Assessment Comments
Assessment remains based on results of (1) 2001 IDNR/UHL biological monitoring data: FIBI = 64 (good); BMIBI = 35 (fair) and (2) results of IDNR/UHL ambient water quality monitoring conducted in 2001 in support of TMDL development.
Basis for Assessment
[Note 1: 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.]
[Note 2: A TMDL for sediment and phosphorus impacts was prepared by IDNR and approved by EPA in October 2007 (see http://www.iowadnr.gov/water/watershed/tmdl/files/final/midfork_southbeaver.pdf ). Thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all Section 303(d) impairments identified for this stream segment are potentially addressed by the TMDL, this waterbody is placed in Category 4a of Iowa's 2008 Integrated Report.
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The presumptive Class B(WW1)(aquatic life) uses continue to be assessed (evaluated) as "partially supporting (=PS)" based on results of biological monitoring in 2001. Results of ambient water quality monitoring in 2001 suggested good water quality but also suggested the potential for continued water quality problems. The sources of data for this assessment are results of (1) biological sampling data collected in 2001 as part of the DNR/UHL stream biocriteria and TMDL development projects and (2) IDNR/UHL monthly ambient water quality monitoring conducted in from March to November 2001 in support of TMDL development (STORET station 11380003; Site 45).
The previous (1998) assessment of support for the general beneficial uses of this stream ("partially supported") was based on the occurrence of repeated fish kills from 1991 to 1997 (see assessment developed for the 1998 report). This assessment was the basis for adding this stream segment to Iowa's 1998 Section 303(d) list of impaired waters. The most recent kill occurred in September 1997. According to DNR's assessment methodology for Section 305(b) reporting, the lack of fish kills during the most recent three-year period (and the lack of kills over the last 10 years) suggest that the stream has fully recovered from the historic fish kill-related impacts.
EXPLANATION: The assessment of the presumptive Class B(WW1) aquatic life uses remains based, in part, on results of biological monitoring in 2001. 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 score was 64 (good) and the BMIBI score was 35 (fair). 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 non-riffle habitat FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52. 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 headwater stream and doesn’t fall in the calibrated watershed size.
The biological assessment of the presumptive Class B(WW1) aquatic life uses 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 are typically placed in either Category 2b or 3b of the IR and thus are added to the state’s list of “waters in need of further investigation”.
The results of monthly water quality monitoring conducted in 2001 by IDNR/UHL at one location approximately 4 miles NW of Wellsburg showed the potential for aquatic life impacts. One of the nine samples (11%) violated the Class B(WW1) chronic water quality criterion for ammonia nitrogen. According to U.S. EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, more than 10% of the samples exceed state criteria for toxics (including ammonia-nitrogen), the aquatic life uses are "not supported" (see pg 3-18 of U.S. EPA 1997b). However, because less than 10 samples were available for this assessment, the assessment type was considered "evaluated," and the degree of support of the aquatic life uses was considered "fully supported." According to IDNR assessment guidelines, "evaluated" assessments are not of sufficient quality to support a Section 303(d) listing.
