Fourmile Creek IA 04-LDM-1112

Assessment Comments

Assessment is based on IDNR/UHL biological monitoring in 1999 both upstream and downstream from the Ankeny WWTP: Downstream FIBI = 24(poor), 30(fair); BMIBI= 55(fair), 49(fair); Upstream FIBI = 38(fair), 37(fair); BMIBI = 69(good), 74(good).

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(LR) aquatic life uses are assessed (evaluated) as "fully supported" based on results of IDNR/UHL biological (biocriteria) sampling in 1999.   The data are now more than five years old; therefore, the assessment has been changed from monitored to evaluated.

EXPLANATION:  The Class A (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.

The assessment of the Class B(LR) aquatic life uses was based on data collected in 1999 as part of the DNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 FIBI scores upstream from the Ankeny WWTP were 38 (fair) and 37 (fair) and the BMIBI scores were 69 (good) and 74 (good).   Downstream from the Ankeny WWTP, the FIBI scores were 30 (fair) and 24 (poor) and the BMIBI scores were 49 (fair) and 55 (fair).   The FIBI average was 32 and the BMIBI average was 62.   The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The non-riffle FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62.