Assessment Comments

Assessment is based on results of (1) TMDL-related monitoring at two stations in 2008 and 2009 (11100001 and 12100002), (2)IDNR/UHL biological monitoring in 2007, 2008 and 2010; (3) results of a fish kill investigation in July 2008; (4) ISU statewide survey of freshwater mussels in 1998-99, and (5) mussel surveys by IDNR staff in 2007, 2009 and 2010.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria (E.  coli) at two stations sampled as part of TMDL monitoring.   The source of data for this assessment is the results of TMDL-related water quality monitoring at sites (LiCr2 (11100001) and at site 154 (12100002) near Brandon in 2008 and 2009.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supporting" based on results of a chemical and biological monitoring conducted from 2008 through 2010.   Based on results of recent (2007-10) surveys, the existing impairment based on a decline in this stream's freshwater mussell community is proposed for removal from Iowa's Section 303(d) list.   Consistent with this proposed de-listing are the results of IDNR TMDL-related water quality monitoring in 2008-09 and results of IDNR/UHL biological (biocriteria, fish/macroinvertebrate) monitoring in 2004, 2007 and 2008 both suggest "full support" of these aquatic life uses based on sampling of the fish and benthic macroinvertebrate communities.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.  

EXPLANATION:  The presumptive Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli) at two monitoring stations in 2008 and 2009.   At site LiCr2 downstream from Brandon, the geometric mean level of indicator bacteria (E.  coli) in the 11 samples collected during the recreational season of 2008 (997 orgs/100ml) far exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml.  

The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 and 2009at station 11100001 were as follows:  the 2008 geometric mean was 997 orgs/100 ml and the 2009 geometric mean was 366 orgs/100 ml.   Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 and 2009at station 12100002 were as follows:  the 2008 geometric mean was 3,247 orgs/100 ml and the 2009 geometric mean was 125 orgs/100 ml.   The 2008 geometric mean far exceed the Class A1 criterion of 126 orgs/100 ml; the 2009 geometric mean was below (barely) the Class A1 criterion of 126 orgs/100 ml.   The drastic decline in bacteria levels from 2008 to 2009 that occurred at this station is unusual and suggests improvement in water quality conditions.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’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.”

A fish kill occurred on Lime Creek on July 9, 2008.   The kill occurred along 4.2 miles of Lime Creek northeast of Brandon and affected approximately 2,720 fish.   High water occurred during, or after, the kill event because some fish were observed 2-3 feet above the water level present during the day of investigation.   Fish carcasses were easily identifiable to family group, but identification to species was not possible for most Cyprinidae species due to poor physical condition of specimens.   The following species were positively identified: Common Shiner, Creek Chub, Northern Hogsucker, Northern Logperch, Rock Bass, Smallmouth Bass, and Stonecat.   It is likely that high water flows flushed a significant number of dead fish from the investigated area, and decay and predation further reduced counts of small-bodied fishes.   The estimated value of the fish was $3,004.36.   No definite source for the fish kill was found, however, two feedlots and an herbicide over-application were investigated.  According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.”  If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.”  Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5).   However, results of chemcial monitoring and biological (fish, macorinvertebrate, and freshwater mussel) monitoring conducted since the July 2008 fish kill suggest full recovery of Lime Creek's aquatic communities.   Thus, this fish kill is not considered as a cause of impairment of the aquatic life uses of this stream.

Results of TMDL-related chemical/physical water quality monitoring conducted in 2008 and 2009 do not suggest impairment of the presumptive Class B(WW1) aquatic life uses.   Approximately 12 samples were collected at each monitoring station (Lime Creek-LiCr2 (STORET station 11100001) and Lime Creek-154 (STORET station 12100002) from July 2008 through June 2009.   None of the combined 24 samples collected violated Class B(WW1) criteria for dissolved oxygen, pH, temperature, or the temperature/pH-dependent Class B(WW1).   The maximum temperature at station LiCr2 was 22.0 C; the maximum temperature at station 154 was 23.9 C.  

Results from the IDNR/UHL biocriteria sampling in 2007, 2008 and 2010 suggest that the Class B(WW1) uses are "fully supported."  The 2007 FIBI scores were 78 and 82 (excellent) and the BMIBI scores were 82 (excellent) and 62 (good).   The 2008 FIBI score was 69 (good) and the BMIBI score was 83 (excellent).   The 2010 BMIBI score was 72 (good).   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 1994-2004.   The natural substrate BMIBI BIC for this ecoregion is 70.   This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 3/4 times in the past five years.   This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2006-2010.  

For previous assesssmetns, 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 IDNR 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 is recommended for removal from Iowa’s Section 303(d) list of impaired waters.   More information on recent mussel surveys at Lime Creek is available in the IDNR report “Delisting justification for Lime Creek, Buchanan and Benton Counties, Iowa” prepared by Jen Kurth of the IDNR’s Watershed Improvement Section.

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.