HIGH WATER -- LOW WATER
by Gray Merriam
As we sought power from flowing water, we built dams to impose unnatural constancy on the water levels of many lakes. Constant lake levels became part of the culture of "cottaging". We wanted convenience without considering how it might affect the health of the lakes. The inconvenience of bothering with an adjustable or floating dock is vastly outweighed by the benefits to the lake from fluctuating water levels.
Water levels in watersheds coming down off the Canadian Shield fluctuate naturally. Communities of organisms that live in those waters are adapted to fluctuating water levels. Fluctuations are part of their optimal habitat.
The exact timing of fluctuations is changing as climate change takes effect but the main pattern is still high water in spring and fall. Low water mid-summer to early fall and ice cover otherwise.
The main variables driving the peaks of rapid runoff from the Shield are seasonal precipitation and impermeable bedrock preventing infiltration of the precipitation into the ground.
On the Canadian (Precambrian) Shield rain and snow move back into the air by evaporation, or they find a fault in the rock that lets them move into the groundwater, or they go into wetlands temporarily, or they run off through rivers, creeks and lakes. If it all flowed off directly, one inch of rain falling over the watershed of Kennebec Lake would raise the level of the Lake by 4.5 feet. We have had rainstorms that dumped 4 inches in a few hours. Four inches of rain across the lake's watershed, if it all ran off directly, would raise the lake's level by 4 times 4.5 feet or 18 feet! Those alternative pathways in the lake's subwatershed prevent such huge fluctuations. The watershed takes the peak off such storms.
What does the normal fluctuating water level do for Kennebec Lake?
The maximum increase in water level usually has been measured to be less than 1.5 metres but that is enough to cover marshes along the shorelines. That high water carries small particles weathered off the bedrock upstream in the lake's watershed. Many of those particles are very fine. They are colloidal in size. Particles that small are coated with negative ionic charges that grab positive nutrient ions and carry them along. Those nutrient-enriched particles are a natural fertilizer system for shoreline marsh areas where the plants slow the flooding water enough to make the particles settle out. Without this fertilization by high water, there would be many fewer cardinal flowers and blue flags. Winterberry holly and buttonbush would offer less protection to shorelines.
The rich shoreline marshes are where most of the reproduction happens that is keeping our frogs from extinction. Frog factories! Ask any Bittern or Great Blue Heron what they would lose without those shoreline high waters. Declines of frog populations are driven by loss of habitat. Floodlands are frog habitat.
Ask any Northern Pike what difference it would make if we did not have high water in spring. Pike spawn up small creeks that are flooded in spring. Some pike go so far up flooded creeks that they get caught in the willows and kids (and adults) know that pike can be speared up creeks that will no longer be there after a few weeks. For spawning pike need flooding.
Where creeks flow into the Lake, the water flowing in pushes surface water out away from the shore. As a result, water moves up from the depths and carries with it the nutrients, other than phosphorus, that are need to make the lake productive, starting with plankton and ending with fish. This process is called "upwelling" and it creates "hotspots" of productivity in many lakes.
High water in spring is changing. If a lot of snow evaporates directly into the air by sublimation rather than melting and running off, we have lower high water. The runoff that we do get is coming earlier each year as the warming of spring moves back up the calendar into March and February. Spring showers are also changing. Without the runoff from snowmelt, the larger showers of last spring created a wave of increases in water level in late spring. In spring of 2014, repeated rains accumulated to raise the water level to a record high since measurement began. Repeating peaks of high water make it difficult or impossible for loons to protect the eggs in nests that are flooded by these peaks of high water. Exceptional high water levels built from accumulating smaller peaks or from freak rainstorms absolutely prevent some natural processes such as loon reproduction. As climate change takes effect we can expect more water level fluctuations outside the norms.
Summer low water bares the organic sediments along shorelines and exposes them to the air. The organic matter oxidizes slowing the rate of filling of the lake with sediments.
Low water in summer is also the season for growth of perennial plants. Cardinal flowers, royal ferns, blue flags and many others all do their growing as the water level recedes. This also is the time for growth of roots of woody plants such as red maple. Although they can survive periodic inundation, red maple roots can't breathe when underwater and need this low water relief. Woody roots of red maples, dogwoods, spiraea, buttonbush and sweet gale stabilize the lake's shorelines.
When high water comes again in the fall, the plants and some animals have produced seeds and other dissemules. The high waters of fall disperse these seeds and starters for next spring's early growth.
Fluctuating water levels is normal for Kennebec and other shield lakes and professional ecological research has pointed out that:
"The biological structure of the natural flood plain is organized according to intensity of floods…." --- and "Flood plain ecosystems are self-organizing through the process of ecological succession and the primary driver is hydrology" (such as fluctuating water levels).