Assessment Comments

Assessment is based on: (1) USGS ambient water quality monitoring conducted on the Nishnabotna River at Hamburg from March 2004 to December 2006, (2) IDNR/UHL biological (REMAP) monitoring in 2003, and (3) EPA/IDNR fish contaminant (RAFT) monitoring in 2002.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are not assessed due to the lack of monitoring data for indicator bacteria upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supported” based on results of biological monitoring in 2003.   The fish consumption uses are assessed (monitored) as “fully supported” based on results of fish contaminant monitoring in 2002.   The sources of data for this assessment include the results of (1) USGS ambient water quality monitoring conducted on the Nishnabotna River at Hamburg from March 2004 to December 2006, (2) IDNR/UHL biological (REMAP) monitoring in 2003, and (3) EPA/IDNR fish contaminant (RAFT) monitoring in 2002.  

EXPLANATION:  The Class A1 uses are not assessed due to the lack of monitoring data for indicator bacteria upon which to base an assessment.   The ambient water quality monitoring conducted by USGS in the river segment from 2004-2006 did not include measurement of indicator bacteria.

The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological (REMAP) monitoring in 2003.   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 2003 FIBI score was 5 (poor) and the BMIBI score was 54 (fair).  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 FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage area (2,812 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 failed the FIBI BIC and passed 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.   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).

In contrast to the results of biological monitoring that suggest only “partial support” of the Class B(WW1) uses, results of water quality monitoring by the U.S.  Geological Survey above Hamburg from 2004-2006 suggest “full support” of these uses.   No violations of state water quality criteria occurred in the 37 samples analyzed for ammonia and pH; no violations occurred in the single sample of November 14, 2005, that was analyzed for pesticides and toxic metals.   One of the 37 samples (3%) violated the Class B(WW1) criterion for dissolved oxygen.   The sample collected on May 10, 2004, contained a dissolved oxygen level of 3.5 mg/l, thus violating the water quality criterion of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations for dissolved oxygen at this station (3%) does not suggest a water quality impairment:  the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated.   Thus, these results suggest "full support" of the Class B(WW1) aquatic life uses.  

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hamburg in 2002.   The composite samples of fillets from common carp had low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.085 ppm; total PCBs: 0.093 ppm; and technical chlordane: 0.03 ppm.   [Note:  Typically, samples of both bottom-feeding fish (e.g., common carp) and predator species (e.g., largemouth bass) are collected at RAFT status sites such as the Nishnabotna River at Hamburg.   Predator species, however, are naturally rare in rivers of southwestern Iowa, and RAFT status samples from these rivers typically contain only the bottom-feeder sample.]  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, 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 2002 RAFT sampling conducted in this assessment segment:  the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.