Why aquatic plants are important to a healthy lake and what we can do to manage (or try and live with) invasive aquatic plants

Jesse Vermaire

Environmental Science

& Geography and Environmental Studies, Carleton University

URLA 2023

Nearshore environment

Littoral zone

Macrophyte Growth Forms

Macrophytes have 3 distinct growth forms

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1) Emergent

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2) Submerged

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3) Floating

wetlandinfo.ehp.qld.gov.au

Potamogeton spp. (Pondweeds)

Myriophyllum spp. (Milfoil)

Vallisneria spp. (Tape grass)

Ceratophyllum spp. (Coontail)

Elodea spp. (Common water weed)

Controls on Submerged Macrophyte Growth

• Nutrients: Rooted macrophytes obtain the vast majority of their nutrients from the sediment

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• Disturbance (waves) near shore limit plant growth

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• Light limits the depth of plant colonization

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• Plant biomass (g/m²⁾ is controlled by underwater slope

(biomass is greatest at slopes <5% and plants cannot grow at slopes ~>15-20%)

Kalff 2002

Ecological Importance

• Breeding habitat
• Protection from predators
• Growth substrate
• Trap sediments & nutrients

Aquatic plants

Turbidity

Algae

Nutrients

Zooplank

Allelopathic

Waves

Fish

Water

Depth

Resusp.

Sed.

Scheffer et al 1993 TREE

Scheffer 1993

Turbid lake

Clear lake

• Clear water
• Macrophyte dominated

• Turbid water
• Phytoplankton dominated

Ecological

Transition

• Understanding regime shifts in natural systems (Smith and Schindler 2009)
• Determining threshold limits
• Finding leading indicators of regime shift (Carpenter and Brock 2006; Scheffer et al. 2009)

Interest in:

• Occur rapidly
• Difficult to reverse
• Shift is often to a less desirable state

Regime Shifts:

Too much of a good thing

What can cause excessive macrophyte growth?

Hydrological or water level changes

Macrophyte removal permits in Rideau Canal

Figure 4. Expected climate change responses of key lake ecosystem processes. Shown are the level of additional risk to ...

BioScience, biac052, https://doi.org/10.1093/biosci/biac052

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Global warming

Longer growing season and warmer water temperatures can increase the likelihood of algae blooms.��What about aquatic plants?

Orchard Lake, Wisconsin

2011

2012

2013

2014

4-year Average

Plant Biovolume over 4 years

Earlier ice-off can lead to more macrophyte growth

Brownification of lakes

Meyer-Jacob, C., et al. Sci Rep 9, 16676 (2019). https://doi.org/10.1038/s41598-019-52912-0

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• Climate change may increase dissolved organic carbon (DOC) also known as “lake browning”

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• Light can not penetrate as deeply in the darker waters reducing the depths that plants can grow at.

Invasive aquatic plant management

Eurasian watermilfoil

Invasive aquatic plant management

Zooplankton communities change where aquatic plants are removed

Can native aquatic plants re-establish?

Biodegradable benthic barriers (Gatineau Park with NCC)

3000m² of coverage in Fall 2022

Good side

Bad side

RVCA

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Bird Index of Biotic Integrity

Ecological

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Water Quality Index

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Benthic Invertebrate Index

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Lower watershed

Credit Valley Conservation

Conservation efforts work

Evidence for improving ecosystem health at the subwatershed scale

Thank you