Assessment Comments
Assessment is based on: (1) results of biological monitoring conducted at three sites in 2003 as part of the DNR/UHL 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 UHL in support of TMDL development.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are not assessed due to the lack of information upon which to base an assessment. The Class B(WW2) uses remain assessed (monitored) as "partially supported" based on results of (1) biological monitoring conducted in 2003, (2) rapid bioassessment sampling in 2000, and (3) monthly chemical/physical water quality monitoring conducted in 2001 and in 2003. Sources of information for this assessment include (1) results of biological monitoring conducted at three sites in 2003 as part of the DNR/UHL 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 UHL in support of TMDL development. Note: IDNR/UHL 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 (2008) assessment remains based on the data and other water quality information used for the 2006 assessment.
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 for the 2006 assessment/listing cycle (organic enrichment, nutrient, and siltation) are potentially addressed by the TMDL, this waterbody remains in IR Category 4a.
EXPLANATION: The presumptive Class A1 (primary contact recreation uses are “not assessed” due to the lack of information on which to base an assessment.
The Class B(WW2) uses remain assessed (monitored) as "partially supported" based on results of biological monitoring conducted in 2003. The 2003 FIBI scores were 25 (poor), 41, 27 (fair) and the BMIBI scores were 42, 50, 38 (fair). The FIBI average was 31 and the BMIBI average was 43. 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 1994-2004. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. 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.
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.
