Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on the Boone River northeast of Stratford (STORET station 10400001 (formerly Station 438056)) from 2006 through 2008, (2) results of IDNR/UHL biological (REMAP) monitoring conducted in 2002, (3) results of IDNR/UHL biological (biocriteria) monitoring in 1998 and 2004, and (4) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2000 and 2007. Data from the 1998-99 survey of freshwater mussels (Arbuckle et al. 2000) was considered but not used in the assessment.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria.    The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported” based on results of biological monitoring in 1998, 2002 and 2004.    Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2000 and 2007.    The sources of data used for this assessment include (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on the Boone River northeast of Stratford (STORET station 10400001 (formerly Station 438056)) from 2006 through 2008, (2) results of IDNR/UHL biological (REMAP) monitoring conducted in 2002, (3) results of IDNR/UHL biological (biocriteria) monitoring in 1998 and 2004, and (4) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 2000 and 2007.  

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E.  coli).   The geometric mean level of indicator bacteria (E.  coli) in the 22 samples collected (121 orgs/100ml) during the recreational seasons of 2006 through 2008 is below, and meets, the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Seven of the 22 samples (32%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   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 less than the state’s geometric mean criterion, the primary contact uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   These guidelines, however, also suggest that if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S.   EPA 1997b).   According to IDNR’s assessment/listing methodology, the monitoring data from 2006-08 suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.”  The relatively low geometric means for this river segment (72 orgs/100 ml for the 2006 assessment cycle, 112 orgs/100 ml for the 2008 cycle, and 121 orgs/100 ml for the current (2010) cycle) is atypical for free-flowing Iowa rivers and suggests that relatively low levels of indicator bacteria occur in this river segment.    

The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported” based on results of IDNR/UHL biological monitoring conducted in 1998, 2002 and 2004 as part of the IDNR/UHL biocriteria and REMAP projects.    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 1998 FIBI score was 70 (good) and the BMIBI score was 67 (good).   The 2002 FIBI score was 49 (fair) and the BMIBI score was 48 (fair).    The 2004 FIBI score was 73 (excellent) and the BMIBI score was 57 (good).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), 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 riffle/non-riffle stable habitat FIBI BICs for this ecoregion are 53/32 and the BMIBI BIC for this ecoregion is 62.    It is uncertain at this time if the sites have stable riffle habitat; however, the FIBI scores were above the higher FIBI BIC 2/3 times and the BMIBI scores met the BIC 1/3 times in the last 11 years.    This assessment is considered evaluated because the drainage area (849 and 903 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 the FIBI BIC (2/3) and failed the meet the BMIBI BIC (1/3), 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.

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 between 2004 and 2008 to be considered “monitored”.   This segment had multiple samples collected in the previous 11 years (1998-2008); however, the multiple samples were not collected during 2004-2008.   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).

Results of IDNR/UHL ambient chemical/physical monitoring suggest relatively good water quality in this river segment.   No violations of Class B(WW1) criteria for conventional parameters (dissolved oxygen, pH) occurred in the 34 samples analyzed during the 2006-2008 assessment period.   Levels of ammonia-nitrogen did not violate the applicable Class B(WW1) criteria in the 33 samples analyzed during the 2006-2008 period; no violations of Class B(WW1) chronic criteria occurred in the three samples analyzed for pesticides or in the five samples analyzed for toxic metals.    

This segment of the Boone River was sampled as part of the 1998-99 statewide study of freshwater mussels in Iowa streams and rivers (Arbuckle et al.   2000).    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.    For stream segments having four or more species reported for the 1984-95 survey, results of this comparison were used by staff of the Iowa DNR Watershed Monitoring & Assessment Section to assess the degree to which the aquatic life uses of the sampled stream segments are supported.    The results of this sampling on this segment of the Boone River, however, do not meet IDNR guidelines for developing an assessment of support for the aquatic life uses.    Species richness of freshwater mussels at the three sample sites in this segment was 2, 3, and 4 in the 1984-85 period and was 3, 1, and 5, in the 1998-99 period, respectively, for an average 1984-85 species richness of 3 and an average percent change of plus 3%.    This site, however, is one of the few in the 1998-99 ISU survey that did not show a drastic decline in mussel richness between the 1985 and 1998-99 survey periods.    Based on these results, the results from the survey of freshwater mussels was not used to assess this river segment due (1) to IDNR’s assessment methodology in which assessment decisions are developed only for those stream segments having an average of four or more species reported in the 1984-85 (Frest) survey and (2) the difficulty of interpreting status of mussel communities showing relatively low species richness during the both the historical (1984-85) and current (1998-99) surveys.    

Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring in this river segment in 2000 and 2007.   The composite samples of fillets from channel catfish and smallmouth bass in 2000 had low levels of contaminants.   The composite samples of fillets from channel catfish and smallmouth bass in 2007 also had low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.178 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.196 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 2000 and 2007 RAFT sampling conducted in 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.