Unnamed Tributary to Mississippi River IA 01-NEM-6333

Even though this segment is designated for Class B(WW1) aquatic life uses, the sampling data strongly suggest that this is a coldwater stream. Below are both the coldwater and warmwater assessments, DNR is using the coldwater assessment for this IR cycle.

Coldwater assessment:

The assessment of the aquatic life uses was based on data collected in 2011 and 2016 as part of the DNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2011 CBI score was 81 and the 2016 CBI score was 74. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 2/2 times in the last six years.This aquatic life assessment is considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR requires a segment have two or more biological samples collected from the segment in multiple years in a five-year period to be considered “monitored”. This segment had multiple samples collected in the last six years.

An updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 also suggests that the aquatic life uses should be assessed as "fully supported". According to the updated summary, UNT to Mississippi River (Lansing WMA) is in the group of Iowa coldwater streams that support natural reproduction of trout. Based on results of surveys by the DNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit consistent natural reproduction and maintain wild populations of Brook and Brown Trout without any stocking (Category I stream).

Warmwater assessment:

The (evaluated) assessment of the presumptive Class B(WW1) aquatic life uses is based on data collected in 2011 and 2016 as part of the DNR/SHL headwater stream sampling project. 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 2011 FIBI score was 29 (fair) and the BMIBI score was 84 (excellent). The 2016 FIBI score was 27 (fair) and the BMIBI score was 88 (excellent). 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 FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. Even though this site failed the FIBI BIC (0/2) and passed the BMIBI BIC (2/2) in the last six years, 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.

This assessment 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 will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.