Assessment Comments
Assessment is based on results of monitoring conducted from 2000-02 as part of the Rathbun Lake Water Quality Project and on 1999-2002 Fisheries data: Fish IBI average (n=3) = 29 (fair).
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses were assessed (monitored) as "not supported" due to levels of dissolved oxygen and ammonia that violate state water quality criteria. The assessment of support of the Class B(LR) uses is based on results of water quality monitoring conducted from 2000 through 2002 on Jordan Creek near Bethlehem (station RA-37) by Iowa State University under contract with the U.S. Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project. This assessment was also based on results of biological monitoirng (fish surveys) conducted by the IDNR Fisheries Bureau from 1999-2002.
EXPLANATION: Although none of the 27 samples collected from 2000 through 2002 violated Class B(LR) criteria for pH, monitoring results for dissolved oxygen and ammonia-nitrogen suggest a potentially significant water quality problem. Four of the 27 samples collected (15%) at station RA-37 from 2000 through 2002 violated the Class B(LR) water quality criterion for dissolved oxygen; three of these violations occurred in the relatively dry year of 2000; one occurred just before the stream was reported as “dry” in August 2002. The violations of the state criterion for dissolved oxygen are as follows: 4.7 mg/l on May 16, 2000; 2.6 mg/l on June 13, 2000; 1.8 mg/l on June 27, 2000; and 4.5 mg/l on August 13, 2002. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), if criteria for conventional parameters (e.g., pH, dissolved oxygen and temperature) are exceeded in from 11% to 25% of the samples "partial support" of beneficial uses is indicated. Thus, the violation frequency of the Class B(LR) criterion for dissolved oxygen (16%) suggests "partial support" of the Class B(LR) aquatic life uses. In addition, three of the 27 samples collected at Station RA-37 exceeded the Class B(LR) chronic criterion for ammonia-nitrogen. These violations occurred in samples collected on June 13, 2000 (1.87 mg/l), on July 19, 2000 (3.0 mg/l), and on August 15, 2000 (2.01 mg/l). According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), if criteria for toxic parameters (e.g., ammonia-nitrogen and toxic metals) are exceeded in more than one sample over a three-year period, "nonsupport" of beneficial uses is indicated. Thus, due to the two violations of the Class B(LR) chronic criteria for ammonia-nitrogen, the Class B(LR) uses of Jordan Creek are assessed as "not supported." Similar to results of monitoring conducted in 1998 and 1999, results from the 2000-2002 period continued to show high levels of nutrient parameters. While levels of total nitrogen in Jordan Creek and other streams in the Rathbun watershed are relatively low for Iowa, levels of total phosphorus tend to be relatively high. The 2000-2002 mean and median levels for total phosphorus at Station RA-37 were 0.20 mg/l and 0.21 mg/l, respectively (N=27); the mean and median levels of total nitrogen for this period were 2.1 mg/l and 1.4 mg/l, respectively (N=27). The Iowa Water Quality Standards do not currently have aquatic life criteria for these nutrient parameters or for other nonpoint source-related parameters (for example, total suspended solids). The Iowa DNR is, however, continues to participate in a nationwide program, led by U.S. EPA, for states to develop and adopt surface water criteria for total phosphorus, total nitrogen, chlorophyll, and some measure of turbidity. Although this stream is not designated for Class C drinking water uses, Jordan Creek does flow into Rathbun Reservoir which is designated for Class C uses. Thus, the seasonal elevation of pesticides levels in this stream and other tributaries of Rathbun Reservoir presents a continuing threat to full support of the Class C (drinking water) uses designated for Rathbun Reservoir. For example, the mean level of atrazine in the 27 samples collected at Station RA-37 from 2000 through 2002 (4.8 ug/l) exceeded the atrazine MCL of 3.0 ug/l; the maximum levels of 40.2 ug/l of atrazine occurred in the sample collected on June 1, 2001.
The assessment was partially based on data collected in 1999-2002 as part of a DNR Fisheries stream sampling project: Chariton research stations. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999-2002 evaluated Fish IBI average score (n=3) was 29 (fair). The aquatic life use support was assessed (evaluated) as Partially Supporting (=PS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
