Thompsons Harbor State Park: Coastal Fen along La EarthCache
Thompsons Harbor State Park: Coastal Fen along La
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Thompsons Harbor State Park is truly a hidden treasure for a hiking adventure. Thompson’s Harbor is located along Lake Huron shoreline. It is an undeveloped park with six miles of walking trails and limited toilet facilities. Bring water & your camera.
Check out the following website for more details, driving directions, and a copy of the trail map: (visit link)
This Earth Cache overlooks a coastal fen. A coastal fen exists along the flat, saturated shorelines of northern Lake Huron, Lake Michigan, and the Georgian Bay on glacial lake plains and where thin, discontinuous layers of glacial till overlay limestone. The community frequently develops where groundwater seepage percolates from either calcareous uplands or joints in the underlying limestone bedrock. Coastal fens frequently occur as part of a larger wetland complex that may include Great Lakes marsh, wooded dune and swale complex, rich conifer swamp, and northern fen. The surrounding uplands are typically dominated by mesic northern forest and boreal forest and can contain a significant component of northern white-cedar (Thuja occidentalis).
Coastal fens are minerotrophic wetlands that receive groundwater inputs rich in calcium and magnesium carbonates. The high mineral content of the groundwater is derived from the limestone and dolomite of the Niagaran escarpment and calcareous glacial tills and lacustrine clays exposed by wave action along the Great Lakes shoreline. The hydrologic regime of coastal fens is directly linked to that of the Great Lakes
The coastal fens form in the low areas between dunes. The dunes formed as the early Lake Huron water level dropped over the last 20,000 years. Each ridge of dune represents an old shoreline. Clay deposited from the lake water in the low areas (swales) and that forms the bottom of the fen soils. Clay slows the percolation of water downward, creating the wetland. Groundwater that has moved though limestones nearby moves up into the low area, bringing with it dissolved calcium and magnesium. This makes the water and soil in a fen alkaline, unlike the mostly acidic water in bogs. In some cases the groundwater is moving upward due to natural springs from confined aquifers. The minerals in the groundwater form tiny crystals that become the marl layers common in these fens.
The underlying limestones formed millions of years ago when Michigan was a shallow sea. Limestone is a sedimentary rock containing at least fifty-percent calcium carbonate. Several different types of limestone exist and are differentiated based on the texture (e.g. oolitic limestone), mineral content (e.g. dolomitic limestone), origin (e.g. coral) and geological age (Carboniferous limestone). Karst topography develops in regions underlain by limestone. Most limestone is partly or wholly are organic in origin and contain the hard parts or shells of mollusks and coral (fossiliferous limestone). Because limestone is mainly calcium carbonate it serves as a store for carbon that is released upon dissolution.
Limestone used to make cement and concrete is quarried in the Rogers City area
Coastal fens share the herbaceous flora of northern fens, but lack the diverse moss flora and tall shrub and tree layers in areas immediately adjacent to the Great Lakes. Most of the graminoids of coastal fens are rhizomatous, an adaptation well suited to the dynamic environment of the Great Lakes shoreline. The most abundant grasses and sedges include twig-rush (Cladium mariscoides), bluejoint grass (Calamagrostis canadensis), little bluestem (Andropogon scoparius), hair grass (Deschampsia cespitosa), hardstem bulrush (Schoenoplectus acutus), tufted bulrush (Trichophorum cespitosum), Baltic rush (Juncus balticus), golden-seeded spike-rush (Eleocharis elliptica), beaked spike-rush (E. rostellata), white beak-rush (Rhynchospora alba), and sedges (Carex flava, C. viridula, C. lasiocarpa, C. buxbaumii, C. capillaris, and C. eburnea).
The common forbs of coastal fen include many species occurring in other calcium-rich habitats along northern Lake Michigan and Lake Huron including false asphodel (Tofieldia glutinosa), Kalm’s St. John’s-wort (Hypericum kalmianum), low calamint (Calamintha arkansana), Kalm’s lobelia (Lobelia kalmii), grass-of-Parnassus (Parnassia glauca), Ohio goldenrod (Solidago ohioensis), bog goldenrod (S. uliginosa), common bog arrow-grass (Triglochin maritimum), Indian paintbrush (Castilleja coccinea), dwarf Canadian primrose (Primula mistassinica), balsam ragwort (Senecio pauperculus), small-fringed gentian (Gentianopsis procera), mermaid-weed (Proserpinaca palustris), bastard toadflax (Comandra umbellata), yellow lady’s-slipper (Cypripedium calceolus var. parviflorum), grass-leaved goldenrod (Euthamia graminifolia), common water horehound (Lycopus americanus), and white camas (Zigadenus glaucus). Several carnivorous plants grow in the coastal fens, including sundew (Drosera rotundifolia), pitcher-plant (Sarracenia purpurea), common butterwort (Pinguicula vulgaris, state special concern), and bladderworts (Utricularia cornuta and U. intermedia). These carnivorous species can survive in habitats where nitrogen supplies are limited and are well adapted to the calcareous environment of coastal fens. [The description of the coastal fen was taken from the MSU Extension Michigan Natural Features Inventory (MNFI) website. Visit MNFI website for more information: (visit link)
This Earthcache is located along a groomed trail system. We recommend that you stay on the trails to avoid encounters with poison ivy and areas of dense vegetation. Please use the principles of “Leave No Trace” while visiting this site. We think the following principles are important:1. Plan ahead and prepare2. Travel on durable surfaces3. Dispose of waste properly4. Leave what you find5. Respect wildlife6. Be considerate of other visitorsWe feel the most fascinating features of this site are the unique plant species that are capable of surviving the harsh environmental conditions imposed on them by the natural processes of Lake Huron. These special protected plant species are able to adapt to the wind, direct sun, changing water levels, and nutrient-poor soils. Enjoy exploring the site from the shoreline of the Lake Huron coastal fen.Encrypted message: Find the bench. [svaq gur orapu] Questions for the observer:1. How would you describe this wetland after visiting the site?2. What time of the year are you visiting this extraordinary site and what do you see? Let us know which plants are in bloom. Either identify the plants seen or describe the plants. Post your photos.3. We especially want you to discover the unique carnivorous plants of this coastal fen. See photos provided to help you locate the pitcher-plant, bladderworts and sundew (hint: look at the base of the pitcher plants to see the inconspicuous sundew plants)How do you feel about the State of Michigan’s efforts for protecting this fragile ecosystem from residential and commercial development and managing this location as a state park? 5. What other discoveries during your visit would you like to share?
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Rapelcgrq zrffntr: Svaq gur orapu. [svaq gur orapu]