Cedar Creek IA 04-LDM-1053

ThepresumptiveClass A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10630002 near Bussey were as follows: the 2014 geometric mean was 464 orgs/100 ml, the 2015 geometric mean was 135 orgs/100 ml, and the 2016 geometric mean was 545 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Nine of the combined 24 samples (38%) exceeded 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (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 "partially supported."

Results of chemical/physical water quality monitoring at DNR station 10630002 near Bussey suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.9 mg/L), 36 Dissolved Oxygen samples (minimum = 6.7 mg/L), 36 Temperature samples (maximum = 27.4° c), 36 Chloride samples (maximum = 15 mg/L), or 36 Sulfate samples (maximum = 350 mg/L) occurred during monitoring from January 2014 to December 2016.1 of the 35 samples (3%) analyzed for pH (range = 6.3 to 8.3) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

In agreement with the water quality data assessment for this segment, the biological data suggest that the aquatic life uses in this segment are "fully supporting." This evaluated aquatic life assessment was based on data collected in 2012, 2015 and 2016 as part of the DNR/SHL large river sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).The 2012 BMIBI score was 12 (poor).The 2015 BMIBI score was 54 (fair).The 2016 FIBI score was 48 (fair) and the BMIBI score was 46 (fair).The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI score and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. This segment passed the FIBI BIC in 2016 and passed the BMIBI BIC 2/3 times in the last five years (2012-2016).

This aquatic life assessment is now considered "monitored" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years between over the most recent five-year period (2012-2016) to be considered “monitored”. This segment had three BMIBI samples collected during that time frame.

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