This Earthcache will introduce you to some of the geological features in the Wetlands of Bentonville. Parking waypoints are provided, use the crosswalk to cross the road. The paved Razorback Greenway will lead you to the posted coordinates and through the Wetlands.
As with all Earthcaches, there is no physical container to find here. To log this Earthcache, You must send the answers to the questions found at the bottom of this page.
What is a Wetland?
Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. Water saturation (hydrology) largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants (hydrophytes) and promote the development of characteristic wetland (hydric) soils.
They are among the most productive and biologically diverse ecosystems in the world. In the lower 48 states they cover close to 5% of the land, but are home to 31% of all plant species. Plants and animal species vary widely between wetland sites because of differences in soil, topography, climate, hydrology, chemistry, and other factors.
Wetland Geology
Wetlands are often formed by a geological obstruction that resist downward erosion, resulting in extensive flat areas where water accumulates. The obstruction often consists of very hard erosion resistant rock, such as dolerite. Alluvial soil deposits may also act as an obstruction. Alluvium is sediment that is left behind by a flowing stream or river. Over time this sediment deposit builds up and forms a natural dam creating the wetlands upstream.
The underlying geology of the wetland is very important and provides the base on which wetlands can form. This includes the softer materials such as silt, clay, and charcoal that can be deposited over the parent rocks below which helps retain the water.
The permeability of the soil is based on how quickly water seeps through the soil. Fine grain soil like clay have a seepage rate of .05 centimeters / hour. Fine grain soils slow the rate of infiltration (movement of water into the soil) and the rate of percolation (movement of water through the soil). Large grain soils like sand are very permeable and have a seepage rate of more than 5 centimeters/ hour.
Soils that have developed in wetlands are known as hydric soils, because they have formed under water-logged conditions. They have distinctive color, texture and, sometimes, odor due to dying organic material.
There are different types of Wetland Landscapes that affect the drainage patterns:
1. Topogenous has water movement that is predominantly vertical and overland, resulting in water ponding in depressions such as valleys, basins and floodplains (a stream, feeding a small pond or marsh with no outlet).
2. Soligenous has water movement that is predominantly lateral through the soil or discharging from the rock, such as spring (water is bubbling or soaking up out of the ground).
3. Flood Plain is a location where the flood rains or high waters form a wetland (an area near a stream or river).
Types of Wetlands
Wetlands are determined by vegetation, soil, and hydrology. It consists primarily of hydric soil, which supports aquatic plants. The water can be saltwater, freshwater, or brackish (mix). There are four types of wetlands.
1. A swamp is a wetland that is forested. Many swamps occur along large rivers where they are critically dependent upon natural water level fluctuations.
2. A marsh is a wetland that is dominated by herbaceous rather than woody plant species. Marshes can often be found at the edges of lakes and streams, where they form a transition between the aquatic and terrestrial ecosystems.
3. A bog is characterized by spongy peat deposits and a floor covered by sphagnum mosses.
4. Fens are usually fed by mineral-rich surface water or groundwater, and not from precipitation.
Wetland Habitat and Ecosystem
Plants growing in wetlands are capable of living in saturated soil conditions for at least part of the growing season. There are 4 main groups of flora in wetlands.
1. Submerged water plants are those where the vegetation is completely underwater.
2. Floating leaved plants have leaves that float on the water's surface while the roots are anchored in the soil.
3. Emergent water plants are rooted in the lake bottom, but their leaves and stems extend out of the water.
4. Surrounding trees and shrubs are forested wetlands that generally are known as swamps.
Because wetlands are among the most biologically productive ecosystems in the world, they are of extreme significance to scores of species, many of which are endangered. In the United States for example, one-third of the nation's threatened and endangered species live only in wetlands, while half use wetlands during a portion of their lives. Without the wetlands, these species would go extinct.
Estuarine and marine fish and shellfish, and some mammals must have wetlands to survive as they are breeding grounds and/or provide a rich source of food via decomposing plant matter. Fish, mammals, reptiles, amphibians, and birds visit wetlands periodically because they provide food, water and shelter. They provide important nesting and feeding grounds for migratory birds.
Environmental Impact
In the past wetlands were thought to be worthless acres where insects like mosquitos bred, unpleasant odors hovered, and disease festered. Since 1780 more than half of the wetlands have been drained and filled in for use as farmland, housing developments, and industrial areas. Estimates of wetland loss averages 50,000 - 60,000 acres annually.
Wetlands act as a filter for pollution and excess sediment. This is important because rainwater runoff is normally laden with dangerous pesticides and other pollutants. By going through a wetland prior to reaching open water, this is filtered out and often, excess sediment naturally builds up in the wetland instead of in rivers or other water bodies. They also convert Carbon Dioxide to solid plant material through the process of photosynthesis. Wetlands store approximately 44.6 million tonnes of carbon per year globally.
Bentonville Wetlands
At the posted coordinates you will see a sign providing information about the Bentonville Wetlands. Take the Greenway south to observe the geology and ecosystem.
To qualify for this Earthcache send me an email or message via my geocaching profile with the answers to the following questions. Please include the name of the cache along with your answers.
Do not post the answers in your log.
Photos are encouraged!
- Walk the Greenway south from the sign to the Refernce Point.
Do you see any geologic obstructions that contributed to the development of this Wetland, what kind of obstruction is it?
- Look at the soil on the East and West of the Greenway near the edge of the water, you may be able to touch / feel the soil without getting muddy or wet.
What kind of soil is it and how did it contribute to the development of this wetland?
- Based on the information on the cache page and your observations, What kind of Wetland Landscape is this location?
- Based on the information on the cache page and your observations, What type of Wetland is this location? (Swamp, Marsh, Bog, or Fen)
- According to the sign at the posted coordinates, How much of Arkansas original Wetlands remain today?
Sources
Arkansas Natural Heritage Commission
World Wildlife Federation
Wikipedia
