Shoreline development of Kawartha Lakes – impacts

to aquatic plant communities.

Andrea Hicks, Paul Frost, Eric Sager

Watershed Ecosystems Graduate ProgramTrent University

NSERC Funding – Paul FrostKawartha Lakes Stewards Association

Ontario Trillium Foundation

Kawartha Lakes - ???

Two very different types of lakes in this region Shield lakes – smaller, oligotrophic systems Low-land lakes – Trent-Severn Waterway lakes,

often large, shallow lakes

Proximity to cities, accessible, clear water=

Shoreline Residential Development

Two studies – same themes:Cottage development & Aquatic plants

Shield lakes− Impacts to aquatic

plant communities from shoreline development

− Abundance and community composition

Trent-Severn lakes− Effectiveness and

impacts of small-scale plant management techniques on aquatic plant communities

− Direct efforts to alter the plant abundance

Impacts of lakeshore cottage development on

aquatic plant communities, Canadian shield lakes,

Ontario.Masters research - Trent University

Supervisor: Paul Frost

Canadian Shield LakesDevelopment pressure Proximity to urban centres

Structural habitat and complexity Stabilize sediment Water and sediment nutrients

13 study lakes

Kawartha Highlands Signature Site Park

Developmentcottages/km shoreline

0 5 10 15 20 25

Mea

n di

vers

ity

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Developmentcottages/km shoreline

0 5 10 15 20 25

Sta

ndar

d de

viat

ion

of d

iver

sity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.60 5 10 15 20 25

Mea

n sp

ecie

s ric

hnes

s

2

4

6

8

10

12

0 5 10 15 20 25

Sta

ndar

d de

viat

ion

of m

ean

richn

ess

0

1

2

3

4

50 5 10 15 20 25

Mea

n bi

omas

s (g

)

-10

0

10

20

30

40

50

60

0 5 10 15 20 25

Sta

ndar

d de

viat

ion

of m

ean

biom

ass

(g)

0

5

10

15

20

25

30

35p=0.666p=0.007p=0.925

p=0.231p=0.433p=0.225

p=0.413p=0.329p=0.414

ANCOVAdepth p=0.044developement p=0.029interaction p=0.042

p=0.021p=0.041p=0.065

p=0.660p=0.034p=0.856*

*

Developmentcottages/km shoreline

Developmentcottages/km shoreline

shallowdeep

We sampled plants along two transects parallel to the shoreline: one at 0.5 m depth and one at 1.5m depth.

As development level of the lakes increased, we found a decrease in the plant biomass at both the shallow (0.5m) and deep (1.5m) transects.

Interestingly, species richness decreased with increasing development only at the shallow depth – effects on community composition tend to be limited by depth.

ANST-1

ANST-2

ANST-3

BEA-1

BEA-2

BEA-3

BIG-1

BIG-2

BIG-3

CAT-1

CAT-2

CAT-3

COON-1

COON-2

COON-3

COP-1

COP-2COP-3

COX-1

COX-2

COX-3

CRAB-1CRAB-2

CRAB-3

LOON-1

LOON-2

LOON-3

RATH-1

RATH-2

RATH-3

SUC-1

SUC-2

SUC-3

WOLF-1

WOLF-2

WOLF-3

development

lake area

lake mean depth

slope of littoral

Sediment % water

Sed % organic

Sediment PpH

Conductivity

Water N

Chl a

fetch

richness

biomass

NMDS0.5Auto

Axis 1

Axi

s 2

Shallow0.5 m depth

This graph plots sites based on the similarity between their species composition and abundance. Two groups are formed in this graph: one in the upper left, the other in the lower right.

The red vectors show the environmental variables that help explain the placement of sites within the groups.

Development is a strong vector showing that sites on developed lakes have similar plant communities which differ from the plant communities found on undeveloped lakes.

Copper (0.0)

Cox (0.0)

Crab (0.0)

Sucker (0.0)

Rathbun (3.4)

Wolf (4.2)

Anstruther (6.3)

Big Cedar (7.8)

Loon Call (8.4)

Coon (8.9)

Catchacoma (18.6)

Beaver (23.1)

Pro

porti

on o

f bio

mas

s

0.0

0.2

0.4

0.6

0.8

1.0Emergent Floating Floating leaf Submersed Submersed low-lying Macroalgae Moss

7 5 6 6 5 5 4 6 6 5 3 3

Increasing development

Structural type of plant communities is also important as it changes the underwater environment. This graph shows the proportion of the biomass on each lake by structural type. On undeveloped lakes, we see large proportions of emergent, floating leaf, and submersed low-lying plants. On highly developed lakes we see mostly submersed species. The loss of floating leaf and emergent species changes the light availability and species composition on these lakes.

Aquatic Weeds Management Study

Summer 2008

Kawartha Lakes Stewards Association

Ontario Trillium FoundationInstitute for Watershed Science – Trent

University

Goals of the research project

Identify the plant management techniques being used.

Evaluate their effectiveness at controlling plant abundance.

Apply a holistic approach.

Plants

Sediment

InvertebratesWater

Selecting sampling sitesLakesManagement typesPaired reference sites

9 Lakes

Selecting sampling sitesLakesManagement typesPaired reference sites

8 Management types

Sand

Benthic mat Mechanical harvester

Rake and Rake/dredge

CuttersHerbicide corn

How similar are the plant communities across these

lakes?

ClearE1

ClearE2LbaldR1

LbaldR2

LbuckW1

LbuckW2

LoveA1

LoveA2LoveB1

PigeonB1

PigeonB2

PigeonM1

Sandy1

Sandy2Sandy3

StoneyG1

StonyS1

StonyS2

SturgK1

SturgK2

SturgV1

SturgW1

SturgW2

WhiteS1WhiteS2

Lake communities

Axis 1

Axi

s 2

ClearLittle BaldLower BuckhornLovesickPigeonSandyStoneySturgeonWhite

Non-metric multidimensional scalingSorensen distance measure3-D solutionFinal stress: 9.477

The sites grouped into two main groups based on their plant communities. This shows that most communities are quite similar across the lakes; however, Sandy lake (a marl lake with only Chara sp. present) and one site on Pigeon lake are quite different.

Results: Lovesick LakeWet weight biomass

July 9 August 14

Pla

nt b

iom

ass

wet

g/m

2

0

200

400

600

800

1000

1200

1400

Benthic matReference

Lovesick Lake

Richness

July 9 August 14

Pla

nt b

iom

ass

richn

ess

0

2

4

6

8

10

12

Benthic matReference

Lovesick Lake

Algae?

A benthic mat site on Lovesick lake showed that it was very effective at reducing plant biomass. The amount of plants found at the reference site increased from July to August, but there were hardly any plants on the mat in August. However, the richness of the plants found also decreased between the mat and the reference site – which species are we favoring on the mat? Of the 5 species that were able to grow on top of the mat in August, one of them was Eurasian milfoil. Also, another benthic mat site showed that there was a large amount of filamentous algae in the managed area.

Results: Pigeon LakeWet weight biomass

June 23 July 30 August 210

500

1000

1500

2000

2500

HerbicideReference

Pigeon Lake

Pla

nt b

iom

ass

wet

g/m

2

Shannon Diversity Index

June 23 July 30 August 210

1

2

3

4

5

6

7

HerbicideReference

Pigeon Lake

Sha

nnon

div

ersi

ty

Three sampling visits were done on a herbicide site on Pigeon lake, the second one was done 1 week after the treatment. Interestingly we didnt see a reduction in wet weight plant biomass after the herbicide. In fact, the treated area had much higher biomass than the reference site. In order to explain why this might be I had to go back to the data for that site. Once the herbicide was applied, we did see a reduction in vascular plants; however, the macroalgae Chara became the dominant species and made up most of this biomass. The presence of this plant has been documented in other studies where plant management has disturbed the community so this result is a surprising but not unusual response. When we look at the diversity index, we can see this dominance of Chara reflected in lower diversity in the treated area.

Results: Raking

wet biomass dry biomass Simpsons Shannon Richness0

500

1000

1500

2000

2500

3000

RakingReference

Raking*

* *

Red stars: significantly different.

Blue stars: marginally significant

By combining all the sites with the same treatment together, we can see what effect the treatment in general is having on plant communities. For example, raking does decrease the abundance of plants at the sites and also shows a decrease in species richness. Diversity is not affected by the raking treatment – this means that the treatment does not affect the evenness of species in the community.

What does all this tell us?

Shield and TSW lakes are different systems with opposite concerns regarding aquatic plants

HOWEVER all lakes are facing increased development pressure because of their location, accessibility, and clear water states

Importance and necessity of aquatic plants as part of a lake ecosystem are poorly understood by shoreline residents