Lake Lariat Bloom - Microcystis aeruginosa
"From Green Water to Clean Water"
"From Green Water to Clean Water"
Lake Lariat Clam Project
What is known: An exotic bloom has infected Lake Lariat throughout the summer of 2007. The bloom
is not consumed by the clams but does not appear to be harmful to them either. The bloom was
originally classified by Dr. Harriette Phelps (University of the District of Columbia) as most likely the
genus Microcystis, which is cyanobacteria, commonly referred to as blue-green algae. In the daytime it
acts like algae by performing photosynthesis from sunlight, at night it sinks into the water column and
acts likes bacteria that consumes oxygen. Microcystis creates toxins, collectively known as microcystin
that can be very toxic.
Richard Lacouture (Morgan State U Estuarine Research Center) has since identified the bloom species
as Microcystis aeruginosa. The conditions for Microcystis are high water temperature, high nutrient
load, poor circulation, and high pH. A higher than normal phosphorous load and pH are the probable
triggers for the bloom. The clam floats and floating upwellers (FLUPSY’s) in the original ‘A’
configuration did not appear to be harmed by the bloom nor did they appear to bring it under control.
Additional water samples were collected and studied by Mr. Lacouture and determined that in addition
to the Microcystis, the lake and pond below the dam environment included other algal communities
such as centric diatoms, red-pigmented phytoflagellates, and an armored dinoflagellate,
Protoperidinium as illustrated in the graphic cross-section below.
is not consumed by the clams but does not appear to be harmful to them either. The bloom was
originally classified by Dr. Harriette Phelps (University of the District of Columbia) as most likely the
genus Microcystis, which is cyanobacteria, commonly referred to as blue-green algae. In the daytime it
acts like algae by performing photosynthesis from sunlight, at night it sinks into the water column and
acts likes bacteria that consumes oxygen. Microcystis creates toxins, collectively known as microcystin
that can be very toxic.
Richard Lacouture (Morgan State U Estuarine Research Center) has since identified the bloom species
as Microcystis aeruginosa. The conditions for Microcystis are high water temperature, high nutrient
load, poor circulation, and high pH. A higher than normal phosphorous load and pH are the probable
triggers for the bloom. The clam floats and floating upwellers (FLUPSY’s) in the original ‘A’
configuration did not appear to be harmed by the bloom nor did they appear to bring it under control.
Additional water samples were collected and studied by Mr. Lacouture and determined that in addition
to the Microcystis, the lake and pond below the dam environment included other algal communities
such as centric diatoms, red-pigmented phytoflagellates, and an armored dinoflagellate,
Protoperidinium as illustrated in the graphic cross-section below.
Clam bag floats were replaced by the original Floating Upweller System (FLUPSY ‘A’) with ~1000 gallon
per hour electric pump since October 2006. A second FLUPSY ‘A’ was deployed to the lake in early
July 2007. The FLUPSY ‘A’ appears to have no effect on Microcystis for the simple reason the clams
won’t eat it. Clam growth assessments confirmed growth of the clams through the first week of August,
but since that date the average mass of the clams declined indicating poor nutrition. In spite of the
poor growth this summer, mortality has been very low and the organic muck that dominated the lake
bottom where the FLUPSY ‘A’ was located since last year, has since tightened up. The sediment
bottom was originally a sticky, organic muck with high organic carbon content that appears to have
since been removed by biochemical processes at the sediment/water interface.
A second configuration specifically designed to combat Microcystis, termed FLUPSY ‘B’, was
developed and deployed to the lake in the first week of September 2007. Whereas the FLUPSY ‘A’
draws warm water from the shallows and discharges it to a deeper location, the FLUPSY ‘B’ draws in
cool water from deep in the lake, adds aeration, and discharges it to the warm shallows. Unlike the
FLUPSY ‘A’, the water within the FLUPSY ‘B’ tank appears clean and clear, with centric diatoms and
suppressed Microcystis.
What is not known: There are a great variety of sources to consider for the chemical nutrients that
impact the lake such as fertilizer run-off, atmospheric deposition, and drainage from broken septic
tanks. Another source of nutrients and other pollutants that need to be considered is the Christmas
trees and tires that were dumped in the lake in the early 1990’s for the stated purpose to improve fish
habitat.
Bacteria counts as sampled and analyzed by the Maryland Department of Health and Mental Hygiene
are used by health and safety professionals to measure water quality. At the lake beach the coliform
bacteria counts have been reasonably low creating a false indicator in reference to water quality
results. What is not known is whether or not the low values are because the coliforms are impacted by
the presence of cyanobacteria. There is a danger for public safety if coliform counts are the only factor
used to determine recreational water quality and low counts can occur during a major algal bloom with
toxic potential. The toxicity of the bloom is pending analysis by a University of Maryland Laboratory in
Baltimore.
Another mystery is the origin of the latent pH increase. The Lake Lariat pH trend has generally been ½
point higher this summer than the previous years since 2004. The source of the pH increase could be
ground water run-off or possibly from the atmosphere. It’s difficult to imagine the community collectively
decided to increase the use of lime fertilizers just this year. Another option to consider is the possibility
that a major local property, such as the golf course, made a major land use policy change and
increased the use of lime. The third option could be atmospheric. The possibility exists that rainfall has
higher pH chemistry this year because power plants to the west are neutralizing their exhaust smoke.
Typically high pH is a good thing, until it contributes to a Microcystis bloom.
per hour electric pump since October 2006. A second FLUPSY ‘A’ was deployed to the lake in early
July 2007. The FLUPSY ‘A’ appears to have no effect on Microcystis for the simple reason the clams
won’t eat it. Clam growth assessments confirmed growth of the clams through the first week of August,
but since that date the average mass of the clams declined indicating poor nutrition. In spite of the
poor growth this summer, mortality has been very low and the organic muck that dominated the lake
bottom where the FLUPSY ‘A’ was located since last year, has since tightened up. The sediment
bottom was originally a sticky, organic muck with high organic carbon content that appears to have
since been removed by biochemical processes at the sediment/water interface.
A second configuration specifically designed to combat Microcystis, termed FLUPSY ‘B’, was
developed and deployed to the lake in the first week of September 2007. Whereas the FLUPSY ‘A’
draws warm water from the shallows and discharges it to a deeper location, the FLUPSY ‘B’ draws in
cool water from deep in the lake, adds aeration, and discharges it to the warm shallows. Unlike the
FLUPSY ‘A’, the water within the FLUPSY ‘B’ tank appears clean and clear, with centric diatoms and
suppressed Microcystis.
What is not known: There are a great variety of sources to consider for the chemical nutrients that
impact the lake such as fertilizer run-off, atmospheric deposition, and drainage from broken septic
tanks. Another source of nutrients and other pollutants that need to be considered is the Christmas
trees and tires that were dumped in the lake in the early 1990’s for the stated purpose to improve fish
habitat.
Bacteria counts as sampled and analyzed by the Maryland Department of Health and Mental Hygiene
are used by health and safety professionals to measure water quality. At the lake beach the coliform
bacteria counts have been reasonably low creating a false indicator in reference to water quality
results. What is not known is whether or not the low values are because the coliforms are impacted by
the presence of cyanobacteria. There is a danger for public safety if coliform counts are the only factor
used to determine recreational water quality and low counts can occur during a major algal bloom with
toxic potential. The toxicity of the bloom is pending analysis by a University of Maryland Laboratory in
Baltimore.
Another mystery is the origin of the latent pH increase. The Lake Lariat pH trend has generally been ½
point higher this summer than the previous years since 2004. The source of the pH increase could be
ground water run-off or possibly from the atmosphere. It’s difficult to imagine the community collectively
decided to increase the use of lime fertilizers just this year. Another option to consider is the possibility
that a major local property, such as the golf course, made a major land use policy change and
increased the use of lime. The third option could be atmospheric. The possibility exists that rainfall has
higher pH chemistry this year because power plants to the west are neutralizing their exhaust smoke.
Typically high pH is a good thing, until it contributes to a Microcystis bloom.