Assessment Comments
Assessment remains based on results of (1) IDNR/SHL biological sampling in 2002 and (2) IDNR/SHL ambient water quality monitoring conducted from March 2002 to December 2003 in support of TMDL development.
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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) 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” (IR 5b-t) based on results of biological sampling for fish and aquatic macroinvertebrates conducted in 2002 as part of the IDNR/SHL REMAP project. This assessment is also based on results of ambient chemical/physical water quality monitoring conducted by IDNR/SHL during the 2002-2004 assessment period as part of TMDL monitoring (TMDL station 11; STORET station 11750003).
EXPLANATION: The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supporting” based on biological data collected in 2002 as part of the IDNR/SHL REMAP 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 2002 FIBI score was 18 (poor) and the BMIBI score was 33 (fair). 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 31 and the BMIBI BIC for this ecoregion is 54. This segment failed both the FIBI and BMIBI BICs in 2002.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a recent five-year period. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).
Habitat assessment and site photographs indicated channel incision, vertical eroding banks, narrow riparian buffer next to row crop land, and silt accumulations. Diurnal dissolved monitoring indicated levels lower than 3 mg/L can occur during summer months. Additional sampling data are needed to evaluate this potential water quality problem.
Despite results of biological monitoring that suggest “partial support” of the aquatic life uses, the results of chemical/physical water quality monitoring conducted from March to December 2003 in support of TMDL development suggest relatively good water quality in this stream. None of the approximately 25 samples collected over this period had levels of ammonia-nitrogen, dissolved oxygen, or pH that violated water quality criteria (these samples were not analyzed for toxic metals or pesticides).
