outline groundwater inflow & marl formation rates in small
TRANSCRIPT
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Groundwater Inflow & Marl Formation Rates in Small Lakes
Model Development & Exploring Implications for Management
P. McGinley & N. Turyk
University of Wisconsin-Stevens Point
Outline
• Background
– Purpose
– Study Area
• Methods/Results
– Groundwater Flow
– Marl Formation
– Phosphorus
• Summarize / Future
Purpose- incorporate marl formation in a planning tool that links land management to
water quality
Multi-lake management study – including water quality, aquatic plants, fishery,
shoreland habitat – and a planning effort
Acknowledgements
Citizens and Lake Associations, Portage Co Land & Water Conservation, Wisconsin Department of Natural Resources,
UW-Stevens Point Water & Environmental Analysis Laboratory, Ryan Haney, Byron Shaw, Dick Stephens, Dave
Mechenich and many others…
Study Area: Central Wisconsin Sand Plain
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Study Area: Central Wisconsin Sand Plain
Green Bay / Lake Michigan
Wisconsin R/ Miss R/ Gulf
• 22 Lakes
• Area < 50 ha
• Depth < 20 meters
Approach
• Explore marl (CaCO3) formation
– Communicate land to water connections
– Estimate deposition rates
• Lake phosphorus concentration tool
– Link lake P to external load P
– Settling velocity approach/link to CaCO3
Rate of Change In Mass
= Rate of Mass In
Rate of Mass Out
Rate of Mass Settled
- -
• Phosphorus – “steady-state,” annual load (watershed, gw), settling velocity
• Calcium– short time step, CaCO3 sed rate & time period, convert to annual g/m2
Mass Balance Models CaCO3
Soil • CaMg(CO3)2 + = Ca2+ + Mg2+ + 4 HCO3
-
Lake • Ca2+ + CO3
2- = CaCO3
Water & Carbon Dioxide
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Soil • CaMg(CO3)2 + = Ca2+ + Mg2+ + 4 HCO3
-
CaCO3
Lake • Ca2+ + CO3
2- = CaCO3
Groundwater
• Calcium=48 mg/l as Ca
=120 mg/l as CaCO3
• Ca/Total Hardness = 0.57
Water & Carbon Dioxide
Soil • CaMg(CO3)2 + = Ca2+ + Mg2+ + 4 HCO3
-
CaCO3
Lake • Ca2+ + CO3
2- = CaCO3
Groundwater
• Calcium=48 mg/l as Ca
=120 mg/l as CaCO3
• Ca/Total Hardness = 0.57
Water & Carbon Dioxide
Phosphorus?
Our Approach
1) Estimate groundwater flow to lakes (MODFLOW)
2) Mass balance fit to Ca and Ca/Hard
Groundwater
Groundwater
Groundwater Divide
32” 20”
12”
Groundwater
Groundwater Divide
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Groundwater Contours
Lakes
FLOW Groundwater Contributing Areas
Lakes
Inflow/Year = (Recharge Area) * (Recharge/Year)
Avg Hydraulic Res Time = 50 days to 10 years
Lakes Estimating Marl Deposition Rates
Fountain
• Marl
formation decreases calcium concentrations
Estimating Marl Deposition Rates
Fountain
• Inflow
• Ca
• Ca/Mg
• Days
• Rate
Estimating Marl Deposition Rates
Fountain
• Inflow
• Ca
• Ca/Mg
• Days
• Rate
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Pickerel
Fountain
• Ca/Mg decreases with residence time
60 days
220 days
Lime
Fountain
• Ca/Mg decreases with residence time
60 days
500 days
• Phosphorus Model w/ Adjusted Settling
• Estimated CaCO3 Deposition Rates
Explore implications of watershed change in lake management plan development
Summary & Observations
• Incorporating calcium into the lake management discussion – useful way to connect land & water – local information into a planning tool
• Very simple model
– A tool to evaluate differences in deposition rates – Some evidence they coincide with productivity – Uniform marl rate is a simplification
• Human impacts to groundwater geochemisty
For More Information
Paul McGinley University of Wisconsin-Stevens Point [email protected] (715) 346-4501