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The State of Webber Pond Understanding the Factors Affecting Water Quality in the Webber Pond Watershed Colby Environmental Assessment Team Colby College.

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Presentation on theme: "The State of Webber Pond Understanding the Factors Affecting Water Quality in the Webber Pond Watershed Colby Environmental Assessment Team Colby College."— Presentation transcript:

1 The State of Webber Pond Understanding the Factors Affecting Water Quality in the Webber Pond Watershed Colby Environmental Assessment Team Colby College Biology Dept. December 5, 2002 Vassalboro Town Office PART 2

2 Presentation Overview Introduction Water Quality Analysis Land Use Analysis - Intermission - GIS Analysis and Models Future Predictions Remediation Measures Recommendations

3 Geographic Information Systems Maps and Models of the Webber Pond Watershed Lauren Bliss

4 GIS and Modeling Geographic Information System (GIS) - Combines geographic data with thematic attributes - Creates layers of maps with themes aligned in a common coordinate system (“georeferenced”) Modeling - Representation of reality that helps to predict how natural systems will work - Simplifies systems by assessing pertinent factors - Uses ModelBuilder extension

5 Bathymetry Map Important for identifying sub-basins and water sampling sites, computing lake volume, and predicting the occurrence of organisms in Webber Pond ModelBuilder Bathymetry MapPEARL Depth Map

6 Bathymetry Map Webber Pond is primarily shallow 61% less than 16 feet deep Basin in southern portion Deepest point is 41 feet

7 Soils Organized into phases and grouped into series Classification depends on a number of factors: Important to consider soil type when developing in watershed Nutrients bind to soil particles and enter lake via runoff Erosion factors important

8 Georeferencing Aligning Print Maps Soil Map: An Overview Digitizing the Print Map Soil Map

9 Soil Map Theme Table with Multiple Attribute Fields K value - Erosion factor (0.00 to 0.49 for Webber Pond watershed soils) - Based on a standard size plot tilled and plowed - Value based on amount of water and sediments in runoff

10 Soil Map 31 phases divided into 16 series Majority (82.3%) of watershed composed of five soil series Septic limitations severe for most Webber Pond watershed soils Majority of K values (erosion factor) range from 0.20 to 0.32

11 Slope Map Contour Map ModelBuilder Slope Map

12 Septic Suitability Model Open residential land increased from 0.7% of the watershed in 1956 to 7.1% in 1997 Inadequate septic systems (leach fields) associated with residential or commercial land can contribute to non-point source nutrient loading into Webber Pond Beneficial to understand where septic system installment is suitable in the Webber Pond watershed

13 + Slope Map Soil MapSeptic Suitability Septic Suitability Model Factors that influence septic suitability: Weighted Overlay

14 Septic Suitability Model Unsuitable areas Steep grade High septic rank Indicated by light purple shading Highly suitable areas Gentle slope Low septic rank Indicated by pale yellow shading

15 Septic Suitability Model 99% of the watershed is highly unsuitable for septic system development (rank of 4 or above) without prior modifications Attributed to steep slopes and soil composition Area near Quaker Lane most suitable Recommend working with the Kennebec County Soil and Water Conservation Service

16 GIS, Phosphorus Model, and Future Predictions Bill McCloy

17 Erosion Potential Model Inputs 1.Soil Map 2.Land Use Map 3.Slope Map Weighted Overlay

18 Soil Map K values represent a soil’s erodibility K values were reclassified to range from 1 to 9 9 represents the most erodible soil types and 1 represents the least

19 Land Use Map Erosion Risk Values Mature Forest - 1 Wetlands - 1 Transitional Forest - 3 Reverting Land - 4 Pasture - 7 Golf Course - 7 Cleared Residential Land - 8 Cleared Land - 9 Crop Land - 9 Commercial / Municipal -9 Roads - 9

20 Slope Map ModelBuilder Contour Map Slope Map

21 Weighted Overlay Combines 1-9 erosion risk value for each input Factors in the percent importance of each input for the model Slope- 50% Land Use - 25% Soil Type- 25%

22 Erosion Model Inputs + + =

23 Final Erosion Potential Map 93.9% of Webber Pond watershed ranks 5 and below for erosion potential Only 6.1% of watershed ranks above 5 No part of watershed ranks very high

24 Water Budget Threemile Pond Mud Pond Threecornered Pond Webber Pond A water budget measures a ponds inputs and output of water The water budget helps determine the flushing rate for a pond or lake The flushing rate is a measure of how many times the pond’s water is replaced per year

25 Data needed for calculation: 1.Evaporation Rates 2.Precipitation (10 year average) 3.Runoff 4.Watershed area 5.Pond area 6.Average pond depth Areas calculated using ArcView® GIS Calculation

26 Flushing Rate Calculation constants I net

27 Phosphorus Loading Model Predicts total phosphorus concentrations Predicts relative phosphorus loading from each input category Input categories: 1.Land use patterns 2.Atmosphere 3.Septic systems 4.Soil retention potential 5.Sediment release Used to predict impact of future development in watershed

28 Creating the Model Area of input categories Export coefficients Surface area of lake Annual total water inflow Number of capita years - Lower for seasonal residences - Higher for year-round residences

29 Examples Mature Forest 0.10 kg/ha/yr ha24.52 kg/yr Camp Roads 3.45 kg/ha/yr6.51 ha22.46 kg/yr Golf Course 1.60 kg/ha/yr52.40 ha83.84 kg/yr Sediment Release 0.7 kg/ha/yr550.0 ha kg/yr Coefficient Area Phosphorus Loading

30 Calculated Phosphorus Concentrations CEAT/MDEP Sampling:22.97 ppb a Phosphorus Loading Model:23.35 ppb b a Mean epicore concentration from Site 1 b Best estimate

31 Percent Contribution for Different External Loading Categories

32 Historical Population Trends and Future Population Predictions : 1.26% annual pop. growth : 10% growth in population Webber Pond watershed population growing at about same rate as Vassalboro population Projected growth: 0.7% annual increase for next 25 years Projected 2022 population: 4,698

33 Future Development Predictions for Webber Pond Watershed Increased Residential Development Scenario 1.Incorporates new shoreline and non-shoreline residential land 2. Incorporates estimated population in Decrease in agriculture in watershed No Increase in Residential Development Scenario 1.Incorporates natural forest succession 2. No increase in residential land 3. Decrease in agriculture in watershed

34 Predicted Land Use Changes with Increase in Residential Land in 2022 Mature Forest acre increase Shoreline Residential10.50 acre increase Non-Shoreline Residential acre increase Transitional Forest acre decrease Reverting Land52.19 acre decrease Agriculture acre decrease Cleared Land10.00 acre decrease

35 Phosphorus Loading Model Predictions Increased Residential Land 2002 phosphorus concentration: ppb 2022 phosphorus concentration estimate: ppb 0.17 ppb increase No Increase in Residential Land 2002 phosphorus concentration: ppb 2022 phosphorus concentration estimate: ppb 0.53 ppb decrease Very small changes due to high level of internal phosphorus release, and also phosphorus input from Threemile Pond

36 Remediation Techniques and Recommendations Melanie Newton

37 Remediation Problem- Reducing phosphorus loading Direct Control - Decreasing amount of phosphorus that enters the watershed Point source diversion Erosion control Nutrient Control - Reducing sediment release of phosphorus Water Drawdown Phosphorus inactivation Hypolimnetic withdrawal

38 Point Source Diversion Diverting tributaries or point sources high in nutrients Seaward Mills Brook Tributary from Threemile Pond

39 Nutrient Interception Erosion carries sediment, nutrients, pesticides, and pathogens into the watershed Methods to control erosion: Maintenance of roads Control of shoreline erosion Construction of vegetated buffers Agriculture BMPs

40 Ideal Road Constructed of proper materials Graded and Crowned Diversions, turnouts, buffers, and ditches

41 Road Surface Larger gravel for base, finer gravel on top A crown should be 1/4 inch high for each foot of road width Grading uses a steel blade to level the soil material on the road’s surface. Grading should be done often and crowning should be done annually

42 Ditches Flat bottom and surface Gradually graded sides Trapezoidal or parabolic in cross-section Stone-lined or vegetated Sufficiently wide and deep

43 Culverts Convey water under road surface Discharge water into ditch or vegetated buffer area Should be adequately sized and have a 2% slope At least a foot of soil covering

44 Vegetated Buffers Remove sediments, nutrients from runoff water Forests: - Uneven surfaces obstruct flow - Roots promote absorption Seeding and mulching is beneficial where forests have been removed

45 Shoreline Erosion 914 m (6%) are high risk shoreline Several residents have taken action by constructing Concrete walls Log crib Riprap

46 Prevents erosion and allows nutrient-rich runoff to be absorbed by shoreline first. Grade of slope should be reduced 2:1 Base of bank should be stabilized with gravel blanket and rock riprap Slope covered by vegetation

47 Water Drawdowns Purpose: Remove water high in nutrients Kills some nuisance macrophytes Benefits: Low cost Facilitate other remediation techniques May increase spawning areas for bass Drawbacks: Could facilitate growth of some macrophytes Interferes with recreational activities Could kill planktivorous fish Removes only water from surface

48 DEP Drawdown Management Plan Presented in 1991 to Webber Pond Association Water Quality Manager, Dam Manager Water Level Coordinator Bi-weekly transparency readings Algal bloom before July, no drawdown Algal bloom late August, drawdown as soon as possible Drawdown 1.5 ft. below spillway by Labor Day Drawdown no later then September 3rd

49 Compromise Residents Recreational use of Webber Pond Swimming, Boating, Fishing, until Labor Day Natanis Golf Course Draws water from Webber Pond to maintain holes Best Biological Practice Drawdown occur as soon as possible after algal bloom, when nutrient levels are highest

50 Phosphorus Inactivation Process Al 2 (SO 4 ) 3 and sodium aluminate added to water, bind with phosphorus forming AlPO 4 Falls as floc onto sediment Aluminum best in anaerobic conditions pH must be between 6-8. pH below 6 forms toxic Al(III)

51 Phosphorus Inactivation as Remediation Purpose To reduce internal phosphorus Benefits Very effective long-term benefits Drawbacks Costly. Estimates for Webber Pond from $180,000-$890,000 Potentially toxic Increase in macrophyte growth

52 Hypolimnetic Withdrawal Purpose To remove nutrient-rich, deoxygenated water from hypolimnion Benefits Cheap Effective reduce from 200 mg/L to 91 mg/L Drawbacks Where will water go? Pipes for hypolimnetic withdrawal

53 Possible Collaboration with Natanis Golf Course Golf Course uses approximately 1 million gallons of water from Webber Pond each year If golf course could extend pipe deeper than 6 m into hypolimnion, it could drain nutrient-rich water Golf course could use this in irrigation and possible fertilization Remove nutrients from Webber Pond

54 Recommendations The primary problem at Webber Pond is cultural eutrophication Nutrient run-off from agriculture, roads, residential, and commercial land uses Historical cultural eutrophication created the problem in high internal phosphorus recycling levels Remediation must address both of these issues

55 Monitoring Suggestions Bi-weekly transparency readings from May through August Test surface and epicore samples for phosphorus yearly DEP Site (Site 1) Green Valley Campground (Site 6), Natanis Golf Course (Site 9), Dam (Site 10). Transparency and Dissolved Oxygen profile at Site 1 monthly May-September

56 Regulatory Measures Agriculture Increase use of BMPs in agriculture Better monitoring of these farms Forestry Restrict future timber harvesting If harvesting occurs follow a BMP Roads Conduct road surveys frequently to identify trouble spots Repair Trouble Spots

57 Residential Measures Encourage addition and enhancement of vegetated buffers and riprap Encourage road improvements and maintenance by residents Limit use of lawn fertilizers Reduce shoreline alteration

58 Nutrient Control Measures Continue the yearly drawdown, investigate the possibility of drawing water down from hypolimnion not just surface Investigate the possibility of using nutrient-rich hypolimnetic water in irrigating the Natanis golf course Investigate the possibility of phosphorus inactivation

59 Educational Measures Encourage the availability of this report to the general public Work closely with the China Region Lake Alliance Develop and distribute pamphlets to homeowners (road repair, riprap, vegetated buffers, detergents, and water level drawdown) Involve local schools in monitoring Webber Pond

60 Acknowledgements Peter AbelloKelly Karter Roy BouchardJim Lucas Bob & Julie BrownKevin Michaud Russell ColeJudy Moody Gene FieldPeter Mosier Dale FinesthRebecca Manthey David FirmageEdward Noel Betsy FitzgeraldFrank Richards Nate GrayBruce Rueger David HalliwellDan Tierney Vassalboro Town Office Staff Maine Department of Environmental Protection Staff Maine Department of Inland Fisheries and Wildlife Staff Maine Soil and Water Conservation Staff Green Valley Campground

61 Questions


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