To Log This Cache:
1. How do you think the formation came about?
2. Describe this land. The more details the better.
3. At the time of your visit, was the area wet or dry?
4. Take a selfie with you and or group at ground zero. If you do not want to be in the picture, post an original object with your picture. Plain picture with no object(s) or person(s) will NOT be accepted.
NOTE: cell phone service may be not so good in this area. You can try to connect to the free wifi from Oval Beach to help.
This magnificent dune ecosystem includes an amazing diversity of habitats and resources: Lake Michigan shoreline, populations of at least six rare plant and animal species including the prairie warbler (state endangered status) and Blanchard’s cricket frog (state threatened), open dunes, interdunal wetlands, natural jack pine forest, hardwood-pine dune forest, Great Lakes marsh, an oxbow lake, the south pier of the Kalamazoo River mouth, Kalamazoo River shoreline, and a historic site known as “Fishtown”.
Notably, Saugatuck Harbor Natural Area has interdunal wetlands which are considered to be globally imperiled because of their rarity and because factors such as coastal development make them vulnerable to extinction throughout their range. Protection of these wetlands provided an important impetus for setting aside the surrounding area as a natural area. More info
The Lesson:
Interdunal wetlands, also known as interdunal ponds or dune slacks, are unique ecosystems found in low-lying areas between coastal sand dunes, particularly along the Great Lakes. These wetlands are characterized by their fluctuating water table, which is influenced by the levels of the adjacent Great Lakes. The geology of these wetlands is closely tied to the surrounding dune system, with the sand typically composed of quartz, feldspar, and magnetite. In some areas, particularly around the Straits of Mackinac, underlying soils can be fine-textured loams or clays rich in calcium carbonate.
Sand Composition:
Interdunal wetlands are typically composed of sand, similar in composition to the surrounding dunes.
This sand is largely made up of quartz, with lesser amounts of feldspar, magnetite, and traces of other minerals like calcite, garnet, and hornblende.
The sand grains are often rounded and frosted due to the constant movement and abrasion within the dune system.
Water Source and Chemistry:
Interdunal wetlands rely on the Great Lakes for their water source, with water levels fluctuating in response to lake level changes.
The wetlands are typically neutral to moderately alkaline, due to the presence of calcareous minerals in the sand and the influence of groundwater that may flow from limestone or dolomite uplands.
In some areas, groundwater rich in calcium carbonate can lead to the formation of marl (a fine, white mud-like substance) as algae metabolize and precipitate calcium carbonate.
Underlying Soils:
In many interdunal wetlands, the sand layer is relatively shallow, with the underlying soil being similar in composition to the surrounding dunes.
However, in some areas, particularly near the Straits of Mackinac, the underlying soil can be finer-textured loams or clays.
These finer-textured soils can be rich in calcium carbonate, influencing the wetland's chemistry and supporting specific plant communities.
Formation:
Interdunal wetlands can form through wind erosion, where the wind scoops out sand to reach the water table, or by the encroachment of dunes onto existing wetlands.
They can also be influenced by changes in lake levels, with wetlands expanding or contracting as water levels rise and fall.
Regional Variations:
The specific characteristics of interdunal wetlands can vary depending on their location along the Great Lakes.
For example, wetlands along Lake Superior tend to have lower alkalinity than those on the other Great Lakes due to differences in mineral composition.
In the Straits of Mackinac region, the presence of marl deposits is more common due to the influence of carbonate-rich groundwater.
More Info on Interdunal Wetlands