Shrickers Slough IA 01-MAQ-1

Results of monitoring conducted by LTRMP at their station M508.1F from 2014-2016 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 the growing seasons from 2014 through 2016 (approximately seven samples per year from May through September), Carlson’s (1977) trophic state index values for total phosphorus, chlorophyll-a, and Secchi depth are 80, 68, 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 2014 through 2016; approximately seven samples were collected during each of the growing seasons of the years 2014-2016.

Using the overall median values from the LTRMP monitoring program from 2014 through 2016, the median growing season total suspended solids (TSS) concentration was 15.5 mg/L (N=24); 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 24.0 in 2014,20.9 in 2015, and14.5 mg/l in 2016, thus, all growing seasons met the 30 mg/l SAV benchmark. The overall median level of turbidity (12.5 NTU) also met the SAV benchmark of 20 NTU. Annual growing season median turbidities all met the SAV benchmark of 20 NTU. Annual growing season average turbidities, however, tended to be below the 20 NTU benchmark with only the 2014 growing season average turbidities being above the 20 NTU threshold.

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 failed to meet the SAV benchmark value of 0.5 meters in all of the three growing seasons. 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 chemical/physical monitoring at station M508.1F monitoring show that 12 of the 89 surface samples (13%) analyzed for dissolved oxygen from 2014-2016 violated the Iowa water quality criterion of 5 mg/l for protection of Class B(WW1) uses (minimum of 0.5 mg/l). None of the 42 samples (0%) violated the acute criterion for ammonia. Two of the 89 samples (2%) analyzed for pH violated the Iowa water quality criterion of 9.0 pH units. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as dissolved oxygen, pH, or ammonia suggests impairment of aquatic life uses. Based on DNR’s assessment methodology, however, the results from LTRM monitoring at Shrickers Slough suggest that the frequency of pH and dissolved oxygen violations is not significantly greater than 10 percent; thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S. EPA/DNR 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.