2008 Shallow Lake Ecology Crooked Lake Annual Meeting

Shallow Lake Ecology

Crooked Lake

Anoka County, MN February 2008

Coon Creek Watershed DistrictWenck Associates, Inc.

Presentation Objectives

Understanding Lake EcologyPhysical Lake Properties Biological Characteristics Water Quality

Drivers Diagnostic Tools

Shallow Lakes

Introduction to Management Tools

Crooked Lake Watershed

Physical DataParameter Crooked

Lake

Surface Area (ac) 114

Average Depth (ft) 9

Maximum Depth (ft) 26

Volume (ac-ft) 1,021

Residence Time (years) 7.4

Littoral Area (ac) 83

Littoral Area (%) 73%

Watershed (ac) 260

Watershed area does not include the lake surface area

http://waterontheweb.org/under/lakeecology/index.html

What is a Shallow Lake?

Generally, any lake that does not stay stratified throughout the summer season is a shallow lake.

MPCA defines a shallow lake as lakes with a maximum depth of 15 feet or less, or with 80% or more of the lake area shallow enough to support emergent and submerged rooted aquatic plants.


Understanding Lake EcologyPhysical Lake Properties

Biological CharacteristicsWater Quality

Understanding DriversDiagnostic Tools

Shallow Lakes


Aquatic Communities –

Plankton & Fisheries

Lake Zones

Pike

Clear-water state

Carp, minnows

Invertebrates

Algae

Submergedplants

SedimentResuspension

Turbid-water state

Trophic Cascades

Adapted from Metropolitan Council Environmental Services

Biomanipulation of Fish Community – Round Lake, MN

Rotenone was used to eliminate planktivorous fish in 1980

Restocked with Bass and walleye to control planktivores

Increase in water clarity for 2 years after manipulation

Shapiro and Wright 1984

Carp Exclusion

Crooked Lake Fish Community

0

500

1000

1500

2000

2500

3000

3500

Fis

h A

bu

nd

an

ce

1951 1969 1973 1979 1984 1986 1989 1991 1993 1994 1996 1998 1999 2004

Survey Year

Crooked Lake Trophic Group Total Abundance Historical Catch Summary for DNR Surveys

Forage Species Rough Fish

Pan Fish Top Predators

Crooked Lake Fish Community

0

50

100

150

200

250

300

350

400

Fis

h B

iom

as

s (

lbs

)

1951 1969 1973 1979 1984 1986 1989 1991 1993 1994 1996 1998 1999 2004

Survey Year

Crooked Lake Trophic Group Total Biomass Historical Catch Summary for DNR Surveys

Forage Species Rough Fish

Pan Fish Top Predators

Refuge for small invertebrates (especially Cladocera) against fish

predations

AQUATIC PLANTS

“Services” to people through bank edge protection against

erosion, products, (reed, sedge, biomass, fish and fowl),

amenity and conservation

Absorb wind and wave energy, minimizing turbidity caused by

sediment resuspension

High production creates sediment conditions

favoring nitrogen loss by denitrification and

phosphate availability through release

Food for invertebrates

Food for adult fish

Habitat, food cover and nesting materials for birds

Provide habitat for attached algae

Refuges for small fish against predators

Cover and habitat for piscivorous fish

Spawning habitat for fish

Maintenance of clear water

Maintenance of clear water

Moss et al. 1996

Typical Littoral Zone Vegetation

Graphic from: Smith, R.L. Elements of Ecology. 1992 Third Addition.

Crooked Lake Aquatic Vegetation

Frequency of Submersed Aquatic Plants in Crooked Lake

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

Najas f

lexilis

P. am

plifo

lius

P. illin

oenis

P. pec

tinat

us

P. pus

illus/

folio

sus

Zannic

hellia

palu

stris

Zoste

rella

dub

ia

P. zos

terif

orm

is

Myr

ophy

llum

spic

atum

P. cris

pus

Species

Fre

qu

ency


Understanding Lake EcologyPhysical Lake PropertiesBiological Characteristics

Water QualityWater Quality Conditions and DriversDiagnostic Tools

Shallow Lakes


Water Quality Drivers

NutrientsTotal phosphorus is a limiting nutrient

The availability of phosphorus controls the amount of algal growth in a lake

Nutrient sourceStormwater runoffDirect deposition from precipitationInternal loading from lake sedimentsGeeseSeptic or Wastewater Discharge or Wastewater Discharge

Trophic States in LakesHypereutrophic - A very nutrient-rich

lake characterized by frequent and severe nuisance algal blooms and low transparency.

Eutrophic - A high level of plant nutrients and biological productivity and low oxygen content.

Mesotrophic – A moderate level of nutrients and photosynthetic productivity.

Oligotrophic - nutrient-poor , low photosynthetic productivity.

Relationship between TPand Transparency

Oligotrophic Mesotrophic Eutrophic Hyper-Eutrophic

Total Phosphorus (µg/L)

MPCA StandardsEcoregions

North Central Hardwood Forest

Western Corn Belt Plains

Parameters Shallow1 Deep Shallow1 Deep

Phosphorus Concentration (g/L)

60 40 90 65

Chlorophyll-a Concentration (g/L)

20 14 30 22

Secchi disk transparency (meters)

>1 >1.4 >0.7 >0.9

1 Shallow lakes are defined as lakes with a maximum depth of 15 feet or less, or with

80% or more of the lake area shallow enough to support emergent and submerged rooted

aquatic plants (littoral zone).

Total Phosphorus and Chlorophyll-a

Crooked Lake

Crooked Lake

05

1015202530354045

2000 2002 2003 2005 2006

Co

nce

ntr

atio

n [

ug

/L]

Summer Average TP [ug/L] Summer Average Chl-a [ug/L]

Secchi Depth Crooked Lake

Crooked Lake

0

1

2

3

4

5

6

7

2000 2002 2003 2005 2006

Sec

chi

Dep

th [

ft]

Summer Average SD [ft]

Lake Response Models

Internal LoadingNurnburg Approach

for Sediment Anoxia

Calculate anoxic factor

Sediment release rate

BATHTUBAnnual model

Phosphorus Sources

Crooked Lake

0

50

100

150

2000 2002 2003 2005 2006Tota

l Pho

spho

rus

Load

[lb

/ yr]

Watersheds Atmosphere Internal Load1

Lake Response Model

Crooked Lake

0

20

40

60

2000 2002 2003 2005 2006

In L

ake

Tota

l P

hosp

horu

s C

once

ntra

tion

[ug/

L]

Model Predicted TP [ug/L] Observed TP [ug/L]


Understanding Lake EcologyPhysical Lake PropertiesBiological CharacteristicsWater Quality


Shallow LakesIntroduction to Management Tools

Turbid and Clearwater States

Competing Equilibria in Shallow Lakes

Turbid StateHigh algal productivityLow aquatic plant

productivityLow grazer (zooplankton)

productivity

Clearwater StateLarge aquatic plant

communityLow algal productivityLarge grazer

populationScheffer 2004

Shallow Lake SwitchesDrivers that cause a lake to shift

from either the turbid or clear water state to the opposite stateClear scientific understanding of

forward switchesUnclear understanding of reverse

switches

More Development

(impervious surface)

= More Runoff

Invasive SpeciesCurly-leaf Pondweed Purple LoosestrifeZebra Mussels

Eurasian Watermilfoil

McComas, Unpublished data

Boating Impacts

Boat wakes contribute to shoreline erosionProp disturbance

Especially in shallow areasSediment scouring prevents plant establishment

(Asplund and Cook 1997)

Direct damage to plantsAreas with boat traffic demonstrate lower biomass

yields (Asplund & Cook 1997)

Turbidity and light limitationsScientific understanding is limited

Wave stress

Shoreline Development

Impacts

Additional runoffNutrients, herbicides,

pesticides

Overwater structures reduce light availability

Shoreline erosion

Loss of vegetation and habitatLower songbird density

(Lindsey et al. 2001)Lower green from density

(Woodford and Meyer 2002)Loss or disturbance of fish

spawning, feeding and rearing

Loss of wood structure from tree fall

Lower diversity of fish species in developed shoreline areas (Brazner 1997)

Reduction in vegetation abundance (66% Radomski 2005)

Crooked Lake Shoreline

Characteristics


Understanding Lake EcologyPhysical Lake PropertiesBiological CharacteristicsWater Quality


Shallow Lakes

Introduction to Management

Changing View of Lake Management

OLD VIEWSimple Cause

Effect RelationshipIncreased

Phosphorus resulted in Decreased water quality

NEW VIEWComplex Adaptive

SystemsHard to predict

Focus on Adaptive ManagementLearn by doingDiversity of

knowledge

Dietz et al. 2003. Science.

Strategy for Restoring Shallow Eutrophic Lakes

Forward switch detection and removal

External and internal nutrient control

Biomanipulation (reverse switch)

Plant establishment

Stabilizing and managing restored system

Lake Response to Restoration

Twin Lakes W.Q. Response Model

020406080

100120140160180

0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Percent Load Reduction

Lak

e T

ota

l P

ho

sph

oru

s [u

g/L

]

Upper Twin

HypotheticalResponse

Lake Response to Restoration

Twin Lakes W.Q. Response Model

020406080

100120140160180

0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Percent Load Reduction

Lak

e T

ota

l P

ho

sph

oru

s [u

g/L

]

Upper Twin

HypotheticalResponse

Competing Management Goals

Design Strategy

Implement

Monitor

Evaluate

Assess Progress

AdaptiveManagement

Implementation Depends on Cooperation

Guide implementation through:PartnershipsProgramsActivitiesAreas

Supports watershed planning:Enhanced description of water

quality concernsImproved understanding of key

processesFocus on solution development

Adaptive Management

Education

2008 Shallow Lake Ecology Crooked Lake Annual Meeting