-
Difficulty:
-
-
Terrain:
-
Size: 
(large)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This earthcache will take you on a tour of Nelson Fen WMA. Nelson WMA has wide mowed trails that will take you to the fen and show points of interest along the way. Keep in mind this area is a wetland. Expect your feet to get wet.
What is a fen?
Fens are places that time forgot. As the world around them rushes swiftly to the future, fens stay rooted in the past. These ancient plant communities are relics of an age when great sheets of ice moved across the land. Following the last retreating glacier, pioneer plants moved into newly created habitats.
The rarest of fens are calcareous. The cold groundwater that feeds the fens also contains dissolved calcium and magnesium to create a unique set of conditions. Fens are kept wet and cold by the groundwater supply and are located on slopes. There are approximately 200 fens in Minnesota, 11 of them are located in Olmsted county.
Calcareous fens contain the rarest wetland plant community in Minnesota, and probably one of the rarest in North America. Calcareous fen communities contain a number of rare, threatened, and endangered plants. Only a select group of calcium tolerant plants, referred to as calciphiles can tolerate these conditions. The rare plants grow on humps called hummocks.
Fens are different from bogs. Fens receive water from the surrounding watershed in inflowing streams and groundwater. Bogs receive water primarily from precipitation. Fens reflect the chemistry of the geological formation through which the water flows. In limestone areas the water is high in calcium carbonate with a resulting neutral pH of 7 also referred to as circumneutral. Bogs are very acidic.
Fen soil is composed of a large quantity of decomposing plant and animal material, which is an organic soil. In contrast, peat soils of bogs contain recognizable bits of plant stems and other material.
Fen soils are saturated with water directly from groundwater sources.
The word fen was first used in the United States in the late 1940’s. Other names used are: alkaline prarie, peat bogs, marl meadows, and calcareous marshes, side-hill seeps, wet prairies, sedge meadows, sloughs, bogs and hillside bogs.
Fens are important as sites of groundwater discharge-good indicators of of shallow aquifers. Vegetation in all wetlands plays an important role in recycling nutrients, trapping eroding soil, and filtering out polluting chemicals.
Fen waypoint: N 43 53.792 W 092 37.576
This waypoint brings you to a rock on the fen edge. Stand on the rock. Do not proceed past this point into the fen. Your steps will be present for many years. Do not step on the “plant humps”.
A fen is home to unique plants. As you will notice, plants and shrubs grow to various heights. The red dogwood is knee high due to the constant presence of water, which is the desired height of surrounding plant community. Rare plants grow on humps called “hummocks”. Do not step on the hummocks. Additional plants are cattails, horsetail and various types of mosses, sedges and marsh marigolds, and various types of swamp grasses. Take the trail west to the fence edge to view the entire plant community present.
Plants in fens can be grouped into three distinct zones: the discharge zone, sedge mat zone and border zone. Actual presence of all three zones, as well as how distinctly they are defined varies among fens.
The discharge zone is where the ground water seeps into the surface, is a very wet area. There is more water then plants. Plants will grow on hummocks.
Sedge mat zone forms when plants begin to form a sedge mat. The mat often quakes when walked on because of it is organic matter held together by fibrous roots suspended over the saturated soil below. By elevating the ground slightly so that it becomes better drained, the mat allows different plants to grow. Sometimes shallow pools form here. It is possible to sink several inches into the soil when walking in these areas.
The border zone is the third ring farthest from the groundwater discharge point. The vegetation here grows on a much thick layer of peat as well as mineral soil which provides better growing condition that the sedge mat. This zone typically has tall, dense plant cover and numerous sedges. The border zone may contain many of the same plants as the discharge zone.
Besides the plant varieties, deer also live in the area and have an impact on the fen. Wildlife disturbances are beneficial. The deer provide balance of keeping the brush controlled so the brush doesn’t overtake the area. Controlled burns are also control taller brush so perennial plants can grow. The plant root structure helps to keep soil in place.
The water in the fen has unique features. Sometimes the water that saturates the soil carries enough dissolved calcium carbonate to form a grayish/white/pink, lime-rich substance called marl when it comes to the surface. Iron dissolved in the water appears as “rust” colored collections. Varying concentrations of the minerals will affect the color of the deposits.
Task: What is the altitude at this waypoint?
If you can not see standing water, list at least 2 pieces of visual evidence that Nelson Fen is a wetland.
Seep waypoint: N 43 53.736 W 092 37.576
As you walk along the trail portion, the ground is wet. A seep is a wet place where groundwater has oozed from the ground to the surface. Seeps usually do not flow, the water remains in place. Seeps are relatively rare.
Oily sheens can come from natural sources. Some bacteria that live in waterlogged places get their energy from iron and manganese, and these harmless bacteria grow and decompose, the iron may appear oily.
How to tell the difference between petroleum spill and natural oil sheens? Poke the sheen with a stick. If the sheen swirls back together, it’s petroleum. If the sheen breaks apart and doesn’t flow back together, it is bacteria or other natural source.
Task: Ideally on the water surface you will notice a “oil type” sheen. Poke the water, what happen with the “oil sheen”?
Stream waypoint: N 43 53.673 W 092 37.497
Fens drain into a stream. As you walk toward the stream, do you sink or quake on the soil?
Let your eyes take you on a tour of both stream edges. Compare and contrast plant and tree growth. Ask yourself what are the differences between the two stream edges?
The farthest edge has a bush that is growing. Under the bush is moss and no plants. The closest edge contains grasses, hummocks, and various types of wildflowers.
Task: At this waypoint, view the two stream edges, what edge will hold the soil in place and why?
Pond waypoint: N 43 53.607 W 092 37.401
This is the point where fen streams meet to form a larger stream.
Task: Evaluate the surrounding area and in a sentence or two, formulate a hypothesis as to why or how a wetland can be sustained in this location.
To complete Nelson Fen WMA earthcache, please email you experiences via profile link. Include the name Nelson Fen, number in your party and cachers names. One email per group.
Last, post a picture of a scenic view from Nelson Fen.
Additional Hints
(No hints available.)