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Lunch in a Dystopian Glacial Kettle

02 Apr 2021 2:58 PM | Anonymous member (Administrator)

by Brian Yates, Yates Environmental Sciences Inc.

On Sunday March 14th, the Brownfield Coalition of the Northeast (BCONE) hiked the Buttermilk Falls Trail in the Delaware Water Gap. We began at the Flat Brook near Walpack Township, and climbed roughly 900 feet up a shaded hemlock and birch valley, passing through sunny pitch pine and scrub oak forests. Eventually, we arrived and ate lunch at a large, open wetland area containing many dead trees, but generally overgrown with reeds, sedges, and rushes.

Some BCONE members later described this area as dystopian – why would so many trees be dead in a remote area at the top of a mountain (View facing east of the dystopian wetland area. Photo courtesy of Kevin Schick via Google Earth). According to historic aerial photos, the area was forested up through 1971. Between 1971 and 1992, the habitat changed to an emergent wetland (marsh), and there is surface water covering the area in 2007 and 2008.

One possible explanation for the change in hydrology is the damming of the stream which runs through the habitat by beavers (Castor canadensis), which have historically been very active in the area. The rise in water level likely saturated the root zone of the trees, depriving them of oxygen and eventually killing them off. As the trees died off and lost their branches, the understory opened up to sunlight, which allowed rushes, sedges and reeds to proliferate.

Glacial Kettles: Based on mapping prepared by the NJ Geological and Water Survey, this area is considered a “kettle.” When the Wisconsin Glacier retreated over 15,000 years ago, a large block of dead ice separated and became surrounded by sediment. When the ice melted, the resulting depression then filled with water. Locations of a few kettles within the Kittatinny Mountains is provided below. Many, such as the nearby Crater Lake, still function as lakes. The beautiful setting attracted developers and was a budding vacation community through the mid-1900s. Others, like the dystopian wetland we visited, have not attracted development and were largely left undisturbed.

Google Earth view facing southeast of several “kettles” pocketing the Kittatinny Mountains east of Walpack Township. 

Ecological Significance: These kettles started as surface water bodies – but something interesting happened. Initially, sphagnum moss (peat) grew in floating mats across the surface of the water. As the mats thickened, other plants grew on top. When the vegetation died, it sank but did not fully decompose. Over thousands of years, peat filled entire lakes, gradually allowing trees and shrubs to grow where the water was once very deep. 

Ecological succession of a lake to a peatland. Image courtesy of Lisa Hirkaler via the New Jersey Division of Parks and Forestry, available here.

Despite the vegetation which has grown on top of the peatland, the underlying substrate is very acidic and infertile. Peatlands are generally classified either as bogs or fens. Bogs have very little to no inflow of water and very low nutrient content (Collins and Anderson 1994). Fens receive some drainage inflow from surrounding areas and have somewhat higher nutrient content. While there is no 100% agreed-upon definition from ecologists, these habitats often provide habitat for carnivorous plants such as sundews and pitcher plants, which  trap and digest insects to obtain nutrients they can’t get from the soil. 

Photo of the carnivorous plant Drosera sp. (sundew) taken at a peat bog in Picatinny Arsenal. Flying insects are lured in by the fluorescent tentacles and sweet odor, but become ensnared by its sticky mucilage which prevents progress or escape. Photo courtesy of Michelle Herman via INaturalist (license accessible here).

Another example of a well-preserved peatland is the Dryden Kuser Cedar Swamp in High Point State Park. This habitat is believed to be the highest elevation Atlantic White Cedar swamp in the world. Historically, it was spared from deforestation on account of its remote location, but is naturally undergoing succession to an oak/hemlock forest. Wildlife are abundant in habitats like these; in the spring, visitors have seen spotted salamanders, red newts, pickerel frogs, migrating warblers, and even heard the drumming of ruffed grouse. 

Atlantic white cedar swamp located in Wawayanda State Park. Photo taken by the author. 

Archaeological Significance: History has demonstrated that peatlands are also particularly good at preserving fossils. In 1954, property owner Gus Ohberg of Sussex County was enlarging a pond when his dragline operator pulled a large object from the marsh. At first believed to be a tree stump, it was later determined to be the skull of an exceptionally large and old animal. Over the next few days, several more bones, including a femur and jaw were recovered. The New Jersey Geological Survey, New Jersey State Museum, and Rutgers and Princeton Universities arrived on the site and determined it to be an 11,000-year old mastodon – a prehistoric relative of the elephant. Mastodons were herbivores which wallowed in bogs and ate pond and bog vegetation as well as twigs and branches. They often became mired, drowned, and were preserved in the oxygen deficient sediment. 

The mastodon nicknamed “Matilda,” was determined to be a young female about eight feet tall. As a reference, the largest mastodon fossil recovered in Sussex county was a leg about nine feet tall, making the animal’s estimated height no less than fifteen feet. 

Mr. and Mrs. Gus Ohberg with the skull and femur of “Matilda.” Photo courtesy of S. Novak via New Jersey Geological and Water Survey Report 43: Garden State Mastodons, available here.

Matilda is one of fifteen distinct mastodon discovery sites located throughout northern New Jersey. Nearly all them have been found in small ponds, lakes, or peat bog “kettles” left behind by the Wisconsin Glacier. Because freshwater wetlands regulations prohibit dredging these habitats without a permit, we are unlikely to find many more prehistoric fossils in these habitats. It does, however, raise the possibility that there are hundreds, if not thousands, of incredibly well-preserved mastodon fossils buried deep within the peat. 

Summary: From an archaeological, geological, and ecological perspective, these kettle holes and peatland habitats are truly unique. In my humble opinion, these are just one of the many “hidden gems” that travelers unknowingly pass by on their way in and out of our area.  

 Thanks to Maria Coler of Hydrotechnology Consultants for organizing the hike and editorial review, Bob Blauvelt of GEI for excellent geological interpretation, Madison Gamba for editorial review and everyone that attended the hike!

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