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Water Wise Watch - March 2024


March Cover Page

This month at Water WiseInvasive Alien Plants – Rand Water’s Control Strategy at the Vaal River Barrage Reservoir

Water Lettuce

What are Invasive Alien Plants (IAPs)?

Invasive Alien Plants (IAPs) refers to plants that are non-native to an ecosystem, which may cause economic, environmental harm or adversely affect human health. Particularly, they impact adversely upon biodiversity, including the decline and/or elimination of native species – through competition, predation, or transmission of pathogens – resultant in the disruption of local ecosystems and ecosystem functions.
Why are they an issue?

Invasive Alien Plants, introduced and/or spread outside their natural habitats, have affected native biodiversity in almost every ecosystem type on earth and are one of the greatest threats to biodiversity. Such invasions are among the top drivers of biodiversity loss and species extinctions across the world with IAPs having contributed to nearly 40% of all animal extinctions, as suggested by a study done by Bellard, Casey & Blackburn (2016).  

The problem continues to grow greatly at an ecological, socio-economic and health aspect around the world. Invasive Alien Plants exacerbate poverty and threaten development through their impact on agriculture, forestry, fisheries and natural systems – which are an important basis of peoples’ livelihoods – particularly in developing countries, like South Africa. This damage is aggravated by climate change, pollution, habitat loss and human-induced disturbance.

Invasive Alien Plants are not static and can be introduced to a new water source from one that is impacted, by birds, humans, boats, jet skis or any moveable object via the transfer of IAP seeds, seedlings or plants. These can regrow asexually (i.e. vegetatively) and sexually (i.e. seeds), allowing for exponential growth in the new water source. Environmental factors such as winds and poor water quality (i.e. high organic nutrients) can exacerbate the spread of IAPs like Pistia stratiotes (water lettuce) and Pondeteria crassipes (water hyacinth) by promoting seeding and seed dispersal, as seen in the Vaal River Barrage Reservoir (VRBR).  

How can IAPs be controlled?

There are four methods of control, that can be utilized to control and/or avert infestations of IAPs. These include mechanical, chemical, biological and an integrated control. The different methods of control, are as follows:

1. Mechanical

Mechanical control refers to the use of machinery to physically remove IAPs from a system. For example, in an aquatic environment, IAPs like P. stratiotes and P. crassipes, are controlled by “raking”, “mowing” or “hauling”. Disturbance stemming from the physical removal can cause the seed bank to proliferate, hence why it is pivotal to have continuous follow-up actions, to improve efficiency. The disadvantages of this method, when used solely, is that the rate of growth of the AIS usually exceeds the control efforts, resulting in inefficiency in control and is also labour intensive.

2. Chemical

Chemical control refers to the application of registered and approved herbicides directly to the IAPs, with the aim of suppressing and subsequently killing it. In order for the process to be most effective, the choice of herbicides, correct application method, dosage, time of application and follow-up actions, are imperative. Improper use can result in the persistence of these in the water, leading to further ecosystem degradation.
3. Biological
Biological control refers to the use of host-specific natural enemies of the IAPs to reduce the population(s) to an acceptable/aesthetically-pleasing level. Host-specific biocontrol agents do not interfere with the indigenous flora and fauna, as these feed predominantly on the IAPs, where the disappearance of the said IAPs would entail the disappearance of the biocontrol agent. An example of this, are the weevils that have been released at the Vaal River Barrage Reservoir to counteract the exponential growth of the P. stratiotes (water lettuce) via herbivory. The weevils damage the plant material, inhibiting further growth and reproduction of the plant, reducing the population therein.
Figure 1: An illustration of a weevil feeding on a hyacinth leaf

4. Integrated

An integrated control method, as employed by Rand Water at the VRBR, encompasses a combination of the three methods, as a strategy to control and reduce the AIP populations, in the system. In essence, mechanical removal will be employed to remove dense mats of these weeds in the mid to lower stream of the river, whilst upstream areas, covered by dense mats, will be sprayed by registered and approved herbicides (by the relevant departments), following a stringent method which aims at limiting the contact of the herbicide to the plants and not the water. Follow-up mechanical removal will then be conducted to ensure that these do not further add to the nutrient load of the system, as they submerge in the water post-spraying. In the longer-term, biocontrol agents will also be released to aid in the control of these large mats, particularly in tributaries and slow-moving parts of the river, creating a population of weevils that will then actively control the VRBR, biologically.

Quick facts about the VRBR & IAP infestation

  1. The area under management for IAPs is approximately 930 hectares in extent with numerous reed beds and other smaller channels.
  2. Poor water quality from numerous upstream pollutants and overflows from sewers have contributed to the reduced water quality which acts as a feeder for these IAPs.
  3. Rand Water, in collaboration with industry-leading scientists from the Centre for Biological Control (CBC), uses host-specific biocontrol agents, that have been approved by the Department of Forestry Fisheries and Environment, which will not alter or disturb the natural/indigenous ecosystems at the VRBR.
  4. Rand Water’s water supply will not be impacted by the integrated control being implemented at the VRBR because:
  • Rand Water does not extract water for purification and subsequent dispersion from the VRBR.
  • The water that is purified and dispersed by Rand Water undergoes a stringent testing process that is ascribed in SANS 241; it cannot cause cancer from the herbicides used at the VRBR.
  • Studies, from credible institutions and scientists, reiterate that following an integrated control method is best in reducing IAP populations and limiting future infestations, over a long-term.

This month at Water WiseWorld Wetlands Day 2024 

Water Wise at ZooWorld Wetlands Day (WWD) pays homage to the intertwined miracles of freshwater, the essence of life, and the existence of wetlands, every 2nd February, each year. It is a global celebration dedicated to fostering awareness about the profound significance of wetlands for both humanity and our planet. Rand Water’s Water Wise commemorated WWD at the Johannesburg Parks & Zoo, in collaboration with Johannesburg Zoo & City Parks and various other stakeholders, including Birdlife South Africa and Pick ‘n Pay. The day was filled with fun activities, aimed at grade 6 school-goers from Molalatladi, Sekwati and Goza Primary Schools. The focus on the day was on the importance of conserving wetlands and the role that wetlands play to humans and biodiversity alike, particularly the flufftail.

Water Wise gardening ideasAutumn - The Season of Change

Autum season

March, a perfect transition between the long hot summer days to the cooler shorter autumn days; a perfect season for planting in the world of gardening. With autumn slowly creeping in, and the leaves starting to fall in and around our garden, this is the best time to get plants established before the winter period. This season enables one to ‘reset’ their garden, where proper weeding and soil feeding can be done, before the onset of winter’s dormancy.

How can you improve your garden?

  1. The falling leaves are a great mulching source – collecting these and repurposing them into your garden will help greatly in conserving soil moisture whilst retaining soil heat, during cooler nights.
  2. Soil preparation is paramount – the addition of compost into your bed as you till and turn can do wonders for your crops in their growing season, post sowing, by availing key nutrients like nitrogen and phosphorous, integral in their growth and development.
  3. Weed out the weeds – as the season of dormancy beckons, it is beneficial to your garden to ensure that you tackle the weeds in your garden, to reduce labour in the summer months, when the seed bank in your soil, blooms. Weeding out in the colder months, limits the reproductive processes of the weeds, inhibiting their future growth.

To access plants to sow in your garden in various regions of South Africa, click here.

WW tip of the monthHigh Water Demand in Gauteng – What Can We Do?

Water demand

Over the past few months there has been a constant reminder from entities like Rand Water on the overutilization of water resources in the Gauteng province, prompting various restrictions, like the use of potable water to tend to your garden during select hours, amongst others. Further, this an issue that will soon be exacerbated by the prevalence of an El Nino cycle, which will prolong periods of drought, increasing the strain on water resources.

As responsible citizens who are #waterwise, how can we pledge a hand?

  1. Leaks – checking for leaks in and around your household, particularly in high use areas such as your bathroom (i.e. faucets, toilets and showers etc.), water meters and piping, can go a long way in saving water. Reports demonstrate that over 40% of potable water is lost to leaks. Fixing a leaky tap can save you over 1Kl of water each month. Another nifty way of checking for leaks in your household is by observing meter readings; unexplained large deviations from monthly averages can indicate a leak within the household, prompting one to investigate on the potential leak.
  2. Greywater – you may have heard of the term greywater; a precious resource that you should not eagerly flush down your drain. Greywater is essentially water that has been used for various activities the household and does not contain human, pet excrement or secretions. It can be recycled from one activity to another, reducing the reliance on potable water, each time. As an example, one may repurpose the water used in washing dishes/laundry into the garden, diluting the soapy elements with potable water. The garden will equally love it as it is high in nutrients.
  3. Irrigation – Be honest, how often do we check the state of our irrigation pipes? Perhaps these are cut and are resultant in the loss of vast amounts of water; perhaps these operate outside of the recommended hours for #waterwise watering (i.e. before 06h00 and after 18h00, in the summer months). Ensure that when you run irrigation lines that you check for leaks, clogs or cuts in the piping. This will enable you to proactively repair, change or improve your system. Also, automated systems need to be checked to ensure that the hours at which they operate are optimal for the season and match the municipal water restrictions, limiting improper/needless watering of our gardens.

Environmental days

March calender
03. World Wildlife Day
04. Community Clean-Up Day
14. Int'l Day of Action for Rivers
18. Global Recycling Day
21. International Day of Forests
22. World Water Day
20-26. National Water Week
25. Earth Hour
30. International Day of Zero Waste

Water and environmental news

Cape Town water confirmed as safe to drink

“… The City of Cape Town has lifted a precautionary boiling notice in the "Deep South Areas", following signs of anomalies in the water … this comes after the City issued the precautionary notice on Friday”.
Cape town story
Confronting South Africa’s water crisis starts with conserving the water we already have

“… As the 30th driest country in the world, South Africa has to ensure that it’s not losing what little water it already has. Maintaining and repairing our water assets has to be our first priority — every water reuse decision and action flows from there…”
SA water crisis
SA advises two-minute shower over water shortage

“… Rand Water and Johannesburg Water jointly announced on Sunday that excessive water consumption by residents … In a bid to avert disaster, these utilities are urging residents to adopt immediate water-saving measures, including reducing shower times to a mere two minutes …”

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