Cedar River IA 02-CED-451

[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 moved 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), the impairment of the Class B(WW1) uses remains in IR Category 5b.]

The Class A1 uses are assessed as "partially supported" based on results of monitoring for indicator bacteria (E. coli).  The geometric mean level of indicator bacteria (E. coli) in the 23 samples collected during the recreation seasons of 2012 through 2014 are as follow:  the 2012 geometric mean was 56 orgs/100 ml, the 2013 geometric mean was 48 orgs/100 ml, and the 2014 geometric mean was 131 orgs/100 ml.  Only the 2014 geometric mean exceeded—and then only very slightly—the Class A1 geometric mean criterion of 126 orgs/100 ml.  Three of the 23 samples (13%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  Only the 2014 geometric mean suggests impairment of the Class A1 uses.  These monitoring results indicate exceptionally low levels of indicator bacteria in this segment of the Cedar River.  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 should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b).  Thus, the Class A1 uses are assessed as “partially supported”. 

Results of monitoring from the IDNR/SHL ambient station downstream from Cedar Rapids from 2012 through 2014 suggest "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, ammonia-nitrogen, or chloride/sulfate in the approximately 35 samples collected.  During the assessment period, one of 34 samples (3%) contained a level of pH that violated the Class B(WW1) criterion of 9.0 pH 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. 

In contrast to the water quality data, the biological data collected from this segment in 2012, 2013 and 2014 suggested "partial support" of the Class B(WW1) aquatic life uses.  This evaluated biological assessment was based on data collected in 2012, 2013 and 2014 as part of the IDNR/SHL stream nutrient sampling project.  A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data.  The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach.  The biological metrics were combined a benthic macroinvertebrate index (BMIBI).  The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2012-2014  BMIBI scores were 36, 45, 52 (all fair).  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.  The BMIBI BIC for this ecoregion is 51.  This assessment is considered evaluated because the drainage area (6955 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.  Even though this site failed the BMIBI BIC (1/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. 

Despite the results of ambient water quality 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 IDNR 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 IDNR’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 ten 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 (evaluated) 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.