Assessment Comments

Assessment based on results of (1) IDNR/UHL biological (biocriteria) sampling from 2000-2002, (2) IDNR/UHL ambient monthly monitoring near Oakland Mills from 2002-04, and (3) USGS/NAWQA fish contaminant monitoring in 1995.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life are assessed (evaluated) as "partially supported" based on results of biological monitoring conducted in 2002.   Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1995.   The sources of data for this assessment include (1) the results of IDNR/UHL ambient monthly monitoring during the 2002-2004 assessment period at STORET station 10440001 approximately 3 miles southwest of Oakland Mills in Henry County (formerly station number 821004), (2) results of IDNR/UHL biological monitoring conducted in 2002 as part of the Iowa stream biocriteria project, and (3) results of fish contaminant monitoring conducted in 1995 as part of the USGS NAWQA program.  

EXPLANATION:  Results of ambient chemical/physical water quality monitoring suggest “full support” of the Class B(WW) aquatic life uses.   None of the approximately 35 samples collected during the 2002-2004 assessment period at the IDNR/UHL monthly station violated Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen; no violations occurred in the nine samples analyzed for toxic metals or in the seven samples analyzed for pesticides.  One of the 35 samples analyzed for pH, however, exceeded the Class B(WW) criterion of 9.0 pH units (this sample contained a pH of 9.1 pH units).   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as pH nonetheless suggest "full support" of aquatic life uses.   Thus, the percentages of violations of the pH criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.   Although the Class B(WW) uses were assessed as "threatened" for the 1998-1999 biennial period due to a single violation of the chronic Class B(WW) criterion for chlorpyrifos (see assessment for the 2000 report), none of the samples analyzed as part of IDNR/UHL ambient monitoring from 2000 through 2004 have contained a detectable level of chlorpyrifos.  

Despite results of ambient chemical/physical monitoring that suggest “full support” of aquatic life uses, the results of biological monitoring conducted from 2000-2002 as part of the IDNR/UHL stream biocriteria project suggest only “partial support” of these uses.   A series of biological metrics which 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 fish species and benthic macroinvertebrate taxa that were collected in the stream sampling reach.   The biological metrics were combined to form a fish index of biotic integrity (FIBI) and a benthic macroinvertebrate index of biotic integrity (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2000 FIBI score was 30.   The 2000-2002 BMIBI scores were 35, 40, 44, 36 (fair).   The BMIBI average was 38.8.   The aquatic life use support was assessed (evaluated) as partially supported (=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 FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41.   This assessment is considered evaluated because the drainage area (529.3 mi2) above this sampling site was 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 (using the UAV +7) but failed the BMIBI BIC, 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.   Therefore, IDNR considers the aquatic life use impairments indicated by these data as “evaluated” assessments that are 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).

Fish consumption uses were assessed (evaluated) as “fully supported” based on results of fish contaminant (RAFT) monitoring near Oakland Mills in 1995 as part of the USGS NAWQA project.   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).  

The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   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, 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, however, does not apply to the fish contaminant data generated from the 1995 sampling conducted near Oakland Mills:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.