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DEEP WATER MECHANICAL HARVESTING OF HYDRILLA IN WEST LAKE TOHOPEKALIGA,
FLORIDA
Dean Jones1, 2, William Haller 2 and Mike Hulon 3
1Osceola County 2University of Florida
3Texas Aquatic Harvesting, Inc.
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Demonstration Project on Hydrilla and Hygrophila
• Osceola County awarded $2.8 million by the EPA for this project
• Goal: To find new and alternative methods of control for hydrilla and hygrophila and to share the findings with the industry and public
• 2006-2012
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Why Reconsider Harvesting?
• Little research on mechanical harvesting since 1970’s, Orange Lake , Florida – Small harvesters – Maximum cutting depth of 5 feet – Visually see hydrilla (surface mats) – Rapid re-growth – High fish by-catch
• Most opinions about harvesting hydrilla are based on this work and data
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Other Considerations • Endangered species restrictions
– Everglades Snail Kite (Rostrhamus sociabilis)
• Limited management resources – Herbicide resistance and costs
• Integrated Pest Management • Equipment and technology advances • Compare results with Orange Lake Study
Haller et al. 1980 – Fish by catch data – Observation – hydrilla did not return in some
areas harvested for approximately one year
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Aquamarine H-650
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Aquamarine Aquatrio
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Aquamarine Aquatrio
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Orange Lake Study
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Model 800 Mechanical Harvester
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Equipment Advances
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Technology Advances
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Goals • Harvest a 40 ha area (100 acres) of deep water
hydrilla in West Lake Toho • Determine Efficacy and longevity of control
– Is Deep Water Hydrilla Harvesting efficient? – Can we harvest root crowns?
• Determine fish by catch and compare with Orange Lake Study results – Is it possible to reduce fish by-catch?
• Determine magnitude and duration impacts of selected water quality parameters before, during and following the harvesting operation
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Efficacy
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Efficacy
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1 DAT Comparison
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2 MAT Comparison
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Efficacy and Longevity
Interval Date PAC PVI
Pre-treatment 1/30/2012 73.34 36.49
1 DAT 3/19/2012 79.75 16.66
2 MAT 5/17/2012 75.10 18.29
3 MAT 6/19/2012 48.10 9.40
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Fish By Catch Comparison
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Fish By Catch Comparison
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Fish By Catch Comparison
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Harvester Performance Transect Number
1 2 3 4
Area (ha) (ac)
0.117 0.289
0.116 0.286
0.138 0.341
0.117 0.289
Area (ha/hr) (ac/hr)
.98 2.35
0.82 2.02
0.88 2.18
0.90 2.22
Weight (hydrilla) kg/trans. lbs/trans. kg/ha lbs/ac
158 348
1,350 1,204
191 420
1,646 1,469
135 296 978 868
129 284
1,102 983
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Fish By Catch Results
Fish
Total
Bluegill No. WT(g)
92 222.1
Redear No. WT(g)
11 311.8
Warmouth No. WT(g)
2 32.0
Black crappie No. WT(g)
2 80.5
Total Sportfish
No. WT(g)
107 646.4
Total All Fish* No.
WT(g) 141
699.5
% sport fish No. WT(g)
75.9 92.4
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Fish By Catch Comparison Fish
Mean ± SD
LAKE TOHO 2012 Total All Fish Harvested
No./ha g/ha
299 ± 151 1,470 ± 712
ORANGE LAKE 1977 Total All Fish
No./ha g/ha
66,000 ± 2,000 85,000 ± 12,000
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Water Quality Impacts
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Water Quality Impacts
• Water samples collected -7, -1, 0, 1, 4, 7, 15 days after harvesting
• 3 samples sites in harvest area • 5 reference sites 1,000 m outside harvest area • Water samples collected at depth of 1m • Average depth of water samples sites is 2m
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Results (harvest area and control)
• Secchi – Higher in harvest plot 1 week before harvesting
• Total Chlorophyll – Lower in harvest area 1 week before harvesting
• Total Nitrogen – Lower in harvest plot 1 week before harvesting
• Total Phosphorus – Lower in harvest area 1 week and 1 day before harvesting and 7 DAH
• Only post harvest statistical difference is phosphorus 7 DAT
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Results (harvest area and control)
• Also no statistical differences observed in – Turbidity – Dissolved Oxygen – pH – Conductivity
• Temperature difference 1 and 4 DAT (result of time of day sampled)
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Dissolved OXYGEN (mg/l) Depth (ft) Reference site Harvest site
1 2 3 4 5 1 2 3 Surf. 9.4 9.9 10.21 9.97 9.85 9.4 9.5 9.8
1 9.3 9.8 10.24 9.88 9.67 9.5 9.4 9.6 2 9.4 9.8 10.13 9.89 9.81 9.4 9.5 9.7 3 9.3 9.8 10.3 9.83 9.65 9.3 9.5 9.7 4 9.4 9.9 9.8 9.85 9.68 9.3 9.4 9.5 5 9.3 9.7 9.6 9.81 9.53 9.2 9.6 9.3 6 9.6 9.8 9.3 9.84 9.49 9.2 9.1 9.4 7 - - 9.1 9.72 9.52 - 9.5 8.8 8 - - - 9.79 - - - - 9 - - - 9.66 - - - -
10 - - - 9.57 - - - - Time of 1st
sample 1618 1640 1455 1433 1406 1556 1537 1521
°C Surface 18.3 18.3 18.3 18.0 18.0 18.2 18.3 18.3 °C Bottom 18.2 18.3 17.3 17.8 17.8 17.6 17.4 17.0
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Dissolved Oxygen on 6/14/12 Site Time Depth DO (mg/l) Toho YSI 1 - Dense hydrilla 6:10 AM 1 7.44
2 7.06 3 7.24 4 7.37 5 6.47 6 3.93 7 2.68
Toho YSI 3 - Dense hydrilla 6:55 AM 1 2.79
2 2.80 3 2.45
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Comparison Summary
Parameter Orange Lake Lake Tohopekaliga Cutting depth 5 feet 10 feet Hydrilla biomass harvested
12 tons per acres < 1 ton per acre
Hydrilla distribution 80% top 2 feet 100% bottom 4 feet Dissolved oxygen Low in bottom ½ of
water column Uniform throughout water column
By catch 66,000 fish per ha 299 fish per ha Length of control 2-4 months > 4 months Acres per hour harvested
<1 2.2
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Conclusions • Deep water harvesting of hydrilla is a potentially
feasible method of control • Equipment/technology advances combined with
the growth stage of hydrilla allow for a more efficient and cost effective harvesting operation
• Limnological conditions, time of year and growth stage of hydrilla determines fish by-catch
• Preliminary water quality data suggests minimal impacts
• Data supports additional R&D and evaluations
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Acknowledgements
• Osceola County Board of County Commission • United States Environmental Protection
Agency • Texas Aquatic Harvesting Inc. • Florida Fish and Wildlife Conservation
Commission • South Florida Water Management District
Analytical Services Lab