Assessment Comments
Assessment based on (1) IDNR/UHL ambient monitoring in 2004, (2) 2000 IDNR biocriteria data: 3/4, 2/4, and 2/4 coldwater indicators, (3) 2004 IDNR/UHL REMAP sampling: 1/4 coldwater indicators, (3) investigation of a fish kill in March 2000.
Basis for Assessment
SUMMARY: The Class B(CW) aquatic life uses are assessed (monitored) as "not supported" due to violations of water quality criterion for dissolved oxygen. Fish consumption uses were “not assessed” due to the lack of fish contaminant monitoring in this stream segment. Sources of data for this assessment include (1) results of IDNR/UHL chemical/physical water quality monitoring conducted from May to December 2004 at the County Road W60 crossing (station 15030003), (2) results of an investigation of a fish kill that occurred in March 2000, and (3) results of IDNR/UHL biological monitoring in August 2000 and September 2004.
EXPLANATION: Based on the relatively large number of violations of the Class B(CW) criteria for dissolved oxygen (7.0 mg/l), the Class B(CW) aquatic life uses of this segment are assessed (monitored) as "not supported". The results of the IDNR/UHL water quality monitoring in 2004 show 16 violations of the Class B(CW) criteria for dissolved oxygen (7.0 mg/l) in the 26 samples (62%) collected. The violations were relatively minor and ranged from a low of 5.5 to 6.7 mg/l. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), however, "nonsupport" of aquatic life uses is indicated if criteria are exceeded in more than 25% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen). Thus, the percentages of violations of the dissolved oxygen criterion in this stream segment (62%) suggests an impairment of coldwater aquatic life uses. Violations occurred in throughout the May-December period of 2004.
A fish kill occurred on this stream reach on March 17, 2000. An estimated 4,800 fish were killed; no cause or source of the kill was identified. The following account is from the IDNR fish kill database and includes comments from the IDNR staff that investigated the kill:
"Dead fish were observed both upstream and downstream of the Smith Rd. bridge on the Yellow River, but only below the confluence with the unnamed tributary in section 17. North of Postville. Water turbid and green, with high flow. The kill affected a 3.1 mile segment of the Yellow River. Dead fish were not observed in the unnamed trib that enters into the Yellow River in Sec. 17. A total of 12 species of fish were affected. After visually inspecting the habitat in the area that the fish kill occurred, we would rate the habitat as excellent. The bottom substrate of much of the stream is composed of gravel and cobble. Deeper water areas for fish overwintering locations are also available. The Smith Rd. Bridge is the upstream extent of the area in which we have stocked fingerling brown and rainbow trout. No trout were seen in any of the counts of dead fish. The total number of fish that were observed was very low for a stream of this size and habitat quality. In previous work by Paragamian (1986), between 3000 and 5000 fish/acre were seen in northeast Iowa streams of comparable sizes. We feel that there has been an unknown factor at work that has severely reduced the total fish community in this section of the Yellow River prior to the total kill that this incident has caused to occur."
According to DNR's assessment methodology for Section 305(b) reporting, because this fish kill occurred more than three years ago, this kill indicates that the aquatic life uses should be assessed (evaluated) as "partially supported". "Evaluated" assessments are of lesser confidence than are "monitored" assessments and are thus not appropriate for justifying addition of a waterbody to Category 5 of the Integrated Report (=the Section 303(d) list). This type of assessment is, however, appropriate for Categories 2b or 3b of Iowa's Integrated Report.
The aquatic life use assessment was also based on data collected in 2000 and 2004 as part of the DNR/UHL stream biocriteria and REMAP projects. A series of four (4) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the biocriteria sampling data. The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa that were collected in the stream sampling reach. Sites that score 3 or 4 are Fully Supporting (FS), sites that score 1 or 2 are Partially Supporting (PS), and sites that score 0 are Not Supporting (NS). The 2000 coldwater biological indicator scores were 3/4, 2/4 and 2/4. The 2004 coldwater biological indicator score was 1/4. Based on the biological sampling the aquatic life uses in this segment should be assessed as Partially Supporting (= PS) based on a comparison of the coldwater biological indicator scores with biological assessment criteria established for this Section 305(b) report. The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2004.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.
