Assessment Comments

Assessment is based on results of (1) IDNR/UHL city monitoring upstream from Ames from 2000-02, (2) IDNR/UHL biological monitoring in 1997, 1998, and 2000; (3) 1999 Fisheries data: Fish IBI = 57 (good), and (4) U.S.EPA/IDNR fish contaminant monitoring in 1998.

Basis for Assessment

SUMMARY:  The Class A uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria that violate state water quality criteria.   The Class B(WW) aquatic life uses remained assessed (monitored) as "fully supported / threatened" based on results of biological monitoring in 1997, 1998, 2000 and 1999 IDNR Fisheries monitoring.   Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 1998  The sources of data for this assessment include (1) the results of monthly monitoring from April 2000 through December 2002 at the IDNR/UHL ambient city monitoring station located upstream from Ames at the Sleepy Hollow canoe access (station 10850003), (2) results of IDNR-UHL biological monitoring in 1997, 1998, 2000, (3) 1999 IDNR Fisheries Monitoring, and (4) U.S.  EPA/IDNR fish tissue monitoring in 1998.  

EXPLANATION:  The Class A uses are assessed as "partially supported" based on results of monitoring for indicator bacteria (fecal coliforms).   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."  Fourteen of the 16 samples collected from the Cedar Bluff station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 14 non-runoff-affected samples (172 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml.   However, five of the 14 samples (36%) exceeded the U.S.  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 samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are only "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

The Class B(WW) aquatic life uses remain assessed (monitored) as "fully supported / threatened."  Monitoring at the IDNR ambient station upstream from Ames showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 28 samples collected, for toxic metals in the 28 samples collected, and for pesticides and other toxic organic compounds in the nine samples analyzed, during the 2000-2002 assessment period.   These results suggest “full support” of the Class B(WW) aquatic life uses.   Based, however, on the results of biological monitoring conducted by IDNR and UHL in 1997, 1998, 2000 and IDNR Fisheries monitoring in 1999, the assessment of the aquatic life uses of this river segment remain "fully supported / threatened" (see below).  

Fish consumption remain assessed (monitored) as "fully supported" based on results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring conducted in 1998 near Story City (see assessment for the 2000 report).

The assessment was partially based on results of IDNR/UHL biological monitoring in 1997, 1998, 2000 and on data collected in 1999 as part of a DNR Fisheries stream sampling project: Manchester research station.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of fish species and benthic macroinvertebrate taxa that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate community index of biotic integrity (BM-IBI).   The indices rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 evaluated Fisheries Fish IBI was 57 (good).   The DNR/UHL Fish IBI average (n=6) was 53 (good) and the BM-IBI average (n=5) was 52 (fair).   The aquatic life use support was assessed as Fully Supporting/Threatened (=FS/T), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.