Assessment Comments
Assessment remains based on: (1) IDNR/UHL monthly monitoring conducted from March to November 2001, near the mouth of Buffalo Creek at Anamosa (Site 11; STORET station 11530001) in support of TMDL development for this stream reach, (2) results of sampling at four sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), and (3) IDNR/UHL biological monitoring in August 2001 conducted as part of the stream biocriteria project.
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, 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 uses (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(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams. This impairment was inadvertently omitted from Section 305(b) assessments for this segment from 2002 through 2006. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach. The sources of data for this assessment include the results of (1) IDNR/UHL monthly monitoring conducted from March to November 2001, near the mouth of Buffalo Creek at Anamosa (Site 11; STORET station 11530001) in support of TMDL development for this stream reach, (2) results of sampling at four sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), and (3) IDNR/UHL biological monitoring in August 2001 conducted as part of the stream biocriteria project.
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 was 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 four sample sites in this stream segment were 7, 5, 3, and 4 in the 1984-85 period and were 1, 4, 1, and 0, respectively, in the 1998-99 period for an average percent change of -68%. According to IDNR’s assessment/listing methodology, these results 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 is 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 biological monitoring suggest “full support” of the Class B(WW1) aquatic life uses. Results of TMDL-related chemical monitoring conducted at TMDL Site 11 (STORET station 11530001) 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.
Results of biological monitoring of fish and aquatic macroinvertebrates also suggest “full support of the Class B(WW1) uses. Biological assessment data were collected in 2001 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 score was 68 (good) and the BMIBI score was 54 (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 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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2006-2010. Additionally, 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).
Thus, despite the indications of good water quality based on TMDL monitoring and biocriteria monitoring in 2001, the Class B(WW1) uses are assessed (evaluated) as impaired based on the decline in freshwater mussel diversity in this stream segment.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream reach.
