A Watershed Analysis of Threemile Pond:

Implications for water quality and land use management

Colby College Environmental Assessment Team

Colby College Biology Department, Waterville, ME

December 4, 2003

Presentation OverviewIntroduction

Water Quality Analysis

Land Use Analysis

-Intermission-

GIS Analysis and Models

Development

Recommendations

Anna Sommo

Introduction

Characteristics of Maine Lakes

Threemile Pond Overview

Study Objectives

The Value of Maine Lakes

• Recreational uses

• Economic value

• Property value

General Characteristics of Maine Lakes

• 10,000 years old

• Lowland areas

• Northwest to Southeast orientation

Watershed Definition

• The total area draining into a particular basin

• Begins at the highest points of land surrounding a basin

Geographical Perspective of Threemile Pond

• China

• Vassalboro

• Windsor

• Augusta

The History of Threemile Pond

• Farmland and residential development

• Annual algae blooms since the first half of the 20th century

• MDEP considers lake water quality poor

Aquatic Flora and Fauna

Aquatic plants Fisheries

Invasive Plants• Spread easily and rapidly

• Overwhelm ecosystems and fill in lakes

Before After

Eutrophication

• Natural and cultural nutrient loading

• High algal growth

• Nutrients cannot cycle through the food chain

• Increased sedimentation and aging of the lake

Turnover

• Threemile Pond is dimictic

• Stratification can lead to anoxic conditions

• Anoxic conditions cause phosphorus release

• P promotes algal growth

Study Objectives

• Water Quality Analysis

• Land Use Assessment

• Future Trends

Water QualityBethany Craig

Overview

• Sample site locations

• Physical measurements

• Chemical tests

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Sample Site Locations

• 3 Characterization Sites

• 5 Spot Sites

• 4 Tributary Sites

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Dissolved Oxygen

• Concentration of oxygen in

water column

• Anoxic levels in

hypolimnion

Dissolved oxygen profile for Threemile Pond on 15-Aug-03 and 11-Sep-03.

Dissolved Oxygen

• August anoxic depths

• 46% of surface area of

lake over anoxic water

• Implications for

nutrient loading

• Implications for

fisheries

Physical Measurements: Selected Results

Transparency• Measures water clarity

and suspended particulate matter

• Transparency < 4 m = eutrophic

• August mean=0.7 m• September mean=2.9 m

Turbidity• Measures light scattered by

suspended particulate matter• Normal <50 NTUs• August mean=23.6 NTUs• September mean=1.62 NTUs

Physical Measurements: Selected Results

True Color• Measures natural dissolved

organic acids• Uncolored < 30 SPUs• Maine average 27 SPUs• September mean=14.2

SPUs

Conductivity• Measures ability of water

to carry electrical current• Normal: 20-40 MHOs/cm • September mean=48.2

MHOs/cm

Chemical Tests: Selected Results

pH• Measures relative

acidity of water• Neutral= pH of 7• September mean=7.1

Alkalinity• Measures ability of

water to buffer against pH changes

• September mean=42.5• Higher than average

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Chemical Tests: Selected Results

Hardness

• Measures concentration of Magnesium and Calcium ions

• Soft water 0 to 60 mg/L

• September mean= 4.04 mg/L

• Soft water implications

Nutrient Loading

• Plants need variety of nutrients to grow

• Nitrogen and Phosphorus most important nutrients in

aquatic systems

• Eutrophication

– Natural

– Cultural

Sources of nutrient loading into a lake.

Nitrates and Nitrites

• Measures total amount of nitrates

and nitrites in water

• Sources

– Fertilizers

– Septic tanks and animal waste

• Normal < 1 ppm

• September mean =0.06 ppm

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Threemile Pond boat ramp

PhosphorusTom Rogers

Phosphorus• Why phosphorus is important to study

• Historical phosphorus data for Threemile Pond

• Current phosphorus data for Threemile Pond

• How Threemile Pond compares with other

Maine lakes

• Water budget

Phosphorus• Necessary for aquatic

plant growth

• Found in all soils and organic matter and on all surfaces

• Carried in ground water and in streams

• Used in fertilizers

• Found in septic systems

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Phosphorus Deposition• Primary cause of algal

blooms in Maine lakes• Deposited through surface

water runoff and in streams• Lakes turn green in color

and unappealing in taste and odor

• Decreases recreational value of lakes and property value within watershed

Historical Total Phosphorus- Threemile Pond

Critical phosphorus limit for algal blooms =15 ppb

0

10

20

30

40

50

60

70

197919811983198519871989199119931997199920012003

Phosphorus (ppb)

AugustSeptember

August 2003 Phosphorus Readings

0

5

10

15

20

25

30

35

40

Site 1 Site 2 Site 3

Phosphorus (ppb)

SurfaceMid-DepthBottomEpicore

Phosphorus for Surrounding Lakes in Recent Years

0

5

10

15

20

25

30

35

Threemile PondThreecornered Pond

Webber PondChina LakeSalmon Lake

East PondNorth PondLake George

Phosphorus (ppb)

September 2003 Phosphorus Readings

0

510

15

2025

30

3540

45

1 2 3 4 5 6 7 8 9 10 11 12Site

Phosphorus (ppb)

Surface

Mid-Depth

Bottom

Epicore

Tributary Water Quality

• Major input to lakes

• Quality of water entering

and leaving lake

• Sources or sinks for

nutrients

• Flow rate changes

seasonally

Tributary Data for Sept. 2003• Sites 9 and 10 -Seward Mills Brook --Outlet

• Site 11 -Unnamed stream from wetlands --Inlet

• Site 12 -Barton Brook from Threecornered Pond & Mud Pond --Inlet

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12Site

Phosphorus (ppb)

Water Budget -Flushing Rate• Rate at which a lake replenishes water• Given for lakes of similar area and depth to Threemile Pond

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Threemile PondLake Wesserunsett

Webber PondSalmon LakeEast Pond North Pond

Times Flushing Per Year

Land UseKelly Welch

Overview• Introduction to land use

• Historical land use trends

• Land use categories

• Results

• Summary of findings

Watershed Land Use

• Examined land use changes between 1956 and 1998

• Why examine land use changes?

– Effects of land use types

– Historic trends

– Identify potential sources of pollution

Regional Land Use Trends

• Decline in agriculture throughout New England

• Maine State trends

– 90% forested

– 3% agriculture

– 2% urban

– 5% other (wetlands, residential, transportation uses)

Maps

• Used digital orthophoto quadrangles downloaded from the Maine Office of GIS for 1998

• Aerial photos for 1956

• Computer program ArcMapTM

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Methods• Polygons drawn

• Color codes to distinguish between land use categories

• Calculated the cumulative area

• Comparison made between 1956 and 1998 watersheds

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Downloaded photo Computer map

Land Use Classifications

Natural

• Wetlands

• Forest types

– reverting

– transitional

– mature

Developed

• Cleared land

• Agriculture

– cropland

– pasture

• Commercial and municipal

• Residential

Wetlands• Transitional zone between terrestrial and

aquatic ecosystems

• Includes all forms of freshwater wetlands

Forests

• Undeveloped land

• Different stages of succession

• Reverting- canopy < 50%

• Transitional- canopy >50%

• Mature- closed, continuous canopy

Reverting

Mature Forest

Transitional Forest

Cleared Land• Cleared patches of forest

•Typically surrounded by forest, not near buildings

Agricultural• Pasture- cleared land,

no crop rows

• Cropland- exhibits even rows

Commercial and municipal• Businesses and public facilities

• Concentrated in China at the north end of the lake

Commercial Municipal

Residential

Shoreline Non-shoreline

Patterns of Land Use in the Threemile Pond Watershed

1956 1998

Wetlands

Mature forest

Transitional forest

Reverting

Cleared

Pasture

Cropland

Residential

Municipal/Commercial

Shoreline residences

Roads

Land Use Types

Percent of the watershed covered by each land use category

1956 1998

10%

16%

27%

27%

1%2%

9%

7% 0%

Wetlands

Mature Forest

Transitional Forest

Reverting

Cleared

Pasture

Cropland

Residential

Commercial/Municipal

10%

47%16%

6%

1%3%

15%

2% <1%

Land Use Summary

• Decline in agricultural uses

• Residential development increased

• Wetlands remained constant

• Commercial and municipal uses increased

• Threemile Pond is similar to regional trends

Intermission