How Does Iowas Water Quality Rate

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How Does Iowas Water Quality Rate?

• The Development of an Improved Water Quality
  Index Specific to the State of Iowa
• Katie Foreman
• IOWATER Snapshot Coordinator
• 6th Annual Water Monitoring Conference
• February 16-17, 2006
• Ames, IA

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What does this mean?
(Iowa Geological Survey 2004,1)
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What is NeededA Yardstick for Measuring Water
Quality

• Large quantities of water quality data on their
  own do not inform water resources decision making
• A quick way to draw meaning from data is needed
• What is clearly needed is a yardstick of water
  quality. (Brown et al. 1970, 339)

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Value of WQIs

• In 1972, the Council on Environmental Quality
  stated that accurate and timely information on
  the state of the environment was essential to
  forming policy
• Indices are one of the most effective tools to
  compare and evaluate environmental conditions
• Examples include Water Quality Index, Air
  Quality Index, Index of Biotic Integrity, Trophic
  State Index, and Species Diversity Index

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Process of WQI Calculation
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Example of a Subindex Rating Curve
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Qualitative Rating
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Motivation

• National Sanitation Foundation Water Quality
  Index (NSFWQI)
• Most respected and utilized WQI in U.S.
• One size fits all structure criticized for
  overlooking regional water quality concerns
• When applied to 3 years of Iowa data
• Rated streams/rivers 79 medium and 21 good

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Does Iowa have waters that can be categorized
on the extremes?

• What about the impaired waters (303 (d) list)???
  (25)
• How about our excellent waters
• (Reference sites)??

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Index Development

• IWQI developed in 2005 by custom-fitting the
  NSFWQI to Iowa.
• Geographically specific water quality index to
  represent a full range of water quality
  conditions in Iowa.
• Index was validated with data of known water
  quality
• Statistics used to answer the question is the
  IWQI better than the NSFWQI at characterizing
  Iowas water quality?

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Attributes of NSFWQI IWQI
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Geographically-Specific Subindex Rating Curves
TDS and TSS
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Index Performance

• Is the IWQI better than the NSFWQI at rating
  Iowas water quality?
• Subset of the validation datasets chosen
• Most pristine and most impaired water quality
  records
• Hypothesis test used to determine relative
  performance of the two indices

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Comparative Analysis Statistics
Most Pristine Water Quality as Rated by the IWQI
and the NSFWQI
Most Impaired Water Quality as Rated by the IWQI
and the NSFWQI
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• Is the IWQI better than the NSFWQI at rating
  Iowas water quality?
• YES!
• Statistical analysis suggests that IWQI rates the
  most impaired water quality worse and the most
  pristine water quality better than does the
  NSFWQI
• Why?
• Index Design Parameters, Subindex Rating Curves
  and Aggregation Function

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Reason 1 Parameters Included

• Non point source pollution is the
• 1 water quality challenge in Iowa
• IWQI includes two more non point source
  pollutants in the index compared to NSFWQI
• 84 of Iowas stream miles have major sediment
  impacts (TSS)
• 81 of Iowas surface water samples have
  detectable levels of pesticides (total
  pesticides)
• Temperature change excluded

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Reason 2 Subindex Rating Curves

• IWQI has geographically specific subindex rating
  curves
• Distinguishes background from impaired conditions
• IWQI has consistent maximum (100) and minimum
  (10) values
• No artificial over or under-estimation of water
  quality conditions
• Subindex curves appropriate for Iowas waters
• Phosphorus, DO, and BOD rated more stringently
  (accounts for eutrophication risk)
• TDS is not rated as stringently (climate and
  geologic variability)

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Reason 3 Aggregation Function

• NSFWQI uses the weighted linear sum
• Eclipsing problems, averages out low numbers
• Tends to overestimate water quality conditions
• Arbitrary weights
• IWQI uses the unweighted harmonic square mean
• Eclipsing problems minimal
• Gives high statistical value to lowest number
• Index score determined with all parameters in
  mind, no arbitrary weights

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NSFWQI vs. IWQI (2000-2004)
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Uses for the IWQI

• Evaluating changes in water quality over time
• Quantify the effectiveness of water quality
  regulations and protection programs
• BMPs
• Comparing water quality conditions in different
  locations ? resource prioritization
• Determining the extent to which existing water
  quality standards are met ? informing policy
• Developing reports required by the Clean Water
  Act (305(b) and 303 (d) list)

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Acknowledgements

• Dr. R. Rajagopal (University of Iowa)
• Dr. Mary Skopec (Iowa Geological Survey)
• Dr. David Bennett (University of Iowa)
• Rick Langel (Iowa Geological Survey)
• Tom Wilton (Iowa Department of Natural Resources)
• Malini De (University of Iowa)
• Dr. Ed Brands (University of Iowa)
• Lynette Seigley (Iowa Geological Survey)
• Eric OBrien (Iowa Geological Survey)