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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 Overview Introduction 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 plantsFisheries
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Invasive Plants Spread easily and rapidly Overwhelm ecosystems and fill in lakes BeforeAfter
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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 Quality Bethany 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 lakes
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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 Threemile Pond boat ramp
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Phosphorus Tom 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
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August 2003 Phosphorus Readings
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Phosphorus for Surrounding Lakes in Recent Years
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September 2003 Phosphorus Readings
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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
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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
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Land Use Kelly 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 ArcMap TM
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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 photoComputer 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 19561998 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 19561998 <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
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