the satellite images, low cell abundance (2.4 x 104 μg/l) and chlorophyll a (12.2 μg/l) was measured in comparison with sites where cyanobacterial scum was visible on the satellite images.Keywords: Hyperscum crust, reverse-transcription PCR, mcyA levels, microcystin, satellite imaging, cyanobacteri

First report on the colony-forming freshwater ciliate Ophrydium versatile in an African river

Ophrydium versatile (Müller 1786) Ehrenberg 1830 – a symbiotic ciliate that forms gelatinous colonies – is widely distributed in temperate lakes in Europe and America, but has not previously been recorded from rivers. In this paper we report the first record of O. versatile in an African river, based on an identity confirmed by molecular taxonomic identification. The limnological conditions within the Lephalala River during the sampling period were characterised as oligotrophic with low DOC concentrations, similar to the conditions observed in temperate northern hemisphere lakes where these organisms have been recorded previously. The majority of O. versatile colonies occurred in areas where thin orange-coloured films containing high concentrations of iron (> 60% Fe) covered the substrate and bedrock of the river; this may be related to the abundant picophytoplankton that were associated with these films and oligotrophic conditions. The planktonic diatom Gomphonema venusta Passy was dominant in the water column throughout the study period and acted as an environmental indicator of low electrical conductivity (EC) conditions in the habitat where O. versatile colonies were recorded. Keywords: Lapalala River, oligotrophic indicator, water qualit

Linking climate change and progressive eutrophication to incidents of clustered animal mortalities in different geographical regions of South Africa

Cyanobacterial blooms have become an increasing problem in South African freshwater bodies. Since certain species of cyanobacteria are well-known for biosynthesis of potent hepatic and neurotoxins, such blooms can pose a significant threat to the health of animals and humans. The massiveproliferation of these organisms in rivers and lakes is largely due to progressive eutrophication. However, a warming trend in the Southern hemisphere, indicated by a threefold increase in the minimum temperature compared to maximum temperature between 1950 and 1990, is likely the cause of the increasing occurrence of toxic cyanobacterial bloom forming species, previously hampered by low water temperatures in different geographical regions of South Africa

Chemical characteristics and limnology of Loskop Dam on the Olifants River (South Africa), in light of recent fish and crocodile mortalities

A declining crocodile population and fish mortalities attributed to pansteatitis, along with increasing blooms of Microcystis aeruginosa and Ceratium hirundinella, have led to serious concerns about water quality in Loskop Dam, on the Olifants River, South Africa. Major impacts include acid mine drainage and eutrophication associated with sewage effluent. However, the specific causes of pansteatitis remain elusive. In 2011 the water chemistry and limnology of Loskop Dam were studied to determine factors that may be influencing aquatic ecosystem health. Long-term monitoring data collected by the Department of Water Affairs were analysed for trends using a seasonal Mann-Kendall trend test, and were used to determine the trophic state of Loskop Dam using the Carlson index. Multiple sites were sampled which showed the reservoir was heterogeneous with regard to nutrient concentrations, algal biomass and dissolved metals. Specifically, the transitional zone was characterised by frequent algal blooms, resulting in fluctuating dissolved oxygen (range = 2.1–14.5 mg/ℓ) and pH (range = 7.35–10.59) levels. Using total phosphorus, Secchi depth, and chlorophyll-a concentrations, the trophic state of Loskop Dam was classified as meso- to eutrophic. Significant positive trends were observed in total (Tau = 0.422) and dissolved inorganic (Tau = 0.193) phosphorus.The reservoir showed a monomictic pattern of summer stratification (October to April) and holomictic winter circulation (June to July), with an increase in the depth and extent of anoxia in the hypolimnion when compared to previous research. Simultaneous elevated concentrations of manganese (>370 μg/ℓ) and iron in near-bottom water samples coincided with hypolimnetic anoxia. Aluminium concentrations exceeded the target water quality range (>10 μg/ℓ) during summer (December) in both surface and near-bottom water samples. We conclude that fish in Loskop Dam are periodically exposed to several physiological stressors including elevated ammonia, aluminium, iron and manganese and possibly hydrogen sulphide, as well as low dissolved oxygen. While these factors have never individually been linked to pansteatitis, their combined impacts have not been studied. To ensure the sustainability of Loskop Dam, catchment management plans must focus on reducing phosphorus inputs, and continue seeking treatment solutions for mine-water associated with abandoned and working coal mines.Keywords: Loskop Dam, limnology, pansteatitis, eutrophication, Olifants Rive

Application of multi‑method approach to assess groundwater–surface water interactions, for catchment management

Globally, the dependence of river systems to delayed discharge of subsurface water to augment flows during dry seasons is well documented. Discharge of fresh subsurface water can dilute concentrated river flow quality during reduced flow. Observed and reported results on the Berg River’s declining water quantity and quality are a concern to the regions socio-economic growth and environmental integrity. Understanding the role of subsurface water discharges on the quantity and quality of receiving surface water courses can improve their management during dry periods. A case study was designed and implemented in the upper Berg River catchment in the Western Cape Province of South Africa to assess the influence of groundwater–surface water interaction on water quantity and quality. This study aimed to quantify and characterize the quality of subsurface water available in the upper catchment to improve observed declining water quality downstream. Hydrograph separation provided estimates of water fluxes during 2012–2014 low and high flow periods, while hydrochemical analysis provided insights on impacts of major land use activity in this catchment on water resources. Hydrograph separation analysis indicated that the Berg River is 37.9% dependent on subsurface water discharges annually. Dominant Na–Cl-type water indicates the quality of water from the upper Berg River is largely affected by natural processes including short residence times of aquifer water, rock–water interactions and atmospheric deposition of NaCl ions. These results provide insights for suggesting management options to be implemented to protect subsurface water for continued dilution and water resources management in the lower catchments

Lack of Phylogeographic Structure in the Freshwater Cyanobacterium Microcystis aeruginosa Suggests Global Dispersal

Background : Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographic structuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwater cyanobacterium Microcystis aeruginosa. Being widely distributed on a global scale but patchily on a regional scale, this prokaryote is an ideal model organism to study microbial dispersal and biogeography. Methodology/Principal Findings : The phylogeography of M. aeruginosa was studied based on a dataset of 311 rDNA internal transcribed spacer (ITS) sequences sampled from six continents. Richness of ITS sequences was high (239 ITS types were detected). Genetic divergence among ITS types averaged 4% (maximum pairwise divergence was 13%). Preliminary analyses revealed nearly completely unresolved phylogenetic relationships and a lack of genetic structure among all sequences due to extensive homoplasy at multiple hypervariable sites. After correcting for this, still no clear phylogeographic structure was detected, and no pattern of isolation by distance was found on a global scale. Concomitantly, genetic differentiation among continents was marginal, whereas variation within continents was high and was mostly shared with all other continents. Similarly, no genetic structure across climate zones was detected. Conclusions/Significance : The high overall diversity and wide global distribution of common ITS types in combination with the lack of phylogeographic structure suggest that intercontinental dispersal of M. aeruginosa ITS types is not rare, and that this species might have a truly cosmopolitan distribution

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

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Using modified multiple phosphorus sensitivity indices for mitigation and management of phosphorus loads on a catchment level

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