Rock Creek IA 01-MAQ-4

Assessment Comments

Two 1991 stream use assessment sites in Clinton County. LTMRP WQ monitoring at Hwy 67 and at County Road Z40.

Basis for Assessment

Continued monitoring by Gritters and Gould (DNR, LTRMP, Bellevue) strongly suggests that a local industry is the source of much of the high levels on nitrate and ammonia in the middle and lower reaches of Rock Creek, including Shricker Slough.   DNR Water Quality, Land Quality, and Field Office 6 met with industry representatives in June 1998 and discussed alternatives to reduce nitrogen levels in Rock Cr.  and Shricker Slough.   Industry will begin implementation of corrective measures and monitoring of surface and groundwater in the near future and report back to DNR in one year on progress.   Due to results of continued upstream/downstream monitoring by LTRMP/Bellevue staff that show excessively high levels of nitrogen in Rock Creek and excessively high levels of chlorophyll-a in Shricker Slough, continue to assess Rock Creek as partially supporting its Class B(LR) aquatic life uses.  A review of the field sheets from the October 1991 DNR stream use assessments supports the assessment of the Class B(LR) aquatic life uses as PS.   That is, results of the stream use assessment near Low Moor show the presence of less than a majority of the expected fish taxa (4 of 9) for streams in the Southern Iowa Rolling Loess Prairies subecoregion and show a relatively low fish community diversity of 8 cyprinid species.  Fish community diversity (11 species from 3 families) is somewhat better at the second SUA site SW (upstream) from Quantum Chemical but is below that suggested by the above average habitat quality.   However, an August 1997 DNR Fisheries survey 2 mi E of Low Moor suggests full support of the Class B(LR) uses (i.e., 10 spp; 3 fams, with 6 of 9 expected fish taxa present).

[NOTE: The 1998 assessment refers to the Rock Creek IA 01-MAQ-0010 waterbody as a whole.  For the 2002 report, Rock Creek was subdivided into three segments:  IA 01-MAQ-0010-1 (lower), IA 01-MAQ-0010-2 (above PCS-Nitrogen), and IA 01-MAQ-0010-3 (headwaters).]