Assessment Comments
Assessment based on the: (1) results of a fish kill investigation in 2004 and (2) IDNR/SHL biological sampling in 2011: FIBI = 45 (fair) and BMIBI = 44 (fair). Riffle habitat FIBI BIC = 53 and BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified 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, this segment is now presumptively designated for Class A1 (primary contact recreation) 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. Thus, for the current assessment, perennial flow is presumed, and 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 a lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" (IR 5b) based on the results of a fish kill investigation in November 2004 and IDNR/SHL biological sampling conducted in 2011.
EXPLANATION: The kill occurred on or before November 2, 2004. Because of high water and extremely turbid conditions, a count of dead fish was not made through the complete kill area, however it was estimated that 1,314 fish were killed. The kill occurred north of Lidderdale, beginning at a tile approx. 300 yards upstream from bridge on east side of Sec 4, T85N R34W Carroll Co. The suspected cause of the kill was runoff from a cattle feedlots. The estimated value of the fish was $149.98. At the time of this assessment there is no information as to whether the DNR sought or 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 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. Thus, this assessment segment was placed, and remains in, Category 5b of Iowa’s Integrated Report. Due to the age of the data from the fish kill investigation that support this assessment (greater than five years), this assessment is changed from a higher-confidence assessment (“monitored”) to a lower confidence (“evaluated”) assessment. Despite this change, this segment remains in IR Category 5b due to the fish kill-related impairment of aquatic life uses.
This evaluated aquatic life assessment was based on data collected in 2011 as part of the IDNR/SHL stream follow-up sampling project. 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 2011 FIBI score was 45 (fair) and the BMIBI score was 44 (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 riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62. The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. This assessment is considered "evaluated" because there were not two or more samples collected in multiple years from this segment. 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 becasue of the fishkill and remains on Iowa’s Section 303(d) list of impaired waters.
