Middle Fork South Beaver Creek IA 02-CED-563

[Note: A TMDL for sediment and phosphorus impacts was prepared by DNR and approved by EPA in October 2007. 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 was placed in Category 4a of Iowa's 2008 Integrated Report and remains in IR Category 4a.]

The presumptive Class B(WW1) aquatic life uses remains assessed (evaluated) as “partially supporting” based, in part, on results of biological sampling in 2001. A series of biological metrics which reflects 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 1994-2008. 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. DNR’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 DNR/SHL 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 "partially supported." According to DNR assessment guidelines, "evaluated" assessments are not of sufficient quality to support a Section 303(d) listing.

The biological and chemical data upon which this assessment is based are now nearly twenty years old. As water quality data age, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasingly suspect. Data approaching 20 years old cannot be expected to reflect current water quality conditions. Despite the age of these data, the aquatic life uses of this assessment segment will remain “partially supporting/evaluated” (IR 3b-u) and will remain on Iowa’s list of waters in need of further investigation (IR Category 3b). Additional monitoring is needed in this assessment segment to update status of its aquatic communities.