African Wildlife & Environment Issue 76 FINAL

CONSERVATION

How many times have you heard someone saying that freshwater flowing into the ocean is a 'waste of a resource'? My response is always one of anger at the ignorance of the individual concerned. Ecosystems are defined by the flow of water, wind and nutrients through a landscape. The operative word in this observation is ‘flow’, because we know that matter can neither be created nor destroyed, merely transformed from one form into another. Water is a key element of that flow, so let us delve deeper into this fact from an environmental perspective. Does freshwater flow into the ocean constitute AWASTEDWATER RESOURCE?

Prof Anthony Turton

reduces its erosion potential. In a desiccated landscape we typically see canyons and gullies sculpted by water of great energy potential. That erosive energy arises from massive flows over short periods of time that have not been attenuated. Intercepted water always implies the presence of vegetation that attenuates the flow by releasing energy. This in turn implies lower soil temperature so that microbiota can survive.

South Africa is mostly semi-arid, except for a few places like the Natal Midlands that are well-watered. Aridity refers to the relationship between water falling as precipitation on the one hand, versus water returning to the atmosphere as evaporation on the other. It’s about the balance of water coming into a system, as opposed to water leaving that system in the form of vapour. Aridity is not about the lack of water. In fact, arid

regions sometimes have masses of water, often to the point of doing serious damage, as we saw in the Laingsburg flood in January 1981, where most of the town was demolished with the loss of 104 lives. So, it is not about the volume of water available, but rather about the balance of water left in the ecosystem after a rainfall event, and after the desiccation by wind and sun. More importantly it's about thefloodpulsebetween events. Arid landscapes are desiccated ones. This is a central feature pertinent to the relevance of water in such ecosystems, because it is the microbiota - the bacteria, fungi and archaea - found in the soil that make the difference. Dried soil is unable to sustain microbiota, so it becomes nutrient- depleted over time. The absence of water, elevated temperatures from the sun, and the parching winds collectively play a role. But what of the rivers and aquifers that receive water from surface flows? When water falls as rain, it is intercepted by vegetation. The more vegetation there is, the greater the interception. This means that where vegetation is present, water striking the surface has been slowed down. This

Image 1 : 27 Apr i l 2012

Image 2 : March 2015

8 | African Wildlife & Environment | Issue 76 (2020)