Lime Creek IA 02-CED-524

The presumptive Class A1 uses remain assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli) at three monitoring stations in 2010 and 2011. The geometric means of indicator bacteria (E. coli) in the 22 samples collected at each of these three stations during the recreational seasons of 2010 and 2011 (11 samples per season) were as follows: at station 11100001, the 2010 geometric mean was 1,426 orgs/100 ml and the 2011 geometric mean was 1,874 orgs/100 ml. At station 15100010, the 2010 geometric mean was 1,615 orgs/100 ml and the 2011 geometric mean was 1,322 orgs/100 ml. And, at station 15100011, the 2010 geometric mean was 1,963 orgs/100 ml and the 2011 geometric mean was 1,819 orgs/100 ml. All geometric means from all three sites are far above the Class A1 criterion of 126 orgs/100 ml. At all three monitoring stations, 21 of the 22 samples (95%) collected during the 2010-2011 period exceed Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”

Results of chemical/physical water quality monitoring conducted in 2010 and 2011 do not suggest impairment of the Class B(WW1) aquatic life uses. Twenty-four samples were collected at each of the three monitoring station (11100001, 15100010, and 15100011) from May 2010 to July 2011. None of the combined 72 samples collected violated Class B(WW1) criteria for dissolved oxygen, pH, or temperature. The maximum temperature at station recorded was 27.9C, and the minimum dissolved oxygen concentration was 6.7 mg/l; pH values ranges from 7.2 to 8.4 units. These results suggest good and stable water quality conditions in this segment of Lime Creek.

Results from the DNR/SHL biocriteria sampling in 2004, 2007, 2008, 2010, 2013 and 2016 suggest that the Class B(WW1) uses are "fully supported." The FIBI scores (n=5) ranged from was 69 (good) to 84 (excellent). The BMIBI scores (n=8) ranged from was 61 (good) to 83 (excellent). The aquatic life use support was assessed as fully supported (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The natural substrate BMIBI BIC for this ecoregion is 70. This segment passed the FIBI BIC 5/5 times and passed the BMIBI BIC 5/8 times in the past 13 years. This aquatic life use assessment is considered "evaluated" because to complete the assessment, data greater than five years old (2004) were used.

For previous assessments, results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams were used to identify an impairment of the aquatic life uses of this stream segment. Thus, the aquatic life uses of this segment were considered Section 303(d)-impaired and placed in Category 5b of Iowa’s Integrated Report. This impairment was based on comparison of sampling results from 1998 and 1999 (Arbuckle et al. 2000) to results from stream sites surveyed in 1984 and 1985 by Frest (1987). For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey. 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 to assess the degree to which the aquatic life uses of the sampled stream segments are supported. Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggests an impairment of the aquatic life uses. Species richness of freshwater mussels at the one sample site in this segment of Lime Creek was 9 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%.

Recent surveys of Lime Creek’s mussel population by DNR biologists were conducted in 2007, 2009 and 2010. Results showed the presence of six of the original (1984-85) nine species in and around the Lime Creek Area (a Buchanan County park). While mussels mostly haven’t been found at the original mussel site, they have been found within the impaired segment. Additionally, the location in the Cedar River floodplain of the original mussel site calls into question its selection for mussel sampling in the first place. The presence of three state-listed mussel species and the fact that the Ellipse (one of the most sensitive species of mussel) is the dominant species would argue that Lime Creek has the water quality and habitat variety to sustain a healthy population of mussels. This is also borne out by the biological, water quality, and habitat sampling conducted at both sites. Based on this information, the impairment of the Class B(WW1) aquatic life uses based on a decline in the freshwater mussel community was removed from Iowa’s 2012 Section 303(d) list of impaired waters. More information on recent mussel surveys at Lime Creek is available in the DNR report “Delisting justification for Lime Creek, Buchanan and Benton Counties, Iowa” prepared by DNR’s Watershed Improvement Section.