Algae Control on Cape Cod: Key Factors, Results and Lessons Ken Wagner, Ph.D., CLM Water Resource Services, Inc.

Cape Cod, Massachusetts  Glacial history  Human use history

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

Bathymetry of Kettleholes  Generally bowl shaped, but considerable variation possible  Often steep side slopes, sandy

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

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

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

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

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

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

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

Track Record on Cape Cod  Circulation by compressed air with few examples; one spectacular failure of implementation/operation

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

Track Record on Cape Cod: Aluminum Treatments Key attributes of Cape Cod treatment ponds

Track Record on Cape Cod: Loading  Hydrologic load dominated by precipitation and groundwater  Phosphorus load includes major internal load

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

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

Track Record on Cape Cod: Water Clarity  Lower algal biomass leads to marked increase in clarity Herring Pond clarity Treatment

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

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

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

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)

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

Track Record on Cape Cod: Duration of Benefit  Latest sediment Fe-P data show values of mg/kg  Accumulated Fe-P or simultaneous breakthrough?

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

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

Inactivated yet? I sure am! QUESTIONS?