South Fork Iowa River IA 02-IOW-748

[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).]

The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment.

IDNR/SHL biological sampling data collected in 2012, 2013 and 2014 as part of the IDNR/SHL stream biological sampling projects suggests "partial support" of the aquatic life uses.  A series of biological metrics which 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 FIBI score was 67 (good) and the BMIBI score was 37 (fair).  The 2013 FIBI score was 66 (good) and the BMIBI scores were 43 and 50 (both fair).  The 2014 FIBI score was 78 (excellent) and the BMIBI scores were 33, 45 and 51 (all fair).  The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and 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 riffle/non-riffle FIBI BICs for this ecoregion are 53/32 and the BMIBI BIC for this ecoregion is 62.  This segment passed the riffle FIBI BIC in 2012 and passed the non-riffle FIBI BIC 2/2 times (2013 & 2014).  This segment passed the BMIBI BIC 0/6 times in the past five years (2010-2014). 

This aquatic life assessment is now considered "monitored" 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 during the recent five-year period to be considered “monitored”.  This segment had multiple samples collected in the previous five years (2010-2014).

The results of continuous dissolved oxygen (DO) and temperature monitoring in 2013 and 2014 for the IDNR/SHL stream biological sampling projects were marginally acceptable for fully supporting the Class B(WW) aquatic life uses. The lowest DO concentration recorded in 109 days of continuous monitoring was 2.3 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (5 mg/L) in 11 of 109 days and the 16-hour DO criterion (5 mg/L) in 3 of 109 days. The 2013 and 2014 combined percentage exceeding the 24-hour DO criterion (10.1%) was slightly greater than (failing) the 10% impairment threshold used to assess conventional water quality parameters; however, the associated statistical analysis confidence level was not high (<90%). The 2013 and 2014 combined percentage exceeding the 16-hour DO criterion (0%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). The maximum stream temperature recorded during the sensor deployment period was 33.2 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 3 of 109 days. The percentage exceeding (2.8%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(WW1) aquatic life use is assessed as not impaired by DO and temperature. The IDNR’s continuous monitoring assessment methodology specifies that the frequency of violations must exceed the 10% threshold with greater than 90% statistical confidence in order to assess the aquatic life use as impaired. The assessment type is considered as “monitored” because the data meet the minumum requirements of the IDNR’s continuous monitoring assessment methodology. Because of the contradictory results showing DO violations in the first year (2013) and not the second year of monitoring (2014), additional continuous monitoring of DO and temperature is strongly recommended.

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).  Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.  Thus, this assessment segment was placed in Category 3b of Iowa’s 2010 Integrated Report and remains in Category 3b for the current report. 

Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this assessment segment.