There are numerous of signs of life everywhere you look when you live in the country. Plants sprout, grow and bloom, followed
by shedding leaves and dropping fruit as the seasons change. Birds sing, fly overhead and bounce in and out of shrubbery. Squirrels and mice scamper through the grass to find food and shelter, while the occasional deer nibbles on your favorite garden ornamentals and vegetables. Bears may browse through your garbage cans, raccoons eat from the pet dishes and moles are very busy underground.
This section will introduce you to some of the good and “not-sogood” (from a human or ecological perspective) animals and plants that use the lake or call it home.
Green links in the chain of lifeIn fresh water, algae are very small to tiny aquatic plants that grow either as single living cells, in variously-shaped colonies, or attached end-to-end in long filaments. Their shapes, forms and colors can be very beautiful when viewed under a microscope.
Algae are one of the first links in the aquatic food chain, using Lake Marcel plants: the good, the bad, and the microscopic sunlight, dissolved gases and water to make and store energy. They also take up inorganic nutrients to use for growth and reproduction, such as nitrogen and phosphorus compounds. Algae make good food for microscopic aquatic animals
called zooplankton, which in turn are food for many fish and other larger aquatic animals. Algae also give off oxygen into the water as a by-product of photosynthesis, which aquatic animals can use to breathe. However, when large quantities of algae or aquatic plants die, the bacteria that decompose the cells can rob the water of that oxygen, taking it away from other lake organisms.
An algae bloom is a sudden explosion of algal growth, typically encouraged by good weather conditions and abundant available nutrients in the water. Quite often one or two species will outcompete the others present to become the predominant form in the group. Most algae blooms die back naturally as conditions change or as nutrients are used up, but overlapping blooms of different species can appear as one continuous bloom over time to lake users. King County lakes can experience blooms throughout the year, but the onset of warmth and sunlight in the spring and summer and the wind mixing of deep water nutrients up to the surface in the fall are all common triggers for blooming.Blooms usually last several weeks, then “crash” as conditions change to slow down growth. Some algae are buoyant, occasionally causing colorful scums to form on the water surface, particularly along the downwind shorelines where they can accumulate. Certain species are known for causing unpleasant smells or tastes to the water. In rare instances, the species producing an algal bloom may produce toxins, causing stomach aches in people who ingest the water or unexplained illness and even deaths among small wildlife and pets.
Toxic algaeCyanobacteria, also known as bluegreen algae, are actually more closely related to bacteria than to algae. These ancient organisms are found among the first fossilized signs of life preserved in rocks on earth and species have persisted up to the present in a variety of wet or humid habitats. They are similar in size to algae, and like algae, can convert light in the presence of the pigment chlorophyll to carry out photosynthesis, capturing energy by making sugars for cell growth and metabolism. Cyanobacteria also have other special pigments that aid in photosynthesis, which can turn them a variety of colors, including blue-green, bright green, brown, olive green, reddish-brown and maroon.
The bluegreen genera Anabaena, Aphanizomenon and Microcystis are among the most commonly found bluegreens in lakes of the Puget lowlands during the summer. All three can produce toxins on occasion that may cause liver or neurological damage to mammals. The toxins stay inside the cells until released by cell death or rupture. This toxicity can remain in lake water from a few days to a week after a bloom disappears.
Signs of toxic damage to the liver include jaundice, shock, abdominal pain and severe thirst; while signs of neurological toxins include staggering, paralysis and involuntary muscle movement. Both types of toxins have been reported to kill fish, waterfowl and animals. No confirmed human deaths in the United States have been reported from contact with a toxic bloom, but skin irritation and gastroenteritis have been documented.
The mere presence of cyanobacteria does not mean toxicconditions are present, as most blooms appear not to produce the toxins or only in trace amounts. However, there is no change in appearance between a toxic and nontoxic bloom. Specific testing must be completed to make the determination as to whether or not a bloom presents a health and safety risk. Because of the expense, toxicity testing is often limited to those lakes where other signs of toxicity have been observed. Studies are underway to understand whether environmental conditions or genetic background are better determinants of what causes the cyanobacteria to produce toxins.Macrophytes: Plants Along the Shoreline and in the Water
Aquatic plants growing in shallow water and along the edge of a lake play significant roles in the delicate system of ecological checks and balances. Native plant species, which evolved along with other plants and animals in the Northwest, offer many benefits for healthy lakes. They provide food and shelter for fish and wildlife, stabilize shorelines, produce oxygen in the water and keep sediments from being re-suspended in the water. Native aquatic plants also add to the natural beauty of lakes.
Branches and trunks of terrestrial plants that fall into the water can also provide shade and refuge for fish, turtles and amphibians such as frogs and salamanders, as well as a place to attach for many microscopic aquatic creatures such as rotifers and juvenile stages of insects. There can be whole unseen worlds of small creatures in and around rocks and large wood. Late in the summer, freshwater sponges and colonies of bryozoans (relatives of marine corals) can make jelly-like
masses attached to underwater branches or logs. Bryozoans may even be found free-floating, looking like clear, squishy baseballs.
There are many different aquatic plant species found in our regional lakes, including plants that have floating-leaves, are grass-like, may be fully submerged and or only have their “feet” in the water. A good source for identifying the
plants in your lake is an easy-touse handbook published by the Washington State Department of Ecology in June 2001 as publication number 01-10-032, entitled “An Aquatic Plant Identification Manual for Washington’s Freshwater Plants.” Information on acquiring the manual, as well as an online version can be found at http://www.ecy.wa.gov/Programs/wq/plants/plantid2/index.html.
Aquatic plants are necessary to the well-being of lake ecosystems, but they can also grow out of control when changes to the system occur that interrupt the balance of life in the lake, such as invasions of non-native species, new diseases or predators, large-scale plant management efforts or increased nutrient sources.When unidentified plants suddenly begin to grow prolifically, possibly out-competing other plants and even causing problems for those who live around and use the lake, they may well be non-native and invasive, a sign of trouble to come.
Non-native species can cause a number of different problems in lakes:
• By crowding out species that provide quality food and shelter for aquatic life, they can lower fish growth and reproduction, causing fish populations to becomeunhealthy or decline in numbers.
• Plant masses can form large, loose mats over the water surface, which can entangle boat motors, rudders and oars, as well
as posing a danger to swimmers.
• When they die back in the fall, bacteria decomposing the plant material can reduce oxygen levels, release nutrients and impart an unpleasant smell and taste to lake water.
• Nutrients released from decaying aquatic plant material become available for algal growth, sometimes causing additional water quality problems.