Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program from 2008 through 2010, and (5) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2005 and 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to exceedances of the state's water quality standard for indicator bacteria and also due to poor water transparency that violates Iowa’s narrative criteria protecting against aesthetically objectionable conditions. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to siltation impacts at this lake. Fish consumption uses are assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program from 2008 through 2010, and (5) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2005 and 2008.
Note: A TMDL for nutrients and siltation at Easter Lake was prepared by IDNR and approved by EPA in 2005. Because not all Section 303(d) impairments identified for the 2012 assessment/listing cycle (pathogens) are addressed by the TMDL, this waterbody remains in IR Category 5a (impaired; TMDL needed) for the 2012 assessment/listing cycle.
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Easter Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (14 samples), 2009 (14 samples), and 2010 (14 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 Easter Lake 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 72 E. coli orgs/100 ml in 2008, 12 E. coli orgs/100 ml in 2009, and 40 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 29% in 2008, 0% in 2009 and 21% in 2010. The percentage of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2008 and therefore suggests impairment. 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 statewide survey of lakes and the UHL ambient lake monitoring program suggest that the Class A1 uses of Easter Lake be assessed (monitored) as "partially supported" due to poor water transparency caused by non-algal turbidity. Using the median values from these surveys from 2006 through 2010 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 63, and 64 respectively for Easter Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Easter Lake in between the eutrophic and the hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were high and suggest non-algal turbidity contributes to poor water clarity at this lake. The median level of inorganic suspended solids in Easter Lake (7.0 mg/L) was the 33rd highest median of the 134 lakes sampled by the ISU and UHL programs.
Data from the 2006-2010 ISU and UHL surveys suggest a moderately high population of cyanobacteria exists at Easter Lake. These data show that cyanobacteria comprised 48% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (40.0 mg/L) was the 73rd highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due the impacts of siltation at this lake. Information from the IDNR Fisheries Bureau also suggests that a poor fishery exists at Easter Lake. Results from the ISU and UHL lake surveys from 2006-2010, however, suggest "full support" of the Class B(LW) uses. These results show no violations of the Class B(LW) criteria for ammonia in 23 samples or pH in 23 samples. The data show three violations of the Class B(LW) criterion for dissolved oxygen in 23 samples (13%). Based on IDNR’s assessment methodology, these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the aquatic life uses at this lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Easter Lake in 2005 and 2008. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Data from the 2005 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0512 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.026 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.172 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Data from the 2008 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: 0.158 ppm, and technical chlordane: 0.065 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.105 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 2005 and 2008 RAFT sampling conducted at Easter Lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
