Assessment Comments

Assessment is based on (1) the statewide assessment of freshwater mussels in Iowa from 1998-99 (see Arbuckle et al. 2000),(2) IDNR/UHL stream REMAP biological sampling in 2006, and (3) results of mussel surveys by IDNR staff in 2012.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses remain “not assessed” due to the lack of monitoring information upon which to base an assessment.   The previous impairment of Class B(WW1) aquatic life uses due to declines in the freshwater mussel community of this segment is de-listed based on results of new (2012) mussel surveys.   Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.   The sources of data for this assessment remain (1) the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al.  (2000), (2) the 2006 IDNR/UHL stream REMAP biological sampling, and (3) results of mussel surveys by IDNR staff in 2012.

EXPLANATION:  The Class A1 uses remain “not assessed” due to the lack of water quality information upon which to base an assessment.  

Results of IDNR surveys of freshwater mussels at two sites in this assessment segment suggest the biological impairment of the Class B(WW1) aquatic life uses based on the apparent decline of freshwater mussels no longer exists.   The following is a summary of these surveys:

--Number of freshwater mussel species from surveys conducted in 1984 (Frest (1987), in 1998 (Arbuckle et al.  2000), and IDNR Watershed Improvement Section staff (J.  Kurth) in 2012:

               1984           1998               2012
Site   9:     6                  0                     9
Site 19:     3                  3                     7

The original impairment was based on a comparison of sampling results from 1998 and 1999 (Arbuckle et al.  2000) to results from stream sites surveyed in 1984 and 1985 by Frest (1987).  Impairment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey.  Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggested an impairment of the aquatic life uses.  Based on IDNR’s assessment approach, the degree of decline (>75%) in the number of freshwater mussel species in this segment suggested “non support” (impairment) of the Class B(WW) aquatic life uses for purposes of both Section 303(d) listing and 303(d) reporting.  Results of the IDNR's surveys in 2012, however, show recovery in the number of freshwater mussel species at the sites used to identify the original impairment (Sites 9 and 19), with more species found at both sites in 2012 than were found in 1984.  Due to the lack of a protocol for identifying biological thresholds that indicate "full support" of a freshwater mussel community, this impairment is moved from Category 5b of Iowa's Integrated Report to IR Category 3a (insufficient information to develop an assessment of support of uses).  

Results of sampling for fish and benthic macroinvertebrate communities in this river segment suggest "full support" of the Class B(WW1) aquatic life uses and are consistent with the removal of the mussel-related biological impairment.   This sampling was conducted in 2006 as part of the DNR/UHL stream REMAP project.   A series of biological metrics that 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 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 2006 FIBI score was 66 (good) and the BMIBI score was 68 (good).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 riffle/non-riffle habitat FIBI BICs for this ecoregion are 65/44 and the BMIBI BIC for this ecoregion is 52.   It is unknown at this time if this site has stable riffle habitat; however, this site passed the higher FIBI BIC.   This assessment is considered evaluated because the drainage area (553 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.  

Fish consumption uses remain not assessed due to the lack of fish contaminant monitoring information for this river reach.