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Algae Control on Cape Cod: Key Factors, Results and Lessons Ken Wagner, Ph.D., CLM Water Resource Services, Inc.
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Cape Cod, Massachusetts Glacial history Human use history
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Kettlehole Ponds Glacial potholes Sandy soils Depths to 27 m, often >10 m Low surface watershed areas Few inlets, often no surface outlet Depend on precipitation and ground water Long detention times
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Bathymetry of Kettleholes Generally bowl shaped, but considerable variation possible Often steep side slopes, sandy
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Watershed Influences and Pond Conditions Pine and oak scrub on sandy soils Residential/related development Historic agriculture Cranberry bogs Backround WQ: low pH ( 5 m) Slow accumulation of organic matter High Fe-P in sediment
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Kettlehole Problems Limited rooted plant issues; surprisingly few invasives, including mainly variable milfoil, fanwort, and hydrilla Cyanobacteria blooms can be severe with increase in fertility, drastically alters water quality
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Cyanobacteria Blooms on Cape Cod Fairly varied, but most commonly Dolichospermum (Anabaena), esp D. lemmermannii or D. variabilis, Aphanizomenon flos-aquae, Microcystis spp., and Planktothrix rubescens, some Pseudanabaena and Planktolyngbya Dolichospermum blooms can appear quickly from rapid rise of colonies grown to maturity on sediment Aphanizomenon and Microcystis blooms tend to develop more slowly (seeded from sediment with expansion in surface water) Planktothrix blooms develop just below thermocline, rise to surface with mixing
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Internal P Loading as a Driving Force Largely linked to P bound by Fe and released under anoxia Largely a summer phenomenon, during stratification and anoxic periods Can be more than half of the annual load Even if only 25% of the annual load, can be the dominant summer P source Tends to come with low N:P ratio (<5:1) Ecology of some cyanos promotes uptake near sediment followed by upward movement to form blooms
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Key Role of Oxygen Oxygen keeps P bound to Fe; even 1-2 mg/L will minimize P release The higher in the water column anoxia extends from the bottom, the greater the exposed area and potential P release If anoxia approaches the thermocline, availability of P to algae increases substantially
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Management Options Watershed management can’t control internal loading Some in-lake options address symptoms – useful but not preferred over nutrient control (sonication, algaecides) In-lake options that address internal P loading Flushing/hypolim. withdrawal – remove poor quality water Dredging – remove the source sediment Oxygenation – maintain Fe-P bonds Circulation – oxygenates plus possible symptom control if deep enough or biological structure is favorable Inactivation – replace Fe binding of P with Al, Ca, or La
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In-lake P Control Track Record on Cape Cod No flushing or hypolim. withdrawal – no extra water, few outlets Very little dredging performed; some reverse layering, some small pond work, usually cost prohibitive Oxygenation rarely practiced; applicable and would improve cold water fisheries, but high operating costs Circulation by updraft pumps with a few examples; limited improvement, still have summer blooms
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Track Record on Cape Cod Circulation by compressed air with few examples; one spectacular failure of implementation/operation
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Track Record on Cape Cod Inactivation experience using aluminum has generally been positive 9 lakes treated so far, one repeat so far One repeat and one new application planned in 2015/16
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Track Record on Cape Cod: Aluminum Treatments Key attributes of Cape Cod treatment ponds
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Track Record on Cape Cod: Loading Hydrologic load dominated by precipitation and groundwater Phosphorus load includes major internal load
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Track Record on Cape Cod: Algae Control Low biomass, but not necessarily low productivity Shift away from cyanobacteria Diatoms, goldens and dinoflagellates most abundant Sometimes greens if N levels elevated Greater edibility by zooplankton, better energy flow in aquatic food web
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Track Record on Cape Cod: Algae Control Usually get rapid results, but where water column P is elevated at start of treatment, may take several years to reach new equilibrium Mystic Planktothrix bloom prior to treatment, mixed assemblage after treatment with Pseudanabaena peaks
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Track Record on Cape Cod: Water Clarity Lower algal biomass leads to marked increase in clarity Herring Pond clarity Treatment
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Track Record on Cape Cod: P Concentrations Aluminum treatment leads to lower P levels as a function of reduced release during anoxic periods Mystic Lake whole lake P mass
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Track Record on Cape Cod: Oxygen Demand Oxygen demand declines as a function of less decaying algae Anoxia still develops, but not throughout hypolimnion Creates “trout water” – portion of cold hypolimnion with enough oxygen to support trout
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Track Record on Cape Cod: Oxygen Demand Oxygen demand varies among years Decline does not appear consistent among lakes Oxygen demand in Long Pond before and after treatment in late 2007
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Track Record on Cape Cod: Toxicity Hamblin Pond fish kill in 1995; none since then Toxicity prevention Maintain pH between 6 and 8 (close to 7 preferred) Keep dose under 5 mg Al/L (divide dose in g/m2 by mixing depth in meters) Treat in non-contiguous patchwork; provide refuge Release chemicals near thermocline (if epilimnetic P already low enough)
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Track Record on Cape Cod: Duration of Benefits Duration of benefits is a function of ongoing external load and effectiveness of internal load inactivation Spreadsheet model applied, shows return rate to problem P level Hamblin Pond case history Treated in 1995; prediction was for 17 years of benefit First bloom in late Sept 2013; Dolichospermum for 2 weeks Cyano blooms from mid-July on in 2014 Termination of benefits rapid, reason not clear, but have two hypotheses
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Track Record on Cape Cod: Duration of Benefit Latest sediment Fe-P data show values of 392-1142 mg/kg Accumulated Fe-P or simultaneous breakthrough?
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Track Record on Cape Cod: Treatment Timing Fall vs. spring treatment poses interesting issues Seasonality of non-target impact potential Lowest P in water column/greatest P in sediment favors spring treatment Limited stripping efficiency in water column limits impact of fall treatments
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Track Record on Cape Cod: Overall Pond Fertility Fertility not eliminated – fishing still good, better in some cases Shifts algae away from cyanobacteria, better food web energy flow Clarity higher, algal standing crop smaller, but productivity not necessarily lower
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Inactivated yet? I sure am! QUESTIONS?
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