Des Moines River IA 04-UDM-1217

Assessment Comments

Assessment is based on results of (1) IDNR/UHL ambient monitoring downstream from Ft. Dodge from 2002-04 and (2) EPA/IDNR fish tissue (RAFT) monitoring in 1999. Data from the 1998-99 statewide survey of freshwater mussels (Arbuckle et al. 2000) was considered but not used for the assessment.

Basis for Assessment

Note:  This assessment was also used for the adjacent downstream segment of the Des Moines River (IA 04-UDM-0040-1).  

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical monitoring from 2002-04.   This river segment was not designated for Class A (primary contact recreation) uses during the 2002-2004 assessment period.   Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of fish contaminant monitoring in 1999.   The sources of data for this assessment include (1) results of monthly monitoring from 2002 through 2004 at the IDNR/UHL ambient city monitoring station located downstream from Fort Dodge near Kalo (STORET station 10940003) and (2) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring near Dolliver State Park in 1999.  

EXPLANATION:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported."  Ambient chemical/physical monitoring at the IDNR city station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 36 samples collected, for toxic metals (including mercury) in the 32 samples collected, and for pesticides in the seven samples analyzed, during the 2002-2004 assessment period.   These results suggest "full support" of the Class B(WW) aquatic life uses.  

This segment of the Des Moines 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 Water Quality Bureau to assess the degree to which the aquatic life uses of the sampled stream segments are supported.   The results of this sampling on the Des Moines 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 one sample site in this segment was 2 in the 1984-85 period and was 0 in the 1998-99 period, respectively, for percent change of minus 100%.   Based on these results, the aquatic life uses are considered “not assessed” 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 were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Dolliver State Park in 1999.   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 1999 RAFT sampling conducted in this assessment segment:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.