Assessment Comments
Assessment is based on results of (1) ambient water quality monitoring by LTRMP staff, Bellevue station and (2) U.S. EPA / IDNR fish contaminant (RAFT) monitoring in 1997.
Basis for Assessment
SUMMARY: The designated uses for Shrickers Slough are those given to the adjoining Mississippi River (i.e., Class A,B(WW)). However, no attempt was made to assess this wetland for support of Class A (primary contact recreation) uses. The Class B(WW) (aquatic life) uses were assessed (monitored) as "not supported" due to very high levels of chlorophyll-a and due to very poor water transparency. This assessment differs from the 2002 assessment in that the trophic state index approach (TSI) was used to identify potential impairments. Fish consumption uses are assessed as "fully supported" based on results of fish contaminant monitoring in 1997. 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 July 2000 through September 2002 and (2) U.S. EPA / IDNR fish contaminant (RAFT) monitoring in 1997.
EXPLANATION: Results of monitoring conducted by LTRMP suggest that the Class B(WW) uses are "not supported" due to very poor water transparency at this backwater lake. Using the median values from surface sampled collected as part of this monitoring from 2000 through 2002 (approximately 70 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth in Shrickers Slough are 78, 71, and 74, respectively, for Shrickers Slough. According to Carlson (1977), these index values place this waterbody in the hyper-eutrophic range and suggest extremely high levels of phosphorus in the water column, very high (but somewhat less than expected) levels of chlorophyll-a, and very poor water transparency. These conditions indicate impairments to the Class B(WW) (aquatic life) uses and general uses through presence of aesthetically objectionable conditions caused primarily by blooms of algae and secondarily by high levels of inorganic turbidity that reduce water transparency.
Results of LTRMP monitoring also that show 6 of the 64 surface samples (9.4%) analyzed for dissolved oxygen exceeded the Iowa water quality criterion of 5 mg/l for protection of Class B(WW) uses. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), this violation frequency is on the border between "full support and impairment of the aquatic life uses. Thus, these uses were assessed as "fully supported/threatened" such that nonsupport of these uses is likely to occur over the next two years. Four of 71 samples collected violated the Iowa water quality criterion for pH. According to U.S. EPA guidelines for Section 305(b) assessments, this frequency of violation (5.6%) does not indicate a water quality impairment. One of the 71 surface samples analyzed for ammonia-nitrogen exceeded the Class B(WW) water quality criteria; this single violation does not suggest a water quality impairment but, according to IDNR’s assessment methodology, does suggest a “threat” to full support of this designated use.
Fish consumption uses are assessed as “fully supported” based on results of fish U.S. EPA /IDNR fish contaminant (RAFT) monitoring conducted in 1997. Levels of all contaminants in the composite samples of fillets from carp and white crappie were well below FDA action levels and DNR levels of concern. his site was again sampled as part of the 2003 RAFT program; the results from this monitoring, however, are not yet available.
