Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 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 2006 through 2008, 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 “not 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 2004 through 2008 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 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 2006 through 2008, 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 2010 assessment/listing cycle (pathogens) are addressed by the TMDL, this waterbody is placed in IR Category 5a (impaired; TMDL needed) for the 2010 assessment/listing cycle.
EXPLANATION: Results of IDNR county beach monitoring from 2006 through 2008 suggest that the Class A1 uses are assessed (monitored) as "not supported." Levels of indicator bacteria at Easter Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (14 samples), 2007 (14 samples), and 2008 (14 samples) as part of the IDNR county beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. If a 5-sample, 30-day 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”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Easter Lake beach, the geometric means of 2 thirty-day periods during the summer recreation season of 2008 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. All 16 geometric means from 2006 and 2007 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2006, 7% in 2007 and 29% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, the exceedences of the geometric mean criterion suggest nonsupport of the Class A1 (primary contact recreation) 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 2004 through 2008 (approximately 25 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 59, and 70 respectively for Easter Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Easter Lake in between the eutrophic and the hypereutrophic categories while the chlorophyll a score places Easter Lake in the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, poor water transparency, and 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 (7.1 mg/L) was the 30th highest median of the 132 lakes sampled by the ISU and UHL programs.
Data from the 2004-2008 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Easter Lake. These data show that cyanobacteria comprised 71% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.0 mg/L) was the 52nd lowest of the 132 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 2004-2008, however, suggest "full support" of the Class B(LW) uses. These results show no violations of the Class B(LW) criteria for ammonia in 24 samples or dissolved oxygen in 25 samples. The data show two violations of the Class A1,B(LW) criterion for pH in 25 samples (8%). 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.
