A Natural History of Minnicock Lake
Thirty Years of Change
by Jonathan Schmidt
All phenomena are transitory
The past thirty years have witnessed many changes in the human community on the shores of Minnicock Lake. Not the least of these has been the steady increase in cottage density from a widely dispersed handful to a level of nearly contiguous shoreline development. But there have also been many more subtle changes: individual comings and goings, generations maturing, departing and returning, all of which have been reflected in shifting patterns of recreational and residential use. In a very similar fashion, the biological communities in, on and around the lake have undergone a combination of large-scale and less obvious transformations during the same period.
Returning each year to Minnicock, a casual first glance suggests that relatively little has altered during the past three decades. Along the shore chattering kingfishers still swoop and dive noisily from the trees. In the shallows the stealthier herons stalk patiently for frogs. Loons and gulls bob on the gently rocking waves. In the quiet bays and shallows great swarms of steel black whirligig beetles gyrate on the glassy surface while water striders skid nimbly between lily pads. The surrounding forests resonate with the drumming of sapsuckers and angry natterings of the red squirrels. And in the moonlit night we recognize the familiar dark silhouette and trailing silvery wake of a foraging beaver. But in many respects this superficial constancy masks important transformations in the ecology of the lake.
Some of the most noticeable changes have occurred in the littoral zone of the lake, that extensive region in which the water is less than two meters deep. This is the zone where relatively large amounts of light can still penetrate to the lake bottom and supports the growth of rooted aquatic plants. Thirty years ago the flora and fauna of this zone differed markedly from what we encounter today. Peering into the sunlit depths thirty years ago one was constantly astonished by the enormous numbers of bullfrog tadpoles grazing on the submerged rocks and logs. Throngs of the fifteen centimeter-long tadpoles basking in the warm shallows often reached densities of ten or more individuals per square meter. In early summer the humid night air pulsed with the throbbing calls of the adult bullfrogs congregated in the western marshes of the lake. Today, adult bullfrogs are seldom seen. Their nightly choruses are muted echoes of the past. The decline in bullfrog numbers during the nineteen-eighties was sudden and catastrophic. The cause remains mysterious, although at the time many obviously infected and dying tadpoles could be observed, suggesting that disease may have been a factor. Certainly Minnicock Lake was not the only area to lose most of its bullfrog population. In contrast, the numbers of green and leopard frogs, always common at the lake, have remained largely unchanged over the past thirty years. Indeed since the heronry north of the county road has been abandoned, the number of Great Blue Herons using the lake for hunting has diminished, perhaps contributing to an upswing in the frog population. Another avian predator, the American Bittern, once bred at the western end of the lake, but to the best of my knowledge this species has not been resident for a decade or more.
The crayfish is another littoral species that has undergone a severe population collapse during the past twenty-five years. Although still locally common at some points along the shoreline, overall numbers are greatly reduced. In the past four or more individuals could be found burrowing beneath a single stone and pairs could often be observed in the open skirmishing for territory. The introduction of Smallmouth Bass over twenty years ago was probably a significant factor in the abrupt decline of the crayfish population. Crayfish are the preferred prey of the bass and, when available, constitute more than two-thirds of their diet. The reduced availability of crayfish, accompanied by clearing of the shoreline and increasing human disturbance may also account for the decline in the local mink population. Both mink and otters were much more frequently sighted along the shores of the lake twenty years ago. At the same time, another important crayfish predator, the raccoon, shows no signs of becoming scarce, in part because it exploits a wider assortment of prey and is less unsettled by human activity.
Given the prevalence of Smallmouth Bass today, it is perhaps difficult to recall that twenty-five years ago the predominant species of larger fish were Bluegill Sunfish, Pumpkinseeds and Yellow Perch. Although these species still occur in the lake, they have been largely displaced in the food chain by the bass, to which sunfish are closely related. Twenty-five years ago large numbers of sunfish nests, circular depressions thirty centimeters in diameter and swept clear by the males to expose the gravel bottom, were often observed packed closely together in the shallow waters of the northern shore. Today these nests rarely occur in groups. In contrast, many of the smaller fish species, including the tadpole madtom (a diminutive black catfish with a painfully poisonous dorsal spine), show no signs of population decline. Large schools of minnows, including dace, continue to shimmer among the weed beds in the western shallows, and indeed their numbers may have increased as nutrient levels in the lake have risen. Overall, the productivity of the lake in terms of fish production appears to have been maintained over the years, supporting as it does one or two pairs of loons and their broods each season, as well as numerous herons and Belted Kingfishers, occasional mergansers, and a pair of Osprey that breed in the vicinity of the lake. The productivity of this small body of water is quite astonishing when one considers that just two adult loons with a single chick require over three hundred and fifty kilograms of fish (much of it perch) each-season.
The lake bottom in the littoral zone has also undergone very significant changes over the past thirty years, changes that reflect the ongoing modification of the lake water itself. Thirty years ago the lake bottom in the shallows near shore was strewn with boulders and waterlogged sticks and logs. Between these were areas of sand and gravel exposed by water currents and wave action. The finer detritus on the bottom consisted of balsam needles, leaf fragments and wood chips generated by earlier sawmill operations. In addition to tadpoles and crayfish, the rocky bottom was home to an enormous assortment of grazing insects, including caddisfly and stonefly larvae, hellgrammites and mayfly naiads, as well as the damselfly and dragonfly nymphs that stalked them. Thirty years ago, spring swarms of adult mayflies often left cottage decks looking as if they had been dusted with several millimeters of snow. Today the populations of many of these benthic species have been greatly diminished, replaced on the lake bottom by a proliferation of various midge larvae and tube-building worms. Interestingly these changes in the composition and density of invertebrate prey have so far not had a net impact on the numbers of adult dragonflies engaged in aerial acrobatics above the lake.
The shifts that have occurred in the bottom-dwelling fauna have accompanied a profound change in the composition of bottom itself. Today any casual observation of the shallows reveals that all surfaces, wood, stone and sand, are coated with a thick, slippery, gelatinous film of decaying algal and plant residues. This layer, which was not present twenty-five years ago, is the most widespread and visible evidence of the increased nutrient loading of the lake. As the concentration of nutrients available in the lake water has increased, the growth of algae has also escalated, resulting in the dramatic seasonal blooms that transform the waters of the lake into a thick green soup. At their peak various microscopic blue-green algae, desmids, unicellular Chlorella, mats of filamentous Spirogyra and other algae form immense, floating pastures containing much of the biomass present in the lake. These aquatic meadows are the base of the food chain on which many of our larger animals, from loons to raccoons, depend. When these algae clump together and die due to changing water temperatures or nutrient depletion, their remains settle to the bottom and mix with other plant debris to form a layer of organic sediment. As nutrient levels in the lake water rise, algal productivity is enhanced and the layer of organic sediment increases. The decomposition of this material by bacteria and aquatic moulds eventually recycles the nutrients it contains back into the water.
Measurements of the phosphorous content of the lake confirm that nutrient levels are slowly increasing. The resulting fertilization of the lake has been accompanied by a steady proliferation of aquatic plants and algae and a continuing accumulation of organic sediments. Unimpeded, this nutrient loading could have disastrous consequences if excessive bacterial decomposition removes much of the dissolved oxygen from the water, effectively killing the lake. However, this is probably not an immediate threat since the shallowness of the lake ensures that it is well oxygenated by wind and wave action. But it does raise questions about the sources of the increasing nutrient load. There are probably many factors involved, several of which are related to human activities around the lake. It is essential to recognize that the majority of the nutrients entering the lake are washed down from the soil of the surrounding drainage basin. Each year the snowmelt and spring rains carry dissolved minerals and silt into the lake. Drainage from the surrounding marshes and beaver ponds is also important. A key factor controlling the quantity of nutrients entering the lake annually is the rate at which the snowmelt and rainwater percolates into the lake. This in turn depends on the density of vegetation and leaf litter covering the soil. Clearing the forest floor and undergrowth, denuding the shoreline of its vegetation, constructing roads, beaches, paths and ditches leading towards the shore have all contributed significantly to more rapid and intense flushing of silt and nutrients into the lake.. The modification of the shoreline resulting from the removal of shrubs and branches has also degraded the habitat of several species, including the Ovenbird. Septic systems and grey water disposal may also contribute to the “enrichment” of the lake. At the same time, natural events must also be taken into account. The gradual shift in forest vegetation from evergreen conifers to deciduous hardwoods is slowly changing the drainage and water-retention characteristics of the surrounding slopes. During the past two decades the repeated collapse of nearby beaver dams has released tens of millions of litres of silt and nutrient-laden pond water into the lake. The collapse of the beaver dam north of the Boundary Road flushed over 40 million litres of swamp water into the lake in a matter of a few hours. It is also important to recognize that the effects of nutrient loading are amplified by the very size and shape of the lake. Because Minnicock Lake is a very shallow body of water, much of the bottom remains relatively warm and well oxygenated throughout the summer. This means that organic materials settling to the bottom are rapidly decayed and their nutrients are quickly restored to the overlying water. In addition, the shallowness of the lake ensures that all of its water is thoroughly mixed during the ice-free season. This contrasts with the situation in deeper lakes, in which much of the organic material descends into the cold, dark, oxygen-depleted depths where decay occurs very slowly. In deeper lakes, the upper and lower layers of water mix only during the spring and fall when their temperatures and densities are similar. As a result, many of the nutrients accumulating in these deeper lakes are effectively sequestered in their depths. This is not the case for Minnicock Lake, in which the accumulating nutrients are more rapidly recycled to the sunlit shallows.
It is not surprising then, that the increasing nutrient load over the past thirty years has manifested itself in a profusion of plant and algal growth. Thirty years ago pondweed (Potamogeton) was confined to relatively small clumps primarily in the shallow western area of the lake. It is now widespread and forms thick underwater forests that in turn are coated in a slimy layer of algae. Although the heavy growths of pondweed may interfere with swimming, boating and angling, their dense stands provide important food and shelter for fish and other aquatic animals. In addition, several duck species feed almost exclusively on pondweed during much of the summer. Other plants that have broadened their distribution during the past twenty years include the Pickerelweeds, once largely confined to the western marshes, and the Water Plantains or Arrowheads. The thickening layers of sediment have contributed to their successful colonization of most of the sunny, northern lakeshore.
Interestingly not all plant species have fared as well during this period. Although the White Water Lily is present now in more locations around the lake, its absolute numbers have greatly declined during the past twenty years. Thirty years ago continuous beds of hundreds of flowering water lilies covered several hectares of the shallows at the western end of the lake. During the peak season the sweet odour drifted across much of the western half of the lake. Today comparatively few of the remaining water lilies bloom, and during some recent years even the plants themselves have been scarce. Part of this decline may be attributed to predation; water lilies fall prey to a variety of moths and beetles, not to mention our ubiquitous beaver population. During the summer, beavers feed primarily on water lilies, eating the leaves, roots and flowers. A canoe trip among the lily pads quickly reveals evidence of their extensive grazing activity. No doubt when beavers are particularly numerous they have considerable impact on the water lily population. At the same time the beavers have helped to spread the water lilies by discarding uneaten pieces of rootstock that then float to other parts of the lake. The severity of the winter is another important factor that has influenced the water lily population. On several occasions the water lily rootstocks have been destroyed when the lake bottom was frozen in shallow areas.
Another plant that has declined during recent years is the tiny duckweed. These are among the smallest flowering plants known, recognizable as confetti-like flecks of green floating on the water surface. In the past dense mats of these plants, a favorite food for waterfowl, were common throughout the marshy shallows of the lake. Now they have almost completely disappeared, and with them a variety of unusual insects, including an aquatic wasp, that once were found in these areas. This disappearance is troubling, since duckweeds are often considered indicators of good water quality. Sampling in the western marshes reveals a disturbing decline in the variety of insects and other invertebrates, including water mites, diving beetles and some snail species. Although one can still find the occasional giant water bug, backswimmer or water scorpion their numbers have dropped, and the general impression is one of an overall decrease in biodiversity. The causes underlying this remain unclear. It is possible that the buildup of organic sediment has degraded the habitat for some of these species. It is also possible that the higher concentrations of algae act as repellents or toxins. At the same time, some new species have made an appearance in our waters. Perhaps the most noteworthy is the sudden abundance of the freshwater jellyfish, Craspedacusta. What is particularly interesting about the occurrence of this previously sporadic and rare species is that large numbers have appeared simultaneously in many Ontario lakes. This suggests that its arrival at Minnicock Lake does not reflect any particular degradation of water quality.
Changes in the waters of the lake have also been accompanied by changes in the biological communities within its drainage basin. As the forests surrounding the lake mature, sugar and red maples are steadily replacing the previous population of short-lived balsams, basswoods and white birch. Except for the sunlit edges of the roadsides, the marshes and the shoreline itself, maples, punctuated by the occasional black cherry, yellow birch or stand of hemlock and cedar, will soon evenly fill the lands around the lake. The dense canopies of the maple trees create dense shade on the forest floor and suppress the growth of other species except ferns and those woodland flowers that grow and bloom in the spring. Hardwood forests in which maples predominate are the typical climax of natural succession in this region, unlike drier regions to the east in which white pines predominate. Two major infestations by forest tent caterpillars in the past twenty years and damaging frosts during several winters with little snow cover have had little long-term impact on this process. Changes in the composition of the tree community are also reflected by changes in the forest floor vegetation and mushroom population. For example, Amanita muscaria, the highly poisonous Fly Agaric, has become much less common as the forest matures. Many fungi have very species-specific relationships with the roots of trees that serve as their symbiotic partners or hosts.
In contrast to this relatively gradual process of succession, there have been a few more dramatic changes to the terrestrial landscape around the lake. Aside from the cyclical appearance and disappearance of beaver ponds and subsequent beaver meadows, the reforestation of abandoned pastures and fields during the seventies and eighties has now eliminated most of the meadows on the north side of the lake. This has had a profound impact on the local fauna, most noticeably precipitating a steady decline in the local populations of Monarch Butterflies, grouse and other species that rely on flowering plants and aspens for food. (This excludes the local hummingbird population, which feeds primarily on aphid honeydew produced in the forest canopy)
Surveying the myriad transformations of the past thirty years, many of which are the byproducts of human activity, one is perhaps inclined to inquire about the “natural” state of the lake. In attempting an answer to this question we need to look much further into the past. After the retreat of the last continental ice sheet ten thousand years ago what was to become Minnicock Lake was a melt water-filled depression strewn with boulders and gravel in the midst of barren landscape. The huge boulders deposited erratically in the forests around the lake bear silent witness to this ice age past. Released from the grip of glaciers kilometers thick, the rebounding land gradually assumed a sparse coating of lichens and moss, which was slowly replaced by grasses, sedges and the first colonizing aspens and willows. At this point the lake contained relatively few organic nutrients and its surroundings closely resembled the tundra of the present day arctic.
Pollen sampling suggests that between nine and ten thousand years ago lakes in this area were already colonized by pondweed and other aquatic plants and probably supported flocks of migratory waterfowl (and perhaps even the odd caribou!). Over time, black spruce, aspens and larch migrated to the shores of the lake, to be succeeded in turn by balsams, cedars, hemlocks and birch. It is sometimes difficult to remember that none of the plants we see in and around the lake today are truly “native”; they are all migrants that colonized the land from the south, some, like ragweed, from as far away as Arizona. Finally as the soil thickened with the accumulation of organic material and the climate came to resemble that of the present, a climax forest of maples established itself on the moist slopes around the lake. In scattered locations south of the lake the huge rotting stumps of maples that were already hundreds of years old when they fell represent the last obvious vestiges of this earlier forest. Defoliating insect outbreaks and several cycles of forest fires and regeneration undoubtedly interrupted even this relatively stable period. Evidence for the latter includes the multiple layers of ash and blackened stones encountered when digging in the forest. Such a fire may have facilitated the establishment of the White Pines prominent on the dry south shore of the middle channel. Drainage patterns and water levels also varied considerably long before the arrival of European settlers, in part as a result of the persistent engineering efforts of the local beaver population. Today the stumps of long drowned forests can be detected more than a meter below the surface along the western shore, demonstrating the existence of a prolonged period during which the lake was considerably shallower. Changes in the drainage basin, the amount of groundwater entering from springs on the lake bottom, as well as the steady accumulation of sediment, have all played roles in defining the current outline of the lake. At the same time the chemical composition of the lake has fluctuated with the steady trickle of nutrients washed down from the surrounding slopes.
The arrival of settlers in the nineteenth century had a huge impact on the local ecology as almost all of the established climax forests were harvested, cleared or burnt. The intense lumber milling activity that denuded much of Minnicock Lake’s shores almost a century ago has left large underwater deposits of wood chips evident along the north shore. The extensive stone boundary walls north of the lake are mute witnesses to the prodigious attempts to convert the forest into pasturage and fields. These early forestry activities and subsequent agricultural efforts had enormous effects on water levels and resulted in an unprecedented increase in the quantity of organic material washed into the lake. Of course these same activities also transformed the distribution of plant and animal species in and around the lake, including the introduction of European weeds and wildflowers. It is interesting to consider that several of these new arrivals were rapidly exploited by native birds and insects and have now been almost seamlessly integrated into the “native” biological community. It is also sobering to realize the relentless spread of the maple tree canopy will ultimately prevail over even the hardiest of these newcomers.
The “natural” state of the lake is ultimately one of flux and change. The more recent ecological history of the lake really presents variations of many earlier themes: the arrival of new species, the loss or replacement of others, changes in the drainage area reflected in the composition of the lake and its interwoven biological communities, and above all a relentless process of sedimentation which will someday create dry land where this summer we swam and paddled our canoes. How long these processes take and how they occur can, in part, be influenced by our stewardship of the lake and its surroundings. Each of us who shares in the enjoyment and appreciation of the lake also participates in its continuing transformation. Understanding the impact of our actions is the key to respecting the wonder-filled, if transitory, phenomenon that is Minnicock Lake.
Jonathan Schmidt, Ph.D.
Department of Environmental Biology, University of Guelph
Lot W7, Minnicock Lake