What are Lake Habitats?
Lakes are formed when water from springs, streams or rivers accumulates in low areas or behind natural barriers. In turbulence, they are usually the source of other streams and rivers. Lakes operate like large mixing bowls, into which rivers and streams deposit nutrients and sediments. Water entering a lake may remain there for hours or years, depending on the size of the lake.
The shape and depth of the lake and its water currents determine the number and types of habitats it supports. Most lakes have deep and shallow areas, regions of fast currents (near inlets and outlets) and quiet areas. Each environment supports its own forms of life.
What Animals and Plants Live in Lakes?
Lake plants and animals are adapted to stable conditions or those that change slowly through the day or year. Attached plants (macrophytes) found in lakes tend to have large leaves and delicate features, characteristics of an environment where the water current is slow. Lake fish and invertebrates tend to be bigger and less streamlined than those found in streams and rivers.
Lakes also support microscopic algae that serve as food for lake animals and produce oxygen in the water.
How are Lake Habitats Disrupted?
Several activities can disrupt lake habitats by reducing the amount of sunlight or oxygen in the water.
Erosion of the lake shore will deposit mud, sand or rubble on the lake bottom. Silt, in the form of muddy runoff, clouds the water and limits the amount of sunlight reaching the plants and algae. Without sufficient sunlight, photosynthesis is reduced, resulting in impaired growth.
Septic fields and sewage from cottages, homes and commercial buildings can disrupt the ecologic balance of a lake.
Decomposition of plants and algae consumes oxygen. If more oxygen is consumed than is produced, organisms, including fish, may not survive. Sensitive species such as trout may die off completely if oxygen is depleted for even a short period of time. Low levels can be critical in summer or winter, when little oxygen enters the water through the ice and plants that are still growing are not producing much oxygen.
Land development can increase siltation, cause chemical runoff or leach freshly exposed soils. Land clearing can remove the protective surface cover of plants and increase the flow of water and eroded materials into the lake. Surface and groundwater may also be more exposed to the sun and become warmer, disrupting productivity in small lakes.
Homes, cottages and commercial buildings can disrupt the ecological balance of a lake through the release of sewage from septic fields or through runoff from fertilized lawns and gardens.
Wave-deflecting structures, such as rock piers, dikes or cribs, can change wave and current patterns. When poorly placed, they may divert wave or current energy to other parts of the lake and erode the shoreline. Wave deflecting structures can change wave patterns and cause shoreline erosion.
Agricultural activity can release high levels of fertilizers and pesticides into a lake. Runoff from manure piles and silage pits may also make its way into a lake. Herbicides commonly used in farming operations can suppress production and growth of many aquatic plants and organisms. High levels of nitrogen and phosphorus, found in fertilizers, can cause massive blooms of plankton and aquatic plants. As these organisms die and decompose, they use oxygen in the water, reducing the oxygen available for fish and plants.
Industrial activity upstream from or on a lake may discharge toxic chemicals that can harm or kill plants and animals outright. Certain chemicals like heavy metals, and organic compounds such as PCBs, may concentrate in plant and animal tissues (bio-accumulation). High levels of some of these compounds could be hazardous to humans. Toxic chemicals from industrial activity can harm fish and plants in a lake.
Introduction of Non-native Species to a Lake
Introducing non-native (nonindigenous) fish or plants can seriously reduce populations of native species. If a newly introduced species is not controlled naturally through predation and competition, its increasing population may reduce the number of fish native to the lake. Experience shows that mixing species from different areas can also spread disease. Canal construction or the diversion of water can cause non-native species to enter a watershed.
How Long Will Disruptive Effects Last?
Lake water moves slowly, which means that material deposited there will remain for a long time. For example, mud washed into a lake after a heavy rainstorm may discolour the water for several days or weeks, while river water soon returns to its usual color because of the faster current.
If the plants and animals in a lake are destroyed, it may take years, or even decades, to re-establish the conditions that previously supported life there. Lake fish, invertebrates and plants must be replaced by species from other lakes or ponds. Although river fish and plants may survive in lakes, they will not thrive in this environment.
The effects of disruptions in a lake may be passed on to receiving waters, such as rivers and streams. Because of their high energy environment, affected rivers or streams will replace oxygen fairly rapidly. If plants and animals are killed, new species may migrate from adjacent streams once the problems have passed.
The long period of time water remains in lakes can help resource managers and biologists remedy problems occurring downstream. This approach is usually considered for headwater lakes and could be used to treat highly acidic conditions in fish habitats, for example.
Since lake water moves slowly, materials remain in a lake for a long time. Sediment takes a long time to move out of the lake because of the slow current.
How Can Disruptions Be Prevented?
In most cases, disruptions can be minimized by taking certain precautions. Before undertaking an activity that may have a disruptive effect on a lake or other watercourse, consult the appropriate regulatory authorities.
Activities that may alter water levels or quality, or introduce new species (by linking adjacent watersheds) are subject to substantial governmental review. Federal, provincial and municipal or county governments share responsibility for freshwater habitats and water use, as well as the types of activities outlined here.