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 2008 through November 2011 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 "partially supported" due to poor water transparency as expressed by (1) the trophic state index (TSI) values for chlorophyll-a and Secchi depth and (2) the UMRCC protocol assessing water transparency to allow growth of submersed aquatic vegetation (SAV). This assessment of the aquatic life uses is consistent with previous Section 305(b) assessments. Fish consumption uses remain assessed (evaluated) 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 Bellevue Office of the Upper Mississippi River Long-Term Resource Monitoring Program (LTRMP) from January 2008 through November 2011 and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring on the Mississippi River near Camanche in 2003.
EXPLANATION: Despite some apparent improvements in water transparency at Shrickers Slough over the 2008-2011 period, results of water quality monitoring conducted at Shrickers Slough from 2008-2011 indicate that the aquatic life uses should be assessed (monitored) as "partially supported" due to high levels of algae and poor water transparency at this UMR backwater lake.
Results of monitoring conducted by LTRMP from 2008-11 suggest that the Class B(WW1) uses should be assessed (monitored) as "partially supported" due to poor water transparency in this backwater lake. Using the overall median values from surface samples collected as part of this monitoring during growing seasons from 2008 through 2011 (approximately eight samples per year from May through September), Carlson’s (1977) trophic state index values for total phosphorus, chlorophyll-a, and Secchi depth are 77, 65, and 73, respectively. 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, high (but somewhat less than expected) levels of chlorophyll-a, and very 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. The elimination of SAV can degrade habitat quality such that undesirable aquatic species such as cyanobacteria, common carp and fathead minnows dominate. As such, the suppression of SAV constitutes a violation of Iowa’s narrative water quality criteria protecting against undesirable or nuisance aquatic life. The SAV 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 overall median growing season (May to September) levels of Secchi depth, total suspended solids, and turbidity for the years 2008 through 2011; the number of samples per growing season ranged from seven to nine.
Using the overall median values from the LTRMP monitoring program from 2008 through 2011, the median growing season total suspended solids (TSS) concentration was 19 mg/L; this median value meets the UMRCC benchmark of 30 mg/l. Thus, these results suggest that the aquatic life uses at Shrickers Slough should be assessed as “fully supported”. Annual growing season TSS averages (means) ranged from 17 to 26 mg/l, thus meeting the 30 mg/l SAV benchmark. The overall median level of turbidity (14 NTU) also met the SAV benchmark of 20 NTU. Median and average turbidity in three of the four growing seasons met the SAV benchmark of 20 NTU. The overall median level of Secchi depth (0.4 m), however, failed to meet the SAV benchmark of 0.5 m. Annual growing season average levels of Secchi depth exceeded the SAV benchmark value of 0.5 meters in three of the four growing seasons with only the median and average Secchi depth for 2010 (0.57 and 0.55 m, respectively) meeting this SAV benchmark. Although water transparency in the 2008-2011 period appears to have improved somewhat compared to previous assessment cycles, the results for Secchi depth 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 show that 2 of the 55 surface samples (4%) analyzed for dissolved oxygen from 2008-11 violated the Iowa water quality criterion of 5 mg/l for protection of Class B(WW1) uses (minimum of 4.4 mg/l). One of the 55 samples collected (2%) violated the Iowa water quality criterion for pH (9.4 pH units). According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the violation frequencies of criteria for dissolved oxygen and pH (less than 10%) do not indicate impairment of aquatic life uses. None of the 55 surface samples analyzed for ammonia-nitrogen from 2008-11 exceeded the Class B(WW1) water quality criteria (mean = 0.24 mg/l, median = 0.05 mg/l; maximum = 1.97 mg/l)
Fish consumption uses remain assessed (evaluated) 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 Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
