Assessment Comments
Assessment is based on results from: (1) IDNR/UHL biological monitoring in 1996: Downstr>Upstr. 1996 Fish IBI scores = 37, 36 (fair), 18,18,15,12 (poor); Benthic IBI= 33,34 (fair), 19,20,27 (poor), 33 (fair); (2) rapid bioassessment sampling results in 2000; and (3) IDNR/UHL ambient water quality monitoring in 2001.
Basis for Assessment
SUMMARY: The Class B(LR) uses remain assessed (monitored) as "not supported" based on results of (1) biological monitoring conducted in 1996, (2) rapid bioassessent sampling in 2000, (3) monthly chemical/physical water quality monitoring conducted in 2001. 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, (2) four rapid bioassessment protocol sites sampled in 2000, and (3) monthly chemcial/physical 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). Rapid bioassessment sampling results from 2000 suggested no significant change in aquatic life conditions from 1996. Benthic macroinvertebrate and fish species composition were similar to 1996 levels. Fish with lesions, an indicator of environmental stress or toxicity, seemed to be less abundant than in 1996, yet still higher than natural background levels. Results of monitoring conducted in 2001 in support of TMDL development, however, show only one violation 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.
