aquatic plants in lake simcoe presentation - lsrca.on.ca documents/board/presentation_2016... ·...

Member of Conservation Ontario

Aquatic Plants in Lake Simcoe

Brian Ginn

Limnologist, Certified Lake Manager

LSRCA Board of Directors

October 28, 2016

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Lake Simcoe Region Conservation Authority

Aquatic Plants -Plants growing above / below / floating on water surface

- Important fish habitat and nursery area (legally protected!)

- Naturally present in “healthy” lakes

- Amount (biomass) increases with surplus nutrients

Lake Simcoe plant species:

- Coontail: 34.5% of community

- Eurasian watermilfoil: 21% (invasive, recorded 1984)

- Muskgrass: 19.5%

-Also Invasive: Crispy / Curly-leaf Pondweed (1984)

Starry Stonewort (2009)

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Water Soldier - Recorded Oct 8, 2015 in Black River, Sutton

▫ 300-400 plants @ 3 sites

▫ All upstream of Sutton Dam

- First recorded in Trent River (2008)

- Source: likely release from ornamental pond

- Rapidly spreading invader

- Submerged but float to surface in summer

- Leaves: sword-shaped with sharp spines

Photo: OMNRF

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Lake Simcoe Region Conservation Authority 4

Trent River: August 2013

Photo: OMNRF

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August 16, 2014

Photo: OMNRF


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August 22, 2015

Photo: OMNRF


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Water Soldier – Black River - Rapid response in Sutton (MNRF, OFAH, MOECC, Town of Georgina):

▫ 2015: Containment and manual removal of plants; herbicide application; visual and eDNA sampling to monitor effectiveness; public awareness

▫ 2016: Minimal re-growth in treated areas, but new colony upstream; manual removal; public outreach; floating barrier at dam; black shading mats on bottom; herbicide application

Photo: OMNRF

Photo: OMNRF

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2008 2013

• Surveyed 215 sites (2008); 245 sites in 2013. • Increased plant biomass in 2013 (Cook’s Bay 4.5 kg/m2 (2013); 3.2 kg/m2 (2008)) • Decrease: Eurasian Watermilfoil (invasive) • Increase: Muskgrass (native plant that washes up on shorelines) /

Plant changes through time

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What controls aquatic plants?

• Weather / climate • Bottom type: nutrients + stability • Resource competition with other species; shading by competitors • Light level / water clarity

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Invasive Mussels Zebra mussels:

- Great Lakes ~1986

- Lake Simcoe ~1991-1995

Quagga mussels:

- Great Lakes ~1989

- Lake Simcoe ~2004

- HUGE ecological changes!

▫ water clarity, foodwebs, nutrient cycling

- Filter Lake Simcoe ~5 days

- Offshore phosphorus nearshore

- Benthic habitat changes:

▫ more detritus / phosphorus deposition / habitats in shell debris

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Invasive mussels impact water clarity

• April-May 2016: Secchi disk depth = 20 m! (Quaggas ate spring algae bloom)

• Secchi disk depth ~7.5-8 m after lake stratification (May-October)

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Zebra Mussel changes (2009, 2015) -2009- Mostly (84%) zebra mussels

-Limited to depths < 20 m (mud clogs feeding filters)

2009 Zebra

2015 Zebra

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Quagga Mussel changes (2009, 2015) -2015: Mostly (88%) quaggas (including a deep water variety)

- Invasion into deep water and on mud!

2015 Quagga

2009 Quagga

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Lake Simcoe has changed!

If light reaches the bottom, plants will grow!

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Influence of Weather

- Seasonal patterns are changing:

▫Large variations between years

▫ 2015 vs 2016

▫La Niña vs El Niño

▫Monitoring is required to understand what is happening

▫Heat and sunlight drive plant biomass!

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Prevailing wind direction

Plant wash-ups follow the wind

Spring/Fall Summer

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Plant cycling is an essential lake process

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How does Lake Simcoe compare?

Grey Graph: Kawartha Lakes plant guide

Biomass (amount of plants) comparison with Kawartha Region lakes:

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How does Lake Simcoe compare?

Comparison with larger, more similar, NY Finger Lakes Region lakes:

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Aquatic plant management

- Management targets must focus on the underlying problem (nutrients) and controlling factors (water clarity, sheltered shorelines)

- Rapid control measures typically only treat the symptoms!

- Must understand ecology AND how the lake adapts to changes!

- Removal of plants restricted by DFO and MNRF

▫Critical habitat and nursery sites for warmwater fish (i.e. perch, bass, muskellunge)

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- Plant harvesting:

▫ No removal of roots

▫ Cut off at top or scoop off surface (equivalent to mowing or raking a lawn)

▫ Plants are spread by fragmentation! (and wind)

Willow Beach

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- Herbicides: don’t treat underlying problem!

- Nutrients used by toxic algae or resistant plants!

- Invasive starry stonewort is resistant Lagoon City, August 2013

Atherley Narrows Atherley Narrows

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Role of LSRCA?

-Plant wash-ups are responsibility of landowner

▫Compost? High phosphorus!

- We assess:

▫Status of aquatic plant community

▫Environmental drivers of plants

▫Annual variations (climate and weather)

▫Productivity and species diversity

▫ Education & science-based management

-Determine consequences of removal:

▫ Increased algae (blue-green algae?)

▫ Increases to invasive plant species

▫Decreases to fish populations (esp. warmwater fish)

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Conclusions

• We are seeing in ecological improvements in Lake Simcoe (nutrients, fish) but…

• Need to understand: invasive spp., climate (cool vs normal spring), species interactions (plant vs algae), environmental drivers (sediment P, water clarity)

• Management options must treat underlying problem (phosphorus) not the symptoms

• Must account for ecological balance: e.g. increases in herbicide resistant species (starry stonewort) or competitors (cyanobacteria)

• Improvements will take time!

aquatic plants in lake simcoe presentation - lsrca.on.ca documents/board/presentation_2016... ·...

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