Assessment Comments
Assessment remains based on the results of (1) IDNR/UHL monthly ambient water quality monitoring in 2001, (2) results of sampling at three sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), and (3) results of IDNR/UHL biological (biocriteria) monitoring in 2001 and 2008: FIBI = 77, 73 (excellent), 67 (good); BMIBI = 71, 69, 57 (good).
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW-1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of a statewide assessment of freshwater mussels. Results of biological monitoring in 2001 and 2008, however, suggest "full support" of the Class B(WW-1) uses. Also, results of ambient water quality monitoring in 2001 did not show violations of state water quality standards. Fish consumption uses remain "not assessed." The sources of data for this assessment include (1) IDNR/UHL monthly ambient water quality monitoring in 2001, (2) results of sampling at three sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), and (3) results of IDNR/UHL biological (biocriteria) monitoring in 2001 and 2008.
EXPLANATION: The Class A1 uses remain “not assessed” due to the lack of water quality information upon which to base an assessment.
Note: The Class B(WW1) aquatic life uses for this assessment segment were assessed as “fully supported” for the 2006 assessment cycle based on results of IDNR/UHL biological monitoring in 2001. This assessment, however, was incorrect: the assessment failed to include data from the 1998-99 statewide assessment of freshwater mussels (Arbuckle et al. 2000). The inclusion of these data suggests an impairment of the Class B(WW1) aquatic life uses of this stream segment.
Arbuckle et al. 2000 compared results from their 1998-99 statewide mussel survey to results from stream sites surveyed in 1984 and 1985 by Frest (1987). In general, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s streams and rivers from the mid-1980s to the late 1990s. Results of this comparison were used by staff of the Iowa DNR 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 period to the 1998-99 period was identified by Iowa DNR as indicating an impairment of the aquatic life uses.
Species richness of freshwater mussels at the three sample sites in this stream segment were 9, 12, and 13 in the 1984-85 period and were 0, 12, and 6, respectively, in the 1998-99 period for an average percent change of -51%. According to IDNR’s assessment/listing methodology, these results—despite the continued high mussel diversity at one of the three sites—suggest only “partial support” of the Class B(WW1) aquatic life uses. Thus, the “full support” of aquatic life uses reported for the 2006 assessment cycle was downgraded to "partial support."
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. (Note: because the data from Arbuckle et al. (2000) are now older than five years, the assessment category is considered “evaluated” (i.e., of lower confidence) as opposed to “monitored” (i.e., a higher confidence assessment). Nonetheless, these data were used by IDNR to make “monitored” (higher confidence) assessments for other stream/river segments for the 2002 through 2006 assessment cycles; only as the data have aged beyond five years has the assessment type been changed to “evaluated.” Despite this change in assessment category, the impairment indicated by these data is appropriate for placement in IR Category 5 (i.e., Section 303(d) list)
Despite the impairment suggested by the results of freshwater mussel surveys, results of IDNR/UHL chemical/physical monitoring and other biological monitoring suggested “full support” of the Class B(WW1) aquatic life uses. Results of TMDL-related chemical monitoring conducted at TMDL Site 13 (STORET station 11570002) from March to November 2001 showed no violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the nine samples collected. These samples were not analyzed for toxic metals or toxic organic compounds. The available data do, however suggest good water quality, including relatively low levels of ammonia-nitrogen.
Despite the biological impairment suggested by surveys of freshwater mussels, results of biological monitoring of fish and aquatic macroivertebrates suggested “full support” of the Class B(WW1) uses. This assessment was based on data collected in 2001 and 2008 as part of the IDNR/UHL stream biocriteria 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 2001 FIBI scores were 73 (excellent) and 67 (good), and the BMIBI scores were 71 (good) and 57 (good). The 2008 FIBI score was 77 (excellent) and the BMIBI score was 69 (good). The aquatic life use support was assessed (evaluated) as fully supported (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 44 and the natural/artificial substrate BMIBI BIC for this ecoregion is 70/52. At one of the sites, artificial substrates were used and that BMIBI score (57) was compared to the artificial substrate BMIBI BIC (52). At the other two sites, a Hess sampler was used and the BMIBI scores (71 and 69) were compared to the the natural substrate BMIBI BIC (70). This segment passed the FIBI BIC 3/3 times and passed the BMIBI BICs 2/3 times in the last eight years.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous eight years (2001-2008); however, the multiple samples were not collected during 2004-2008. Despite this change in assessment methodology and type, this aquatic life use assessment based on the biological data remains "fully supporting".
The fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this stream reach.
