water quality in catchments and its impact on human and ecological health kenneth h. reckhow
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Water Quality in Catchments and its Impact on Human and Ecological Health Kenneth H. Reckhow Duke University. Primary Theme: Improvements in basic scientific understanding and advances in predictive modeling are essential for effective water quality management. Secondary Theme: - PowerPoint PPT PresentationTRANSCRIPT
Water Quality in Catchments andits Impact on Human and Ecological Health
Kenneth H. ReckhowDuke University
Primary Theme:Improvements in basic scientific understanding
and advances in predictive modeling are essential foreffective water quality management.
Secondary Theme:There exist a number of useful practical
strategies in the areas of technology, economics, government institutions, and stakeholderinvolvement.
Ref: Peters and Meybeck
ISSUES
• Scientific understanding• Abatement technologies• Economic approaches• Political institutions• Predictive modeling
Approach - use a case study to illustrate issues
Facts About the Neuse River
• 3rd Largest River Basin in NC (16,000 Km2)• 320 kilometers long, 5000 stream kilometers• Estuary in lower 80 kilometers• 1.5 million people in basin, mostly near
headwaters
Nonpoint sources treatment practices
Wastewater lagoons served by effluentspraying on agricultural fields at agronomicrates are the current low-cost technology for theconfined animal feedlots.
What is the ultimate fate of the nitrogenintroduced into these lagoons?
What other low-cost technologies are effectivefor the high concentration pollutant loads fromanimal feedlots?
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Streets Ferry
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Askin
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Washington Forks
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New Bern
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Fairfield Harbour
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Thurman
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Riverdale
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Minnesott Beach
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Oriental
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Mouth of Neuse
De
se
aso
na
lize
d C
on
ce
ntr
atio
n (
mg
/l)
Date
Total Nitrogen
Basin scale processes affecting thenitrogen cycle
What is the fate of the fixed nitrogenintroduced into the Neuse basin?
How much is volatilized? How much istransported to the groundwater?
We understand nitrogen transformations at thesmall scale; however, how effectively can wepredict denitrification and other nitrogen sinksat the basin scale?
Vegetative stream buffers and mitigation
What soil, vegetative, and hydrologic criteriaare predictors of the effectiveness of streambuffers for nitrogen loss?
Can an effective mitigation program beestablished to “trade” newly establishedbuffers for lost buffers?
Low DO and Fish Kills: 94-96
Cherry Point
StreetsFerry
TMDLs – The US Approach for Basinwide Water Quality Management
Total Maximum Daily Load (TMDL)
For water bodies that do not meet water qualitystandards, states will be required to develop amanagement plan and determine the allowablepollutant loading (the TMDL) necessary to achieve compliance with the standard.
Local involvement and stakeholders
Ultimately, local governments must participatein the local land use decisions that are essentialto the success of pollutant abatement plans.
Active participation of citizen stakeholdersthroughout the process helps achieve “buy in”and effective implementation.
Political institutions
Upper and Lower Neuse Basin Associationshave been formed to provide a political body forcommunication and coordination among stateand local governments that cut across watershedlines. This is a promising approach to facilitatepollutant trading among dischargers.
Decision criteria
Ambient water quality standards are fixed, pointexceedance levels (e.g., 40 g/l chlorophyll a), yetnatural water quality is variable and water qualitypredictions are uncertain.
Probabilistic standards are needed to resolve theseincompatible quantities and provide a basis fordecision.
Application of Water Quality Standards
North Carolina Dissolved Oxygen Standard - “not less than average of 5.0 mg/l with a minimum instantaneous valueof not less than 4.0 mg/l”
How can this standard be effectively implementedwhen natural water quality is variable
and predictions are uncertain?
5 mg/l
ProbabilisticWater Quality
Standards
Actual Violations - based on a specified fraction of samples exceeding the numeric limit (5 mg/l)
Predicted Violations - based on specified fraction ofthe posterior density function exceeding the numeric limit
Water quality assessment and modeling
Water quality modeling is vital, yet current modelingapproaches tend toward overparameterization withoutrigorous testing or error analysis.
As an alternative, we are developing a probability (Bayes) network model using a set of simple mechanistic expressions that are identifiable using available data.
As necessary, this model is being extended to incorporate judgmental probability assessment for narrative endpoints characterizing consequences of particular concern to stakeholders (e.g., harmful algal blooms and Pfiesteria).
Summer Total
Nitrogen LoadSpring Total
Nitrogen Load
SummerProductivity
Spring
Productivity
Summer
Average
Chl a Level
Summer Total
Phosphorus Load
Avg. Days to
Deplete DO
Bottom DO
Upon Mixing
Benthic
02 Demand
Existing
Benthic
Organic
Water Column
O2 Demand Continuous# of Days of
Stratification
Freq. of
Trapping
Wind
Days Between
Mixing Events
Anoxic Days
in Season
Presence
of Active
Pfiesteria
Water
Clarity
# of Severe
Algal Blooms
Reduction
in Shellfish
Habitat
# of Major
Fishkills
Matter
Human Health Impacts
Example: A probability network for a subset of the relationships --
Nutrient Load
Algal Growth Frequency of
Mixing EventsSedimentOxygenDemand
FishHealth
Frequency of Hypoxia
WaterTemperature
Frequency of Mixing Events
SedimentOxygenDemand
Frequencyof Hypoxia
WaterTemperature
C)(CkCkdt
dCsvd
Rd
Rv
C
Cu
vRRdtdC
d
)( CCkR uvv CkRdd
20Td20dd
kTk )(
8 Years of bi-weekly measurements at multiple mid-channel locations
• Oxygen Concentration• Water Temperature• Salinity
Nonlinear regression parameter estimation
R2=0.79RSE=1.49 mg/l
4 mg/l
mix] since time ),Temp( SOD[ fConc. Oxygen
Pro
babi
lity
Predicted Number of Summer Days
DO < 4 mg/l DO < 2 mg/l
mean = 46.8 days mean = 23.8 days
Days Days
s = 4.7 days s = 4.2 days
Nutrient Load
Algal Growth
FishHealth
Frequency of Mixing Events
SedimentOxygenDemand
Frequencyof Hypoxia
WaterTemperature
WaterClarity
NutrientRecycling
PfiesteriaPresence
HumanHealth
Some Useful Practical Lessons:• Low cost technologies (stream buffers)• Economic strategies (pollutant trading)• Political institutions (watershed associations)• Citizen involvement
Scientific Needs:• Improved process understanding at the basin scale• Better approaches to uncertainty in predictive modeling and WQ standards