Saunders Branch IA 03-SKU-902

The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supported” based on data collected in 1998 as part of the DNR/SHL stream biological sampling project. The 1998 FIBI scores were 20, 24 (both poor) and 32, 37 (both fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 33. This segment passed the FIBI BIC 1/4 times in 1998 (19 years ago). Even though this site failed to meet the FIBI 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 monitoring data are now greater than 10 years old. As water quality data age, they become less able to represent current water quality conditions. According to DNR’s assessment/listing methodology, waterbodies with assessments based on data older than ten years will be considered “not assessed” unless the previous assessment indicated impairment of the assessed use. Because the presumptive Class B(WW1) aquatic life uses of this assessment segment have been assessed as Section 303(d)-impaired (IR Category 5), the impairment of the presumptive aquatic life uses will remain in IR Category 5b-t.

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.