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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
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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 -Intermission- GIS Analysis and Models Development Recommendations
Anna Sommo Introduction Characteristics of Maine Lakes Threemile Pond Overview Study Objectives
Recreational uses Economic value Property value The Value of Maine Lakes
10,000 years old Lowland areas Northwest to Southeast orientation General Characteristics of Maine Lakes
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 plants Aquatic Flora and Fauna 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 Quality Bethany Craig
Overview • Sample site locations • Physical measurements • Chemical tests
Sample Site Locations • 3 Characterization Sites • 5 Spot Sites • 4 Tributary Sites
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
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 Physical Measurements: 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 Chemical Tests: Selected Results
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 Threemile Pond boat ramp
Phosphorus Tom 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
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
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
Water Budget -Flushing Rate • Rate at which a lake replenishes water • Given for lakes of similar area and depth to Threemile Pond
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
Decline in agriculture throughout New England Maine State trends 90% forested 3% agriculture 2% urban 5% other (wetlands, residential, transportation uses) Regional Land Use Trends
Maps • Used digital orthophoto quadrangles downloaded from the Maine Office of GIS for 1998 • Aerial photos for 1956 • Computer program ArcMapTM
Methods • Polygons drawn • Color codes to distinguish between land use categories • Calculated the cumulative area • Comparison made between 1956 and 1998 watersheds
Downloadedphoto Computer map
Natural Wetlands Forest types reverting transitional mature Developed Cleared land Agriculture cropland pasture Commercial and municipal Residential Land Use Classifications
Wetlands • Transitional zone between terrestrial and aquatic ecosystems • Includes all forms of freshwater wetlands
Forests Reverting • Undeveloped land • Different stages of succession • Reverting- canopy < 50% • Transitional- canopy >50% • Mature- closed, continuous canopy
Transitional Forest Mature Forest
Cleared Land • Cleared patches of forest • Typically surrounded by forest, not near buildings
Pasture- cleared land, no crop rows Cropland- exhibits even rows Agricultural
Commercial and municipal • Businesses and public facilities • Concentrated in China at the north end of the lake Commercial Municipal
Shoreline Non-shoreline Residential