Des Moines River IA 04-LDM-1010

The Class A1 uses are assessed (monitored) as "partially supporting" based on results of DNR ambient monitoring near downstream of Ottumwa. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at station 10900002 were as follows: the 2012 geometric mean was 90 orgs/100 ml, the 2013 geometric mean was 96 orgs/100 ml, and the 2014 geometric mean was 159 orgs/100 ml. The 2012 and 2013 geometric means are below the Class A1 geometric mean criterion of 126 orgs/100 ml, while the 2014 geometric mean slightly exceeds this criterion. Seven of the 22 samples (32%), however, exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired” (partially supported).

The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” due to fish kills on July 10, 2006 and on July 2, 2012 on the reach of river between Eldon (Wapello Co.) and Douds (Van Buren Co.). These kills are in a series of kills that have occurred over the last 15 years or so that appear to involve primarily shovelnose sturgeon (Scaphirhynchus platorynchus). Although the cause of the previous kills remains unknown, the leading hypotheses are (1) that very high water temperatures, very low river flows, and elevated pH levels combine to make ambient levels of ammonia in the river toxic to the ammonia-intolerant shovelnose sturgeon and (2) that the kills are caused by a virus specific to shovelnose sturgeon. The most recent kill in July 2012 was especially severe. According to the local DNR Fisheries biologist, the kill was reported on the lower Des Moines River on July 7, 2012, from approximately Eldon (downriver from Ottumwa) to Farmington in Van Buren County. An estimated 57,000 fish were killed including at least 35,000 shovelnose sturgeon. No specific cause of the kill was identified, but low flow conditions, flow alterations, and very high water temperatures (95+F) are believed to have contributed to the kill.

According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates that the aquatic life uses of a waterbody are only "partially supported.” Thus, the Class B(WW1) aquatic life uses of this river reach were assessed as "partially supported” (303(d) impaired). Also, according to DNR’s assessment methodology, if a cause of a fishkill was not identified during the DNR investigation (cause = "unknown"), or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, typically lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (Category 5 of the Integrated Report). Waterbodies affected by such fish kills at usually placed in IR subcategories 2b or 3b and are added to the state’s list of “waters in need of further investigation”. Due however to (1) the repeated occurrence of these kills over the last 15 years in Wapello and Van Buren counties, (2) the often large numbers of sturgeon killed (thousands), (3) the likelihood that these kills are caused by a pollutant and (4) the possibility that the kills have extended further downstream (possibly to Bonaparte), this impairment was added to Iowa’s Section 303(d) list (Category 5 of the Integrated Report).

In contrast to the poor water quality suggested by the reoccurring fish kills, results of ambient chemical/physical water quality monitoring from the DNR/SHL station downstream from Ottumwa at Cliffland Road from 2012 through 2014 show no violations of Class B(WW1) criteria and suggest generally good water quality. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia-nitrogen, temperature, chloride, or sulfate in the 33 samples analyzed. One of the 36 samples collected (3%) exceeded the Class A, B(WW1) criterion for pH. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to DNR’s assessment/listing methodology, however, the results from DNR station 10900002 do not indicate that greater than 10% of the samples exceed either the Class B(WW1) criteria for pH. Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

Regardless of the indication of “full support” of the Class B(WW1) aquatic life uses from results of chemical/physical monitoring, the Class B(WW1) uses remain assessed as Section 303(d) impaired to the repeated severe fish kills in this river segment.

Results of biological sampling conducted in 2003 and 2012 suggest “partial support” of the aquatic life uses. This assessment is based on data collected in 2003 and 2012 as part of the DNR/SHL stream sampling projects. A series of biological metrics that 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 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 2003 FIBI score was 40 (fair) and the BMIBI score was 46 (fair). The 2012 BMIBI score was 13 (poor). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), 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 1994-2008. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This assessment is considered evaluated because the drainage areas (13,443 and 13,435 mi2) above the sampling sites were far greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC (1/1) and failed the BMIBI BIC (1/2), it is uncertain as to whether or not this segment is meeting the aquatic life criteria becausethe sites used for the assessmentdon’t fall in the calibrated watershed size. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of DNR fish contaminant monitoring at the Cliffland Access downriver from Ottumwa in 2016. The 2016 composite samples of fillets from channel catfish also had low levels of the primary contaminants: mercury: 0.07 ppm; total PCBs: <0.06 ppm; and technical chlordane: <0.02 ppm. All four of the 2016 tissue plug samples collected from white bass had non-detectable levels of mercury (<0.05 ppm). The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. Although results of previous fish contaminant monitoring showed that this river segment has a history of somewhat elevated levels of chlordane in fish, the levels of chlordane in the 2016 channel catfish samples are well below the DPH/DNR advisory trigger level of 0.6 ppm. Also, the levels of the other contaminants did not exceed Iowa’s advisory trigger levels for mercury and PCBs, thus suggesting no justification for issuance of a consumption advisory.