Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) sampling in 2002, (2) IDNR/UHL ambient monthly water quality monitoring from 2000-2002, and (3) data from the 1998-99 statewide survey of freshwater mussels (Arbuckle et al. 2000).
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses were assessed (evaluated) as "partially supported" based on information from the 1998-99 statewide survey of Iowa's freshwater mussels (Arbuckle et al. 2000). Results of ambient water quality monitoring from 2000-02 and results of biological monitoring conducted in 2002 indicated "full support" of the Class B(WW) aquatic life uses. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment. The sources of data used for this assessment include (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on Lizard Creek at Highway 169 at Fort Dodge (STORET station 10940001, formerly station 500990) from 2000-2002, (2) results of IDNR/UHL biocriteria monitoring in 2002, and (3) information from the 1998-99 statewide survey of Iowa's freshwater mussels (Arbuckle et al. 2000).
EXPLANATION: The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported" based on results of the 1998-99 statewide survey of freshwater mussels. Results of of IDNR/UHL biological monitoring conducted in 2002 as part of the stream biocriteria project, however, suggest "full support" of these uses. The 2002 Fish IBI score was 85 (excellent) and the BM-IBI score was 56 (good). The aquatic life use support was assessed as fully supporting/threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores 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.
Similarly, results of ambient chemical/physical monitoring suggest very good water quality. None of the 36 samples collected during the 2000-2002 assessment period at the Hwy 169 station violated Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen (the minimum dissolved oxygen concentration (8.0 mg/l) is relatively high for ambient monitoring stations and suggests excellent water quality. In addition, no violations occurred in the approximately 30 samples analyzed for toxic metals or in the 10 samples analyzed for pesticides and other toxic organic compounds.
The results of the statewide assessment of freshwater mussels, however, suggests the potential for an impairment of the aquatic life uses due to a decline in the community of freshwater mussels in this stream segment. This segment of Lizard Creek 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 this segment of Lizard Creek, however, do not meet IDNR guidelines for developing a monitored assessment of support for the aquatic life uses that is appropriate to support addition of this waterbody to Iowa's Section 303(d) list. That is, 303(d)-level assessment decisions are developed only for those stream segments having an average of four or more species reported in the 1984-85 (Frest) survey due to 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. This information can be used, however, to indicate the potential for an impairment of the aquatic life uses and to indicate the need to conduct additional sampling. Species richness of freshwater mussels at the four sample sites in this segment of Lizard Creek was 0, 1, 2, and 3 in the 1984-85 period and was 0, 1, 0, 0 in the 1998-99 period, respectively, for an average 1984-85 species richness of approximately 2 and a percent change of minus 50%. Based on these results, the aquatic life uses are assessed (evaluated) as “partially supported." For reasons stated above, the confidence level of this assessment is relatively low; thus the assessment type is considered “evaluated” in the context of Section 305(b) reporting. According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on an “evaluated” assessment are not candidates for Section 303(d) listing. Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairment of these uses that may exist.
The results of this sampling at Lizard Creek, however, do not meet IDNR guidelines for developing an assessment of support for the aquatic life uses. Species richness of freshwater mussels at the four sample sites in this segment of Lizard Creek was 0, 1, 2, and 3 in the 1984-85 period and was 0, 1, 0, 0 in the 1998-99 period, respectively, for an average 1984-85 species richness of approximately 2 and an average percent change of minus 50%. 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 not assessed due to the lack of fish contaminant monitoring in this stream segment.
