Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997 and 2006 and turtle contaminant monitoring in 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of the Class A1 indicator bacteria standard. Algae blooms that violate Iowa's narrative criteria protecting against aesthetically objectionable conditions also cause an impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997 and 2006 and turtle contaminant monitoring in 2009.
Note: Fish populations were renovated in fall 2003 due to an increasingly large population of yellow bass at this lake.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Lake Anita beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (25 samples), 2009 (26 samples), and 2010 (15 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Lake Anita beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 16 E. coli orgs/100 ml in 2008, 16 E. coli orgs/100 ml in 2009, and 122 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 4% in 2008, 4% in 2009 and 47% in 2010. The number of sample exceeding the single-sample maximum was significantly greater than 10% of the samples in 2010 and therefore suggests impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Lake Anita are (monitored) as “partially supported” due to the occurrence of aesthetically objectionable conditions caused by nuisance algae blooms. Using the median values from these surveys from 2006 through 2010 (approximately 17 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 66, and 64 respectively for Lake Anita. According to Carlson (1977) the chlorophyll a, Secchi depth, and total phosphorus values all place Lake Anita in between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column.
The level of inorganic suspended solids was relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Anita was 2.0 mg/L, which was the 21st lowest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lake Anita, which contributes to an impairment at this lake due to nuisance aquatic life. These data show that cyanobacteria comprised 90% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (45.0 mg/L) was the 31st highest 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 2006-2010 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.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that the fishery at this lake has improved since the renovation in 2003. The ISU and UHL lake survey results show good chemical water quality at Lake Anita. During 2006 and 2010 there were no violations of the Class B(LW) criterion for ammonia (17 samples) or pH (17 samples). There was one violation of the Class B(LW) criterion for dissolved oxygen. Based on IDNR's assessment methodology this violation is not significantly greater than 10% of the samples and therefore does not suggest an impairment of the Class B(LW) uses.
Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Anita in 1997 and 2006 and turtle contaminant monitoring in 2009. 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 1997 RAFT sampling conducted at Lake Anita show that levels of all contaminants from this monitoring were below advisory trigger levels. Follow up sampling conducted in 2006 showed that the composite samples of fillets from largemouth bass had levels of mercury below the advisory trigger level of 0.3 ppm. The level of mercury in the composite sample of largemouth bass fillets was 0.252 ppm. In addition turtle contaminant monitoring in 2009 showed low levels of primary contaminants. Levels of primary contaminants in the turtle shoulder muscle were as follows: mercury: 0.171 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. According to IDNR's assessment methodology these results suggest "full support" of the fish consumption uses at Lake Anita.
