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HISTORY
"The occurrence of massive floating blue-green algae blooms in Liberty Lake beginning in 1960 has prompted its citizens to seek advice on ways to improve water quality in the lake. This irreplaceable resource had once been a beautiful, clean, clear lake heavily used by area fisherman, boaters, swimmers, and picnickers. However the natural eutrophication process of the lake was being speeded up by human activities, and the water was starting to lose its clarity. If left alone, Liberty Lake would soon have become unfishable, unswimmable, and unusable. The surface was covered by slimy blue-green algae and decaying weeds for longer periods of time each year. Residents became concerned about the continued deterioration, and started asking questions about lakes, taking water samples for testing, becoming knowledgeable about the causes of lake problems and exploring possible solutions. At the same time residents became concerned about the continued deterioration and were beginning to realize the extent of the environmental problems facing them, people all across the nation were becoming aware of the limits of the environmental resources. Lakes and rivers throughout the country, to some degree, are showing the negative effects of human's impact, and there are responses at the national, state, and local levels to this growing environmental awareness (Liberty Lake Sewer District, 1989)." INFORMATION In general, there are a number of environmental factors that influence algal growth. The major factors include:
However, it is a combination of these and other environmental factors that determine the type and quantity of algae found in a lake. These factors are almost always in a state of flux, where change of seasons, development in the watershed, and rainstorms constantly create "new environments" in a lake. "Excessive growth of one or more species of algae is termed bloom. Algal blooms, usually occurring in response to an increased supply of nutrients, are often a disturbing symptom of cultural eutrophication (Informational Handout, author unknown)." When dissolved oxygen levels in the lake bottom decrease to levels near 1 mg/l (anaerobic conditions, without oxygen), then large amounts of phosphorus can be released from bottom sediments. Considering a large portion of the phosphorus reservoir in a lake is trapped in bottom sediments, release would largely contribute to extreme eutrophication conditions and pervasive algae blooms. Dissolved oxygen depletion in the lake bottom is attributed to consumption of organic matter by bacteria, unavailability of oxygen to be distributed deep within the water column, and respiration by benthic invertebrates. This is why the lake environment is such a delicate balance. "Blooms of algae can give water an unpleasant taste or odor, reduce clarity, and color the lake a vivid green, brown, yellow, or even red, depending on the species. Filamentous and colonial algae are especially troublesome because they can mass together to form scums or mats on the lake surface. These mats can drift and clog water intakes, foul beaches, and ruin many recreational opportunities (Informational Handout, author unknown)." Typical blue-green algae blooms observable in Liberty Lake primarily consist of Gloeotrichia, Anabaena, Microcystis and Aphanizomenon (EPA, 1982). Examples of these blue-green algae colonies may be viewed at: http://www-cyanosite.bio.purdue.edu/images/images.html Of the nutrients necessary for algal growth, phosphorus is commonly the one that limits the amount of algae present. Phosphorus is taken up as Phosphate (PO4), which is the only inorganic form of phosphorus that organisms can use. If an overabundance of phosphorus comes into the lake faster than it can be assimilated, the result can be blue-green algae blooms. "Diverting the source of nutrients, both point and non-point sources, is certainly the best long-term solution to controlling the growth of algae in a lake. The results of this action, however, are not always immediate and supplemental methods may be required (Informational Handout, author unknown)." One of these techniques is chemical inactivation and precipitation (Alum). Alum (aluminum sulfate, Al2(SO4)3·18 H2O) has been used successfully to control internal phosphorus loading and improve water clarity in lakes. The alum can form an Al(OH)3 "blanket" over the sediments, reducing P release from the sediments to the water column. When aluminum sulfate [Al2(SO4)3·18 H2O)] is added to the water, a reaction occurs that produces aluminum hydroxide [Al(OH)3]. Through a series of subsequent reactions the phosphorus is either precipitated out of solution as aluminum phosphate (ALPO4) or by sorption onto the surfaces of the aluminum hydroxide polymers. Internal loading supplies significant phosphorus to the water column, the alum treatment should reduce water column phosphorus and thus planktonic algae, resulting in increased water clarity (Informational Handout, author unknown). LIBERTY LAKE PAST AND PRESENT Alum treatments, conducted by Washington State University, occurred in Liberty Lake in 1980-1981. The treatments were successful as clarity increased from a few inches to meters. Below are photographs from an intense algae bloom in the late 1970's, where the algae blooms were so pervasive that the entire lake surface would be covered for weeks at a time. The blooms shaded the weeds from the sun, causing them to die and float to the surface in large dark mats. These mats are observable floating on the lake surface in the following aerial photographs.
Click to enlarge the photos Below are aerial photographs of how Liberty Lake is seen today after an intensive restoration project in the late 70s and early 80s; including the building of a sewage treatment system, dredging a 50 acre parcel to remove a two foot layer of nutrient rich sediment, and an alum treatment. Ongoing lake protection activities, monitoring, and water quality studies are conducted by Washington State University and the Liberty Lake Sewer and Water District to protect the lake's water quality and aesthetic beauty.
Notice the red structure on the beach, this is the county park swimming area. Compare with the photograph above and observe the increased water quality and clarity from pre-restoration activities. Although Liberty Lake may still display algae blooms from year to year, the overall intensity and duration of the blooms are not as pervasive as earlier pre-restoration blooms.
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