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
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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 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 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 lt 4 m eutrophic
• August mean0.7 m
• September mean2.9 m

• Turbidity
• Measures light scattered by suspended particulate
  matter
• Normal lt50 NTUs
• August mean23.6 NTUs
• September mean1.62 NTUs

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Physical Measurements Selected Results

• True Color
• Measures natural dissolved organic acids
• Uncolored lt 30 SPUs
• Maine average 27 SPUs
• September mean14.2 SPUs

• Conductivity
• Measures ability of water to carry electrical
  current
• Normal 20-40 ?MHOs/cm
• September mean48.2 ?MHOs/cm

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Chemical Tests Selected Results

• pH
• Measures relative acidity of water
• Neutral pH of 7
• September mean7.1

• Alkalinity
• Measures ability of water to buffer against pH
  changes
• September mean42.5
• 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 lt 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 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
Reverting

• Undeveloped land
• Different stages of succession
• Reverting- canopy lt 50
• Transitional- canopy gt50
• Mature- closed, continuous canopy

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Transitional Forest
Mature Forest
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Cleared Land

• Cleared patches of forest
• Typically surrounded by forest, not near buildings

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Agricultural

• Cropland- exhibits even rows

• Pasture- cleared land, no crop 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
Land Use Types
Wetlands
Mature forest
Transitional forest
Reverting
Cleared
Pasture
Cropland
Residential
Municipal/Commercial
Shoreline residences
Roads
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Percent of the watershed covered by each land use
category
lt1
1956
1998
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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