Assessment Comments

Assessment is based on: (1) results of IDNR ambient monthly monitoring approximately 4 miles southeast of Charles City (STORET station 10340001) from 2010 through 2012, (2) results of IDNR/SHL biological sampling in 2008, 2011 and 2012, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 2003 and 2012.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to violations of Class A1 criteria for indicator bacteria during recreational seasons of 2010 through 2012.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting" (IR 3b-u) based on results of biological monitoring in 2008, 2011 and 2012.   The fish consumption uses are assessed (monitored) as "fully supporting/threatened" (impaired) (IR 5a) based on results of fish contaminant monitoring in 2012 that show an adverse trend of levels of mercury in predator fish.   This is a new impairment for this assessment segment.   The primary sources of data for this assessment are (1) results of IDNR ambient monthly monitoring approximately 4 miles southeast of Charles City (STORET station 10340001) from 2010 through 2012, (2) results of IDNR/SHL benthic macroinvertebrate monitoring in 2008, 2011 and 2012 and (3) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 2003 and 2012.  

Note:  A TMDL for indicator bacteria impairments in eight segments of Cedar River was prepared and approved by EPA in February 2010.   Because the bacterial impairment in this segment (IA 02-CED-0110_1) was not included in the EPA TMDL, this impairment is considered appropriate for Category 5a of Iowa's Integrated Report.  

EXPLANATION:  The Class A1 uses are assessed as "partially 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 10340001 near Charles City were as follows:  the 2010 geometric mean was 163 orgs/100 ml, the 2011 geometric mean was 99 orgs/100 ml and the 2012 geometric mean was 120 orgs/100 ml.   Only the geometric mean for 2010 exceed the Class A1 criterion of 126 orgs/100 ml.   Six of the 24 samples (25%) 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 should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  Despite the recent assessments of the Class A1 uses as impaired, this river segment has a history of relatively low E.  coli levels, and the monitoring results from the current (2010-2012) assessment period, with only one of three geometric means slightly exceeding the Class A1 criterion, are consistent with that history.  

In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the Class B(WW1) aquatic life uses are "partially supporting".   This evaluated biological assessment was based on data collected in 2008, 2011 and 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 2008 BMIBI score was 63 (good), the 2011 BMIBI score was 55 (fair) and the 2012 BMIBI score was 27 (poor).  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 artificial substrate BMIBI BIC for this ecoregion is 52 and the natural substrate BMIBI BIC is 70.   This assessment is considered evaluated because the drainage area (1095 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   The BMIBI scores of 55 and 63 were natural substrate samples and failed the natural substrate BIC of 70.   The 27 score was an artificial substrate score and failed the artificial substrate BIC of 52.   Even though this site failed the BMIBI BIC (0/3), 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).  

Despite results of biological monitoring that suggest impairment of aquatic life uses, results of ambient water quality monitoring from this segment continue to show very few violations of Class B(WW1) water quality criteria and thus suggest good water quality conditions.   Results of IDNR/UHL ambient monitoring SE of Charles City from 2010-2012 show no violations of water quality criteria in the 36 samples analyzed for pH, ammonia-nitrogen, chloride and sulfate.   One of the 36 samples (3%) violated the Class B(WW1) criteria for dissolved oxygen of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, however, the results from station 10340001 do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criteria for dissolved oxygen.   Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.  

Fish consumption uses are assessed (monitored) as “fully supported/threatened” (impaired) based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Midway in 2012.   This monitoring showed an increase in levels of mercury in predator species in this river segment.   In 2003, the composite samples of fillets from channel catfish and smallmouth bass had low levels of contaminants.   Levels of primary contaminants in the 2003 composite sample of channel catfish fillets were as follows: mercury: 0.107 ppm; total PCBs: 0.119 ppm; and technical chlordane: < 0.03 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.124 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm.  

Results of monitoring in 2012, however, showed an increase in levels of mercury in predator fish.   The composite samples of fillets from channel catfish continued to have low levels of contaminants:  mercury: 0.172 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm.   Levels of mercury in tissue plug samples of smallmouth bass, however, were much higher than in the 2003 composite samples of smallmouth bass fillets.   The average level of mercury in the tissue plugs from five smallmouth bass was 0.464 ppm (SD=0.089 ppm; maximum=0.572; minimum=0.344).   The average and minimum levels of mercury were well below Iowa’s “do not eat” advisory threshold of 1.0 ppm but were above Iowa’s threshold for issuance of a one meal per week fish consumption advisory.   According to the IDNR/IDPH advisory protocol, two consecutive samplings showing that contaminant levels are above the advisory threshold level are needed to justify issuance of a consumption advisory.   Additional monitoring of levels of mercury in smallmouth bass will be conducted in 2014 to determine whether a one-meal/week consumption advisory should be issued.   Because, however, levels of mercury in the 2012 sampling of smallmouth bass were well-above the one-meal/week advisory threshold, the fish consumption uses of this segment are assessed as “fully supported/threatened”.   Waters assessed as “threatened” demonstrate an adverse water quality trend such that impairment is anticipated within the next two years.   Waters assessed as “fully supported/threatened” are thus candidates for addition to a states list of Section 303(d) (impaired) waters (IR Category 5).