Assessment Comments
Assessment is based on results of a statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000). Potential causes & sources of impairment were applied to all sites in study.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (evaluated) as "not supported" based on results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
EXPLANATION: This segment of Lytle 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. The results of this sampling on this segment of Lytle 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 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. Species richness of freshwater mussels at the one sample site in this segment of Lytle Creek was 3 in the 1984-85 period and was 0 in the 1998-99 period, respectively, for a percent change of minus 100%. Based on these results, the aquatic life uses are assessed (evaluated) as “not 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. Such waters will, however, be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”. 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.
