Assessment Comments
Assessment based on (1) 2006 SHL special project benthic macroinvertebrate sampling data: CBI = 22, 30; CW BIC = 60, (2) on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, and (3) results of IDNR TMDL monitoring at station LTR1 in 2010.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life 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) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.
SUMMARY: The presumptive Class A1 (primary contact recreation) uses and presumptive Class A2 (secondary contact recreation) uses are assessed as "not supported” due to high levels of indicator bacteria (E. coli) that exceed state water quality criteria. This is a new impairment for this assessment segment. The source of E. coli data and data for chemical/physical parameters for this assessment is IDNR TMDL monitoring station LTR1 (STORET No. 11280002). The Class B(CW1) coldwater aquatic life uses remain assessed (evaluated) as "partially supported" based SHL benthic macroinvertebrate sampling data. This assessment is also based, in part, on the February 2011 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau. Fish consumption uses remain "not assessed."
EXPLANATION: The presumptive Class A1 and A2 uses are assessed (monitored) as “not supported due to levels of indicator bacteria (E. coli) that exceed the respective Class A1 and A2 geometric mean criteria. The geometric mean of indicator bacteria (E. coli) in the 16 samples collected during the recreational season of 2010 at TMDL Site LTR1 was 2,523 orgs/100 ml. This recreation season geometric mean far exceed Iowa’s Class A1 geometric mean criterion of 126 E. coli orgs/100 ml and also exceeds the Class A2 geometric mean criterion of 630 E. coli orgs/100 ml, thus indicating nonsupport of both the Class A1 and A2 water contact recreation uses. Fourteen of the 16 samples (88%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, and nine of 17 samples (53%) exceeded Class A2 single-sample maximum criterion of 2,880 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1 and 630 orgs/100 ml for Class A2)., the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2006 as part of an SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2006 CBI scores were 22 and 30. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 0/2 times in 2006.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years in a recent five-year period to be considered “monitored”. This segment had two samples collected in 2006. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
In contrast to the impairment suggested by benthic macroinvertebrate sampling data, the results of chemical/physical monitoring at IDNR TMDL station LTR1 do not suggest impairment of the aquatic life uses. No violations of state water quality criteria for Class B(CW1) aquatic life uses for ammonia, dissolved oxygen, or pH occurred in the approximately 15 samples collected during 2010.
Also in contrast to the benthic macroinvertebrate sampling data, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, suggests the Class B(CW1) uses are "fully supported". According to the updated summary, Little Turkey River is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the resident trout species at this time. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
