Assessment Comments
Assessment is based on results of (1) IDNR/UHL biocriteria monitoring in 2001 and (2) LTRMP ambient water quality monitoring from 2000-02.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (monitored) as "partially supported" based on results of biological monitoring in 2001. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach. The sources of data for this assessment include (1) results of IDNR/UHL biological monitoring in 2001 and (2) results of routine water quality monitoring conducted at station TM04.1 from 2000 through 2002 by IDNR staff of the Upper Mississippi River "Long-Term Resource Monitoring Program (LTRMP) at Bellevue, IA.
EXPLANATION: The assessment of the Class B(WW) uses is based on results of IDNR/LTRMP chemical/physical monitoring and IDNR / UHL biological monitoring. In part, the assessment was based on data collected in 2001 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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2001 Fish IBI score was 58 (good) and the BM-IBI score was 48 (fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
In addition to biological monitoring, the IDNR/LTRMP staff at Bellevue supplied water quality data for 36 samples collected from Tete de Mortes Creek during the period January 2000 through September 2002. Samples were collected approximately monthly; samples were collected during all months of the year. The parameters analyzed included dissolved oxygen, pH, ammonia-nitrogen, total phosphorus, total nitrogen, total suspended solids, and chlorophyll. A summary of these data show no violations of the Class B(WW) water quality criteria for temperature, pH, dissolved oxygen, or ammonia-nitrogen in the 36 samples collected. Based on this monitoring, levels of total phosphorus and chlorophyll-a appear to be relatively low in this stream.
Despite the results of chemical monitoring that suggest good water quality in Tete de Mortes Creek ("full support" of the Class B(WW) uses), the results of biological monitoring suggest an impairment ("partial support") of the aquatic life uses. Because stream biota (fish and aquatic macroinvertebrates) integrate water quality impacts over the long-term, the results of biological monitoring are typically weighted more than results of chemical monitoring when determining support of aquatic life uses for purposes of Section 305(b) reporting. This approach is consistent with recommendations in U.S. EPA's guidelines for Section 305(b) reporting (see U.S. EPA 1997b, page 3-21). Thus, considering the "full support" suggested by results of chemical monitoring, and the "partial support" suggested by results of biological monitoring, the aquatic life use of this segment of this stream are assessed as "partially supported" for the 2004 report.
Fish consumption uses remain "not assessed" due to the lack of monitoring in this stream reach.
