Gavin Snow

University of the Witwatersrand | wits · School of Animal, Plant and Environmental Sciences

The treatment works under investigation uses a recovered wash water plant (RWWP) to remove impurities prior to recycling filter backwash water. Filter backwash water (raw water) is characterized by high quantities of cyanobacteria cells and associated organic compounds; a potential threat when recovered water is recycled. The aim of this study is t...

Globally, approximately 65% of aquatic ecosystems (i.e., freshwater, estuaries, marine) are considered threatened to some extent. Pressures on these fragile ecosystems are on the rise due to the demands for emanating from global human population increases. This chapter focuses on phytoplankton mostly diatoms and flagellates in environmental monitor...

The possible impacts of extreme events on the ecology of selected aquatic biota within the Mbhashe Estuary were investigated during a four year (2010–2013) spring sampling programme. During periods of low to average flow conditions the estuary is shallow, turbid and characterised by the presence of fluid mud and the build-up of mud and clay deposit...

Urbanisation in South Africa has resulted in the degradation of aquatic ecosystems across a rural-to-urban gradient; impacting the availability of clean water. Biological organisms, including fish assemblages, have been used as indicators of environmental change, as part of monitoring programmes designed to protect and improve aquatic ecosystem con...

Water quality characteristics of the heavily urbanised and industrialised Swartkops River and Estuary in the Eastern Cape have been the focus of several studies since the 1970s. Overloaded and poorly maintained wastewater treatment works (WWTWs), polluted stormwater runoff and solid waste have all contributed to the deterioration in the water quali...

To evaluate the effects of managed river flow and artificial breachings the primary aim of the study was to determine if there was a predictable biotic response (phytoplankton chlorophyll a) to measured environmental drivers (hydrology, water quality and mouth condition).

Water hyacinth (Eichhornia crassipes Mart. Solms Pontederiaceae) mainly occurs as a free-floating aquatic plant, but can survive decreasing water levels when rooted in soil. This adaptation to seasonal fluctuations in hydrology may contribute to its invasive potential in natural and man-made water bodies, where stranded plants can take root. To und...

The Great Brak Estuary is a temporarily open/closed estuary located on the south coast of South Africa. The construction of the Wolwedans Dam in the catchment has reduced flow to the estuary by 56%; reducing the intensity of flushing events and causing the mouth to breach less often. The estuary experiences dense growth of the macroalga Cladophora...

Microalgae, composed of phytoplankton and benthic microalgae, are used in estuary freshwater requirement studies as they respond quickly to changes in water quality and river flow. The aim of this paper is to show how microalgae are used to determine the present ecological status of river-dominated estuaries by determining the changes in biomass an...

The Great Brak is a temporarily open/closed estuary (TOCE) located on the south coast of South Africa. The construction of the Wolwedans Dam in 1989 reduced baseflow to the estuary by 56%, decreasing the intensity of flushing events and causing the mouth to breach less often. The aim of this study was to investigate the flux of inorganic nutrients...

The aim of this project was to develop a desktop method for the Provisional EcoClassification (the term used for the Ecological classification process under the NWA) for estuaries that provided for a comparative, regional scale assessment. The Provisional EcoClassification – in the context of this study – refers to the Present Ecological Status (PE...

This report is a summary of the findings of the Reserve Determination for the Mzimvubu Estuary, prepared in support of the broader feasibility study for the Mzimvubu Water Project. The assessment has followed the methods supported in Version 2 of the Reserve Determination methods outlined by the Department of Water Affairs. Summer and winter sampl...

A popular article describing the Marine and Coastal field trip for the University of the Witwatersrand University undergraduate students. The article was published in August/September 2014 South African Network for Coastal and Oceanic Research (SANCOR) newsletter; pages 8-9.

The Great Brak Estuary is a temporarily open/closed system situated along the warm temperate coast of the Western Cape, South Africa. The estuary is subject to a variety of anthropogenic impacts (e.g. freshwater abstraction and sewage discharge) that increases its susceptibility to prolonged periods of mouth closure, eutrophication, and ultimately...

Temporarily Open/Closed Estuaries (TOCEs) generally have low river inflow, a long water residence time due to weak flushing, and prolonged mouth closure (Whitfield 1992, Taljaard et al. 2009 b) which makes this type of estuary vulnerable to nutrient enrichment and the accumulation of organic matter (Newton and Mudge 2005, Human and Adams 2011). In...

The Sundays Estuary is permanently open to the sea and experiences regular freshwater inflow in the form of agricultural return flows with large supplies of nutrients. The objectives of this study were to measure microalgal biomass and community composition and relate these to freshwater inflow, water quality and other environmental variables. Thes...

The Berg Estuary is permanently open in the Mediterranean-type climate of the Western Cape Province, South Africa. Construction of the Berg River Dam was completed in 2007 and is expected to influence the quantity and quality of river water entering the estuary at the head. This study examined the distribution of phytoplanktonic and benthic microal...

The dynamics of the world's larger permanently open estuaries have been well documented, but much less is known about the complex dynamics of smaller temporarily open/closed estuaries (TOCEs). Seventy per cent of South Africa's 250 estuaries are classified as TOCEs, and many are less than 50 ha. A conceptual model of the water-quality dynamics of T...

In 2005/2006 a multidisciplinary research programme that included studies on the hydrodynamics, sediment dynamics, macronutrients, microalgae, macrophytes, zoobenthos, hyperbenthos, zooplankton, ichthyo-plankton, fish and birds of the temporarily open/closed East Kleinemonde Estuary was conducted. Particular attention was given to the responses of...

Of the five types of estuaries found in South Africa, temporarily open/closed estuaries comprise approximately 70% of the total. This paper provides an overview and a simple conceptual model of the water quality features and characteristics of temporarily open/closed estuaries in South Africa. Available literature on estuaries in the warm- and cool...

The Mngazi estuary, a near pristine and wave-dominated estuary located on the subtropical east coast of South Africa, requires careful management to ensure that land use does not alter its ecological function. The present study investigated the quality and quantity of water in the estuary and related these to the microalgae. There was no evidence o...

The Kromme is a permanently open estuary that receives little freshwater input because the capacity of the dams is equivalent to the mean annual runoff from the catchment. The estuary is marine dominated and phytoplankton chloro-phyll a is low because of the low freshwater pulses that introduce nutrient-rich freshwater. Water released (2 x 10 6 m 3...

The effect of high (ambient) and low (shaded to 50 % of ambient) light on microphytobenthic biofilm. primary production, vertical migration and allocation of photoassimilated carbon into extracellular carbohydrates was investigated over the low tide emersion period at Sarilhos Pequenos on the Tagus estuary, Portugal, in July 2000. Carbon uptake (C-...

Impoundments and abstraction from rivers have reduced the amount of riverwater flowing into estuaries. This has necessitated research on the riverwater requirements of these important ecosystems. A study was initiated on the structure and biomass of microalgae in the Gamtoos estuary (Eastern Cape Province, South Africa) in order to improve our capa...

The release of freshwater from the Mpofu Dam in November 1998 resulted in a short-term (6 d) longitudinal and vertical gradient of both salinity and nitrate in the estuary. There was no significant increase in phytoplankton chlorophyll a during the period of the study. The phytoplankton communities were dominated (> 10%) by diatoms and flagellates...