Assessment Comments
Assessment is based on (1) results of a fish kill investigation in August 2006, (2)results of IDNR/UHL biological (biocriteria) monitoring in 2001: FIBI = 17, 19, 16 (all poor); BMIBI = 65, 71, 70 (all good), and (3) results of 2002 Fisheries data: FIBI = 24 (poor). FIBI BIC = 36, BMIBI BIC = 51.
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 the lack of information upon which to base an assessment. The Class B(WW-2) aquatic life uses remain assessed (monitored) as "partially supported" based on results of a fish kill investigation in 2006, IDNR/UHL biological (biocriteria) sampling in 2001 and IDNR Fisheries sampling in 2002. The impairment based on the fish kill is due to a pollutant caused fish kill and therefore is appropriate for Category 5b of the Integrated Report. For previous assessments, the impairment of the Class B(WW-2) uses is due to impacts of habitat alterations caused by stream channelization. This type of impairment is appropriate for Category 4c of the Integrated Report (i.e., impairment caused by non-pollutant stressor).
EXPLANATION: The Class B(WW-2) aquatic life uses are assessed (monitored) as "partially supported" based on results of a fish kill investigation in 2006. The kill occurred on or before August 11, 2006 and was attributed to runoff from an open feedlot where 1300 hogs were housed. The runoff occurred following heavy rains when manure from the open hog lot had overflowed a retention structure and run into a tributary of the North Skunk River. Several hundred dead fish accumulated at the low head dam on the North Skunk River near Lynnville. Both dead carp and gamefish were found. 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.
The assessment of the Class B(WW-2) aquatic life uses based on data collected in 2001 as part of the IDNR/UHL stream biocriteria project and on 2002 Manchester Fisheries stream sampling data also suggests "impairment" of the aquatic life uses. 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 2001 FIBI scores were 17 (poor), 19 (poor) and 16 (poor); the BMIBI scores were 65 (good), 72 (good) and 71 (good). The 2002 Fisheries FIBI score was 24 (poor). The FIBI average (n=4) was 19 and the BMIBI average (n=3) was 69.3. 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 1994-2004. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.
