Honey Creek IA 05-CHA-1337

Assessment Comments

Assessment is based on results of monitoring conducted from 2002-04 as part of the Rathbun Lake Water Quality Project.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses are assessed (monitored) as "fully supported".   This (2006) assessment differs from that for the previous (2004) reporting cycle (“partially supported”) due to the lack of violations of Class B(LR) criteria for dissolved oxygen in the 2002-04 period versus the 2000-02 period.   The 2006 assessment of support of the Class B(LR) uses is based on results of water quality monitoring conducted from 2002 through 2004 on Honey Creek near Melrose (station RA-40) 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.  

EXPLANATION:  None of the 25 samples collected during the 2002-04 period at station RA-40 violated Class B(LR) criteria for ammonia-nitrogen (maximum level = 0.9 mg/l), for dissolved oxygen, or for pH.   These results are in contrast to the violations for Class B(LR) dissolved oxygen criteria during the previous assessment period (2000-2002) when monitoring results for dissolved oxygen suggested a potentially significant water quality problem.   Three of the 24 samples (12.5%) collected at station RA-40 from 2000 through 2002 violated the Class B(LR) water quality criterion for dissolved oxygen; all of these violations occurred in the relatively dry year of 2000 and were as follows:  June 13:  2.9 mg/l; June 27:  1.9 mg/l; August 15:  4.7 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 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, for purposes of the 2004 Section 305(b) reporting cycle, the violation frequency of the Class B(LR) criterion for dissolved oxygen (12.5%) suggested "partial support" of the Class B(LR) aquatic life uses.   The lack of violations for dissolved oxygen in the 41 samples collected at Station RA-40 since 2000 suggest improved water quality in this stream segment and the absence of any aquatic life impairments due to low levels of dissolved oxygen.  

Similar to results of previous monitoring in the Rathbun watershed, results from the 2002-2004 period continued to show high levels of nutrient parameters.   While levels of total nitrogen in Honey Creek and other streams in the Rathbun watershed are relatively low for Iowa, levels of total phosphorus tend to be relatively high.   The 2002-2004 mean and median levels for total phosphorus from Station RA-40 were 0.23 and 0.22 mg/l, respectively.   .   The corresponding mean and median levels of total Kjeldahl nitrogen for this period were 1.1 mg/l and 0.9 mg/l, respectively (N=22).   The Iowa Water Quality Standards does 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, 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, Honey Creek does flow into Rathbun Reservoir which is used as a source of drinking water for a public water supply.   Thus, the seasonal elevation of pesticide levels in this stream and other tributaries of Rathbun Reservoir presents a continuing concern for full support of the Class C (drinking water) uses designated for the Chariton River immediately downriver from Rathbun Reservoir.   In contrast to mean levels of atrazine above the MCL in most other tributaries of Rathbun Reservoir, the mean level of atrazine in the 17 samples collected at station RA-40 from 2002 through 2004 (1.7 ug/l) was well below the atrazine MCL of 3 ug/l.   The maximum level of 14.4 ug/l of atrazine occurred in the sample collected on May 14, 2002.