Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009 through 2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL),(3) information from the IDNR Fisheries Bureau, and (4) IDNR RAFT fish tissue monitoring.
Basis for Assessment
SUMMARY: This lake is not designated for Class A1 primary contact recreation uses. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supporting.” Information from the IDNR Fisheries Bureau suggests poor water transparency due to algae and inorganic turbidity (suspended solids) have led to a poor fishery that suggests an impairment of the aquatic life uses. Fish consumption are assessed as "fully supporting." Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2009 through 2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from in 2008 by University Hygienic Laboratory (UHL),(3) information from the IDNR Fisheries Bureau, and (4) IDNR RAFT fish tissue monitoring.
EXPLANATION: For the 2014 reporting cycle, the Class B(LW) uses for Avenue of the Saints Lake are assessed (monitored) as “fully supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. The water chemistry data from the ISU and UHL lake surveys show no violations of the Class B(LW) criteria for ammonia in 13 samples and 1 violation to the dissolved oxygen criteria in 13 samples. The pH data show 3 violations of the Class B(LW) criterion in 13 samples (21%). These violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses. Avenue of the Saints Lade was assessed as "partially supporting" its Class B (LW) use in the 2010 reporting cycles due to significant violations to the pH criteria (6 violations in 22 samples). Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations. Because there have been two consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criteria, the Class B(LW) uses will be listed as "fully supported" based on results of the ISU and UHL lake monitoring programs.
Using the median values from these surveys from 2008 through 2012 (approximately 13 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 72, 65, and 74 respectively for Avenue of the Saints Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Avenue of the Saints Lake in the hypereutrophic category while the chlorophyll a value places Avenue of the Saints Lake between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and very high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were high and suggest water quality problems exist related to non-algal turbidity. The median level of inorganic suspended solids in Avenue of the Saints Lake (10.9 mg/L) was ranked 117th among the 134 lake monitored.
Data from the 2008-2012 ISU and UHL surveys suggest a large population of cyanobacteria exists at Avenue of the Saints Lake, which contributes to water quality problems at this lake. These data show that cyanobacteria comprised 98% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (91.1 mg/L) was ranked 130th of the 134 lakes sampled. This median is in the worst 25% of the 134 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2008-20012 period. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Avenue of the Saints Lake in 2013. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2013 RAFT sampling conducted at Avenue of the Saints Lake show that levels of mercury are sufficiently high for concern and thus justify follow-up monitoring. Results from the 2013 sampling show that the level of mercury in the sample of largemouth bass fillets (0.786 ppm) exceeds the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Thus, follow-up monitoring is needed at Avenue of the Saints Lake is needed. Levels of primary contaminants in the composite sample of fillets were as follows: total PCBs: <0.6 ppm; and technical chlordane: <0.2 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 2013 RAFT sampling conducted at this Avenue of the Saints Lake show the need for follow-up monitoring.
