Post on 24-Feb-2021
Mitigating Freshwater Cyanobacteria Blooms
K.G. Sellner1, A. Place2, M. Paolisso3, Y. Gao4, E. Williams2, E. VanDolah3, J. Biondi1, & S. Shah5
1Chesapeake Research Consortium, Edgewater, MD, USA
2Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Sciences, Baltimore, MD, USA 3Department of Anthropology, University of Maryland, College Park, MD, USA
4Horn Point Laboratory, University of Maryland Center for Environmental Sciences, Cambridge, MD, USA 5GEMSTONE Program, University of Maryland, College Park, MD, USA
NOAA HAB-PCM Grant NA10NOS4780154
Microcystis Blooms on MD’s Eastern Shore, USA
• Dog mortalities in 24-48 h in 2009 at Higgins Mill Pond; [microcystin] = 2 x 104 µg/L. Continued blooms today
• Summer blooms in Lake Williston in 2009-2011, exceeding WHO levels for recreational use
• Goal: To adapt Chinese freshwater sediment-cyanobacteria flocculation technology for MD waters as a potential routine mitigation technique by non-science personnel
– Any local sediment + chitosan
– 100 mg sed/L + 10 mg chitosan
• Foundation: GEMSTONE Team lab results (Crete, 2010)
• Preliminary flocculation expt. in 2011 at Williston brought cyanobacteria to the bottom
Established Methods: Preliminary Lab Results
To minimize costs + facilitate easy mixing in the field
• Pan et al. (2006) chitosan soln lowers pH<4; same soln in diluted table vinegar (0.5% HAc) & filtered lake water results in pH>6.7
• Flocculation as effective (97%-98% in 51 h)
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HAc&DI
Hac&DI stan stan+chit DI Control
t50=25 h
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Vin&LW
vin&LW stan stan+chit LW Control
t50=20.5 h
[200 mg sed+50 mg chit]/L
Preliminary Lab Results
Contrary to Pan et al. (2006), little flocculation at
[100 mg sed+10 mg chit]/L regardless of sediment size or
mineralogy 0
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1-2 mm Quarry Sediment
sieved, no chit sieved+10 mg chitsieved+25 mg chit sieved+50 mg chit
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<63 um Quarry Sediment
<63 um, no chit <63 µm &10mg chit<63µm &25mg chit <63µm &50mg chit
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Stancill's Clay
stan, no chit stan+10 mg chit stan+25 mg chit stan+50 mg chit
Sand Flocculation of HMP Blooms • Greater flocculation of cyanobacteria with smaller sand grain size &
chitosan addition (similar result for all Chl a) • Much more sediment & chitosan required vs. Pan et al. (2006)
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Sand <125um
1.5g/L 3g/L 5g/L
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Sand (<125um):Chitosan=50:1
1.5g/L 3g/L 5g/L
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Sand (125-250um):Chitosan=50:1
1.5g/L 3g/L 5g/L
Stancill’s Clay Flocculation of HMP Blooms
• To rapidly remove HMP cyanobacteria blooms, must add very high sediment & chitosan levels
-25%
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Stancill's
1.5 g/L 3 g/L 5 g/L
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Stancill's+Chitosan 50:1
1.5 g/L Stancill's+chit 3 g/L Stancill's+chit 5 g/L Stancill's+chit
Note: Near 100% & faster removal at [5 g Stancill’s+0.15 g Chit/L] vs. SANDS+Chit
Summary Table of Flocculation Abilities for Field Blooms
SEDIMENT + CHITOSAN/L t50 (h)
1.5 g <125 µm SAND + 0.03 g 6.9
3 g 125-250 µm SAND + 0.06 g 2
5 g <125 µm SAND + 0.15 g 0.98
5 g 125-250 µm SAND + 0.15 g 1.15
1.5 g STANCILL’S + 0.03 g 28.19
3 g STANCILL’S + 0.06 g 20.44
5 g STANCILL’S + 0.15 g 0.3
102 g STANCILL’S + 1.235 g to 4650 L* 0.16
All other lower concentrations of sediments with or without chitosan never removed 50% of bloom cyanobacteria
t50 = time (h) to remove 50% of the field cyanobacteria bloom
*October, low cyanobacteria abundance
Lake Draining+Barley Straw: Cyanobacteria from Cores
Geitlerinema acutissimum
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PC
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Incubated Samples, Chl/PC<10
Core/Water Over Core PC Growth
0 d, 20o 19 d, 20o 27 d, 25o 34 d, 28o
CORE15
Pseudanabaena sp.
Synechococcus
•Cyanobacteria bloom in 2011 with microcystin >10 ug/L •Drained lake in fall, flushing bloom and sedimented vegetative populations out •Exposed 2/3 of lake bottom for >5 months •Deployed barley straw along lake shore in early spring •Collected and incubated cores in May 2012, gradual inc to 28.5oC •For samples with chl/PC<10, collected samples for PP composition
RESULT: No Microcystis from cores or overlying water
Barley Straw & M. aeruginosa • Previous lab & field results
have indicated barley straw effects on freshwater cyanobacteria
• M. aeruginosa LE3 + 4.5 & 9.1 g barley straw/L
• 46% reduction in M. aeruginosa over 29 d, with removal beginning at day 13
• Extract from water logged barley straw inhibited cultured M. aeruginosa growth on occasion
• Short half-life of extract
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IVF
Day
Aged Barley Straw & M. aeroginosa
Low High Low Control High Control
Removal Effic=46%,
Cel
ls/m
L
Day
2012 Lake Draining + Barley Straw
• Absence of vegetative Microcystis in sediments
• Very late appearance of M. aeruginosa
• Low toxin levels Oct July
Fro
m B
ott
om
2013 Barley Straw
• Just begun barley straw bale deployments in – Lake Williston (yr 2)
– 240 acre saline (S=11) pond on dredge material island in Chesapeake Bay
• Monitoring sediment & water column cyanobacteria & toxins
Future Research
• Large 4 m3 lake limnocorral expts (before, during, late bloom)
• Chitosan additions, then sediment? • Kill surface bloom, then
flocculate+ballast • Conduct ‘impacts’ assessments (fish,
in- and epi-fauna) • Assess lake draining/flushing effects • Barely straw exposures in lake & saline
pond: cyano growth & toxin production
• Hand-off effective, inexpensive strategies to state for routine use?
So Practical, Inexpensive Options for Freshwaters/Tidal-freshwaters?
• Little confidence in previously published clay flocculation results for freshwaters, i.e., any sediment + low chitosan can remove Microcystis
• Sediment additions effective in removing Microcystis in freshwaters are far above TSS levels permitted in loads allowed
• Increasing chitosan concentrations might work but then $$$ become an issue
• Lake draining & pre-bloom barley straw looks promising and are CHEAP!
Management in Future
Ultimately mitigation is a BAND-AID for much larger problem of nutrient load reductions
Need political will to
manage land use to insure nutrient inputs decline
Acknowledgements • G. acutissimum: http://nordicmicroalgae.org/taxon/Geitlerinema%20amphibiium; F. Acker, ANSP
• Pseudanabaena: http://enpub.fulton.asu.edu/pwest/myweb/Taste%20and%20Odor%20Stuff/Taxonomic%20guide/Guide_Images/Pseudanabaena_2_photos.html
• Synechococcus: http://protist.i.hosei.ac.jp/pdb/images/Prokaryotes/Chroococcaceae/Synechococcus/index.html
• Stancill’s = kaolinite, illite, and some quartz (D. Vanko, pers. comm.)