Assessment Comments
Assessment based on 2008 IDNR/UHL biological monitoring and on 1999 and 2001 fish monitoring conducted by the IDNR Fisheries Bureau.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY/EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.
The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting” (impaired), and this waterbody remains in Category 5 of Iowa’s Integrated Report. Although originally placed in Category 3b of Iowa's 2004 Integrated Report by Iowa DNR, U.S. EPA Region VII, in their May 23, 2006 transmittal of Iowa's final approved 2004 Section 303(d) list, added this waterbody segment to Iowa's 2004 Section 303(d) list (IR Category 5b). Iowa DNR maintained that addition of this assessment segment to Iowa’s 2004 Section 303(d) list was inappropriate. That is, the bioassessment data generated by the IDNR Fisheries Bureau for this assessment segment lacked the necessary documentation or metadata to determine whether the data meet quality and completeness criteria required of higher confidence (i.e., “monitored”) assessments that IDNR considers appropriate for Section 303(d) listing. Thus, the assessment type was considered of lower confidence (i.e., "evaluated"), and thus this "partially supported" waterbody was considered not appropriate for Section 303(d) listing. U.S. EPA Region VII, however, based on their review of the IDNR Fisheries bioassessment data for this assessment segment, concluded that these data are, in fact, scientifically adequate and representative of current water quality. Thus, EPA added-back this assessment segment to Iowa's 2004 final approved Section 303(d) list (Category 5b).
The assessment of the Class B(WW2) aquatic life uses was based on data collected in 2008 by IDNR/UHL in support of SI/TMDL development and on data collected in 1999 and 2001 as part of a DNR Fisheries stream sampling project: Chariton research station. 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 2008 FIBI score was 26 (fair) and the 2008 BMIBI score was 26 (poor). The 1999 FIBI score was 8 (poor) and the 2001 FIBI score was 27 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC is 41. Even though this site passed the FIBI BIC twice (using the UAV of 7 points) and failed to meet the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b and remains on Iowa’s 2010 Section 303(d) list of impaired waters.
