Walnut Creek IA 02-IOW-708
mouth (S31 T82N R12W Benton Co.) to confluence with North Walnut Cr in S7 T81N R13W Poweshiek Co. trib S24T81NR15W Poweshiek Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 5/14/2019 7:23:28 AM
- Updated
- 5/14/2019 7:25:39 AM
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 remain assessed (evaluated) as “partially supported” based on biological data collected in 2003 and 2008 as part of the DNR/SHL stream REMAP and TMDL sampling projects.
This evaluated biological assessment was based on data collected in 2003 and 2008 as part of the DNR/SHL REMAP and TMDL stream sampling projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species 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 2003 FIBI scores were 41, 42 (fair) and the 2008 FIBI score was 51 (good). The 2003 BMIBI scores were 70 (good), 24 (poor) and the 2008 BMIBI score could not be calculated due to low benthic macroinvertebrate density. 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 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 1/2 times in the past 14 years. This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 12years (2003-2014); however, the multiple samples were not collected during a five-year period. According to DNR’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). DNR 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-t and remains on Iowa’s Section 303(d) list of impaired waters.