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
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