Home
Forgot your password?
Mega-transect of Senqu-!Gariep River system sets baseline for the future
|
A little over two months have passed since reaching the end-point of our journey down the Senqu and !Gariep (previously called the Orange) rivers.
This is about as much time as it took Dr Ian Durbach (Senior Lecturer, Statistical Sciences Department, UCT), James Puttick (PhD student, Biological Sciences Department, UCT) and I to paddle from Qachas Nek, high in the Maluti Mountains of Lesotho, to the Atlantic Ocean at Alexander Bay; a distance of over 2 000 km.
So, perhaps this is a fitting time to reflect on what was a truly grand adventure...
Our river journey was born from a collective desire to experience the wild outdoors for an extended period of time, and to get a taste of what it meant to live a simpler, less frenetic lifestyle. But we also wanted the journey to have some greater purpose. So, being (two-thirds) natural scientists, the obvious choice was to document our changing natural surroundings, and collect potential baseline ‘change-indicator’ samples as we progressed downriver.
A quick web-search suggested that, while there had been several broad-scale studies on the condition of the !Gariep and Senqu basins, no systematic river-based data collection effort spanning the full lengths of these rivers had been attempted. Therefore, what we envisaged - a data capturing mega-transect of the Senqu and !Gariep Rivers - was something quite novel.
Unsung heroes of the natural world
Yolandi Els, the former Coordinator of the SAEON Arid Lands Node expressed keen interest early in the evolution of the project, given the importance of the !Gariep River system in the generally arid environment that characterises the north-western parts of South Africa. Yolandi soon recruited an enthusiastic Dr Jonathan Taylor of the North West University as a key collaborator with a passion for diatoms, unsung heroes of the natural world.
Interesting aside: Diatoms come in many shapes and sizes and are probably one of the most underappreciated forms of life on planet Earth. There are approximately 100 000 extant diatom species, many of which are free-floating in the world’s oceans and freshwater bodies (just the ocean component accounts for a staggering 45% of primary productivity!). According to a National Geographic article, diatoms make up a quarter of all plant life by weight, and produce at least a quarter of the oxygen we breathe!
One grouping of diatoms that Jonathan is interested in form a thin, slippery layer on submerged rocks and vegetation. Species have differing sensitivities to the physico-chemical properties of water, and tracking changes in their assemblages can therefore be a useful indicator of water quality. For us, an additional advantage was the rapidity with which they could be sampled and the simplicity of the equipment involved.
Historical vegetation changes at landscape level
Professor Timm Hoffman, Director of the Leslie Hill Chair for Plant Conservation within the Biological Sciences Department at UCT, was another early and eager collaborator. His chief interest is in documenting and accounting for historical landscape level vegetation changes, using the technique of repeat photography. As such, he was interested in establishing a current baseline photographic record for the !Gariep River, the most important (and arguably most transformed) waterway in South Africa.
While acknowledging that the river system has seen profound changes in the 20th century, primarily due to the erection of numerous dams and weirs, the establishment of a current baseline would nevertheless prove useful for assessing ongoing modification (due to additional weirs, for example), agricultural, mining and housing development, changes in vegetation composition and structure due to changing climate, etc.
With regard to the latter point, the east-to-west course of the Senqu and !Gariep rivers not only provides a useful means of documenting vegetation response along a moisture gradient, but also provides an opportunity to assess changes at the interfaces of at least four different biomes. While the photographic data might not necessarily be useful at present, the data are certain to be invaluable to future researchers hoping to understand what the system used to look like, and what changes have taken place.
The exercise required some high-tech equipment, and also greater expertise, and we were fortunate to have James - an accomplished photographer - along to lead this aspect of the data gathering process.
Further data collection
Suggestions from numerous other interested individuals led to further data collection. Examples include water samples collected for isotope analysis (in collaboration with Roger Diamond of the Department of Geological Sciences at UCT), daily recording of all bird species (as well as counts for selected species), the location of fishing and mining activity, as well as water abstraction points, and several others.
We were embarking on this journey with little kayaking experience, so the initial few days proved a steep learning curve, with impromptu swims happening frequently. Learning progressed quickly, though, as the cost of failure meant a bumpy swim and a tough job trying to muscle several hundred kilos of water-filled kayak to the bank before being sucked down the next rapid! Thankfully river levels were high due to good summer rains, so the river was much less ‘boney’ than it could have been. An added plus was that the kilometres were ticking by nicely due to the swift flow.
However, what proved to be good fortune in terms of injury-avoidance and greater speed due to water levels, turned out to be bad fortune from a diatom sampling viewpoint. Seasonal rains cause a frightening amount of sediment to be washed into the river; a serious and ongoing problem in Lesotho. The sediment acts as both a light-excluder and a fine sandpaper, scouring the delicate film of diatoms from submerged rocks. Despite this problem, we persevered with the sample collection in the hope that some diatoms might have survived the ill treatment and that Jonathan might find these few survivors using nifty lab techniques!
Fortunately, as the river leaves the mountain kingdom of Lesotho the flow gradually slows and sediments settle out of the water column. Diatoms consequently become far more abundant. I never thought I would let out a ‘whoop’ of delight at the sight of a thriving green slimy film, but that is exactly what happened when the diatoms’ presence started becoming more conspicuous in the vicinity of Aliwal North.
Meanwhile, James was having no such troubles. The deep green valleys, the majestic sandstone cliffs, the faraway views, the rich evening colours ... he was in his element! But not without one or two scares ... These usually took the form of a desperate scramble, steel tripod in hand, trying to rapidly lose elevation from a high vantage point as thunder and lightning crackled ominously around him. Fortunately he survived these frenetic descents, often only to find Ian and I frantically waving our steel tent-poles around in an effort to erect shelter before the impending downpour.
Rich bounty
Now back in Cape Town, the laborious task of entering, organising and collating the data is finally complete and various bits have been shipped off to the parties involved. All told, we collected a total of 61 diatom samples and took 60 high resolution landscape images, so roughly one sample per paddling day.
In addition, James took kayak-based panoramas of the river surrounds at approximately 2 km intervals, amounting to well over a thousand panoramas. We also collected 53 isotope samples and recorded more than 1 400 locations of interest, including approximately 600 water abstraction locations and 700 fish eagle, goliath heron and giant kingfisher sightings.
The next step is data analysis, specifically of the diatom data, and this is something Jonathan is currently busy with. Hopefully the data will help characterise the health state of the river along various sections of its course in higher resolution than has previously been possible. For example, it would be interesting to see to what extent water quality deterioration after the Vaal confluence affects diatom assemblages. Similarly, it would be interesting to know if the absence of agricultural activity bordering the river within the national parks (Augrabies and Richtersveld) leads to improvements in water quality.
For the future...
Ultimately our concern is for the long-term health of the Senqu-!Gariep system, not just for maintaining the services it currently provides, but for the benefit of future generations. We hope that this baseline dataset will be useful in helping manage for this forward thinking, truly sustainable outcome.
This scientific expedition was co-funded by SAEON’s Arid Lands Node and the Plant Conservation Unit within the Biological Sciences Department at the University of Cape Town. A courtesy vehicle was provided by the Mazda Wildlife Vehicle Fund.
