Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2006 through December 2008 at the IDNR ambient city monitoring station located downstream from Iowa City at the county road F62 bridge east of Hills, IA (station 10520003), results of USGS monitoring from January 2006 through June 2008 at Iowa City (station 05454500), (3) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (4) results of a fish kill investigation in March 2007, and (5) results of EPA/IDNR fish tissue (RAFT) monitoring at Iowa City in 2007 and 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria. This assessment represents a change from the “fully supporting” assessment developed for the 2008 listing cycle. The Class B(WW1) aquatic life uses remain assessed (evaluated/impaired) as "partially supported" based on results of a statewide survey of freshwater mussels in 1998-99. The fish consumption uses remain assessed as "fully supported" based on results of fish contaminant monitoring in 2003, 2007, and 2008. The sources of data for this assessment are (1) the results of monthly monitoring from January 2006 through December 2008 at the IDNR ambient city monitoring station located downstream from Iowa City at the county road F62 bridge east of Hills, IA (station 10520003), (2) results of ambient water quality monitoring by USGS at Iowa City (station 05454500) from December 2006 through June 2008, (3) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (4) results of a fish kill investigation in March 2007, and (5) results of EPA/IDNR fish tissue (RAFT) monitoring at Iowa City in 2007 and 2008.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 22 samples collected at the IDNR/UHL station downstream from Iowa City during recreational seasons of 2006 through 2008 (145 orgs/100ml) slightly exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml. Six of the 22 samples (27%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. 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 "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).. Despite this impairment, assessments developed for this segment for recent Section 305(b) cycles demonstrate that levels of bacteria in this segment of the Iowa River are low relative to other Iowa rivers and are probably not significantly different than the Class A1 criterion of 126 orgs/100 ml. Although bacterial impairments have been identified in past Section 305(b) cycles based on the percentage of samples exceeding single sample maximum criteria, geometric mean levels of indicator bacteria have typically been below the applicable Class A1 criterion since routine ambient monitoring began in this segment in 2000. As noted in the assessment narrative for this river segment developed for the 2008 cycle, additional changes from “full support” to “impaired” (and back again) can be expected in future assessment/listing cycles.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of the statewide survey of freshwater mussels (see below). Results of monitoring from the IDNR ambient station downstream from Iowa City from 2006 through 2008, however, continue to suggest full support of the Class B(WW1) uses: none of the approximately 35 samples analyzed for dissolved oxygen, pH, or ammonia-nitrogen, and none of the five samples analyzed for toxic metals showed violations of the respective Class B(WW1) criteria. Similarly, none of the approximately 15 samples from the USGS station at Iowa City during the 2006-2008 period showed violations of Class B(WW1) criteria for dissolved oxygen or pH, and none of the 14 samples from this station analyzed for pesticides exceeded their respective Class B(WW1) criteria.
Despite results of IDNR/UHL and USGS ambient water quality monitoring that suggest “full support” of aquatic life uses, results of the 1998-99 statewide survey of freshwater mussels suggest a potential impairment to these uses. [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.] 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. 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. Species richness of freshwater mussels at the 9 sample sites in this stream segment were 22, 10, 9, 18, 6, 16, and 6 in the 1984-85 period and were 10, 3, 2, 8, 6, 8, and 4, respectively, in the 1998-99 period for an average percent change of approximately minus 50%. [Note: mussel species richness numbers for the sample sites in this river segment were revised in December 2009 based on an IDNR review of Iowa FW mussel data. The revisions to the species richness numbers for this segment, however, did not affect the assessment decision regarding support of the Class B(WW1) aquatic life uses.] Despite the moderate diversity of freshwater mussels found in this river segment during the 1998-99 survey, the nearly 50% decline in species richness suggest a significant modification of this aquatic community in the short timeframe of less than 15 years. Based on these results, and based on IDNR’s assessment methodology, the “full support” of aquatic life uses suggested by results of IDNR/UHL ambient monitoring is downgraded to "partial support." Because results of chemical/physical monitoring suggest good water quality in this river segment, the impairment of aquatic life uses suggested by the apparent decline of freshwater mussels is likely related to problems with the quality of aquatic habitat as opposed to poor chemical/physical water quality. 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 as well as the site-specific causes and sources of impairments of these uses that may exist.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at the Iowa River in 2007 and 2008. The composite samples of fillets from channel catfish from the 2007 sampling had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.058 ppm; total PCBs: 0.125 ppm; and technical chlordane: 0.045 ppm. The composite samples of fillets from common carp and white bass from the 2008 sampling had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of white bass fillets were as follows: mercury: 0.218 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 2007 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.
This river segment has a history of relatively high levels of chlordane, and RAFT follow-up monitoring has thus been conducted on an every-other-year basis since 1994 (see assessments for the 1994 through 2008 reports). The level of chlordane in the sample of channel catfish fillets collected in 2001 was 0.049 mg/kg; this level was much lower than chlordane levels in previous samples (1997: 0.17 mg/kg; 1999: 0.16 mg/kg). The level of chlordane in the sample of channel catfish fillets collected in 2003 was 0.10 mg/kg. The results form 2001 and 2003, as well as the results from 2007 and 2008 suggest that levels of chlordane have decreased in these fish.
