Assessment Comments

Assessment is based on: (1) results of bacterial monitoring from April 2010 to November 2012 at two IDNR/SHL stations monitored as part of the Cedar River/Mitchell County project (at Halvorson Park, STORET No. 15660004 and at IA/MN state line, STORET No. 15660010); (2) results of an IDNR mussel survey in July 2012, (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001, 2005, 2007, 2008, and 2009, and (5) 2006 IDNR/SHL stream REMAP biological sampling at two sites: near St. Ansgar and near Osage.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 4a) based on levels of indicator bacteria (E.  coli) that slightly exceed Class A1 criteria.   The Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supported" (IR 2a) based on results of the IDNR/SHL biological monitoring in 2006; the previous biological impairment due to declines in the freshwater mussel community is delisted due to new information that shows recovery of the mussel community in this segment.   The fish consumption uses remain assessed (monitored) as "partially supporting" (IR 5a) based on results of fish contaminant monitoring in 2001, 2005, 2007 and 2008 and the issuance of a "one meal per week" fish consumption advisory in 2006.   Sources of information for this assessment include (1) results of monitoring from two IDNR/SHL stations monitored from April 2010 to November 2012 as part of the Cedar River/Mitchell County project (at Halvorson Park (STORET No.  15660003) and at IA/MN state line (STORET No.  15660010); (2) results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al.  2000), (3) results of an IDNR mussel survey in July 2012, (4) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001, 2005, 2007, 2008, and 2009, and (5) 2006 IDNR/SHL stream REMAP biological sampling at two sites: near St.  Ansgar and near Osage.  

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 moves 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).  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E.  coli) at two stations in the Cedar River/Mitchell County project.   The geometric means of indicator bacteria (E.  coli) in the 20 samples collected during the recreational seasons of 2010 through 2012 at the State Line station were as follows:  the 2010 geometric mean was 89 orgs/100 ml, the 2011 geometric mean was 133 orgs/100 ml and the 2012 geometric mean was 84 orgs/100 ml.   The geometric mean of the six samples collected at the Halvorson Park station from May to November 2012 was 28 orgs/100 ml.   Of all these geometric means, only the 2011 geometric mean from the State Line station exceeded—and then only very slightly—the Class A1 criterion of 126 orgs/100 ml.   Three of the 20 samples (15%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml at the State Line station; none of the six samples from the Halvorson Park station exceeded the single-sample maximum criterion.   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 bacterial impairment, levels in this segment of the Cedar River continue to be very low:  the only data point that suggests bacterial impairment during the 2010-2012 period is the very slight exceedance of the Class A1 geometric mean at the State Line station in 2011.   The geometric mean levels of E.  coli do not suggest major sources of bacterial inputs.

Results of IDNR surveys of freshwater mussels at one site in this assessment segment suggest that the biological impairment based on the apparent decline of freshwater mussels no longer exists.  The original 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 (100%) in the number of freshwater mussel species in this segment 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 2012, however, show recovery in the number of freshwater mussel species at the site used to identify the original impairment.  Twelve species were found in this segment in 1984 with eight species found in July 2012.  Because more than 50 percent of the species present in 1984 were found in the 2012 survey, this impairment is moved from Category 5b of Iowa's Integrated Report to IR Category 3a (insufficient information to develop an assessment of support of uses).  

The 2006 IDNR/SHL stream REMAP biological sampling at two sites also suggested (evaluated) "full support" of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2006 as part of the IDNR/SHL stream REMAP project.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2006 FIBI scores were 46 (fair) and 74 (excellent) and the BMIBI scores were 76 (excellent), 75 (good).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The non-riffle habitat FIBI BIC for this ecoregion is 44 and the natural substrate BMIBI BIC for this ecoregion is 70.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 2/2 times in the last five years.   This assessment is considered evaluated because the drainage areas (675 & 862 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed both the FIBI and BMIBI BICs, 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.  

Results of ambient water quality monitoring from April 2011 through November 2012 at the two Cedar River/Mitchell County project sites (Halvorson Park and State Line) also suggest good chemical water quality and “full support” of the Class B(WW1) aquatic life uses.   Results of this monitoring from April 2011 through November 2012 show no violations of water quality criteria in the approximately 20 samples analyzed for dissolved oxygen and ammonia.   One of the combined 22 samples (3%) from these two monitoring station violated the Class B(WW1) criteria for pH (9.0 pH units) and water temperature (32C).   Both violations occurred at the State Line station with a pH of 9.2 units recorded on September 19, 2012, and a water temperature of 33C recorded at 11:15 AM on June 19, 2012.   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 pH and temperature, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, however, the results from the State Line and Halvorson Park monitoring stations do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criteria for pH or temperature.   Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.  

Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001, 2005, 2007, 2008, and 2009.   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 level of mercury in the composite sample of smallmouth bass fillets (0.305 ppm) from the 2001 RAFT sampling slightly exceeded the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory (this levels is well below the “do not eat” trigger level for mercury of 1.0 ppm).   According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified.   Because the level of mercury in composite sample of walleye fillets from the 2005 sampling (0.33 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory is justified.   This advisory was issued by IDNR and IDPH in January 2006 and covers the reach of the Cedar River from the Highway 218 bridge at Floyd, IA upriver to the Iowa/Minnesota state line.   According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “partially supported.”  

Follow-up sampling was conducted in 2007, 2008, and 2009 to better assess the amount of mercury in fish in this river segment.   The composite samples of smallmouth bass fillets in 2007 and 2008 had low levels of mercury (2007: 0.219 ppm, 2008: 0.19 ppm).   These levels are below the advisory trigger level (0.30 ppm).   Based on IDNR's assessment methodology two consecutive samples with levels below the advisory trigger level are necessary to suggest "full support" of the fish consumption uses.   While this is the case for this segment of the Cedar River, there were no samples of walleye collected, therefore it is not known if levels of mercury in walleye are also below the advisory trigger level.   The composite samples of smallmouth bass fillets in 2009 had a level of mercury (0.351 ppm) that again exceeded the advisory trigger level.   Therefore the fish consumption advisory will remain and the fish consumption uses will remain assessed as "partially supported".   Additional follow-up monitoring will be conducted to determine if the levels of mercury in walleye are also below advisory trigger levels.