Assessment Comments

Assessment is based on results of (1) IDNR monthly ambient monitoring station at Hwy 61 bridge NW of Maquoketa from 2000-02, (2) IDNR/UHL TMDL monitoring in 2001, (3) ISU statewide freshwater mussell survey, (4) EPA/IDNR fish tissue (RAFT) monitoring NE of Maquoketa in 1999 and 2001.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to levels of indicator bacteria that exceeded state water quality criteria.   The Class B(WW) aquatic life uses were assessed (monitored) as "not supported " due the apparent elimination of the freshwater mussel community from this river segment.   Fish consumption uses remain "fully supported" based on results of fish contaminant monitoring in 1999 and 2001.   Sources of data for this assessment include (1) results monthly monitoring from January 2000 through December 2002 at the IDNR ambient station at the Hwy 61 bridge NW of Maquoketa (station 10490002), (2) results from IDNR/UHL monthly monitoring conducted at five locations between Maquoketa and Canton from March to November 2001 as part of monitoring in support of TMDL development (3) results of monitoring at one site for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al.  2000), and (4) U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 1999 and 2001 northeast of Maquoketa.  

EXPLANATION:  The Class A (primary contact recreation) uses were assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric mean of indicator bacteria (fecal coliforms) in the 20 samples not materially affected by surface runoff during the recreational seasons of 2000, 2001, and 2002 at the IDNR ambient monitoring station exceeded the Iowa water quality criterion to protect primary contact recreation uses.   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  The geometric mean of fecal coliform bacteria in the 20 non-runoff-affected samples was 262 orgs/100 ml, with nine samples (45%) exceeding the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of the sample exceeds the single-sample maximum value of 400 orgs/100 ml, the primary contact uses are “partially supported.”  If the geometric mean is greater than 200 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Results of monitoring at the five TMDL stations during the recreational season of 2001 support this assessment:  geometric means in seven samples at these stations ranged from 697 to 830 organisms/100 ml (N=7) with from 47 to 71% of the samples exceeding the single-sample maximum value of 400 organisms/100 ml.  

Results of monitoring from the IDNR ambient station NW of Maquoketa in 2000, 2001, and 2002 and from the five stations from Maquoketa to Canton monitored in 2001 in support of TMDL development for this river reach suggest “full support” of the Class B(WW) uses.   Monitoring at these stations show no violations of Class B(WW) water quality criteria for conventional or toxic pollutants.  

Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al.  2000), however, suggest a potential impairment to the aquatic life uses of this stream segment.   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).   In general, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s 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 period to the 1998-99 period suggests an impairment of the aquatic life uses.   The confidence level of this assessment is relatively high; thus the assessment type is considered “monitored” in the context of Section 305(b) reporting.   According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on a “monitored” assessment are candidates for Section 303(d) listing.

For purposes of Section 305(b) reporting only, low species richness reported in the 1998-99 survey was used as an indication of a potential impairment of the aquatic life uses.   Staff of the IDNR Water Quality Bureau used results from Arbuckle et al.  (2000) to define categories of species richness for Iowa's mussel communities for ecoregions in Iowa that historically supported a diverse community of freshwater mussels.   Based on information in Cummings and Mayer (1992), all ecoregions except 47d, 47e, and the portions of ecoregions 47f and 40 in the Missouri River basin, historically supported at least 19 stream/river mussel species.   Based primarily on species richness values reported by Arbuckle et al.  (2000), the following assessment framework was developed:  less than three species indicates low species richness and "nonsupport" or "partial support" of aquatic life use; from four to seven species indicates moderate species richness and potential minor impacts (="fully supported / threatened"); more than seven species indicates high species richness and "full support" of aquatic life uses.   The confidence level of this assessment is relatively low; thus the assessment type is considered “evaluated” in the context of Section 305(b) reporting.   According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on an “evaluated” assessment are not candidates for Section 303(d) listing.   No generally-accepted estimates of the expected species richness of freshwater mussels for Iowa’s streams and rivers are available.   Thus, the framework of expected species richness and is relation to support of aquatic life uses may be in error, especially by underestimating current expectations of species richness.  

Species richness of freshwater mussels at the one sample site in this stream segment was 5 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%.   Based on these results, the “full support” of aquatic life uses suggested by results of chemical monitoring from IDNR ambient and TMDL monitoring programs is downgraded to "non-support" for purposes of both Section 303(d) listing (greater than 50% decline in species richness) and Section 305(b) reporting (low species richness reported in the 1998-99 survey).   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 in-stream levels of nutrients (phosphorus and nitrogen).   Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness.   Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairments of these uses that may exist.  

Fish consumption uses remain assessed as "fully supported" based on the 1997, 1999 and 2001 EPA/DNR fish tissue (RAFT) samplings on the Maquoketa River northeast of Maquoketa.   This site is sampled for whole-fish common carp on an every-other-year basis as part of RAFT trend monitoring.   Results from all three samplings show that levels of all contaminants in the composite samples of whole-fish carp were less than ½ of the respective FDA action levels and DNR levels of concern.   This site was again sampled in 2003; the results from this monitoring are not yet available.