Mud Creek IA 02-CED-488

Assessment Comments

Habscrs/fshscrs: 26/12; 16/10. (1997v.) Fish IBI scores: 18,20,18,18,32,34. Downstr>Upstr. 1996 Biocriteria: Fish (1999v.) IBI= 43,38 (fair), 18,18,16,13 (poor); BM-IBI= 33,34 (fair), 20,20,27 (poor), 34(fair).

Basis for Assessment

SUMMARY:  The Class B(LR) uses remained assessed as "not supported."  Sources of information for this assessment include (1) results of biological monitoring conducted at six sites in 1996 as part of the DNR/UHL watershed assessment project and (2) water quality monitoring conducted at five sites in this stream segment from March to November 2001 by IDNR and UHL in support of TMDL development.   EXPLANATION:  The Class B(LR) uses remain assessed as "not supported" based on results of biological monitoring conducted in 1996 (see assessment for the 2000 report above).   Results of monitoring conducted in 2001 in support of TMDL development, however, show only one violations of Class B(LR) 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(LR) 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.   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 monthly TMDL monitoring sites.