Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2010 through December 2012 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 the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (3) results of freshwater mussel surveys in 2011 and 2012, (4) results of a fish kill investigation in March 2007, (5) IDNR/SHL biological sampling conducted in 2012, and (6) 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" (IR 5a) based on results of ambient monitoring for indicator bacteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supporting” (IR 3b-u) based on results of 2012 IDNR/SHL biological sampling. The previous Section 303(d) impairment due to declines in the freshwater mussel community was de-listed for the 2010 IR cycle based on results of recent survey data that show recovery of the mussel community in this river segment. The fish consumption uses remain assessed (monitored) as "fully supported" (IR 2a) 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 2010 through December 2012 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 the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (4) results of seven IDNR surveys for freshwater mussels in 2011 and 2012, (4) results of a fish kill investigation in March 2007, (5) IDNR/SHL biological sampling conducted in 2012, and (6) 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 means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10520003 were as follows: the 2010 geometric mean was 117 orgs/100 ml, the 2011 geometric mean was 132 orgs/100 ml and the 2012 geometric mean was 75 orgs/100 ml. Only the 2011 geometric mean slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Four of the 24 samples (17%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported". Thus, because at least one recreation season geometric mean exceeded the criterion for Class A1 uses, these uses are assessed as “impaired.”
Despite this bacterial 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 for this segment 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.
Results of monitoring from the IDNR ambient station downstream from Iowa City from 2010 through 2012 continue to suggest full support of the Class B(WW1) uses: none of the 36 samples analyzed for dissolved oxygen, temperature, pH, or ammonia-nitrogen, chloride, or sulfate showed violations of the respective Class B(WW1) criteria.
Results of IDNR surveys of freshwater mussels at seven sites in this assessment segment in 2011 and 2012 suggested that the biological impairment based on the apparent decline of freshwater mussels no longer exists; thus, this impairment was delisted for the 2012 IR cycle. The following is a summary of the mussel surveys in this assessment segment:
--Number of freshwater mussel species from surveys conducted in assessment segment IA 02-IOW-0030_1 in 1984 (Frest (1987), in 1998 (Arbuckle et al. 2000), and IDNR Watershed Improvement Section staff (J. Kurth) in 2011-2012:
SITE 1984 1998 2011-12 Percent difference
Site 49 22 10 16 -27
Site 51 10 3 11 +10
Site 52 9 2 5 -44
Site 82 18 8 13 -27
Site 83 6 6 8 +33
Site 84 16 8 13 -19
Site 85 6 4 8 +33
The original aquatic life impairment was based on a comparison of sampling results from 1998 and 1999 (Arbuckle et al. 2000) to results from stream sites surveyed in 1984 and 1985 by Frest (1987). Impairment 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 suggested an impairment of the aquatic life uses. Based on IDNR’s assessment approach, the degree of decline in the number of freshwater mussel species in this segment between 1984 and 1998 (~50%) suggested “partial support” (impairment) of the Class B(WW) aquatic life uses for purposes of both Section 303(d) listing and 303(d) reporting. Results of the IDNR's surveys in 2011 and 2012, however, showed recovery in the number of freshwater mussel species at the seven sites used to identify the original impairment, with more mussel species found at three sites in 2011-2012 than were found in 1984; and all seven sites having more than 50 percent of the respective number of species present during the 1984 survey. Due to the lack of a protocol for identifying biological thresholds that indicate "full support" of a freshwater mussel community, this impairment is moved from Category 5b of Iowa's Integrated Report to IR Category 3a (not assessed: insufficient information to develop an assessment of support of uses).
In contrast to the fresh water mussel data, the aquatic life assessment based on 2012 biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2012 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 BMIBI score was 30 (poor). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI score 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 (3323 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, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
Fish consumption uses remain 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. The level of chlordane in follow-up samples 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 suggested that levels of chlordane had decreased in these fish.
