Assessment Comments
Assessment remains based on results of (1) 2004 IDNR/UHL REMAP monitoring [(FIBI = 46, 55 (good); BMIBI = 69 (good), 77, 86 (excellent)], (2) ISU statewide survey of freshwater mussels in 1998-99 and (3) EPA/IDNR fish contaminant monitoring in 2003.
The non-riffle habitat FIBI BIC = 44, the artificial substrate BMIBI BIC = 52 and the natural substrate BMIBI BIC = 70.
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 completion and approval 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(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on a decline in the freshwater mussel community of this river segment. Sources of data for this assessment include (1) results of IDNR/UHL REMAP biological monitoring in 2004 and (2) results of the 1998-99 statewide assessment of freshwater mussels in Iowa streams by Arbuckle et al. (2000). Fish consumption uses are assessed (monitored) as “fully supported” based on results of fish contaminant monitoring in 2003 conducted as part of the U.S. EPA/IDNR (RAFT) fish tissue monitoring program.
EXPLANATION: Results from the IDNR/UHL REMAP sampling in 2004 suggest that the Class B(WW1) uses should be assessed (monitored) as "fully supported." This assessment is based on data collected in 2004 as part of the IDNR/UHL stream REMAP project. The 2004 REMAP FIBI scores were 46 (fair), 55 (good); and BMIBI scores were 86 (excellent), 77 (excellent), and 70 (good). The aquatic life use support assessment was assessed 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 non-riffle habitat FIBI BIC for this ecoregion is 44 and the natural substrate BMIBI BIC for this ecoregion is 70. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BICs (2x natural and once artificial) 3/3 times in 2004. For the 2006 assessment, this segment was assumed to contain stable riffle habitat based on best professional judgment and anecdotal data. However, quantitative habitat data from the 2004 REMAP sampling was discovered and analyzed. After comparing the results of the quantitative habitat data analysis to the riffle habitat requirements, it was determined that the sample site should be classified as "non-riffle" instead of "riffle".
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 five years (2004-2008); however, the samples were not collected in multiple years. Despite this change in assessment methodology and type, this waterbody remains in IR Category 5b based on the results of the mussel sampling (see below).
In contrast to the REMAP biological sampling results, the results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams suggest a potential impairment to the aquatic life uses of this stream segment and are consistent with the assessment based on biological monitoring in 2004. 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). In general, this comparison showed sharp declines in the numbers of mussel species ("species richness") from the mid-1980s to the late 1990s. For purposes of Section 305(b) reporting, 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. This assessment included the following factors: (1) the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey and (2) the number of mussel species found in the 1998-99 survey. Greater than a 50% decline in species richness from the 1984-84 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 segment of the Wapsipinicon River were 10 and 9 in the 1984-85 period and were 2 and 6, respectively, in the 1998-99 period for a percent change of -56%. These results suggest that the Class B(WW1) aquatic life uses are "partially 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 instream 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. Because these FW mussel 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.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Twin Ponds Park in 2003. The composite samples of fillets from channel catfish and walleye had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.142 ppm; total PCBs: 0.094 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.095 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the sample collected from this assessment segment as part of the 2003 RAFT do not exceed any of Iowa’s advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
