WiDs reflections

The backstories to wetlands in drylands research sometimes may be told around campfires or over a drink or two at conference dinners, but rarely are written down.  Here we provide an opportunity for researchers to tell us how they become interested and involved in wetlands in drylands science or management.  What papers, talks or events have particularly inspired them?  What continues to motivate them?  Where is wetlands in drylands research going?

On the back of his success at winning the 2020 South African National Wetland Award (see ‘Latest News’), we have invited Spike McCarthy (University of the Witwatersrand, South Africa) to kickstart what we hope will be a regular series of reflections from wetlands in drylands researchers or managers.


Spike McCarthy, November 2020

“Stephen Tooth asked me to write a brief history of how research on wetlands in drylands originated. It may sound amazing, but I can trace the origin of this branch of wetland research to events that took place on a single day back in September 1985, a diem mirabilis. To put this day in context, I need to give a brief summary of my academic roots, what inspires me and how this day came about.

I have always had very broad interests in matters geological and became an avid mineral collector while still at school. I studied geology and chemistry at Wits and after a year’s break at a teachers’ training college (JCE) went on to UCT to follow my passion, geochemistry. After graduating with BSc Hons, I signed on for an MSc at UCT under the famous geochemist Professor Louis Ahrens. The subject of my research was the chemical composition of a group of meteorites known as achondrites, which consisted of fragments of Mars and the asteroid Vesta, although we didn’t know that at the time. I was also fortunate to be appointed to the UCT Lunar Sample Investigation Team under Ahrens, studying the chemistry of samples from the early Apollo missions. I learned a lot, especially about analytical chemistry, and made some interesting cosmological discoveries (e.g. refs. 1, 2).

My MSc was completed in record time because my wife was about to deliver our first child, so I needed a job. I was fortunate to land an appointment at Wits in a newly created lectureship in geochemistry (mid 1971). I abandoned cosmic chemistry after joining Wits and chose to focus on the geochemistry of granites (the subject of my PhD), but being the only geochemist around I also became involved in many of my colleagues’ research projects, such as the Messina copper deposits (e.g. ref. 3) and the ancient dolomitic rocks in the northern and western provinces of South Africa (e.g. ref. 4). These were interesting asides and provided a lot of fun and excitement, and on many occasions that unique euphoria which comes from making a new discovery. However, granites remained my primary focus (e.g. refs. 5, 6).

University salaries were not great, even then, so in order to make ends meet on the home front, I became a part-time consultant to a small diamond exploration company in the late 1970s. At that stage I had become quite versatile in my knowledge base and skills. The reason for this was our student field programme which exposed the staff in particular to the geology of the entire country. In addition I learned a huge amount from the weekly research seminars in the Geology Department. I was responsible for organizing them, so for me attendance was compulsory, no matter what the subject was. I had also gained experience in geomorphology as a result of a study colleagues and I did on the National Nuclear Waste Repository site at Vaalputs in the Northern Cape (ref. 7).

The exploration company I consulted to was searching for alluvial diamonds in the old, high level river terraces of the Vaal and Orange rivers. These rivers were, and still are, relatively fast flowing and hence deposit fairly coarse gravels along their beds. As they gradually incise in response to the epeirogenic uplift of Southern Africa, they leave remnant gravel mantles along their courses (e.g. ref. 8). These gravels contain diamonds, derived from erosion of the numerous kimberlite pipes and fissures in their catchments. During systematic mapping of the types of cobbles and pebbles in the high level gravels along the Orange River during the early 1980s, I noticed a distinctive and sudden change in the gravel mix about 50 km downstream of the present Vaal-Orange confluence, which indicated the influx of a different mix of pebbles from the north, i.e. an ancient, now vanished tributary of the Orange River. From the change in pebble types, I was able to calculate that this vanished river had a discharge of about five times that of the Orange itself at their confluence! This massive river clearly arose somewhere to the north in Botswana or beyond, so I named it the Trans-Tswana River (ref. 9).

After a cursory look at geographic maps of Botswana and surrounds it didn’t take long to formulate key questions about the fate of the mighty Trans-Tswana River. In the centre of Botswana is a huge depression, the Makgadikgadi Basin, which is a sink into which all surrounding rivers discharge. There is evidence that it accommodated large lakes at various time in the past, but there is presently no surface outflow. Discharging into the Makgadikgadi basin from the north is the very large Okavango River, with a catchment extending deep into the highlands of Angola. Does this river system represent the headwaters of the long-lost Trans-Tswana River? Did subsidence of the Makgadikgadi depression sever this river from the Orange River to the south, forming mega-lake Makgadikgadi? What role did climate change play in this scenario? With these questions in mind, I decided look for answers on the ground: searching for answers in the field is always much more fun than ploughing through dusty journals in libraries, although often not as effective.

A visit to the Okavango was high on the agenda for another reason as well. At that time (early 1980s), the Okavango was just beginning to become an upmarket tourist destination, and luxury camps with their own airfields were beginning to spring up. Nevertheless, it was still a place where outdoor lovers could go, if they had the necessary gear. Oddballs Camp serviced this section of the travelling community whereas luxury camps such as Xugana serviced the wealthy, including royalty, notably Prince Charles, who was a frequent visitor. Game viewing was reputed to be outstanding, and being poled about in dug-out canoes (mokoros) even more so. So a trip to the Okavango was definitely on.

I thought of putting together a combined field trip to the Okavango, part holiday, part investigative science. Two acquaintances joined in the venture, and together with our sons, we set off to the Okavango in July 1985. Also with us was my friend and colleague, Bruce Cairncross, a sedimentologist at Wits (now Professor of Geology at UJ). We travelled extensively through northern Botswana, including a few days in the Okavango seasonal swamps. We saw the swamps from the air and from the water, and went on several mokoro trips and walks around the myriad of islands that constitute this part of the Okavango. At the end of the trip, Bruce and I were completely mystified: what is this landscape that we have seen? We just couldn’t figure it out. Shallow water everywhere, surrounding very low islands, some lush, others sparsely vegetated and dusted with salt crusts. What sedimentological and geomorphological processes could create such a landscape?

After we got back, Bruce and I got together with Kevin Rogers, Professor of Ecology at Wits, whom I had heard was involved in research in the Okavango and who had two postgrad students working there, namely Karen and Fred Ellery. As far as I recall, we had a workshop at Wits where they introduced Bruce and I to the permanent swamps. Kevin very kindly invited me to join him in September of 1985 to visit Karen and Fred at their home-base in the depths of the permanent swamps. When I arrived there, I found that this was a terrain completely different from the seasonal swamps that Bruce and I had seen earlier. It was a place of water and papyrus, with the odd island here and there. The contrast between this and the seasonal swamps was difficult to comprehend.

I was also struck by the remoteness of their camp. Karen and Fred were extremely brave (irresponsible?) to operate as they did in this remote and potentially dangerous environment. They had no radio communication and their closest contact with the outside world was Xugana Camp, a two hour boat drive away. Had anything gone wrong (e.g. snake bite, medical issues, attack by animals), they would have been in serious trouble. Today, their project would definitely not get Health and Safety approval.

Kevin, Karen and Fred had formed a very good relationship with Pete Smith (MBE), a vegetation specialist with the Botswana Department of Water Affairs who kept surveillance on possible infestation of the Okavango by Kariba weed and other invasive exotic species and he acted as an informal advisor to Kevin, Karen and Fred. Karen was studying successional processes in the open water bodies in the permanent swamps and Fred was studying the role of papyrus in channel blockage. Channel blockage was a problem for boat navigation in the Okavango, and was believed to cause channel failure and diversion. Channel blockage was believed to be caused by some property of papyrus plants, which Fred was looking to find. Elaborate efforts had been attempted since the early 1900s to combat this problem, including the launching of large papyrus harvesting machines and straightening channels by excavation. Pete Smith explained that once a channel fails, the surrounding swamp and underlying peat dried out. The dry peat eventually caught fire and burned away, leaving a dry landscape. He suggested that we take a walk to one such burnt out swamp on the old Nqogha Channel, which had been one of the major waterways of the Okavango in the early 1920s, well described in a classic paper in 1924. We did that, and discovered the most amazing landscape. The swamp was gone, replaced by dark grey, dry, dusty soil. The the bright yellow sandy channels were clearly visible, but their “topography” had somehow become inverted. Former channels, especially hippo trails and channel sand bars and point bars stood out in positive relief as ridges and mounds in an otherwise flat landscape of consolidated ash formed from the burning of the enclosing peat. Some of these mounds were clearly sand bars that formed on the former channel bed, now rising in some cases more than two metres above the elevation of the surrounding plains.

We learned a lot in the field that day. We realized that sediment accumulation (in this case channel bed sand), was a major factor in channel evolution – how else could hippo trails become sinuous mounds? That evening, we sat around the camp fire under Cadac lamps poring over Fred’s copies of the most recent and older aerial photographs of this portion of the swamps, “testing” the sedimentation hypothesis. In particular, we examined the filling of lakes in the permanent swamps as indicators of accumulation of waterborne sediment. The evidence was incontrovertible. Sedimentation was clearly a major driver in channel evolution. It was a euphoric day, a day that opened the door to understanding wetlands in drylands. If you asked me to name a day on which research on the functioning of wetlands in drylands began, this was that day. The Trans-Tswana River was brushed aside and wetland science became the new focus. Perhaps one of the nicest aspects of this new research was that there were very few, if any, parallels or other examples to learn from. Most wetland research has been done in the northern hemisphere. These northern wetlands mostly formed in response to melting of the ice sheets at the end of the last ice age a few thousand years ago. In contrast, our wetlands are hundreds of thousands to millions of years old. So we were breaking new ground at every step.

In the ensuing months we wrote up the hypotheses we had developed along the old Nqogha Channel and around the camp fire, having fleshed them out with additional data Fred obtained from Pete Smith and Botswana Water Affairs. We produced our first paper in 1986 (ref. 10). Alongside it we published findings of a mineralogical study on the salt crusts Bruce and I had sampled in the seasonal swamps (ref. 11). In a matter of a few months we laid the foundations for the understanding of this remarkable wetland. We had discovered that the structure of the ecosystem is a product of the interactions between water and sediment discharge, waterborne nutrient distribution, key plant species, climate (evapotranspiration) and animals (hippos and termites). We spent the next twenty or so years adding detail to the original hypotheses, exploiting the amazing technological advances that were taking place in this period.

There is another aspect which played a crucial role in the further development of the nascent ideas we had developed, and that was funding. Up until the early 1980s, research funding in South Africa was based on the submission of detailed proposals to the main funding body, the CSIR. The formation of large research teams was encouraged by the CSIR through what were called the Cooperative Scientific Programmes (CSP). Small groups like ours didn’t stand much chance of getting funding. What made it worse was that I had been pigeonholed as a hard rock geochemist so my chances of getting funding for wetland research were virtually zero, no matter how good my proposal might be, and in any event, the Okavango is in Botswana, which at that time was perceived as an enemy of South Africa.

The CSIR became concerned about the large juggernaut groups created by the CSP which were gobbling up most of research funding, often utilizing it very ineffectively. Good scientists who didn’t want to work in large teams were being side-lined, and many were emigrating. The CSIR engaged Prof Jack de Wet, a former Dean of Science at UCT and a highly respected scientist in his own right, to investigate this problem. He came up with a very novel solution. He reasoned that good, productive scientists would always generate high quality science, as long as they had funding and were not distracted by competitive research applications or excessive reporting. He developed the notion of grading scientists based on their past research performance and their standing in their international peer community. The plan was accepted by the CSIR and grading of scientists was introduced in 1984. Graded scientists would be funded in proportion to their grade (C to A). Research proposals would no longer be required, but recipients of funding were expected to produce short annual reports. Every five years, rated scientists would have to give a full account of their activities, and would be re-graded accordingly. They could form groups and share resources if they wished, but were under no obligation to do so. This suited me perfectly. I was graded as a B3 category scientist in the initial round, based on my hard rock geochemical research, but I ploughed all of the funding I received into Okavango research, which was augmented by small amounts of money from other sources. By the following re-grading period, I had retooled myself as a wetland geomorphologist and generalist, and was re-graded as a B2 scientist. Had it not been for Jack de Wet’s grading system, I would have become die-cast as an igneous geochemist and the Okavango research would probably have floundered.

Research in the Okavango flourished, but as we got to understand the Okavango system, new discoveries became increasingly few and far between. As far as we were concerned, there were no longer any real key questions to answer. We understood how the Okavango system worked, so we moved on to more fertile ground in other wetlands such as Nylsvlei, Seekoeivlei and the Klipspruit wetland, with its interesting anthropogenic impacts, thus opening new, more fertile research horizons.

For me, research has always been a social activity and I especially enjoy the cut and thrust of scientific debates during our projects. I believe in sharing ideas, even nascent ones, so that they can become tested and honed through debate. The knowledge thus gained is the property of the team, not of individual members. I have been privileged to work with many incredibly talented people in the course of my career, who have greatly enriched the outcome of our research endeavours. One can never know everything and that’s why team work is so important. As a consequence, I have very few single authored papers. For teamwork to be effective, openness, frankness and mutual trust between team members is essential. But the most important thing of all is to enjoy the challenges and have fun. If you’re not having fun then you should quit and go and do something else.”

Cited references:

1. McCarthy, T.S., Ahrens, L.H. and Erlank, A.J. (1972). Further evidence in support of a mixing model for Howardite origin. Earth Planet. Sci.Letts.15. 86-93.

2. McCarthy, T.S., Erlank, A.J. and Willis, J.P. (1973). On the origin of eucrites and diogenites. Earth Planet. Sci.Letts. 18, 433-442.

3. McCarthy, T.S. and Jacobsen, J.B.E. (1976). The mineralizing fluid at the Artonvilla copper deposit : an example of a silica deficient, alkaline hydrothermal system. Econ. Geol. 71, 131-138.

4. Eriksson, K.A., McCarthy, T.S. and Truswell, J.F. (1975). Limestone formation and dolomitization in a lower Proterozoic succession from South Africa. J. Sed.Petr. 45, 604-614.

5. McCarthy, T.S. (1976). Chemical interrelationships in a low pressure granulite terrain in Namaqualand, South Africa and their bearing on granite genesis and the composition of the lower crust. Geochim.Cosmochim. Acta. 40, 1057-1063.

6. Groves, D.I. and McCarthy, T.S. (1978). Fractional crystallization and the origin of tin deposits in granitoids. Mineralium Deposita, 13, 11-26.

7. McCarthy, T.S., Moon, B.P. and Levin, M. (1985). Geomorphology of the western Bushmanland Plateau, Namaqualand, South Africa. South African Geograph.J. 67, 160 -178.

8. McCarthy T S and Tooth S (2004) Incised meanders along the mixed bedrock-alluvial Orange River, Northern Cape Province, South Africa. Z. Geomorph. N. F. 48, 273-292.

9. McCarthy, T.S., (1983) Evidence for the former existence of a major, southerly flowing river in Griqualand West. Trans.Geol.Soc. S. Afr., 86, 37-49.

10. McCarthy, T.S., Ellery, W.N., Rogers, K.H., Cairncross, B. and Ellery, K. (1986). The roles of sedimentation and plant growth in changing flow patterns in the Okavango Delta, Botswana. S. Afr. J. Sci., 82, 579-584.

11. McCarthy, T.S., McIver, J.R. and Cairncross, B. (1986). Carbonate accumulation on islands in the Okavango Delta. S. Afr. J. Sci., 82, 588-591.



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