Assessment Comments

Assessment is based on: (1) results of bacterial monitoring from three IDNR/UHL stations monitored as part of the Cedar River/Mitchell County project (at Mitchell, STORET No. 15660003; at Halvorson Park, STORET No. 15660004 ; at IA/MN state line, STORET No. 15660010); (2) information from the IDNR Fisheries Bureau, (3) results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), (4) results of monitoring by the Minnesota Pollution Control Agency (MPCA) three miles south of Austin, MN, (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001 and 2005, and (6) 2006 IDNR/UHL 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 "not supported" based on levels of indicator bacteria (E.  coli) at three IDNR/UHL 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 and 2005 and issuance of a "one meal per week" fish consumption advisory in 2006.   Sources of information for this assessment include (1) results of bacterial monitoring from three IDNR/UHL stations monitored as part of the Cedar River/Mitchell County project (at Mitchell, STORET No.  15660003; at Halvorson Park, STORET No.  15660004 ; at IA/MN state line, STORET No.  15660010); (2) information from the IDNR Fisheries Bureau, (3) results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al.  2000), (4) results of monitoring by the Minnesota Pollution Control Agency (MPCA) three miles south of Austin, MN, (5) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001 and 2005, and (6) 2006 IDNR/UHL stream REMAP biological sampling at two sites: near St.  Ansgar and near Osage.  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E.  coli) at three stations in the Cedar River/Mitchell County project.   [Note:  due to (1) the general lack of bacterial data for this assessment segment and (2) the historical reliance on fecal coliform data from the Minnesota PCA for this assessment, monitoring data for the Mitchell County stations from 2007 were combined with data from 2006 for this assessment.   Although the data cutoff period for the 2008 assessment/listing cycle is the end of calendar year 2006, the inclusion of the 2007 data is necessary to develop a higher confidence assessment and to confirm the existing Section 303(d) impairment based on the MPCA fecal coliform data.]  

Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) at two of the three Cedar River/Mitchell County stations monitored in 2006 and 2007 exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml:  the geometric mean of the 16 samples at the Halvorson Park station was 143 orgs/100 ml, and the geometric mean of the 15 samples at the IA/MN state line was 226 orgs/100 ml.   The geometric mean at the Mitchell station (94 orgs/100 ml) was below the Class A1 criterion.   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).   Significantly more than 10% of the samples at all three of these stations exceeded Iowa’s single-sample maximum criterion of 235 E.  coli orgs/100 ml (Mitchell:  31% (5 of 16 samples); Halvorson Park:  38% (6 of 16 samples); IA/MN state line:  47% (7 of 15 samples).   The results from the three 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.  

The Class B(WW1) uses are 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.

Information from the IDNR Fisheries Bureau also suggests potential impairments to the aquatic life uses designated for this river segment.   Recent surveys have shown that the smallmouth bass population of the Cedar River from the Iowa/Minnesota state line downriver to St.  Ansgar is relatively poor and will not support the "catch and release" fishery planned for this river reach.   Potential explanations for this problem include (1) habitat alterations caused by flooding in 1993 and (2) water quality impacts.   For example, a pesticide-related fish kill occurred on the Cedar River in March 2001 downstream from the Austin, MN, wastewater treatment plant.   Additional monitoring is needed to more accurately characterize the water quality of this river reach.

However, contrary to the late 1980s freshwater mussel findings and IDNR Fisheries Bureau data on smallmouth bass, 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 DNR/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 77, 76 (both excellent).   The FIBI average was 60 and the BMIBI average was 76.5.   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 assessment is considered evaluated because the drainage area (676 & 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.  

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 and in 2005.   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.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health (IDPH), in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario applies to the fish contaminant data generated from the RAFT sampling conducted in this segment of the Cedar River:  levels of mercury in fillet samples of smallmouth bass and walleye from consecutive samplings exceeded advisory trigger levels, thus suggesting the need for a consumption advisory.   According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “partially supported”.  

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.