Many, many years ago, an invasion was launched into northern Pennsylvania. Although it first charged across what ( would be the state's borders nearly half a million years ago, the changes it wrought are still clearly evident today.
The formidable invaders massed and stormed into Pennsylvania as many as four times, finally retreating about 15,000 years ago. The hulking foot soldiers in this army were the huge glaciers of the Ice Age, scientifically known as the Pleistocene Epoch. They were capable of grinding over mountains several thousand feet high and leaving a legacy of valleys filled with gravels, marshes and lakes.
In northeastern Pennsylvania, primarily in the Pocono region, the lakes and ponds formed by the last glacial advance (known as the Wisconsin) are numerous and somewhat acidic in nature. In contrast, the eight or so "kettles," as these glacial lakes are known, that were formed in Pennsylvania's northwest comer are more alkaline. They have been named "calcareous glacial lakes" by researchers.
As the main glacial sheet retreated toward Canada for the final time, near the present village of Arbuckle, in Erie county, a large chunk of ice broke away and lay stranded in the shallow valley bottom. Its weight and meltwater formed a beautiful kettle lake 64 acres in size and 40 feet in depth. Centuries later it would be named Lake Pleasant. Today, Lake Pleasant is the crown jewel of Pennsylvania's glacial lakes. Having been spared, for the most part, the human-related impacts that have befallen other northwest kettles lakes, like Conneaut, and fed with the alkaline water that Pocono glacial lakes lack, this Ice Age vestige harbors a bewildering array of natural diversity. While Lake Pleasant may look like many other lakes at first glance, a plunge beneath its quiet waters immerses an observer in the aquatic equivalent of a lush rainforest. Large beds of delicate water plants reach to the surface like forest giants, and shiners and sunfish flit through patches of sunlight like tropical birds.
The waters of the lake, and its adjacent wetlands, support over 80 species of plants, 24 of which are species of special concern, and three rare fishes. According to Jim Bissell, Curator of Botany at the Cleveland Museum of Natural History, and the lake's principal floral explorer, "Lake Pleasant is the most spectacular glacial lake in northwest Pennsylvania." Bissell equates survey work on the lake to "time travel," visiting a dynamic historic site with all the original pieces still in place.
Bissell illustrates this comparison with a graphic example involving Lake Pleasant's vegetation. Northern water milfoil, a native aquatic plant listed as endangered in Pennsylvania, thrives in the lake. But it is now extirpated from the rest of the region and all of Lake Erie, having been replaced by Eurasian water milfoil, an aggressive alien species that is rapidly overtaking many waterways. The invader hasn't yet been detected in Lake Pleasant. Eurasian water milfoil's primary mode of colonization is hitchhiking on motorboat propellers. Boats with motors have never been permitted on Lake Pleasant. This prohibition has likely prevented the spread of the alien water milfoil, as well as allowed several other fragile water plants to flourish. If motorboats had been allowed to use the lake, it's unlikely that Beck's water-marigold would still grow there in abundance. A bushy but frail submerged plant with finely dissected leaves resembling an unbranched stalk of coontail, Beck's water-marigold sends a solitary yellow flower straining upward toward the surface late each summer. Endangered in Pennsylvania, it is extinct in Ohio's glacial lakes and nearly gone here as well, with Lake Pleasant holding the only secure population.
In 1987, Bissell and Edwin Masteller, of the Behrend Campus of Penn State University, conducted an intensive vegetational analysis of the lake. Based on their results, they divided Lake Pleasant into five plant community zones. The "submerged" zone, where rooted plants grow primarily under the surface, is characterized by the two species previously mentioned, plus an aquatic buttercup and 10 pondweed species.
The "floating" zone, characterized by plants whose leaves float on the surface, is dominated at Lake Pleasant by fragrant water lilies, spatterdock (yellow pond lily), and duckweed, a tiny vascular plant that grows unattached to any object, but floats freely about in the lake shallows. The "emergent" zone, where plants grow partly in and partly out of the water, is occupied primarily by pickerel-weed and water-willow.
Lake Pleasant's plant community zone with the greatest diversity is the "mixed emergent marginal," which generally includes most of the marshy area surrounding the lake. Cattails, sedges, rushes, several asters, and smartweeds are part of the roster of 45 or so species that flourish here.
Where alkaline springs and seeps discharge at or near the surface in the marshy areas, "fens," the rarest of the plant communities, may form. Fens are peatlands, where organic materials don't completely decompose, that are rich in minerals. This is different from a bog, which is acidic and mineral-poor. Lake Pleasant's fens host at least nine rare plant species. In addition, three carnivorous plants grow in the fens and marshes, waiting to ensnare unsuspecling animals. Pitcher plants, sundews and bladderworts all vie for their portion of Lake Pleasant's riches.
The abundance of submerged vegetation provides ideal habitat for two diminutive species of fish with northern affinities. The blackchin shiner and Iowa darter withdrew southward ahead of the ice sheets, and then returned to the north behind the retreating glaciers. Both fish are now considered "glacial relicts" here. Since the waters of lake Pleasant flow into French Creek, and eventually to the Mississippi River, these populations are effectively stranded and permanently separated from others of their species in the bulk of their range.
The blackchin shiner, which now occurs nowhere else in Pennsylvania, formerly swam the waters of Conneaut Lake, but hasn't been seen there since 1938. The Iowa darter, which hides its brilliant spawning colors in the bottom muck and debris, also occurs in Lake LeBoeuf, in Erie County. Both are classified as candidate species for listing by the Pennsylvania Fish and Boat Commission.
The third rare fish found in Lake Pleasant, the warmouth, has a southern distribution that barely meets that of the other two. It is a member of the
sunfish family and superficially resembles the rock bass. In Pennsylvania, the warmouth occurs only in very small numbers in the Ohio River drainage.
How could Lake Pleasant's rich floral and faunal diversity have survived intact when all the others suffered considerable degradation? Paul Wiegman, Director of Natural Areas for the Western Pennsylvania Conservancy, credits the adjacent landowners and lake-using public. By simply being responsible land stewards and vigilantly ensuring that the "no motors" rule was adhered to, they afforded Lake Pleasant a much higher degree of protection than the region's other lakes enjoyed. These water bodies were variously impacted by the construction of dams and levees to raise their water levels, heavy shoreline development, powerboating pressure, nutrient and sewage infiltration, siltation, destruction of adjacent wetlands, and the introduction of exotic vegetation.
The Western Pennsylvania Conservancy, looking to conserve an example of a calcareous glacial lake, earmarked Lake Pleasant as a high priority for protection in the early 1980s. As field investigators revealed its treasures, the lake's importance became more and more obvious, and contacts were initiated to begin acquiring property. Finally in 1993, after 10 years of negotiations, land was purchased from the Myers and Johnson families that secured two-thirds of the lake's shoreline, and totaled 206 acres.
The acquisition was made possible through an interesting mix of funding sources. The Western Pennsylvania Land Protection Fund, consisting of a settlement for a water pollution violation, was tapped for one-third of the purchase price. An additional third came through the Keystone Recreation, Park and Conservation Fund (Key 93), and the Western Pennsylvania Conservancy provided the remainder.
Lake Pleasant' new majority landowner has no intention of becoming complacent. The Western Pennsylvania Conservancy is still interested in land on and around the lake and its watershed, and has adopted a lofty goal of maintaining, and even enhancing, the quality of the lake's environs.
This will be no easy task, and Wiegman has two concerns. The first is the possibility of a pollution event occurring along Lake Pleasant Road, which parallels approximately one-quarter of the shoreline. This could come in the form of a traffic accident that causes gasoline, oil or chemicals to quickly spill into the lake's waters.
The second is more complicated. Lake Pleasant not only is a refuge for rare species, but is home to many common species of fish, particularly game fish. According to Ron Lee, Area Fisheries Manager for the Pennsylvania Fish and Boat Commission. Lake Pleasant supports a high-quality largemouth bass fishery. During the last survey, in 1989, his crew captured (and I~ released) 10 bass in excess of 20 inches in length. But Lee considers this fishery underutilized, possibly due to the prohibition of boat motors. Panfish, too, reach desirable sizes, but are not abundant due to predation by the bass.
Trout, however, are another story. Each spring throngs of coldwater anglers flock to Lake Pleasant in search of the large numbers of trout the Pennsylvania Fish and Boat Commission stocks each year. The plantings began with rainbow trout in 1937 and have continued unabated to the present day, attracting boat fishermen in numbers that seem to fill the lake to capacity, and shore anglers that claim most of the area along the road. Interest in trout continues at Lake Pleasant all the way through Memorial Day, and renews during ice-fishing season.
Striking a balance between this intense recreational use and protection of the lake's biodiversity and integrity is the Western Pennsylvania Conservancy's greatest challenge. With the city of Erie a mere 13 miles away, pressure from canoeists, swimmers and hunters, as well as the ever-present anglers, is not likely to abate. This will make one of the conservancy's objectives, restoring native vegetation to Lake Pleasant's eastern shore, a genuine undertaking.
This stretch of shoreline, along the main road, has been heavily used for decades. Gravel fill has been placed over the bottom to facilitate boat launching, parking, shore fishing and even swimming (for a short time Erie released a section as public beach). In this heavily impacted area, aquatic vegetation has been greatly reduced. It will take considerable effort to return it to its former condition. On the western shore, where a handful of residences are situated and which is still in private hands, adverse effects have been minimal.
But what may be an even more sinister threat is the specter of an invasive nonnative aquatic weed, especially the Eurasian water milfoil, slipping into the lake and choking out the native vegetation, thereby upsetting the entire plant community. Consider foreign milfoil's firm establishment in other waters close by, it's amazing the plant hasn't already invaded lake Pleasant. Many states and Canadian provinces now have active public education programs in place in an attempt to thwart Eurasian water milfoil's progress.
Barring an environmental catastrophe, in the future Lake Pleasant's eminence should only heighten and its list of unique organisms lengthen. There are undoubtedly still a few rare plants tucked away that have thus far managed to escape keen eyes. The invertebrates, like dragonflies and damselflies, fresh-water mussels and snails, have yet to be surveyed. So far, the special attributes of Pennsylvania's premier glacial kettle gleam on.
August 19, 2000
http://www.pawildflower.org/