Assessment Comments

Assessment remains based on: (1) the results of monthly monitoring from 2004 through 2006 at the IDNR ambient station located at the County Road F28 bridge near Cedar Bluff (station 10160001), (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999, and (3) results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids in 2005 and 2008.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "not supported" based on results of a 1998-99 statewide survey of freshwater mussels.   Fish consumption uses remain assessed (monitored) as “fully supported” based on results of fish contaminant monitoring downstream from Cedar Rapids in 2005 and 2008.   The sources of data for this assessment are (1) the results of monthly monitoring from 2004 through 2006 at the IDNR ambient station located at the County Road F28 bridge near Cedar Bluff (station 10160001), (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999, and (3) results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids in 2005 and 2008.   Note:  routine ambient monitoring at IDNR station 10160001 was terminated in 2006.

Note:  A TMDL for indicator bacteria in this segment of Cedar River was prepared and approved by EPA in February 2010.   The approval of this TMDL moves the bacterial impairment for this segment from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).   Because, however, this TMDL does not cover all the impairments identified for this assessment segment (biological:  freshwater mussel decline), this assessment segment remains in IR Category 5.

EXPLANATION:  The Class A1 uses remain assessed as "not supported" based on results of monitoring for indicator bacteria (E.  coli).   The geometric mean level of indicator bacteria (E.  coli) in the 21 samples collected (158 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Eleven of the 21 samples (52%) also exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   Note:  routine ambient monitoring at IDNR station 10160001 was terminated in 2006.  

Results of monitoring from the IDNR/UHL ambient station near Cedar Bluff from 2004 through 2006 suggested "full support" of the Class B(WW1) aquatic life uses.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 31 samples collected or for pesticides and toxic metals in the ten samples analyzed during this biennial period.   During the assessment period, levels of pH occasionally violated the Class B(WW1) criterion of 9.0 pH units:  two of the 31 samples (6%) had pH values greater than 9.0 units, with a maximum value of 9.2 units.   According to U.S.  EPA assessment guidelines, if less than 10% of samples exceed state criteria for pH, the primary contact (Class A) and aquatic life (Class B) uses should be assessed as fully supported (see pgs 3-17 of U.S.  EPA 1997b).   Violations of pH in ambient waters tend to reflect high levels of primary productivity and do not typically reflect the addition of pollutants to surface waters.  

Despite the results of ambient water quality monitoring that suggest "full support" of the Class B(WW1) uses, 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.   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 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 to the 1998-99 period suggests an impairment of the aquatic life uses.   Species richness of freshwater mussels at the five sample site in this river segment were 4, 5, 5, 9, and 5 in the 1984-85 period and were 0, 0, 0, 2, and 0, respectively, in the 1998-99 period for an average percent change of minus 92%.   Based on these results, the full support of aquatic life uses suggested by results of IDNR ambient water quality monitoring is downgraded to "not supporting."  The confidence level of this assessment is relatively high; thus the assessment type is considered “monitored” in the context of Section 305(b) reporting.   According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on a “monitored” assessment are candidates for Section 303(d) listing.   (Note:  because the data from Arbuckle et al.   (2000) are now older than five years, the assessment category is changed from a “monitored” (i.e., a higher confidence assessment) to “evaluated” (i.e., lower confidence assessment).   Despite this change in assessment category, the impairment indicated by these data remains in IR Category 5 (i.e., Section 303(d) list) until more recent data suggest a good cause for de-listing.)  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.  

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids at Palisades Park in 2005 and 2008.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   Results of RAFT monitoring in 2002 indicated elevated levels of mercury in the composite sample of channel catfish fillets.   This suggested a need for additional monitoring to better define contaminant levels in fish from this river segment.   Follow-up samples of channel catfish fillets were collected in 2005.   This 2005 RAFT sampling showed low levels of mercury in the composite sample of channel catfish fillets (0.0731 ppm).   This indicated that mercury levels were much lower in these fillets and therefore a consumption advisory was not justified.  

Additional monitoring in 2008 also showed low levels of primary contaminants and suggested that the fish consumption uses be assessed as "fully supported."  Levels of primary contaminants in the composite sample of common carp fillets were as follows: total PCBs: 0.132 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of white bass fillets were as follows: mercury: 0.132 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 fish contaminant data generated from the 2005 and 2008 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.