Assessment Comments
Assessment is based on: (1) monitoring conducted at Shrickers Slough by staff of the Upper Mississippi River Long-Term Resource Monitoring Program (Bellevue Office) from January 2004 through November 2008 and (2) U.S. EPA / IDNR fish contaminant (RAFT) monitoring on the Mississippi River near Camanche in 2003.
Basis for Assessment
SUMMARY: Shrickers Slough is part of a backwater complex in Clinton County in Pool 14 of the Upper Mississippi River between river miles 508 and 510. Shrickers Slough receives year-round flow directly from Rock Creek. The designated uses for Shrickers Slough are those given to the adjoining Mississippi River (i.e., Class A1,B(WW1)). No attempt was made to assess this wetland for support of Class A1 (primary contact recreation) uses. The Class B(WW1) (aquatic life) uses were assessed (monitored) as "not supported" due to very poor water transparency as expressed by the trophic state index (TSI) values for chlorophyll-a and Secchi depth. This assessment is consistent with previous Section 305(b) assessments. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2003. The sources of data for this assessment include the results of (1) monitoring conducted approximately twice per month at Shrickers Slough by staff of the Upper Mississippi River Long-Term Resource Monitoring Program (Bellevue Office) from January 2004 through November 2008 and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring on the Mississippi River near Camanche in 2003.
EXPLANATION: Results of monitoring conducted by LTRMP suggest that the Class B(WW1) uses are "not supported" due to very poor water transparency in this backwater lake. Using the median values from surface sampled collected as part of this monitoring from 2004 through 2008 (approximately 75 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and Secchi depth are 82, 70, and 76, respectively, for Shrickers Slough. According to Carlson (1977), these index values place this waterbody in the hyper-eutrophic range and continue to suggest extremely high levels of phosphorus in the water column, very high (but somewhat less than expected) levels of chlorophyll-a, and extremely poor water transparency. These conditions indicate impairments to the Class B(WW1) (aquatic life) uses.
In 2003, the Upper Mississippi River Conservation Committee’s Water Quality Technical Section proposed water quality benchmarks necessary to sustain submersed aquatic vegetation in the Upper Mississippi River (“Proposed water quality criteria necessary to sustain submersed aquatic vegetation in the Upper Mississippi River, Upper Mississippi River Conservation Committee Water Quality Technical Section October 2003). Submersed aquatic vegetation is an important component of the aquatic habitat in the Upper Mississippi River (UMR) navigation pools. Leaves, seeds and vegetative propagules are a source of food for waterfowl. The submerged plants provide a substrate for invertebrate and periphyton colonization, habitat for larval and adult fish, and help stabilize fine sediments from boat waves and wind-induced sediment resuspension. Submersed aquatic plants have been used to assess water quality and to provide a measure of ecosystem health. These benchmarks are designed to ensure that that the annual 1% light penetration depth will be between 1 to 1.5 m. The benchmarks are as follows: Secchi depth: 0.5 meters; total suspended solids: 25 mg/l (updated to 30 mg/l by Wisconsin DNR); and turbidity: 20 NTU. The benchmarks are to be applied as a growing season average (May 15 -September 15). These benchmarks reflect the minimum light criteria necessary to sustain and enhance SAV on the river. LTRMP data were used to calculate average growing season levels of Secchi depth, total suspended solids, and turbidity for the years 2004 through 2008; the number of samples per growing season ranged from seven to nine. A comparison of these averages shows that average levels of total suspended solids were below (met) the SAV benchmark of 30 mg/l in all years, with the average growing season TSS values ranging from 25 to 28 mg/l. Average levels of turbidity exceeded the SAV benchmark of 20 NTU in four of the five growing seasons with averages ranging from 18 to 25 NTU. Average levels of Secchi depth, however, exceeded the SAV benchmark value of 0.5 meters in all five growing seasons with averages ranging from 0.41 to 0.3 meters. These results support the assessment based on TSI values that suggest high levels of turbidity in Shrickers Slough are impairing the designated aquatic life uses.
Results of LTRMP monitoring also show that 6 of the 74 surface samples (8%) analyzed for dissolved oxygen from 2004-08 violated the Iowa water quality criterion of 5 mg/l for protection of Class B(WW1) uses. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), this violation frequency does not indicate impairment of aquatic life uses. Eight of the 74 samples collected (11%) violated the Iowa water quality criterion for pH. Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class B(WW1) uses of Shrickers Slough. None of the 71 surface samples analyzed for ammonia-nitrogen from 2004-08 exceeded the Class B(WW1) water quality criteria
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring downstream from Camanche in 2003. The composite samples of fillets from common carp and white crappie had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.079 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.03 ppm. Levels of primary contaminants in the composite sample of white crappie fillets were as follows: mercury: < 0.0181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 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. The fish contaminant data generated from the 2003 RAFT sampling conducted downstream from Camanche do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
