Assessment Comments
Assessment remains based on results of a fish kill investigation in September 2008 and results of 2002 IDNR/SHL biological sampling data: FIBI = 48 (fair), BMIBI = 48. Non-riffle habitat FIBI BIC = 32, BMIBI BIC = 62.
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, 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 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" (IR 3a) due to the lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” (IR 5b) based on results of a fish kill investigation in September 2008. Results of IDNR/SHL biological sampling conducted in 2002 as part of the REMAP project also suggest "partial support" (IR 3b-c) of the aquatic life uses.
EXPLANATION: The fish kill occurred on or before September 9, 2008. The kill occurred along two miles of Lotts Creek south of Whittemore. At the time of the investigation DNR observed a blue-gray color in the water near the B44 bridge, and dead fish at the 180th and 190th St. bridges. No live fish were observed. No counts of the dead fish were done and no estimate of the value of the fish was calculated. The cause of the kill was not identified, but was suspected to be human caused.
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 in Category 5b of Iowa’s 2010 Integrated Report and remains in IR Category 5b.
The assessment of aquatic life uses was also based on biological data collected in 2002 as part of the IDNR/SHL 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 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 48 (fair) and the BMIBI score was 48 (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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC and failed the BMIBI BIC in 2002.
This assessment is considered "evaluated" because there were not two or more samples collected in multiple years from 2008-2012. Also, 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).
As part of the REMAP project, diurnal dissolved oxygen/temperature monitoring conducted during July-August 2002 found substantial fluctuation of d.o. levels, including nighttime sags (<3 mg/L), associated with very high estimated levels of community respiration and primary production. Levels of BMIBI metrics that are sensitive to organic enrichment suggest a nutrient enrichment/algal growth-related water quality problem. Habitat modification that has resulted in a wide and shallow stream channel with high solar input may contribute to algal growth. Additional sampling data are needed to evaluate the extent, causes and sources of this water quality problem.
