Assessment Comments
Assessment is based on: (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 2002 through November 2006 and (2) U.S. EPA / IDNR fish contaminant (RAFT) monitoring on the Mississippi River near Camanche in 2003.
Basis for Assessment
SUMMARY: The designated uses for Shrickers Slough are those given to the adjoining Mississippi River (i.e., Class A1,B(WW1)). However, 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 high levels of chlorophyll-a and due to very poor water transparency. This assessment is consistent with the 2004 and 2006 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 2002 through November 2006 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 at this backwater lake. Using the median values from surface sampled collected as part of this monitoring from 2002 through 2006 (approximately 75 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and Secchi depth are 82, 70, and 75, 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 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. The trend for TSI values for total phosphorus, chlorophyll-a, and Secchi depth over the 2000-2004 period is stable to a potentially worsening trend: these data do not indicate any improvements in water quality conditions at this wetland. On a per-sample basis, over 80% of the chlorophyll-a and Secchi depth samples collected at Shrickers Slough over the 2002-2006 period would fail to meet IDNR assessment guidelines for trophic state index for identifying “full support” of designated uses.
Results of LTRMP monitoring show that 6 of the 75 surface samples (8%) analyzed for dissolved oxygen from 2002-06 exceeded 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. Ten of the 75 samples collected (13%) 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 62 surface samples analyzed for ammonia-nitrogen from 2002-06 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. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses. This scenario, however, does not apply to the fish contaminant data generated from the 2003 RAFT sampling conducted downstream from Camanche: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
