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Receiving her doctoral degree in geology at Nelson Mandela University’s autumn graduation is Carla Dodd. She has been getting to grips with the little understood origin, chemistry and complexity of groundwater from source to sea in the Nelson Mandela Bay region of the Eastern Cape.


Carla Dodd in the Elands Mountain catchment; coastal spring water sampling in Nelson Mandela Bay with, Professor Gudrun Massman hydrogeologist from Oldenburg University, Germany; and sampling microbiolites in Seaview, Nelson Mandela Bay.  

This is critical research that provides the first groundwater quality baseline related to coastal springs in a region beset by drought.

“The goal is that this research will ultimately contribute to a better understanding of the groundwater resources from source to sea and ensure that the aquifer systems are managed responsibly for the benefit of Nelson Mandela Bay residents and the environment,” says Carla.

A shining example of relevant research, Carla’s study was presented at local and international conferences, it is being published and she received two of the most prestigious awards for it in 2023: the National Research Foundation (NRF) Research Excellence Award for Next Generation Researchers and the Department of Science and Innovation (DSI)I South African Women in Science Award - the Ndoni Mcunu Fellowship.

“During the prolonged drought in the Nelson Mandela Bay Metro, increasing amounts of groundwater (water in underground aquifers, as opposed to the surface water from rivers wetlands and lakes) have been extracted for domestic and municipal use,” Carla explains.

“The problem was that we didn’t know where the groundwater discharging at the coast was coming from and how its composition, is influenced by flow paths, both from a geological and anthropogenic (human-related pollution) point of view.

To establish this, she worked with a hydrogeologist from the University of Oldenburg, Germany, and a marine geologist from the Council of Geoscience, South Africa. “It is more complicated than we thought,” she says.

“There are lower and upper groundwater aquifer sources, emanating from the hard bedrock of the Table Mountain Group in the catchment areas (including the high-lying mountain belts of the Elands, Kouga and Kareedouw Mountains) and from the infiltration of rainwater through the coastal dune systems. From my PhD results we determined that coastal springs receive groundwater from both the hard-rock and dune systems.”

Geologically, in the catchment they found the groundwater to be of a sodium chloride type, which changed to a more calcium bicarbonate type closer to the coast. The groundwater from the catchment supports, in part, the aquifer-fed springs in the coastal zone the Nelson Mandela Bay Metro extending across the coastline between Cape Recife and Maitland Beach.

This area is rich in microbialite systems that occur in the supratidal (above the high tide) coastal zone at the convergence of the groundwater springs and the sea.

“For my research I looked at utilising the microbialites as easily accessible monitoring systems for the quality of groundwater that emerges from the coastal springs here, which we found to be contaminated by wastewater,” Carla explains.

“Microbialites improve water quality, helping to purify it like a wetland; they are an amazing resource and a saving grace from the water quality aspect and the scientific value they add to our coastal zone.”

Carla’s co-supervisor, Dr Gavin Rishworth, from the Department of Zoology, specialises in microbialite ecosystems. These are ancient living ecosystems created by microorganisms, represent Earth’s earliest ecosystems. Some of the oldest examples globally, found in Greenland are believed to date back 3.7 billion years and in Australia they date back 3.4 billion years.

“The South African coastal microbialites that we study are much younger, our best estimate is less than 6000 years old, and the systems are active, so new microbialite deposits are produced constantly but only at a rate of a few millimetres per year,” Carla explains.

In 2012 they were discovered along the southern Nelson Mandela Bay coastline (close to Mandela University’s South Campus) by Professor Renzo Perissinotto – the then holder of the SARChI Chair in Shallow Water Ecosystems – as well as Professor Tommy Bornman from the South African Environmental Observation Network (SAEON) – a coastal and marine research partner of Mandela University – who started mapping them.

“Professor Perissinotto encouraged me to work on the microbialite systems from a groundwater perspective,” says Carla, who was first attracted to geology while at school in Kariega, when she attended the science week at Nelson Mandela University. She was subsequently offered a bursary to study geology here. She has remained in the Department of Geosciences ever since.

She adds that Dr Rishworth has been instrumental in her research path.

“He is a global expert in microbialite systems, and I would not be where I am today without him,” she says. “He co-supervised my Honours and Master’s and was the main supervisor of my PhD. He is a compassionate supervisor, which I really appreciate as academia can be a harsh working environment. He is committed to his postgraduate students, to growing our professional capacity and encouraging us take opportunities that will advance our careers.”

During her PhD Carla attended a range of international events in her field, including an international summer school in the Bahamas, conferences in Reunion and Italy, and a field trip to Western Australia with Dr Rishworth who is working with researchers from Australia and the United Kingdom there.

She also had a three-month research stay at the University of Oldenburg in Germany, which, she says, was a highlight of her research studies. “It was amazing working with the hydrogeology team there, learning from them and about how their groundwater systems work and are managed.”

Carla is now on a two-year National Research Foundation postdoctoral contract. “I am working with Dr Rishworth on a long-term monitoring system for rainfall and its chemical composition, which we will then compare with the groundwater and microbialite systems,” she explains. Other research has emanated from this, including a master’s study to see how much water is entering the coastal zone. 

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Contact information
Mrs Debbie Derry
Deputy Director: Communication
Tel: 041 504 3057