Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 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) results of beach monitoring in 2011 and 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to (1) poor water transparency caused by inorganic suspended solids that violates Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions (IR 4a) and (2) levels of indicator bacteria at a swimming beach that exceed state water quality criteria (IR 5a). The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” (IR 3b) due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. Fish consumption uses are "not assessed" due to a lack of information upon which to base an assessment. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 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) results of beach monitoring in 2011-2012.
Note: A TMDL for turbidity at Storm Lake was prepared by IDNR and approved by EPA in 2005; thus, this impairment is placed in IR Category 4a (impaired; TMDL approved) for the 2010 cycle. Because, however, the bacteria impairment is not addressed by the TMDL, this impairment will be placed in Category 5a of the 2014 Integrated Report (i.e., Section 303(d) list).
EXPLANATION: Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Storm Lake are “not supported.” Using the median values from these surveys from 2008-2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 51, and 67 respectively for Storm Lake. According to Carlson (1977) the Secchi depth value places Storm Lake in the hypereutrophic category, the chlorophyll a value places Storm Lake in the eutrophic category, and the total phosphorus value places Storm Lake in between the eutrophic and hypereutrophic categories. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very poor water transparency, and high levels of phosphorus in the water column.
The level of inorganic suspended solids is extremely high at Storm Lake and suggests that non-algal turbidity contributes to the impairment. The median inorganic suspended solids concentration at Storm Lake was 23.2 mg/L, and ranked 131st of of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Storm Lake, which does not contribute to the impairment at this lake. These data show that cyanobacteria comprised 100% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (30.6 mg/L) and ranked 98thof the 134 lakes sampled.
Results of IDNR county beach monitoring in 2011-2012 suggest that the Class A1 uses should be assessed (monitored) as "not supported." Levels of indicator bacteria at Awaysis Beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2011 (15 samples) and 2012 (15 samples) as part of the IDNR county 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) all recreation season geometric means for the 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.
At Awaysis Beach, the geometric mean for 2012 was below the recreation season standard of 126 E.coli orgs/100 ml. in 2011, however, the geometric mean exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean in 2011 was 162 E.coli orgs/100 ml and the geometric mean was 65 E.coli orgs/100ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 33% in 2011 and 20% in 2012. According to IDNR’s assessment methodology and U.S. EPA guidelines, violation of both the geometric mean and single-sample maximum criteria suggest impairment of the Class A1 (primary contact recreation) uses at this beach.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment although information from the IDNR Fisheries Bureau suggests that water quality is generally improving at this lake. The ISU and UHL lake surveys results, however, show relatively good chemical water quality at Storm Lake. During 2008-2012 there were no violations of the Class B(LW) criterion for ammonia in 14 samples, no violations for dissolved oxygen in 14 samples, and no violations for pH in 14 samples.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Storm Lake in 2011. The composite samples of fillets from walleye and channel catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.078 ppm. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0453 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. The fish contaminant data generated from the 2011 RAFT sampling conducted at this Storm 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.
