IDENTIFICATION, ECOLOGY AND CONTROL OF …conference.ifas.ufl.edu/aw11/presentations/Wednesday/Session B/am... · identification, ecology and control of nuisance freshwater algae.
Post on 19-Jul-2018
215 Views
Preview:
Transcript
IDENTIFICATION, ECOLOGY AND CONTROL OF NUISANCE
FRESHWATER ALGAE
KENNETH J. WAGNER, Ph.D, CLMWATER RESOURCE SERVICES
ALGAL PROBLEMS
Algal problems include:• Ecological imbalances
• Physical impacts on the aquatic system
• Water quality alteration
• Aesthetic impairment
• Taste and odor
• Toxicity
ALGAL PROBLEMSEcological Imbalances
High algal densities:• Result from overly successful growth processes
and insufficient loss processes
• Represent inefficient processing of energy by higher trophic levels
• May direct energy flow to benthic/detrital pathways
• May actually reduce system productivity (productivity tends to be highest at intermediate biomass)
ALGAL PROBLEMSAesthetic Impairment
High algal densities lead to:
• High solids, low clarity
• High organic content
• Fluctuating DO and pH
• “Slimy” feel to the water
• Unaesthetic appearance
• Taste and odor
• Possible toxicity
ALGAL PROBLEMSTaste and Odor
• At sufficient density, all algae can produce taste and odor by virtue of organic content and decay
• Some algae produce specific taste and odor compounds that are released into the water
• Geosmin and Methylisoborneol (MIB) are the two most common T&O compounds; these can induce T&O at very low concentrations
ALGAL PROBLEMSTaste and Odor
T&O by blue-greens• Anabaena, Aphanizomenon, Microcystis, and
Oscillatoria are most common T&O producers, but many other genera produce T&O as well
• Geosmin and MIB often produced• Odors usually include musty, grassy, and
septic• May be produced by planktonic or benthic
growths
ALGAL PROBLEMSTaste and Odor
T&O by greens• Chara, Cladophora, Chlorococcales
(Dictyosphaerium, Scenedesmus, Pediastrum, Hydrodictyon), Volvocales (Chlamydomonas, Volvox), and desmids (Staurastrum, Closterium, Cosmarium, Spirogyra) are primary greens causing T&O, but almost any genus can induce T&O at high density
• Main odors are fishy, skunky, musty, grassy and septic (wide range, species-specific)
• Not usually as severe as with blue-greens
ALGAL PROBLEMSTaste and Odor
T&O by diatoms• Melosira/Aulacoseira, Stephanodiscus,
Cyclotella, Asterionella, Fragilaria/Synedra, and Tabellaria are primary diatoms causing T&O, usually only at high density
• Main odors are geranium, spicy and fishy, with occasional musty or grassy scent
• Not as severe as with blue-greens unless diatom density is very high
ALGAL PROBLEMSTaste and Odor
T&O by goldens• Synura, Dinobryon, Mallomonas, Uroglenopsis,
and Chrysosphaerella are major T&O producers, others impart odor at high density Main odors are cucumber, violet, spicy and fishy
• Can produce substantial T&O even at low density
ALGAL PROBLEMSTaste and Odor
T&O by other algae• Dinoflagellates can produce a
fishy or septic odor at elevated densities
• Euglenoids can produce a fishy odor at elevated densities
• Major die-off of high density algae may produce a septic smell
• Actinomycetes, a non-photosynthetic bacterium, can also produce geosmin and MIB
ALGAL PROBLEMSTaste and Odor
Control of T&O• Minimizing algal density and specific T&O
producers is desirable for T&O control• Activated carbon removes most T&O, but
effective use is slow and increases treatment cost
• Aeration/mixing may oxidize/volatilize T&O compounds, but not completely effective
• Possible toxic link, but no severe direct health effects known from T&O; aesthetic issues can be major
ALGAL PROBLEMSToxicity-Cyanotoxins
• Cyanobacteria are the primary toxin threats to people from freshwater; acute toxicity is rare, but chronic effects may be significant and are difficult to detect.
• Research (e.g., 3 papers in Lake and Reservoir Management in September 2009) indicates widespread occurrence of toxins but highly variable concentrations, even within lakes.
• Water treatment in typical supply facilities is adequate to minimize risk; the greatest risk is from substandard treatment systems and direct recreational contact.
• Some other algae produce toxins - Prymnesium, or golden blossom, can kill fish; marine dinoflagellates, or red tides, can be toxic to many animals and humans.
ALGAL PROBLEMSToxicity-Cyanotoxins
• Dermatotoxins– produce rashes and other
skin reactions, usually within a day (hours)
• Hepatotoxins– disrupt proteins that keep
the liver functioning, may act slowly (days to weeks)
• Neurotoxins– cause rapid paralysis of
skeletal and respiratory muscles (minutes)
ALGAL PROBLEMSToxicity-Which Blue-Green Has Which
Toxin?Blue-Green Algae Microcystin Nodularin Cylindro-
spermopsin Anatoxin Saxitoxin Dermato-
toxin Anabaena X X X X Anabaenopsis X Aphanizomenon X X X Cylindrospermopsis X Cylindrospermum X X Hapalosiphon X Lyngbya X X Microcystis X X Nodularia X X Nostoc X Oscillatoria X X X Schizothrix X Umezakia X
More forms found each year – methods or actual increase?
ALGAL PROBLEMSToxicity-Analytical Methods
0
25
50
75
100
1101001000
Sel
ecti
vity
100
75
50
25
Bioassay(mouse)
µg ng pg
Sensitivity
MassSpec LC/MS
HPLC
ELISAPhosphatase Assay
ALGAL PROBLEMSToxicity- Key Issues
• Acute and chronic toxicity levels -how much can be tolerated?
• Synergistic effects - those with liver or nerve disorders at higher risk
• Exposure routes - ingestion vs. skin
• Treatment options - avoid cell lysis, remove or neutralize toxins
ALGAL PROBLEMSRecommended Toxicity Precautions
• Monitor algal quantity and quality
• If potential toxin producers are detected, increase monitoring and test for toxins
• For water supplies, incorporate capability to treat for toxins (PAC or strong oxidation seem to be best)
• For recreational lakes, be prepared to warn users and/or limit contact recreation
• Avoid treatments that rupture cells
Algal FormsAlgal “Blooms”
♦ Water discoloration usually defines bloom conditions
♦ Many possible algal groups can “bloom”
♦ Taste and odor sources, possible toxicity
♦ Potentially severe use impairment
Algal FormsAlgal Mats
♦ Can be bottom or surface mats -surface mats often start on the bottom
♦ Usually green or blue-green algae
♦ Possible taste and odor sources
♦ Potentially severe use impairment
Algal Types: Planktonic Blue-greensCylindrospermopsis
•A sub-tropical alga with toxic properties is moving north.
•Most often encountered in turbid reservoirs in late summer, along with a variety of other bluegreens.
Algal Types: Planktonic GreensPediastrum
Scenedesmus
Lagerheimia Dictyosphaerium
Schroederia
Oocystis
(Order Chlorococcales)
Algal Types: Mat Forming Greens
Cladophorales, with Cladophora (above), Rhizoclonium and Pithophora
Zygnematales, with Spirogyra (above), Mougeotia and Zygnema
Hydrodictyon, an unusual type of Chlorococcales
Oedogoniales, with Oedogonium and Bulbochaete
Algal Types: Mat Forming GreensZygnematales - Unbranched filaments, highly
gelatinous
MougeotiaSpirogyra
Zygnema
Mats trap gases and may float to surface
Cladophorales - Large, multinucleate cells, reticulate chromatophores, filamentous forms
Pithophora
RhizocloniumCladophora
Algal Types: Mat Forming Greens
Algal Types: Other Plankton
Ceratium
Peridinium
Euglena
Trachelomonas
Phacus
(Euglenoids)
(Dinoflagellates)
ALGAL ECOLOGYKey Processes Affecting Abundance
Growth Processes• Primary production – controlled by light
and nutrients, algal physiology• Heterotrophy – augments primary
production, dependent upon physiology and environmental conditions
• Release from sediment – recruitment from resting stages, related to turbulence, life strategies
ALGAL ECOLOGYKey Processes Affecting Abundance
Loss Processes
• Physiological mortality – inevitable but highly variable timing – many influences
• Grazing – complex algae-grazer interactions
• Sedimentation/burial – function of turbulence, sediment load, algal strategies
• Hydraulic washout/scouring – function of flow, velocity, circulation, and algal strategy
ALGAL ECOLOGYKey Processes Affecting Abundance
Annual variability in growth/loss factors in dimictic temperate lakes
• Winter –– Possible ice cover, reverse stratification
– Under ice circulation is an important factor
– Low light and temperature affect production
– Variable but generally moderate nutrient availability
– Possibly high organic content
– Grazer density usually low
ALGAL ECOLOGYKey Processes Affecting Abundance
Annual variability in growth/loss factors in dimictic temperate lakes
• Spring/fall –– Isothermal and well-mixed
– Relatively high nutrient availability
– Light increases in spring, decreases in fall
– Temperature low to moderate
– Stratification setting (spring) or breaking down (fall)
– Grazer density in transition (low to high in spring, high to low in fall)
ALGAL ECOLOGYKey Processes Affecting Abundance
Annual variability in growth/loss factors in dimictic temperate lakes
• Summer –– Potential stratification, even in shallow lakes
– Often have low nutrient availability
– Light limiting only with high algae or sediment levels
– Temperature vertically variable – highest near surface
– Vertical gradients of abiotic conditions and algae
– Grazer densities variable, often high unless fish predation is a major factor
ALGAL ECOLOGYPhytoplankton Succession - Winter
• Under ice, mainly cryptophytes, chrysophytes, diatoms, naked dinoflagellates
• Some non-nitrogen fixing blue-greens, but also possibly Aphanizomenon
ALGAL ECOLOGYPhytoplankton Succession – Early Spring
• Most lakes experience rapid increase in algal density
• Diatoms, cryptophytes, and chrysophytes tend to dominate
• Temperature is a primary control factor
ALGAL ECOLOGYPhytoplankton Succession – Late Spring
• Diatoms tend to dominate, often with Chlorococcalean greens and cryptophytes
• Chrysophyte blooms possible
• The later the spring maximum, the less likely that diatoms will dominate
• Overwintering benthic colonies may be recruited to the plankton community
ALGAL ECOLOGYPhytoplankton Succession – Late Spring
• Increasing light cues spring blooms where nutrients are available
• Grazing and algal settling increases during spring with rising water temperature
• Clear water phase often results from loss processes overshadowing growth in
late spring
ALGAL ECOLOGYPhytoplankton Succession – Early Summer• Increasing light and temperature• Nutrient availability may decrease as internal sources
are isolated by stratification - N, P, Si• Grazing, sinking and metabolism all increasing• Composition will depend upon resource gradients -
low N:P favors blue-green Nostocales and green Volvocales, high N:P favors other chlorophytes, chrysophytes and dinoflagellates
• N:P ratio at sediment:water interface can be more important than ratio in epilimnion
• High variability among lakes and within lakes among years
ALGAL ECOLOGYPhytoplankton Succession – Early Summer
• Greens increase, especially Volvocales and Chlorococcales
• Some blue-greens appear at increased density
ALGAL ECOLOGYPhytoplankton Succession – Early Summer
• May get metalimneticblooms of cryptophytes, chrysophytes, dinoflagellates or blue-greens, especially Planktothrix
ALGAL ECOLOGYPhytoplankton Succession – Late Summer
• High bloom potential -most often blue-greens, but also thecate dinoflagellates, large desmids
• Temperature is a major factor in blooms
ALGAL ECOLOGYPhytoplankton Succession – Late Summer
• Nitrogen-fixing blue-greens especially common bloomers
• May get blooms of non-N fixing blue-greens if N is high
• May get population oscillations between N-fixers and non-N-fixers
ALGAL ECOLOGYPhytoplankton Succession – Late Summer
• May also get green or blue-green mats floating to the surface
• Most often Cladophorales or Oscillatoriales
• Mats tend to start on bottom, floating to surface after trapping gases
ALGAL ECOLOGYPhytoplankton Succession – Late Summer
• A variety of other algae may be mixed in, but dominance by one taxon or a few taxa is typical in fertile lakes
• Growth often nutrient limited, but dense surface growths may create light limitation below
• Grazing may be high, may be selective
ALGAL ECOLOGYPhytoplankton Succession - Autumn
• “Leftover” blue-greens may remain abundant well into autumn, exception is Cylindrospermopsiswhich often blooms late summer into mid-fall
• Metalimnetic growths often reach surface upon mixing
• Diatoms often assume dominance after turnover
ALGAL ECOLOGYPhytoplankton Succession - Autumn
• Desmids also respond positively to mixing
• As the water cools, the oil-laden Botryococcus may become abundant
• Nutrients tend to be abundant after turnover
ALGAL ECOLOGYPhytoplankton Succession - Notes
• Biomass can vary by 1000X from winter minimum to late summer maximum in temperate to polar waters
• Primary productivity and biomass may not correlate due to time lags, cell size and nutrient or light limitations
• Highest productivity normally at intermediate biomass (Chl a = 10 ug/L)
• High pH during blooms may trigger resting cyst formation
ALGAL ECOLOGYTrophic Gradients
• Based on decades of study, more P leads to more algae
• More algae leads to lower water clarity, but in a non-linear pattern
0102030405060708090
100110120130140150160170180190200
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Ch
l (u
g/l)
TP (ug/l)
Total Phosphorus vs. Chlorophyll a
0
1
2
3
4
5
6
7
8
9
10
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
SD
T (
m)
TP (ug/l)
Total Phosphorus vs. Secchi Disk Transparency
ALGAL ECOLOGYTrophic Gradients
• As algal biomass rises, a greater % of that biomass is cyanobacteria. So more P = more algae + more cyanobacteria.
From Canfield et al. 1989 as reported in
Kalff 2002
ALGAL ECOLOGYTrophic Gradients
• High P also leads to more cyanobacteria, from considerable empirical research. Key transition range is between 10 and 100 ug/L
(10 ug/L) (100 ug/L)From Watson et al. 1997 L&O 42(3): 487-495
Three step process:– Don’t lose your head– Get ducks in a row– Don’t bite off more than you can chew
PART 4: METHODS OF ALGAL CONTROL
Algal Control: Watershed Management♦ Source controls• Banning certain high-impact actions• Best Management Practices for minimizing risk of
release
♦ Pollutant trapping• Detention• Infiltration• Uptake/treatment• Maintenance of facilities
Watershed management should be included in any successful long-term algal management plan
Algal Control: In-Lake ManagementData needs include:♦ Algal types and quantity (planktonic and benthic)♦ Water quality (nutrients, pH, temp., oxygen,
conductivity, and clarity over space and time)♦ Inflow and outflow sources and amounts, with
water quality assessment♦ Lake bathymetry (area, depth, volume)♦ Sediment features♦ Zooplankton and fish communities♦ Vascular plant assemblage All of which facilitate a hydrologic and nutrient
loading analysis and biological assessment essential to evaluating algal control options
Algal Control: In-Lake Management
In-lake detention and wetland
systems to limit nutrient inputs
Fulfilling a watershed
function in the lake
Algal Control: In-Lake ManagementDredging
♦ Dry (conventional)
♦ Wet (bucket/dragline)
♦ Hydraulic (piped)
♦ Removes nutrient reserves
♦ Removes “seed” bank
♦ Potential mat control
Algal Control: In-Lake Management
Harvesting
♦ Not feasible for many algal nuisances
♦ Possible to collect surface algal mats
Algal Control: In-Lake Management
Dilution and Flushing
♦ Add enough clean water to lower nutrient levels
♦ Add enough water of any quality to flush the lake fast enough to prevent blooms
Algal Control: In-Lake ManagementSelective withdrawal
♦ Often coupled with drawdown
♦ May require treatment of discharge
♦ Best if discharge prevents hypolimnetic anoxia
Algal Control: In-Lake ManagementDye addition
♦ Light limitation -not an algaecide
♦ May cause stratification in shallow lakes
♦ Will not prevent all growths, but colors water in an appealing manner
Algal Control: In-Lake ManagementSonication
♦ Disruption of cells with sound waves – may break cell wall or just dissociate plasma from wall
♦ Used in the lab to break up algal clumps
♦ Won’t eliminate nutrients, but may keep algae from growing where running all the time
♦ Varied algal susceptibility
Algal Control: In-Lake ManagementAlgaecides
♦ Relatively few active ingredients available
♦ Copper-based compounds are by far the most widely applied algaecides
♦ Peroxides gaining acceptance
♦ Some use of endothall
♦ Effectiveness and longevity are issues
Algal Control: In-Lake ManagementAbout copper
♦ Lyses cells, releases contents into water♦ Formulation affects time in solution and
effectiveness for certain types of algae♦ Possible toxicity to other aquatic organisms♦ Long term build up in sediment a concern, but no
proven major negative impacts♦ Resistance noted in multiple nuisance blue-greens
and greens♦ Usually applied to surface, but can be injected
deeper by hose♦ Less effective at colder temperatures
Algal Control: In-Lake ManagementAbout peroxide
♦ Lyses cells, but more effective on thin walled forms; less impact on most diatoms and greens
♦ Degrades to non-toxic components; adds oxygen to the water, may oxidize some of the compounds released during lysis
♦ Typically applied to surface, but may reach greater depth with adequate activity (slower release/reaction rate)
♦ No accumulation of unwanted contaminants in water or sediment
♦ Considerably more expensive than copper
Algal Control: In-Lake ManagementProper Use of Algaecides
♦ Prevents a bloom, not removes one♦ Must know when algal growth is accelerating♦ Must know enough about water chemistry to
determine most appropriate form of algaecide♦ May involve surface or shallow treatment where
nutrients are fueling expansion of small population♦ May require deep treatment where major migration
from sediment is occurring♦ May require repeated application, but at an
appropriate frequency - if that frequency becomes too high, recognize that the technique requires adjustment or will not be adequate for the long-term
Algal Control: In-Lake Management♦ Iron is the most
common natural binder, but does not hold P under anoxia
♦ Aluminum is the most common applied binder, multiple forms, permanent results, toxicity issues
♦ Calcium used in some high pH systems
♦ Used for water column or sediment P
Algal Control: In-Lake Management
Factors in Planning LakeTreatments:
• Existing P load, internal vs external
• Sources and inactivation needs – field and lab tests
• System bathymetry and hydrology
• Potential water chemistry alteration - pH, metals levels, oxygen concentration
• Potentially sensitive receptors - fish, zooplankton, macroinvertebrates, reptiles, amphibians, waterfowl
• Accumulated residues - quantity and quality
Algal Control: In-Lake Management
Lake Water Column Treatment:
• Doses vary - need 5-20 times TP conc.
• Can achieve >90% P removal, 60-80% more common
• Effects diminish over 3-5 flushings of the lake
Algal Control: In-Lake ManagementLake Sediment
Treatment:
• Can reduce longer-term P release
• Normally reacts with upper 2-4 inches of sediment
• Dose usually 25-100 g/m2 - should depend upon form in which P is bound in sediment
Algal Control: In-Lake ManagementSediment Dose Calculation
1. Oldest approach is to treat at maximum level that maintains pH >6; may need to do jar tests and repeat application over time to achieve goal
2. Alternative older method is to measure accumulated hypolimnetic P during stratification, or change in lake P over a dry period, or release from incubated sediment, translate into sediment P concentration (per square meter), then treat with dose at least 10 times that level on areal basis – buffer if necessary to control pH
3. Most current approach is to determine available P in sediment (Rydin and Welch method), treat aliquots of sediment slurry with aluminum, re-test for P availability, graph results and evaluate in context of target P level, diminishing returns, and cost; dose of 10 to 100 times available sediment P level expected
Algal Control: In-Lake ManagementMethods for Minimizing Aluminum Toxicity
Aluminum dose at any one time should be <10 mg/L, preferably <5 mg/L
When buffering alum with aluminate, use a 2:1 ratio of alum to aluminate, by volume, to avoid pH change (can be adjusted – 1.8 to 2.1 common)
Treat defined areas of the lake in a pattern that minimizes contiguous area treated at once (patchwork with adjacent blocks not treated sequentially)
Apply aluminum at enough depth to create a surface refuge (can even treat below thermocline)
Secchi Disk Transparency in Hamblin Pond, 1992-2003
0.0
2.0
4.0
6.0
8.0
10.0
2/27/1992
4/28/1992
6/10/1992
7/14/1992
8/13/1992
9/18/1992
10/23/1992
7/6/1993
7/31/1993
8/14/1993
8/30/1993
9/12/1993
6/26/1994
7/11/1994
7/31/1994
8/11/1994
9/15/1994
5/23/1995
6/4/1995
6/23/1995
7/21/1995
9/22/1995
6/28/1996
7/22/1996
8/10/1996
10/1/1996
6/26/1997
8/8/1997
8/31/1997
9/30/1997
8/28/1998
5/26/1999
7/6/1999
8/25/1999
9/18/1999
6/12/2000
8/4/2000
9/4/2000
6/18/2001
9/10/2002
9/10/2003
Date
SDT
(M)
Treatment Date
SDT = 1.22 m
Hamblin Pond ExampleCape Cod, MA
P levels dramatically reduced, water clarity substantially increased
Long Pond ExampleCape Cod, MA
P levels dramatically reduced, but only for a year; clarity remains high through 3 years
0.00
0.05
0.10
0.15
0.20
0.25
Phos
phor
us (m
g/L)
Phos
phor
us (m
g/L)
Jul 9
7Ju
l 97
Au
g 97
Ju
l 00
Au
g 00
Jul-0
7Au
g-07
Sep-
07O
ct-0
7N
ov-0
7De
c-07
Jan-
08Fe
b-08
Mar
-08
Apr-
08M
ay-0
8Ju
n-08
Jul-0
8Ju
l-08
Aug-
08Se
p-08
Oct
-08
Nov
-08
Dec-
08Ja
n-09
Feb-
09M
ar-0
9Ap
r-09
May
-09
Jun-
09Ju
l-09
Aug-
09Se
p-09
Oct
-09
Nov
-09
Dec-
09Ja
n-10
Feb-
10M
ar-1
0Ap
r-10
May
-10
Jun-
10Ju
l-10
Aug-
10Se
p-10
Oct
-10
Nov
-10
Dec-
10
Surface
Bottom
Algal Control: In-Lake ManagementSelective nutrient
addition♦ Addition of nutrients
(most likely N or Si) to shift ratio (N:P:Si) to favor more desirable algae
♦ Sometimes practiced in association with fertilization for fish production, but rare in water supplies or recreational lakes
Algal Control: In-Lake ManagementAeration/mixing can work by:
♦ Adding oxygen and facilitating P binding while minimizing release from sediments
♦ Physical mixing that disrupts growth cycles of some algae
♦ Alteration of pH and related water chemistry that favors less obnoxious algal forms
♦ Turbulence that neutralizes advantages conveyed by buoyancy mechanisms
♦ Creation of suitable zooplankton refuges and enhancement of grazing potential
Algal Control: In-Lake ManagementKey factors in aeration:
♦ Adding enough oxygen to counter the demand in the lake (usually about 75% from sediment) and distributing it where needed in the lake
♦ Maintaining oxygen levels suitable for target aquatic fauna (fish and invertebrates)
♦ Having enough of a P binder present to inactivate P in presence of oxygen
♦ Not breaking stratification if part of goal is to maintain natural summer layering of the lake
Algal Control: In-Lake ManagementDestratifying aeration:
Lake is mixed, top to bottom, input of oxygen comes from bubbles and interaction with lake surface
Algal Control: In-Lake ManagementNon-destratifying aeration:
Bottom layer is aerated, but top layer is unaffected; oxygen input comes bubbles (can be air or oxygen)
Algal Control: In-Lake ManagementKey factors in mixing:
♦ Moving enough water to prevent stagnation; may mix whole lake or just the top layer (if any)
♦ Fostering greater homogeneity in mixed zone and greater interaction with the atmosphere (oxygen and pH effects may be large)
♦ Getting enough motion or change in water quality to disrupt target algal species; moving algae to dark zone helps, but may be possible to disrupt with only surface layer mixing
Algal Control: In-Lake ManagementBarley straw as an algal
inhibitor
♦ Decay of barley straw appears to produce allelopathic substances
♦ Bacterial activity may also compete with algae for nutrients
♦ Limited success with an “unlicensed herbicide” in USA
Algal Control: In-Lake ManagementViral controls were
attempted without much success in the
1970s, but recent research suggests renewed potential.
Virus SG-3 in tests at
Purdue Univ.
Algal Control: In-Lake ManagementBacterial additives
♦ Many formulations, details proprietary
♦ Seem to focus on limiting N; competitive with algae
♦ Claims of sediment reduction
♦ Often paired with aeration/mixing
♦ Variable results, inadequate scientific documentation
Algal Control: In-Lake ManagementBiomanipulation -
altering fish and zooplankton
communities to reduce algal
biomass
Algal Control: In-Lake ManagementTechniques for algal control with highest
probability of success♦ Watershed management (where external load is high)
♦ Phosphorus inactivation (for internal load or inflow)
♦ Aeration/mixing (possibly with dyes or bacteria)
♦ Dredging (where feasible, especially for mats)
♦ Algaecides (with proper timing, limited usage)
♦ Sonication (for susceptible algae, ltd nutrient control)
♦ Biomanipulation (but with high variability)
♦ Other techniques as scale and circumstances dictate (do not throw away any tool!)
top related