Mud Creek IA 02-CED-488

[Note:  A TMDL for organic enrichment in Mud Creek was prepared by IDNR and approved by EPA in 2003; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle.  Because all Section 303(d) impairments identified (organic enrichment, nutrient, and siltation) are potentially addressed by the TMDL, this waterbody remains in IR Category 4a.]  

Sources of information for this assessment include (1) results of biological sampling conducted at three sites in 2003 as part of the IDNR/SHL watershed assessment project, (2) four rapid bioassessment protocol sites sampled in 2000, and (3) monthly chemical/physical water quality monitoring conducted at five sites in this stream segment from March to November 2001, and at four sites from June to September 2003, by IDNR and SHL in support of TMDL development.  Note:  IDNR/SHL monitoring was conducted in this segment at TMDL monitoring station 11700001 in September 2005.  Only two samples were collected as part of this monitoring; the next most recent sampling was conducted in 2001.  The amount of data collected in 2005 (two samples) is insufficient for developing an assessment of support of designated uses; thus, this assessment remains based on the data and other water quality information used for the 2006 assessment.

EXPLANATION:  The presumptive Class A1 (primary contact recreation uses remain “not assessed” due to the lack of information on which to base an assessment. 

The Class B(WW2) uses remain assessed (evaluated) as "partially supported" based on results of biological monitoring conducted in 2003.  The 2003 FIBI scores were 25 (poor), 40, 27 (fair) and the BMIBI scores were 42, 50, 39 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.  This segment passed the FIBI BIC 1/3 times and passed the BMIBI BIC 0/3 times in 2003. 

Rapid bioassessment sampling results from 2000 suggested no significant change in aquatic life conditions from 1996.  Benthic macroinvertebrate and fish species composition were similar to 1996 levels.  Fish with lesions, an indicator of environmental stress or toxicity, seemed to be less abundant than in 1996, yet still higher than natural background levels. 

This aquatic life assessment is also 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 over a five-year period to be considered “monitored”.  This segment had multiple samples collected in 2003; however, the multiple samples were not collected during a five-year period and were not collected in multiple years.  Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).  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).  However, despite this change in assessment methodology and type, this waterbody remains in IR Category 4a. 

Results of monitoring conducted in 2001 in support of TMDL development showed only one violation of Class B(WW2) water quality criteria for conventional parameters and ammonia-nitrogen in the nine monthly samples collected between March and November 2001:  the level of dissolved oxygen in the sample collected at Site 3 downstream from Durant on August 16, 2001 (4.7 mg/l) violated the water quality criterion of 5.0 mg/l.  Although no violations of Class B(WW2) criteria for ammonia-nitrogen occurred, the maximum levels were moderately high for Iowa streams (downstream to upstream):  0.48 mg/l at Site 1 SE of Wilton, 0.70 mg/l at Site 2 upstream from Wilton, 0.49 mg/l at Site 3 downstream from Durant, 0.42 mg/l at Site 4 at the SE edge of Durant, and 0.19 mg/l at Site 5 upstream from Durant.  Four of the six maximum ammonia values occurred on August 16. 

Additional TMDL-related monitoring was conducted from June to September 2003 at four stations on Mud Creek:  three stations are near Wilton (IDNR stations 11700006, 11700007, and 11700008); one station is located west of Durant (11700005).  Five samples were collected at each station during the June-September period and the samples were analyzed for ammonia, dissolved oxygen, pH, and temperature.  No violations of Class B(WW2) criteria for ammonia, pH, or temperature occurred in the combined 20 samples.  At station TMDL S2 (11700007), however, three of the five samples violated the Class B(WW2) criterion for dissolved oxygen (5.0 mg/l).  Although violations were relatively minor (the minimum value was 4.5 mg/l), these results suggest the potential for an ongoing water quality impairment in this segment of Mud Creek. 

Despite the indications of relatively good water quality from TMDL-related monitoring in 2001 and 2003, biological monitoring is better able to reflect cumulative impacts of water quality over time and thus is believed to more accurately represent water quality conditions of this segment of Mud Creek than do results from the 2001 or 2003 TMDL monitoring sites.  Thus, the assessment of support of the designated aquatic life uses for this segment (partially supported) remains based on results of biological monitoring.