water quality in catchments and its impact on human and ecological health kenneth h. reckhow duke...

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?

0.5

1.5

1/75 1/80 1/85 1/90 1/95

Streets Ferry

0.5

1.5

1/75 1/80 1/85 1/90 1/95

Askin

0.5

1.5

1/75 1/80 1/85 1/90 1/95

Washington Forks

0.5

1.5

1/75 1/80 1/85 1/90 1/95

New Bern

0.5

1.5

1/75 1/80 1/85 1/90 1/95

Fairfield Harbour

0.5

1.5

1/75 1/80 1/85 1/90 1/95

Thurman

0.2

0.6

1.0

1/75 1/80 1/85 1/90 1/95

Riverdale

0.2

0.6

1.0

1/75 1/80 1/85 1/90 1/95

Minnesott Beach

0.2

0.6

1.0

1/75 1/80 1/85 1/90 1/95

Oriental

0.2

0.6

1.0

1/75 1/80 1/85 1/90 1/95

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