Assessment Comments
Assessment is based on results of water quality monitoring, fish contaminant monitoring, and fish kill reporting conducted downstream from Red Rock Reservoir during the 2006-2008 assessment period by Iowa State University (under contract with the U.S. Army Corps of Engineers) at ISU/ACOE Station 9 at the Howell Station Landing (STORET station 17630001).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "fully supporting" based on results of routine monitoring for indicator bacteria (E. coli). The Class B(WW1) aquatic life uses remain assessed (monitored) as "not supported" due to repeated fish kills immediately downriver from Red Rock Dam. The fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2006, 2007, and 2008. The assessments of support of the beneficial uses are based on results of water quality monitoring, fish contaminant monitoring, and fish kill reporting conducted downstream from Red Rock Reservoir during the 2006-2008 assessment period by Iowa State University (under contract with the U.S. Army Corps of Engineers) at ISU/ACOE Station 9 at the Howell Station Landing (STORET station 17630001). This monitoring was conducted as part of the Des Moines River Water Quality Study (see Lutz and Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009).
EXPLANATION: The Class A1 uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from the ISU/ACOE station 0.7 mi downstream from Red Rock Dam. At this monitoring station, the geometric mean of the 29 samples collected during summers of 2006, 2007 and 2008 was 4 orgs/100 ml; none of the 36 samples exceeded the 235 organism/100 ml single sample maximum criterion. These results, combined with results of previous monitoring, continue to indicate (1) extremely low levels of indicator bacteria in this reach of river and (2) that the lowest levels of indicator bacteria in the state’s streams and river occur immediately downriver from Iowa’s federal flood control reservoirs. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean of E. coli is less than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Results from this ISU/ACOE monitoring station also suggest that the Class B(WW1) aquatic life uses are "fully supported"; however, the Class B(WW1) aquatic life uses remained assessed as "not supported" due to reoccurring fish kills in this river segment. No violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen, pH, ammonia-nitrogen) occurred in the 66 samples collected at this station during the 2006-2008 assessment period. Also, none of the 12 samples analyzed for toxic metals violated their respective Class B(WW1) or human-health (fish) criteria.
The Des Moines River immediately downriver from Red Rock Dam is prone to fish kills caused by gas bubble trauma. For the period 1983 though 2008, 32 kills in the Red Rock Dam tailwater area have been attributed to gas bubble trauma (Lutz and Steffen 2009). Fish kills caused by gas bubble trauma occur due to a large imbalance between the concentrations of atmospheric gasses in the water and the levels of these gasses dissolved in the blood of the fish. The concentrations of dissolved gasses such as oxygen and nitrogen in river water tend to equal the concentrations in the blood of a fish. When the levels of atmospheric gasses dissolved in river water become very high (i.e., super-saturated)—such as can happen when water moves through or over a large dam—the levels of these gasses will also rise in the blood of fish. As long as fish can stay in deeper water, the hydrostatic (water) pressure will keep these gasses fully dissolved in the fish’s blood. If, however, the flow of water downstream from the dam is decreased suddenly, the depth of the water will also decrease. With shallower water, fish are not able to move to deeper areas to keep the hydrostatic pressure sufficiently high to keep the gasses fully dissolved in their blook. During these conditions, the gasses dissolved in the fish’s blood will gradually come out of solution as bubbles, and these bubbles will interfere with blood circulation. Symptoms of gas bubble trauma in fish include gas blisters on the skin at the margins of the scales and as pop-eye (exophthalmia) where the eyes of the fish distend from the eye sockets. In the extreme case, blood circulation is disrupted to the point that fish kills occur.
Two fish kills caused by gas bubble trauma were reported for this river segment for the 2006-2008 assessment period; these kills occurred July 2007 and June 2008. According to IDNR'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, due to the two fish kills during the 2006-2008 period caused by gas bubble trauma, and due to the history of this type of fish kill in this river reach, the Class B(WW1) aquatic life uses are assessed as "not supported” and will remain in IR Category 4c (i.e., impairment due to a non-pollutant stressor; TMDL not required).
Fish contaminant monitoring conducted downstream from Red Rock Reservoir by ISU/ACOE in 2006, 2007, and 2008 showed low levels of contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish and fillets of common carp. In addition to these pesticide parameters, composite samples fillets from common carp and channel catfish from this station were analyzed for mercury in 2004, and composite fillet samples from common carp and largemouth bass were analyzed for mercury in 2005 (this was the first analysis of fish tissue samples for mercury conducted as part of the ISU/ACOE program since 1994). The results showed low levels of mercury in these samples: common carp: 0.04 ppm in 2004 and 0.05 ppm in 2005; channel catfish fillets: 0.06 ppm in 2004; largemouth bass fillets: 0.11 ppm in 2005. This supplemental monitoring for mercury in fish was not conducted during the 2006 sampling season. Based on this information, fish consumption uses are assessed (monitored) as "fully supported".
The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2006, 2007, or 2008 ISU/ACOE samplings (or from previous ISU/ACOE monitoring) conducted in the segment of the Des Moines River immediately downstream from Red Rock Reservoir show that levels of contaminants (chlordane and mercury) do not exceed any of the IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
For more information on ISU/ACOE water quality monitoring in this river reach, see (Lutz and Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009); the URL for the Des Moines River Water Quality Monitoring Network web site is http://home.eng.iastate.edu/~dslutz/dmrwqn/dmrwqn.html.
