Des Moines River IA 04-UDM-1219

Assessment Comments

Assessment is based on results of IDNR ambient city monitoring upstream from Ft. Dodge from 2002 through 2004. Data from the 1998-99 statewide survey of freshwater mussels (Arbuckle et al. 2000) was considered but not used in the assessment.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality 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 "not assessed" due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of monthly monitoring from 2002 through 2004 at the IDNR/UHL ambient city monitoring station located upstream from Fort Dodge (STORET station 10940002).  

EXPLANATION:  The Class B(WW) aquatic life uses are assessed as "fully supported".   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 in the 32 samples collected, and for pesticides in the seven samples analyzed, during the 2002-20042 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 five sample sites in this segment was 0, 0, 1, 1, and 2 in the 1984-85 period and was 0, 0, 0, 0, and 3 in the 1998-99 period, respectively, for an average 1984-85 species richness of approximately 1 and an average percent change of minus 30%.   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 are "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.