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 of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2001, and (5) results of beach monitoring in 2008 and 2009.
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 and (2) levels of indicator bacteria at a swimming beach that exceed state water quality criteria. 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. Fish consumption uses are assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 2001. Sources of data for this assessment include (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 of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2001, and (5) results of IDNR city/county beach monitoring in 2008 and 2009.
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 2010 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 2004 through 2008 (approximately 24 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 60, 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 moderately high 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 very high at Storm Lake and suggests that non-algal turbidity contributes to the impairment. The median inorganic suspended solids concentration at Storm Lake was 14.5 mg/L, which was the 11th highest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Storm Lake, which does not contribute to the impairment at this lake. These data show that cyanobacteria comprised 72% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (10.6 mg/L) was also the 48th lowest of the 132 lakes sampled.
Results of IDNR county beach monitoring in 2008 and 2009 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 2008 (10 samples) and 2009 (13 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 thirty-day 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. 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.” Also, if significantly more than 10% of the samples in any one of the recreation seasons assessed 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).
At Awaysis Beach, the geometric means of 5 thirty-day periods during summer 2008 and 7 thirty-day period during summer 2009 exceeded 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 less 30% during summer 2008 and was 54% during summer 2009. 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 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 23 samples, no violations for dissolved oxygen in 24 samples, and one violation for pH in 24 samples (4%). Based on IDNR’s assessment methodology the one violation for pH is less than 10% of the samples and therefore does not suggest an impairment of the Class B(LW) uses at Storm Lake.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Storm Lake in 2001. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 2001 RAFT sampling conducted at Storm Lake showed that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
