Assessment Comments

Assessment is based on: (1) results of bacterial monitoring from April 2008 to November 2010 at two IDNR/UHL stations monitored as part of the Cedar River/Mitchell County project (at Mitchell, 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 monitoring by the Minnesota Pollution Control Agency (MPCA) three miles south of Austin, MN, (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001, 2005, 2007, 2008, and 2009, (5) 2006 IDNR/UHL stream REMAP biological sampling at two sites: near St. Ansgar and near Osage, and (6) results of IDNR Fisheries Bureau surveys for smallmouth bass at two sites in 2008.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria (E.  coli) at two monitoring stations in Mitchell County.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "not supported" based on results of the 1998-99 statewide survey of freshwater mussels.   The fish consumption uses were assessed (monitored) as "partially supporting" 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/UHL stations monitored from April 2008 to November 2010 as part of the Cedar River/Mitchell County project (at Mitchell, STORET No.   15660003; 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 monitoring by the Minnesota Pollution Control Agency (MPCA) three miles south of Austin, MN, (4) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001, 2005, 2007, 2008, and 2009, (5) 2006 IDNR/UHL stream REMAP biological sampling at two sites: near St.   Ansgar and near Osage, and (6) results of IDNR Fisheries Bureau surveys for smallmouth bass at two sites in 2008.  

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).   Because, however, the impairments due to (1) the decline of the freshwater mussel community in this river segment and (2) the existence of the mercury-related fish consumption advisory were not covered by this TMDL, this segment of the Cedar River remains in Category 5 (impaired and TMDL required) of Iowa's Integrated Report (the fish consumption impairment is in IR Category 5a; the aquatic life use impairment due to decline of the freshwater mussel community is in IR Category 5b).    

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not 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 19 samples collected during the recreational seasons of 2008 through 2010 at the Mitchell and State Line stations were as follows:  the 2008 geometric mean was 312 orgs/100 ml, the 2009 geometric mean was 111 orgs/100 ml and the 2010 geometric mean was 135 orgs/100 ml.   The 2008 and 2010 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Six of the 19 samples (33%) 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" (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.”  The results from the Mitchell County stations confirm the previously-identified impairment based on data for fecal coliform bacteria collected at the Minnesota Pollution Control Agency's fixed monitoring station approximately three miles north of the Iowa/Minnesota state line.   Despite the bacterial impairment, levels in this segment of the Cedar River continue to be relatively low, and the geometric mean levels of E.  coli do not suggest major sources of bacterial inputs.

The Class B(WW1) uses remain assessed (evaluated) as "not supported" based on information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al.   (2000).   [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.]  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 Iowa DNR Water Quality Bureau 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 one sample site in this stream segment was 12 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%.   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.   Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   Despite this change in assessment type, this waterbody remains in IR Category 5b.  

However, contrary to the late 1990s freshwater mussel findings, the 2006 IDNR/UHL stream REMAP biological sampling at two sites 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/UHL 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 1994-2004.   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 area (675 & 862 mi2) above the sampling sites was 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.  

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”.    This segment had multiple samples collected in the previous five years; however, the samples were not collected in multiple years.  

Results of ambient water quality monitoring from March 2006 through July 2008 at the two Cedar River/Mitchell County project sites (Mitchell 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 2008 through November 2010 show no violations of water quality criteria in the approximately 25 samples analyzed for dissolved oxygen and pH; none of the 13 samples analyzed for ammonia-nitrogen violated chronic criteria to protect Class B(WW1) uses.   Due to the impact to the freshwater mussel community, however, the Class B(WW1) aquatic life uses of this segment will remain assessed as “not supported” and will remain in Category 5b of Iowa’s Integrated Report.  

Fish consumption uses were 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" for the 2012 assessment/listing cycle.   Additional follow-up monitoring will be conducted to determine if the levels of mercury in walleye are also below advisory trigger levels.