Michael Samways
Cape Town - People need healthy freshwater.
It supplies our basic needs, whether for drinking, washing, irrigating our crops, or for driving power and production industries.
But water systems only remain healthy and vibrant when the biodiversity associated with them is maintained intact.
Plants take in water through their roots and store it aboveground in their structures. Water is then slowly delivered back into the atmosphere to fall as rain again somewhere else. Plants also hold the soil in place, which prevents erosion and redistributes water across the landscape.
The soil that supports the plants is also a living system, hosting millions upon millions of microbes, tiny animals and fungi that keep it alive, stable, and rejuvenated.
In short, water, soil and biodiversity are highly connected. Other water gently drains off the healthy green landscape to eventually find its way into stream systems. These streams then join as one, growing into rivers. Where the land is level or at the base of slopes, water is retained as pools, lakes, or marshlands.
These are sponges that not only support a magnificent suite of organisms but also circulate water to the surrounding soils. And so, the cycle of water and life continues, at least, until we over-exploit them.
The International Day for Biological Diversity, celebrated annually on May 22, serves as a timely reminder that freshwater ecosystems, along with their marginal and bankside vegetation and other biodiversity, are among the most biodiverse on the planet, providing essential services for people.
Yet these ecosystems are declining on every continent and in every river basin. Today, about one-third of global freshwater flows through agricultural, industrial, or urban areas.
In turn, about one-fifth of farmable land is irrigated, with this proportion likely to go higher than one-third by mid-21 st century. Also, only about one-fifth of the world’s pre-industrial freshwater wetlands remain, with less than one-tenth likely to remain intact by 2050.
Projections are that human use of critical water resources will approach 50% by 2050.
However, with some firm policy actions, the decline of freshwater ecosystems can be slowed. This is among the highest of all our priorities for a sustainable future if we are to survive in the long term.
The challenge lies with freshwater ecosystems being disadvantaged in several ways. Firstly, they can be influenced by events that take place far upstream.
Secondly, they are also subject to the impact of many land-use effluents and are prone to human activities on the surrounding land and along the banks.
Thirdly, there are competing interests among many types of human water consumers. From a biodiversity point of view, freshwater ecosystems support many irreplaceable and localised species that are unable to escape the multitude of harmful impacts.
Human impacts on freshwater fall into five categories: over-exploitation, water pollution (agricultural, industrial, urban, pharmaceutical), flow modification, degradation and destruction of habitats, and invasion by alien species.
There are also many new types of impact, such as rapidly changing climate, increase in intensity of commerce, rise of infectious diseases, harmful algal blooms, expanding hydro-power, emerging contaminants, engineered nano materials, micro plastic pollution, light and noise pollution, freshwater salination, declining calcium, and cumulative impacts. All the impacts, together, are damaging food webs, making them increasingly difficult to repair.
Another challenge is to address the relationship between landscape change and its effect on water movement and ecological processes, especially in terms of the amount and quality of water run-off, water quality, and soil loss.
Landscape topography and its spatial distribution can change rainfall run off processes.
In turn, water quality is intimately related to composition and spatial patterns on high ground versus low ground, which affects the amount of sediment passing along the length of a river.
Research suggests that for sediment and many nutrients, the effects of harmful effect of adjacent land use can be detected up to four kilometres away from streams.
This means that the wider landscape and its biodiversity must always be uppermost in our minds, as the overall system is connected by the dynamic movement of groundwater.
One of the greatest concerns is that there is overall impoverishment of fresh water biodiversity and ecosystem change arising from the interactive effects of habitat degradation and loss, loss of specialist indigenous species, and invasion by alien species.
Overall, the result is often not so much a loss of species but their replacement. This changeover makes for a much duller and less resilient world.
This compares with the effect of polluting chemicals which may not be so obvious yet can be very widespread.
There are about 100 000 chemical compounds in daily use which can enter freshwater systems. These are strongly associated with land use in catchments caused by intensive agriculture and/or urban activities. Yet we know so little about the chemical risks that many of these compounds may pose for biodiversity.
A pan-European study of 4 000 sites and 223 compounds showed that the most impactful compounds on small water crustaceans were pesticides by far, at 87% of the sites, followed by polycyclic aromatic hydrocarbons (chemicals found in coal, crude oil, and gasoline), organotin compounds (chemical compounds in wood and textiles preservatives, plastic, anti-fouling paint), and brominated fire retardants, as well other compounds.
The significance of this is that these little creatures are at the base of the food chain for so many other animals.
Given these challenges, what is South Africa doing to conserve its freshwater biodiversity?
Without doubt, the Working for Water programme, whose primary goal is to remove aggressive foreign trees, has made a massive contribution.
These alien trees smother streams and rivers, blocking out sunlight and making the water and ground areas largely unsuitable for many local species.
Removal of the invasive trees returns the sunlight allowing the indigenous species, whether plant or animal, to return on their own.
Other protection measures are also playing a major role. The responsible sector of the timber industry has put in place large conservation corridors along streams and rivers between plantation tree blocks.
These corridors are well-managed and allowing much local biodiversity to occupy these areas and be resilient in this ever-changing world.
Finally, it is important to recognise that South Africa, being a dry country, has well over half a million artificial water bodies, mostly in the form of farm dams. When these are well maintained and managed, they make a massive contribution as refuges for a whole swathe of local biodiversity.
Michael Samways is Emeritus Distinguished Professor in the Department of Conservation Ecology and Entomology at Stellenbosch University.
Cape Times