Honey Creek IA 05-CHA-1337

Assessment Comments

Assessment is based on results of monitoring conducted in 1998 by the U.S. Geological Survey and in 1999 by Iowa State University as part of the Rathbun Lake Water Quality Project.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses were assessed (monitored) as "fully supported."  EXPLANATION:  The previous assessment of support of the Class B(LR) uses was based, in part, on results of DNR stream use assessments conducted in 1990.   The results of these assessments are now considered too old (greater than five years) for characterizing current water quality conditions.   The current assessment of support of the Class B(LR) uses is based on results of water quality monitoring conducted on the Honey Creek near Melrose (station RA-40) by the Geological Survey (1998) and by Iowa State University/Limnology (1999) under contract with the U.S.  Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project.   The results of this monitoring are summarized in the "Rathbun Lake Water Quality Reports" for 1998 and 1999 (see ACOE 1999 and Kirsh and Leonard 2000).  

Results of this monitoring show no violations of Iowa Class B(LR) water quality criteria for pH in the 10 samples from this station in 1999 or for ammonia-nitrogen in the 17 samples from this station collected during 1998 and 1999.   In addition, none of the nine samples analyzed for dissolved oxygen during the 1998-1999 period violated the Class B(LR) criterion of 5 mg/l.   These results suggest "full support" of the Class B(LR) uses.    Additional monitoring is being conducted in 2000 as part of the ongoing Rathbun Water Quality Project.   Monitoring conducted during 1998 and 1999 showed high levels of both nutrient parameters (total nitrogen and total phosphorus) and pesticides at station RA-40 and at stations on other reservoir tributaries, with the highest levels often associated with storm runoff.   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).   Although this stream reach is not designated for Class C drinking water uses, the stream does flow to Rathbun Reservoir which is designated for Class C uses.   The seasonal elevation of pesticides levels in the tributaries of the Rathbun watershed presents a continuing threat to full support of the Class C (drinking water) uses designated for Rathbun Reservoir.   For example, of the 20 samples collected at station RA-40 1998 and 1999, the three samples that exceeded the atrazine MCL of 3.0 ug/l were collected from late May through mid-June following application of herbicides to farm fields and during months with typically high levels of rainfall.   The mean level of atrazine at Station RA-40 was 4.90 ug/l in 1998 (N=10; maximum of 39.90 ug/l) and 4.89 ug/l in 1999 (N=10; maximum of 34.1 ug/l).