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The World Beneath the Reeds

If you come to a wilderness area such as the Umbabat Private Nature Reserve, you immediately notice the myriads of different land animal forms of all different shapes and sizes.

Mammals, reptiles, birds and even the small invertebrates and insects - you find that they never cease to amaze you with their different characters and appearances. This is why we all love a place like Ingwelala so much as it allows us to enjoy such wonders within a completely natural, undisturbed environment that just seems to speak to the soul of many.

Yet, what if I told you that the wonders of nature go far beyond the dry, on land ecosystem of the wilderness area that is Ingwelala and the Umbabat? Yes, there is a whole other world, beneath the fresh water reeds in so many of the zones where natural river water still remains in the vast river network system on the reserve.

There is complex fresh water, aquatic ecosystem that exists within the natural water systems in the Lowveld region. A fresh water ecosystem usually consists of:

Autotrophs/Food Producers:
These are aquatic plants such as the floating water fern and cabbage weed. There are also submerged plants such as Alligator weed and; Aquatic plants occur within the Littoral Zone of a fresh water pond or river.

Heterotrophs/Consumers of other biotic material:
These include all the organisms (animals) that depend on the consumption of other organisms to survive. There are different consumer categories, these are: Primary Consumers or herbivores, Secondary Consumers or carnivores and Tertiary Consumers or scavengers (these organisms feed on dead biotic or waste material which is formally known as “detritus).

What is especially interesting about the organisms in fresh water systems is that they are indicators of whether the water quality is high or poor. The balance of the chemical make-up in the water has a major influence on the organisms that can survive within a fresh water system. There is in fact, a whole study dedicated to the analyzing of the organisms that occur in fresh water to determine whether the system is under threat or not. This all forms part of Limnology (the ecological study of fresh water ecosystems).

Bioindicator Macroinvertebrate Orders:

  • Ephemeroptera (Mayfly)
  • Plecoptera (Stonefly)
  • Trichoptera (Caddisfly)
  • Megaloptera (Dobsonfly / Hellgrammite)
  • Coleoptera (Aquatic Beetles)
  • Diptera (True Flies)
  • Odonata (Dragonfly & Damselfly)
  • Pelecypoda (Clams)
  • Gastropoda (Snails)
  • Hemiptera (True Bugs)

Aquatic organisms are placed into groups, based on their tolerance to pollution. When there is abundance of highly sensitive organisms it indicates that the water is clean, because these animals require such conditions to thrive.
The groups are as follows:

Group 1 - pollution sensitive (require higher oxygen levels, neutral pH, and cold water):
Mayflies, stoneflies, caddisflies

Group 2 – somewhat pollution tolerant
Scuds, dragonflies, damselflies

Group 3 - pollution tolerant (can tolerate low oxygen, lower/higher pH, and warmer water):
Aquatic worms, midge larva

Case Study Motswari Corner
A program has begun on Ingwelala where ecologists from the AWARD conservation organization will be coming over the next few months to train staff personnel on Ingwelala to monitor the fresh water systems on the reserve, such as the river pool at Motswari Corner.

Three days in October have already been dedicated to the start of the training and involved taking live samples from the water at Motswari corner.

Aquatic Organisms found at Motswari Corner and their Indication of Water Pollution:

Cased Caddisfly Larvae (Group 1) are sensitive to pollution and therefore indicate good water conditions.

Horsefly larvae have a pollution tolerance of 6, which means that they occur within Group 3 and are relatively tolerant to polluted water conditions. They may indicate substantial pollutant concentrates in the water.

Dragonfly nymphs (Group 2) are somewhat tolerant to pollution meaning they live in good to mediocre water conditions. One will have to compare their densities compared to Group 1 and Group 3 to reach a conclusion about the water quality.

Damselfly Nymphs also belong to Group 2 and they can live in good to mediocre conditions.

Stonefly larvae belong to Group 1 and are therefore sensitive to pollution, which means they live in good water conditions (high oxygen levels, cooler water temperatures, no toxic constituents, and neutral PH)

Spiny-crawler Mayfly larvae or nymphs are very sensitive to pollution and belong to group 1. They therefore indicate good water quality.

Whirligig beetles have a pollution tolerance of 4, which means they belong to Group 2, which indicates that the water quality is good; however, some organic pollution is probable.

Predacious diving beetles are somewhat pollutant tolerant and belong to Group 2. They occur in good to medium quality waters.

Creeping water bugs are somewhat pollutant tolerant and indicate good to mediocre water quality conditions.

Water Boatman belong to the bug family. They are tolerant to pollution with a sensitivity reading of 9, which means they belong to Group 3 and indicate that the water conditions may be seriously poor.

Water scorpions are in fact bugs and belong to the Hemiptera family. They are pollution tolerant and belong to Group 3. Their presence may indicate high pollution levels.

Midges are very similar to the well known mosquitoes, and share very similar bodily characteristics, and they do feed on the blood of humans. They belong to Group 3 and are tolerant to pollutants.

Leeches are pollutant tolerant and belong to Group 3, which may indicate pollutants in the water.

Conical Shelled or Pouched Snails are pollutant tolerant

Gilled snails belong to Group 1 and are therefore sensitive to pollution in water systems

 

In order to determine a health reading for the pool at Motswari Corner, a data collection sheet is filled in with all observations from the samples gathered. This data is then taken back to the ecologist’s base, where it is processed further. One of the ecologists explained that the monitoring of the pool would have to be conducted regularly over a long period of time in order to build up long term data. It is only when long term data is formulated that trends can be picked up. This is due to these freshwater systems changing all the time. The density patterns of organisms can indicate in which direction the health of the fresh water system is leaning. So for instance, if, over a long period of time, there is a build up of Group 3 organisms and a decline in Group 1 organisms, it will show that the system’s integrity is declining as a result of pollution.

Who knew that so much life existed in such a small space? These organisms play an important role in the indicating of the health of a freshwater system and it is therefore important for reserve managers to have a good inventory of what has been found within the fresh water systems on their land.

Life on earth is all interconnected, and if we destroy our water resources through careless wastage, it will have many negative impacts on many forms of life, especially us who need so much water every day. This is why it is essential to take care of the last remaining water habitats in this country.

 

By Paige Ezzey (Conservation Intern)

References:

  • Bioindicators of Water Quality Quick-Reference Guide. - Julie Speelman and Natalie Carroll.
  • Macroinvertebrates as Bioindicators of Stream Health. - Schumaker Chadde, M.S. Water Resource Specialist.

John L: Thank you, Paige, for a well written and enlightening article on “the world beneath the reads”. River ecosystems can be so fragile and deserve a lot more attention, research and understanding than they have been afforded in the past. Much is still to be learned, and I look forward to understanding future diagnosis of the general health of our river systems and how we can better manage these processes going forward.