Assessment Comments
Assessment based on results of (1) a fish kill investigation in August 2006 and (2) 2003 IDNR/UHL biological monitoring data: FIBI = 32 (fair), BMIBI = 27 (poor). FIBI BIC = 31; BMIBI BIC = 54.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2010) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment. The Class B(WW-1) aquatic life uses are assessed (monitored) as "partially supported" due to a fish kill in August 2006. Results of an evaluated biological assessment based on data collected in 2003 as part of the IDNR/UHL stream REMAP project also suggest "partial support" of the aquatic life uses.
EXPLANATION: The fish kill occurred on or before August 1, 2006 and was attributed to animal waste. Recent heavy rains in the area likely washed manure into many northwest Iowa streams with low flow conditions. Three additional kills were reported on other streams in the area. Ammonia levels in this segment ranged from 7.5 to 10 parts per million (ppm). An estimated 14,272 fish were killed. The estimated value of these fish was $2320.74. At the time of this assessment there are no records that IDNR has sought/received restitution for this fish kill.
According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2007-2009) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources. For previous assessment/listing cycles, IDNR had considered fish kill-impaired (IR 5b) waters with no subsequent kills in the three year subsequent to the kill as appropriate for de-listing and for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Due, however, to EPA uncertainty regarding the full recovery of the aquatic life following the kill, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s 2010 Integrated Report.
Results of an evaluated biological assessment based on data collected in 2003 as part of the IDNR/UHL stream REMAP project continues to suggest "partial support" of the aquatic life uses. A series of biological metrics that 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 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 score was 32 (fair) and the BMIBI score was 27 (poor). 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 31 and the BMIBI BIC for this ecoregion is 54. Even though this site passed the FIBI BIC and failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small general use stream and doesn’t fall in the calibrated watershed size.
This assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for headwater streams. Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. IDNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality. Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams. For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.
