Iowa DNR
Iowa DNR
ADBNet
Water Quality Assessments
Impaired Waters List

North Skunk River IA 03-NSK-859

from the Mahaska/Poweshiek line to confluence with Sugar Cr. in S20 T78N R16W Poweshiek Co.

Assessment Cycle
2006
Result Period
2002 - 2004
Designations
Class B(LR)
Assessment Methodology
Assessment Type
Monitored
Integrated Report
Category 5b
Legacy ADBCode
IA 03-NSK-0020_2
Overall Use Support
Partial
Aquatic Life Use Support
Partial
Documentation
Assessment Comments

Assessment is based on results of IDNR/UHL biological (biocriteria) monitoring in 2001: FIBI = 15 (poor), BMIBI = 74 (good). FIBI BIC = 36, BMIBI BIC = 51.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses remain assessed (monitored) as "partially supported"  based on results of IDNR/UHL biological (biocriteria) sampling in 2001.   This is the same assessment as that developed for the 2004 reporting cycle.

EXPLANATION:  The assessment was based on data collected in 2001 as part of the DNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2001 FIBI score was 15 (poor) and the BMIBI score was 74 (good).  The aquatic life use support was assessed as partially supporting (= PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.

Monitoring and Methods
Assessment Key Dates
8/6/2001 Biological Monitoring
8/6/2001 One-time Chemical Monitoring
Methods
330 Fish surveys
375 Visual observation-- may not quantify some parameters-- single season-- by prof.
380 Quan. measurements of instream parms-- channel morphology-- floodplain-- 1-2 seasons-- by prof
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
Monitoring Levels
Biological 4
Habitat 4
Physical Chemistry 1
Toxic 0
Pathogen Indicators 0
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 1
BioIntegrity Fair
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Other habitat alterations Aquatic Life Support Moderate
  • Agriculture
  • Bank or Shoreline Modification/Destabilization
  • Channelization
  • Grazing related Sources
  • Habitat Modification (other than Hydromodification)
  • Hydromodification
  • Pasture grazing - Riparian
  • Moderate
  • Moderate
  • Moderate
  • Moderate
  • Moderate
  • Moderate
  • Moderate
Siltation Aquatic Life Support Moderate
  • Agriculture
  • Bank or Shoreline Modification/Destabilization
  • Grazing related Sources
  • Pasture grazing - Riparian
  • Moderate
  • Moderate
  • Moderate
  • Moderate
Suspended solids Aquatic Life Support Moderate
  • Agriculture
  • Grazing related Sources
  • Pasture grazing - Riparian
  • Moderate
  • Moderate
  • Moderate
Turbidity Aquatic Life Support Moderate
  • Agriculture
  • Grazing related Sources
  • Pasture grazing - Riparian
  • Moderate
  • Moderate
  • Moderate