Welcome to the The Winthrop University Wetlands. Generally, wetlands are located within topographic features that are lower in elevation that the surrounding landscape such as depressions, valleys, and flat areas.
This 1.1-acre wetland area adjoins Winthrop Lake and offers a research and learning opportunity for visitors of all ages. It is a great glimpse of the fast-disappearing Piedmont wetlands. This active wetlands area not only provides study opportunity for area teachers and students but also improves the overall health of Winthrop Lake. Below you’ll learn about the geology of the wetlands located here on the Winthrop University Campus.
Geology of Wetlands
Geology is the study of rocks. The average person thinks of rocks as hard materials such as granite, limestone, and sandstone, but geologists also include softer materials in their definition of rocks. Silt, clay, mud, and peat are all relatively soft substances that accumulate on parts of the Earth's surface, and they are regarded as rocks by scientists who study geology. Geology is an important aspect of wetland studies for a variety of reasons. Wetlands lie on the surface of the Earth and are underlain by rocks; the extent of the wetlands, the chemistry of their waters, and the kind of sediments that build up within a wetland are therefore influenced by the underlying geology of the region.
Geology and Wetland Landscapes
Wetlands can develop only in regions where water accumulates, and this means that the ground underlying the wetland must be impervious to water. Some rocks are much more easily penetrated by water than others. Limestone, for example, absorbs water, so water gradually sinks through it. Water also dissolves limestone, especially if the water is acidic, which is usually the case for rainwater, and acidic drainage water excavates cracks, caves, and caverns that quickly carry away any water that lies on the surface of the rocks. Sandstone
is made up of numerous sand grains compacted and cemented together, but there are usually tiny spaces remaining between the grains. Therefore water can seep through the rock and drain away. Granite is formed by volcanic activity, which produces a molten rock that subsequently cools and crystallizes. As a result all air spaces in the rock have been sealed, and it is impervious to water. Shale and slate are sedimentary rocks, meaning that, like sandstone, they have been formed either under the oceans or in former wetlands, where
waterborneparticles have been deposited and gradually compacted into rock. Unlike sandstone, which has undergone no further process following compaction, shale and slate have been heated to high temperatures because of nearby volcanic activity. The intense heat changes their form by sealing any pores in their structure, making them impervious to water. Thus the physical constitution of rocks plays an important part in determining whether a wetland can develop at a particular site. Where there is standing water in a valley, it is certain that the underlying ground is waterproof, resisting the tendency of water to soak downward under the influence of gravity and disappear beneath the surface.
Even porous rocks, however, can be made impervious if fine particles of material block up the pores. This can happen if the waters draining into a valley carry a load of eroded material from the catchment rocks, which settles onto the surface of the porous rocks and forms a layer that seals them. Clay consists of very fine particles, less than 0.00008 inches (2 mm), so they are easily carried long distances by moving waters. Many rocks contain embedded clay particles, including granite, so the erosion of these rocks in a catchment liberates clay into the drainage water. When the water arrives in the valley, some of these clay particles settle as the speed of the water decreases, and they may block up the pores in the underlying rocks and create a waterproof barrier that allows a wetland to develop. One other fine particle that can play a similar part in the formation of wetlands is charcoal. Charcoal consists of partially burned fragments of plant material that are very resistant to decay. Following a wildfire, charcoal particles are blown over the surface of soils and are often washed into valleys, where they accumulate as a black, waterproof layer, and this, like a clay layer, can lead to the development of wetland.
Underlying geology, therefore, including the softer materials such as silt, clay, and charcoal that can be deposited over the parent rocks below, provides the base on which wetlands can form. But the form of the landscape also has an effect on wetland development. Under conditions of very high rainfall, peat-forming wetlands may develop even on mountain ridges and slopes. However, wetlands are generally more abundant in hollows in the landscape, where water can accumulate. If we consider a region where the underlying bedrock is imperviousto water (granite, shale, or slate, for example), then wetlands are most likely to be found in valleys or in hollows in the general landscape. Wetlands of this kind are called topogenous, which means that they are dependent on the topography (the shape and form) of the landscape. These are among the most abundant of wetland types, especially in regions where precipitation is not excessive and water can accumulate only when gathered together from a wider catchment.
A second type of wetland is the soligenous wetland. This is similar to the topogenous wetland in that it lies in hollows, but it is fed by the emergence of water from the ground as a result of porous, water-laden rocks meeting impervious rocks below. Where the two come into contact, the water descending under the influence of gravity through the porous rocks is unable to continue its descent but is forced to move sideways over the surface of the impervious rock until it emerges as a line of springs. These springs then feed the wetland that develops along the line of the rock boundary and in the hollows that lie below that line. This type of wetland occurs only where two very different types of rock come together, as when limestone overlies shale, for example. When this occurs, the wetland that develops may have different water chemistry than appearances would suggest. In the case of limestone overlying shale, for example, water rich in calcium carbonate (lime) drains onto the surface of an acidic rock and creates an unexpectedly lime-rich wetland with distinctive flora and fauna.
A third type of wetland that is dependent on the general form of the landscape is the floodplain wetland. This occurs in the lower parts of river valleys, where the landscape is broad and flat on either side of a river that often meanders down a gentle slope on its way to the ocean. At this stage in its development a river has often traveled great distances and has been joined by many tributaries, so its water is supplied by a wide catchment. If there are heavy rains over that catchment, or even over a small part of it, floodwater accumulates in the river channel and moves swiftly downriver. A sudden rush of water may lead to the river overflowing its banks and spreading out across the wide plain, the floodplain, on either side. Human populations have often settled these floodplains because their rich soils, frequently fertilized by the suspended sediments of the floodwaters, are ideal for agricultural development. The Nile in Egypt and the Mississippi in North America both have extensive floodplains that have been developed in this way. The floods that once spread over the flat landscape and supported wetlands have now been drained and the river channel embanked to prevent floods, and reservoirs have been constructed to control the movement of waters. These measures starve the floodplain wetlands of their water supply, so this type of wetland is becoming increasingly scarce.
Geology and Water Chemistry
The water that flows through a wetland is the source of nutrient elements for the plants and therefore is ultimately the basis of mineral nutrition for all the inhabitants of wetlands. The most abundant elements in living plants and animals are carbon and oxygen. Both of these elements are present in the atmosphere as the gases carbon dioxide (CO2) and oxygen (O2), and are also easily dissolved in water, so there is not usually any problem in obtaining them. When the gases are in a dissolved state, however, they move (diffuse) much more slowly than in air, which means that they can be in short supply if the water itself is stagnant, causing problems.
Hydrogen is also an important element in plants and animals, and its concentration in water has an important effect on many other chemical reactions, for hydrogen concentration controls the acidity, or pH, of the water.
Nitrogen, as a major constituent of protein, is the next most important element. Nitrogen is also present in the form of the nitrate ions. Nitrates arise as a result of the decomposition of the dead proteins from plant and animal matter, or from the excreted material of animals.
Calcium is an important element for both plants and animals, but especially for animals that have a bony skeleton (including many fish and amphibians) and also those mollusks that have a shell (such as mussels and snails). Calcium comes from the erosion of rocks in the catchment, and the abundance of calcium in water is highly variable, depending on whether there is a lime-rich rock present. This great variation in the calcium content of waters has a considerable influence on the types of plants and animals that are found in a wetland.
Phosphorus is another essential element for all living organisms. It is needed for energy storage and exchange in every cell and is also an important component of all the membranes that surround each cell and regulate the movement of other materials both into and out of the cell.
Sodium and potassium are considerably more common in nature than phosphorus, and animals need both. Potassium is needed for muscle and kidney function in animals, and sodium is required for the activity of nerves. In plants potassium plays an important role in regulating the movement of water between cells, but sodium does not seem to be needed at all.
Magnesium is the remaining element of significance. This is an important component of the pigment chlorophyll, which green plants need to carry out their photosynthesis. Together with calcium, magnesium is responsible for the "hardness" of water. This term is most commonly used to describe the difficulty one encounters when trying to use soap to generate lather while washing. Water rich in calcium and magnesium is said to be "hard," and it is difficult to produce soapy bubbles in such a medium. Water poor in calcium and magnesium, on the other hand, is said to be "soft" and is more suitable for washing. Hard water can also generate lime scale in vessels used for boiling water, forming a hard crust over heating elements and often causing failure of the mechanism.
Record Citation: Moore, Peter D. "geology of wetlands." Wetlands, Biomes of the Earth.
New York: Chelsea House Publishing, 2006. Science Online. Facts On File, Inc.
http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=
BEWET0002&SingleRecord=True (accessed March 17, 2009)
Logging Requirements
Please stay on the boardwalk at all times and obey all posted signs and placards!
Email me your answers using the link above on the cache page.
1. Using the Information learned what type of wetland landscape do you see here?
A) topogenous
B) soligenous
C) floodplain
2. As described what geological materials do you see present?
3. During your visit was the water in the wetlands moving or not?
4. (Optional) Post a picture of yourself or team on the boardwalk.