Assessment Comments

Assessment based on (1) the statewide assessment of freshwater mussels in Iowa from 1998-99 (see Arbuckle et al. 2000) and (2) IDNR/UHL stream REMAP biological sampling in 2006.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are “not assessed” due to the lack of monitoring information upon which to base an assessment.   The Class B(WW1) aquatic life are assessed (evaluated) as "not supported" due to the apparent decimation of freshwater mussel species in this river segment.   Fish consumption uses are “not assessed” due to the lack of fish contaminant monitoring in this river segment.   The sources of data for this assessment are (1) the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al.  (2000) and (2) the 2006 IDNR/UHL stream REMAP biological sampling.  

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

Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams suggest a potential impairment to the Class B(WW1) aquatic life uses of this stream segment.   As part of this study, sampling results from 1998 and 1999 (Arbuckle et al.  2000) were compared to results from stream sites surveyed in 1984 and 1985 by Frest (1987).   On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s rivers and streams from the mid-1980s to the late 1990s.   Results of this comparison were used by staff of the Iowa DNR Water Quality Bureau to assess the degree to which the aquatic life uses of the sampled stream segments are supported.   For purposes of Section 303(d) listing, this assessment 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 suggests an impairment of the aquatic life uses.   In addition, low species richness in the 1998-99 survey suggests potential impairment.   Species richness of freshwater mussels at the two sample sites in this stream segment were 6 and 3 in the 1984-85 period and were 1 and 3, respectively, in the 1998-99 period for an average percent change of 42%.   Based on the decline at the one site from 6 species in the 1984-85 period to 1 species in the 1998-99 period (83% decline), and based on IDNR’s assessment approach, the aquatic life use are assessed as "not supported."  As presented by Arbuckle et al.  (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high in-stream levels of nutrients (phosphorus and nitrogen).   Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness.   Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairments of these uses that may exist.  

Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   Despite this change in assessment type, this waterbody remains in IR Category 5b.

Contrary to the mussel findings in the late 1990s, the fish and benthic macroinvertebrate communities appear to be healthy.   This evaluated biological assessment was based on data collected 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.