Assessment Comments
Assessment based on (1) 2006 REMAP data: FIBI = 13 (poor) and 19 (poor), FIBI average = 16; BMIBI = 50 (fair), 17 (poor). FIBI BIC = 43; BMIBI BIC = 54; and (2) results of an IDNR fish kill investigation in 2007.
Basis for Assessment
[Note: Prior to the current (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 (2008) 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 are "not assessed" due to a lack of water quality information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (monitored) as "partially supported" based on results of biological sampling (REMAP) in 2006, and a fish kill investigation in August 2007.
EXPLANATION: This aquatic life assessment was based on data collected in 2006 as part of the DNR/UHL stream REMAP 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 2006 FIBI scores were 13 (poor) and 19 (poor); the 2006 BMIBI score was 50 (fair). The 2006 FIBI average was 16 and the BMIBI average was 33.5. 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 FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
Sampling staff also indicated that there was evidence of a recent fishkill in the segment that may have contributed to the aquatic life impairment.
Results of a fish kill investigation also suggest "partial support" of the aquatic life uses. A fish kill occurred on or before August 17, 2007 and was attributed to runoff from a dairy farm after a heavy rainfall event. It was noted that the kill likely occurred a few days before it was reported. The kill affected approximately 10.9 miles of the stream from 100th Street bridge at Sioux/Plymouth Co Line to L12 Bridge, Remsen. The value of the fish was estimated to be $345.50. At the time of this assessment there are no records that IDNR has sought/received restitution for this 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 (2005-2007) 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 will be placed in Category 5b of Iowa’s 2008 Integrated Report.
