Jeremiah's Pan EarthCache

Wetlands:

According to the South African Water Act a wetland is a “land which is transitional between terrestrial and aquatic systems, where the water table is usually at or near the surface or the land is periodically covered with shallow water, and which land in normal circumstances supports vegetation typically adapted to life in saturated soil”.

Wetlands are among the most productive ecosystems in the world, comparable to rain forests and coral reefs. An immense variety of species of microbes, plants, insects, amphibians, reptiles, birds, fish, and mammals can be part of a wetland ecosystem. Physical and chemical features such as climate, landscape shape (topology), geology, and the movement and abundance of water help to determine the plants and animals that inhabit each wetland.

Wetland formation is influenced by a combination of the geology, hydrology and topography of a landscape. Wetlands form in parts of the catchment where the movement of water is slowed down or obstructed, causing the soils to become temporarily, seasonally or permanently waterlogged.

1. Geology plays a role in the formation of wetlands in two main ways:
   • A geological obstruction may resist downward erosion, resulting in extensive flat areas where water accumulates if there is enough surface groundwater. This obstruction often consists of very hard erosion-resistant rock, such a dolerite, but alluvial soil deposits may also act as an obstruction. An obstruction may even be caused through geological faulting.
   • Impervious material close to the surface forces groundwater to discharge upwards. Wetlands that form around these are called seeps.
   
   
   
2. The hydrological cycle is the continuous movement of water, over, above and beneath the earth’s surface. Hydrological characteristics which influence wetland formation are:
   • Water sources (precipitation, surface water inflow and ground water inflow).
   • Water movement through the wetland (surface flow and subsurface flow).
   • How water exits the wetland (evaporation, surface water outflow and groundwater outflow).
     
     
     The Hydrological Cycle
   
   
   
3. Topography is the term used to describe the three-dimensional features of the earth’s surface, and specific landforms. The topography of a landscape influences if and where wetlands will form. For example, under the right conditions, wetlands are likely to occur in floodplains, valley bottoms, hillslopes, depressions and coastal flats.

Hydrogeomorphic types in South Africa

Three indicators of wetlands:

1. Hydromorphic (waterlogged) soils: As soil becomes increasingly wet, water starts to fill the spaces between soil particles. When all the spaces are filled with water the soil is said to be saturated. In wetlands the water persists or drains away very slowly and the soil is flooded for long periods. Depending on factors such as temperature, it usually takes a week or so for the plant roots and other living organisms in the soil to use up the oxygen, causing anaerobic conditions to develop. If the soil is saturated and the anaerobic zone is within the upper 50cm of soil (the main rooting zone) it is generally close enough to the soil surface to significantly influence the plants growing in the soil. This will cause the area to develop characteristics of a wetland.
   
   Anaerobic conditions affect organic matter in the soil. The wettest parts of the wetland, which are most anaerobic, tend to have the highest amounts of organic matter. Low temperatures also promote organic matter accumulation. Soil with a very high organic matter content is referred to as peat.
   
   The water regime has a strong effect on the colour patterns of the soil. This means that we can indirectly determine what the water regime is for a particular area by interpreting these patterns. When a wetland is drained and the water regime is changed the soils retain their characteristic colour signatures forever. Therefore, soils are useful for indicating if a drained area used to be a wetland. This helps in mapping where wetlands used to be and assists in working out the extent of wetland loss. Because colour patterns develop slowly they reflect ‘average’ conditions over a long time. They save us the time and effort of measuring the water regime continuously. These colour patterns are read by looking at the soil colour, and the presence of mottles in the top 50 cm of the soil profile.
   
   
   • Soil colour - Well drained soils (dry land) that are seldom saturated have enough oxygen present to oxidise the iron, resulting in a uniform red/brown/yellow colour. Under anaerobic conditions, when the soils are waterlogged, the iron oxides are reduced and broken down so wetland soils are generally grey in colour.
   • Organic matter - Most micro-organisms which decompose organic matter use oxygen in the process. This means that organic matter is not as readily broken down in waterlogged soils. The wettest parts of the wetland, which are most anaerobic, tend to have the highest organic matter content. This results in darker soil (and more grey) as you move into wetter sections of the wetland.
   • Mottles - When anaerobic soil dries out, iron oxides form orange, yellow or red spots called mottles. So, soil, which is grey, but has many mottles, will indicate a zone with fluctuating (rising and falling) water table. In permanently wet soils, mottles will not form in the soil, as no oxygen is present. However in some instances for permanently waterlogged soils, mottles may form in tubes around plant roots, where oxygen has diffused out of the root into the surrounding oxygen deficient soil.
   
   
   
   Mottles in wetland soil
   
   
2. Hydrophytes: These are plants that have adapted to surviving in waterlogged soils. They generally have a rooting depth of 50cm, and therefore need to be in contact with the water table at this depth, or less.
   
   
3. High water table: In most parts of the landscape the water table lies many metres below the soil surface. However, in wetlands the water table usually lies close to or above the soil surface. Do all wetlands have similar water regimes (changes of wetness in soil over time)? Not at all. Wetlands range from permanently waterlogged areas, which remain flooded or saturated to the surface for the entire year, to temporary waterlogged areas, which are flooded or saturated close to the soil surface for only a few weeks in the year (but still long enough to develop anaerobic conditions).

This Earthcache will take you to an area that contains an Ephemeral Wetland (seasonal pond).

Ephemeral Wetlands are depressional wetlands that temporarily hold water in the spring and early summer or after heavy rains. Periodically, these wetlands dry up, often in mid-to-late summer. They are isolated without a permanent inlet or outlet, but may overflow in times of high water. Spring rains fill ephemeral wetlands and these are free of fish, providing breeding habitat for many amphibians and aquatic invertebrates. The developing larvae provide an important food source for migrating birds. By mid-summer the wetland begins to dry out and the surrounding upland habitat becomes critical for the newly emerging amphibians. Many amphibians over-winter in the surrounding upland habitat during the winter months.

African Giant Bullfrog

At the given coordinates, you will find one of the last remaining African Giant Bullfrog (Pyxiecephalus Adspersus Tschudi) breeding pans in the world, proclaimed a nature reserve in 1994. The wetland area was, until the mid 90’s, privy to the summer season migrations of these, now critically endangered, bullfrogs where literally thousands of Giant Bullfrogs (the second largest frog species in the world) invaded the surrounding properties and roads.

But times have changed and, as the area and its surrounds have grown, so has ignorance towards the preservation of this wetland. People are taking little cognisance of Midrand’s indigenous frogs, which has led to a dramatic decline in their numbers, and that which has led to a set of other environmental impacts including a growing number of termites in the area which are traditional prey to the frogs. As an endangered species it is critical to preserve and conserve the Giant Bullfrogs and their territory, which includes the surrounding Grassland and its existing water-source.

Due to the ephemeral status of the site the water table remains high, and in the rainy season the areas come alive, small springs appear and shallow clay pans fill with water, creating a perfect habitat for the frog population during the breeding season. The bullfrog spends about 11 months burrowed under the soil (up to a kilometre from their chosen wetland) in a state approaching suspended animation. They secrete fluid that sets around their body in a keratin shell, with two small holes for their nostrils. In a drought, they might stay buried for two years. When the rain comes, they make their way to their breeding grounds. After mating, females retreat to their burrows, but males stay and protect the fertilized eggs and the tadpoles against any predators. The male frogs will sometimes dig a channel to lower water as the puddles dry up and herd the tadpoles down the channel, emitting noises like a motorcycle in a low gear.

The bullfrogs are a muddy olive colour with lurid orange underarms and creamy bellies and can live to about 20 years in the wild. Unfortunately, because of habitat loss, frogs in Midrand are surviving only five years and are now significantly smaller than they had been in the previous century.

But the pan is not only home to our friends the Bullfrogs, it also plays witness to a menagerie of animal, bird and plant life. The pan remains a favourite migration stopover for the Yellow Billed Stork, Spoon Billed Stork, Cormorants, White-faced Ducks, Flamingos, Egrets as well as droves of Egyptian Geese. Besides the ecological importance of the Wetlands, they also act as sponges during heavy rains, absorbing excess water and preventing flash floods. Furthermore, scientists are beginning to realize that atmospheric maintenance may be an additional wetlands function. Wetlands store carbon within their plant communities and soil instead of releasing it to the atmosphere as carbon dioxide. Thus wetlands help to moderate global climate conditions.

Historically, wetlands have had been undervalued by people. The soils are rich, but are waterlogged, so wetlands have been drained to make room for fields and farms (as can be witnessed here). In many places, wetlands have been filled in to build houses, office buildings, and factories. It is imperative that people understand how important wetlands are to the health of the greater ecosystem.

What are the threats to this wetland (and the endangered African Bullfrog breeding here)??

• Illegal Dumping. During the rainy season, poisonous parts from batteries, motor oil, varnish, paints, etc. seep into the pan
• Drainage and embanked plots have altered the flow of the water
• Uncontrolled development on the agricultural holdings and industrial businesses abound in the vicinity of the wetland
• Electrical fencing, razor wires and walls restrict the natural migration routes of the bullfrogs to the wetland
• Invasion of alien vegetation such as the Wattle, Prickly Pears, Silver Leaf Bitter Apple, Creeping Milkweed, Purple Top, Pom-Pom Weed and a host of waterweeds
• Burning and unsolicited cutting of the surrounding grassland affects the wetland ecology and threatens the frogs in hibernation

To claim this Earthcache please complete the following tasks:

1) Observe the surrounding area and explain how geology, hydrology and topography plays a role in the formation of this wetland. Read the content of this listing to guide you in what to look for.
2) Three indicators of wetlands are mentioned in this listing. Which are clearly present at this wetland and elaborate on what exactly you observe here (comment on soil colouration, presence of mottles, hydrophytes and the water table levels). Please do not enter the restricted area, respect the environment!
3) Why should wetland areas be protected?
4) Can you observe any potential threats to the future existence of this wetland? Please elaborate, be specific.
5) Name two precautionary measures that people living around this wetland area should take to preserve it for the sake of the future existence of the endangered African Giant Bullfrog. Are these precautions taken in the area? Tell me what you’ve noticed.

If you like, please share your experience of visiting this Earthcache by posting some photos (please don’t add photos that will give answers to the above questions). Hopefully, in summer, you can spot some African Giant Bullfrogs! Careful not to step on the babies!!!

Please send your answers to 'teamginger@gmail.com' for approval of your log (don't post them in your log). Find-logs posted without the required answers will be deleted, thanks for your understanding.

I have earned GSA's highest level:

Credit is given to the Mondi Wetlands Programme (MWP) and WaterWise (Rand Water’s environmental brand) for providing information on South African wetlands.

I hope you enjoy your visit!

Drive slowly during the rainy season! Speeding cars during and after a good summer rain are bad news for all kinds of animals but especially for our Bullfrogs. Give them the right of way!