Nishnabotna River IA 05-NSH-1412

The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 23 samples collected during the recreational seasons of 2012 through 2014  at the USGS station on the Nishnabotna River above Hamburg were as follows: the 2012 geometric mean was 900 orgs/100 ml, the 2013 geometric mean was 296 orgs/100 ml, and the 2014 geometric mean was 1734 orgs/100 ml.  All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Twelve of the combined 23 samples (52%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. 

The geometric means of indicator bacteria (E. coli) in the 5 samples collected during the recreational seasons of 2012 through 2014 at the IDNR station on the Nishnabotna River near Hamburg were as follows: the 2012 geometric mean was 2615 orgs/100 ml and the 2014 geometric mean was 2296 orgs/100 ml.  Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Five of the combined 5 samples (100%) 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 IDNR’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 "not supported."

The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of IDNR/SHL biological sampling in 2003, 2012 and 2013.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria 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 2003 FIBI score was 5 (poor) and the BMIBI score was 54 (fair).   The 2012 BMIBI score was 23 (poor) and the 2013 BMIBI score was 26 (poor).    The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage areas (2,807 and 2,818 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this segment failed the FIBI (0/1) and BMIBI (1/3) BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size.   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 results of biological monitoring that suggest only “partial support” of the Class B(WW1) uses, results of water quality monitoring by the U.S.  Geological Survey above Hamburg and by IDNR near Hamburg from 2010-2012 suggest “full support” of these uses.  No violations of Class B(WW1) water quality criteria for 42 Ammonia samples (maximum = 0.5 mg/L), 42 Dissolved Oxygen samples (minimum = 6.4 mg/L), 43 pH samples (range = 7.5 to 8.7), 43 Temperature samples (maximum = 28.8° c), 42 Chloride samples (maximum = 24 mg/L), or 42 Sulfate samples (maximum = 36.3 mg/L) occurred during monitoring from January 2012 to December 2014. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

Results of this monitoring for toxics also suggest “full support” of the Class B(WW1) aquatic life uses. No violations of Class B(WW1) criteria occurred for the following parameters monitored by USGS: chlorpyrifos (33 samples) or dieldrin (33 samples). One of the 33 samples (3%) analyzed for DDE violated the Class B(WW1) criteria during the 2012-2014 monitoring period. Results of monitoring for toxics suggest “full support” as none of the parameter exceed their respective criteria in more than one sample over the three year period (2012-2014).

The Human Health designated use (including the fish consumption use) remains assessed (evaluated) as “partially supporting” (IR 3b-potentially impaired) due to detectable levels of DDE and dieldrin. Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Hamburg in 2011.   The composite samples of fillets from common carp had low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.06 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm.   The average level of mercury in the tissue plug samples from three black crappie was 0155 (SD=0.041).   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   The fish contaminant data generated from the 2011 RAFT sampling conducted in this assessment segment show that the levels of contaminants do not exceed any of Iowa’s advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.   In addition, none of the 35 samples analyzed by USGS for dieldrin in water exceeded the state human health/fish criterion of 0.0054 ug/l.

The results of USGS monitoring from 2012 and 2014 showed One of the 33 samples (3%) analyzed for DDE and three of the 33 samples (9%) analyzed for Dieldrin. The sample collected on January 16, 2013 at USGS station 06810000 (near Hamburg) had a detectable level of DDE of 0.003 ug/l, thus exceeding the HH-fish criterion of 0.0022 ug/l. Levels of DDE the remainder of the samples at this monitoring stations were reported as less than the levels of detection (0.002 ug/l and 0.005 ug/l). The samples collected on June 10, 2014, July 15, 2014 and September 16, 2014 at USGS station 06810000 (near Hamburg) had detectable levels of dieldrin of 0.004 ug/l, 0.003 ug/l and 0.003 ug/l respectively, thus exceeding the HH-fish criterion of 0.00054 ug/l. Levels of dieldrin the remainder of the samples at this monitoring stations were reported as less than the level of detection (0.008 ug/l).According to IDNR’s assessment/listing methodology, if the average level of a toxic metal or pesticide is greater than its respective human health criterion, impairment ("nonsupport") of the Human Health use is indicated. The number of samples with detectable levels of DDE and dieldrin at these monitoring stations (one of 33 and 3 of 33), however, is too few and the method detection level is far too high (~16 times greater than the HH criterion for dieldrin) to allow calculation of a meaningful summary statistic (e.g., mean) for DDE and dieldrin at this monitoring station. Based on sampling that shows detectable levels of DDE and dieldrin, however, the Human Health designated use will be considered (evaluated) as “partially supporting” (IR 3b-potentially impaired).