a watershed analysis of threemile pond: implications for water quality and land use management
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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 Overview. Introduction Water Quality Analysis Land Use Analysis - PowerPoint PPT PresentationTRANSCRIPT
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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
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Presentation OverviewIntroduction
Water Quality Analysis
Land Use Analysis
-Intermission-
GIS Analysis and Models
Development
Recommendations
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Anna Sommo
Introduction
Characteristics of Maine Lakes
Threemile Pond Overview
Study Objectives
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The Value of Maine Lakes
• Recreational uses
• Economic value
• Property value
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General Characteristics of Maine Lakes
• 10,000 years old
• Lowland areas
• Northwest to Southeast orientation
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Watershed Definition
• The total area draining into a particular basin
• Begins at the highest points of land surrounding a basin
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Geographical Perspective of Threemile Pond
• China
• Vassalboro
• Windsor
• Augusta
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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
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Aquatic Flora and Fauna
Aquatic plants Fisheries
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Invasive Plants• Spread easily and rapidly
• Overwhelm ecosystems and fill in lakes
Before After
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Eutrophication
• Natural and cultural nutrient loading
• High algal growth
• Nutrients cannot cycle through the food chain
• Increased sedimentation and aging of the lake
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Turnover
• Threemile Pond is dimictic
• Stratification can lead to anoxic conditions
• Anoxic conditions cause phosphorus release
• P promotes algal growth
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Study Objectives
• Water Quality Analysis
• Land Use Assessment
• Future Trends
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Water QualityBethany Craig
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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.
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Dissolved Oxygen
• August anoxic depths
• 46% of surface area of
lake over anoxic water
• Implications for
nutrient loading
• Implications for
fisheries
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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
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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
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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
Maine lakesQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
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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
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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.
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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
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PhosphorusTom Rogers
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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
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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
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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
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August 2003 Phosphorus Readings
0
5
10
15
20
25
30
35
40
Site 1 Site 2 Site 3
Phosphorus (ppb)
SurfaceMid-DepthBottomEpicore
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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)
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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
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Tributary Water Quality
• Major input to lakes
• Quality of water entering
and leaving lake
• Sources or sinks for
nutrients
• Flow rate changes
seasonally
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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)
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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
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Land UseKelly Welch
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Overview• Introduction to land use
• Historical land use trends
• Land use categories
• Results
• Summary of findings
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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
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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)
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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
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Land Use Classifications
Natural
• Wetlands
• Forest types
– reverting
– transitional
– mature
Developed
• Cleared land
• Agriculture
– cropland
– pasture
• Commercial and municipal
• Residential
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Wetlands• Transitional zone between terrestrial and
aquatic ecosystems
• Includes all forms of freshwater wetlands
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Forests
• Undeveloped land
• Different stages of succession
• Reverting- canopy < 50%
• Transitional- canopy >50%
• Mature- closed, continuous canopy
Reverting
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Mature Forest
Transitional Forest
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Cleared Land• Cleared patches of forest
•Typically surrounded by forest, not near buildings
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Agricultural• Pasture- cleared land,
no crop rows
• Cropland- exhibits even rows
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Commercial and municipal• Businesses and public facilities
• Concentrated in China at the north end of the lake
Commercial Municipal
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Residential
Shoreline Non-shoreline
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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
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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%
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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
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Intermission