Assessment Comments

Assessment is based on results of (1) IDNR ambient monthly monitoring at Cedar Bluff from 2000-02, (2) statewide survey of freshwater mussels in 1998-99, and (3) U.S. EPA/IDNR fish contaminant monitoring near Cedar Rapids in 2002.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses remain assessed (monitored) as "partially supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW) aquatic life uses are assessed (monitored) as "not supported" based on results of a 1998-99 statewide survey of freshwater mussels.   Fish consumption uses are assessed  as “fully supported” based on results of fish contaminant monitoring downstream from Cedar Rapids in 2002.   The sources of data for this assessment are (1) the results of monthly monitoring from 2000 through 2002 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 2002.  

EXPLANATION: The Class A uses were assessed as "partially supported" based on results of monitoring for indicator bacteria (fecal coliforms).   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  Nineteen of the 21 samples collected from the Cedar Bluff station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 19 non-runoff-affected samples (146 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml.   However, five of the 19 samples (26%) exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% or less of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are only "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

Results of monitoring from the IDNR ambient station near Cedar Bluff in 2000, 2001, and 2002, however, suggest "full support" of these uses.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for pesticides in the nine samples analyzed during this biennial period.   Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units.   Three of the 36 samples had pH values greater than 9.0 units, with a maximum value of 9.3 units.   All violations occurred on days when dissolved oxygen levels were well above 100% saturation: April 6, 2000 (pH=9.3; DO saturation>140%), May 3, 2000, (pH=9.2; DO saturation>140%); November 1, 2000 (pH=9.2; DO saturation>140%) [no samples violated the pH criteria during 2001 and 2002].   These conditions suggest that high levels of primary productivity resulted in the high levels of pH.   Because these violations are more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.  

Despite the results of ambient water quality monitoring that suggest "full support" of the Class B(WW) 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 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.   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.   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.  

Fish consumption uses were assessed as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids at Palisades Park in 2002.   The composite samples of fillets from channel catfish and freshwater drum had very low levels of contaminants.   Neither sample contained levels of contaminants that approached even one-half the respective FDA action levels or IDNR levels of concern.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.259 ppm; total PCBs: 0.143 ppm; and technical chlordane: 0.034 ppm.   Levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.085 ppm; total PCBs: 0.164 ppm; and technical chlordane: 0.032 ppm.