Algae Control on Cape Cod: Key Factors, Results and

Lessons

Ken Wagner, Ph.D., CLMWater 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

(<6.5), alkalinity (<10 mg/L), TP (<10 µg/L), TN (<300 µg/L), chl a (<4 µg/L), high Secchi (>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 pondsYear

Pond Area Mean MaximumDetention Tributary Treated(ha) (m) (m) (yr)

Hamblin 46 8.3 18.8 1.0 No 1995Ashumet 82 7.0 20.0 1.9 No 2001Ashumet 82 7.0 20.0 1.9 No 2010Long 296 8.8 21.2 3.5 No 2007Mystic 59 4.6 14.3 1.0 No 2010Lovers 15 4.6 10.0 1.2 No 2010Stillwater 8 6.8 13.9 1.2 from Lovers 2010Great 45 3.6 11.0 0.4 2 small 2012Herring 18 6.2 10.9 2.8 Tidal infl. 2012Lovells 22 5.7 11.4 2.1 Blocked 2013

Cliff 83 8.6 26.7 5.3 No 2015

Depth

Track Record on Cape Cod: LoadingHydrologic load dominated by precipitation and

groundwaterPhosphorus load includes major internal load

Pond Precip Grdwtr Internal Surf Flow Grdwtr(%) (%) (%) (%) (%)

Hamblin 11 87 67 9 11Long 51 44 64 17.3 9.4Mystic 18 80 46 15 21Lovers 39 55 43 27 12Stillwater 13 25 55 32 5Great 14 83 26 8 45Herring 43.5 56.5 40 1 46Lovells 43 53 62 4 16

Cliff 71 23 67 5 6

Hydrologic Load Phosphorus Load

Track Record on Cape Cod: Algae ControlLow biomass, but not necessarily low productivityShift away from cyanobacteriaDiatoms, goldens and dinoflagellates most abundantSometimes greens if N levels elevatedGreater edibility by zooplankton, better energy flow in

aquatic food web

Track Record on Cape Cod: Algae ControlUsually get rapid results, but where water column P is elevated at start of treatment, may take several years to reach new equilibriumMystic Planktothrix bloom prior to treatment, mixed assemblage after treatment with Pseudanabaena peaks

Track Record on Cape Cod: Water ClarityLower algal biomass leads to marked increase in clarity

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Long Pond Secchi Disk TransparenciesLP-1 in gray, LP-2 in black

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Herring Pond clarity

Summer Secchi DepthPond Pre-trtmt Post-trtmt

(m) (m)Ashumet 2001Ashumet 2010Hamblin 0.9 5.6Long 2.8 5.4Mystic 1.2 3.9Lovers 1.0 3.3Stillwater 1.3 3.5Great 2.3 2.5Herring 0.5 4.7Lovells 1.3 5.2

Treatment

Treatment

Track Record on Cape Cod: P ConcentrationsAluminum treatment leads to lower P levels as a

function of reduced release during anoxic periods

Mystic Lake whole lake P mass

Pond Pre-trtmt Post-trtmt Pre-trtmt Post-trtmtµg/L µg/L µg/L µg/L

Hamblin 42 10 454 46Long 30 16 163 62Mystic 35 10 - 19 555 65Lovers 32 13 116 22Stillwater 28 9 290 30Great 21 <10 29 <10Herring 27 12 1537 37Lovells 61 12 167 35

Surface Total P Bottom Total P

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

Oxygen DemandPond Pre-trtmt Post-trtmt

(mg/m2/d) (mg/m2/d)Hamblin 1720 219Ashumet 2001 1034Ashumet 2010Long 1200 - 2600 800 - 2100Mystic 780 213Lovers 1500 555Stillwater 1500 311Great 1625 300Herring 433 167Lovells 1310 No data yet

Cliff 2630 No data yet

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 392-1142 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 treatmentsSeason Summer Secchi Depth

Pond Treated % change Abs change % change Abs change % change Abs change% ug/L % m % ug/L

Hamblin Spring 76% 32 84% 4.7 91% 19.3Lovells Spring 80% 49 75% 3.9 84% 12.0Long Fall 47% 14 48% 2.6 56% 7.1Mystic Fall 57% 20 69% 2.7 82% 16.2Lovers Fall 59% 19 70% 2.3Stillwater Fall 68% 19 63% 2.2Great Fall 62% 13 8% 0.2Herring Fall 56% 15 89% 4.2

Surface Total P Summer Chl-a

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?