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, and (4) results from the IDNR-county voluntary beach monitoring program.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due aesthetically objectionable conditions caused by poor water transparency and nuisance algae blooms. [Note: The Class A1 designation was added to this lake in the March 2006 Surface Water Classifications.] The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” although nutrient loading and the impacts of sedimentation remain concerns at this lake. Fish consumption uses remain “not assessed.” 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, and (4) results from the IDNR-county voluntary beach monitoring program.
Note: A TMDL for algae and turbidity at Littlefield Lake was prepared by IDNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2012 assessment/listing cycle (algal growth, and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: Results of IDNR county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (evaluated) as "fully supported." Levels of indicator bacteria at Littlefield Lake beach were monitored approximately once per week during the primary contact recreation season (June through August) of 2004 (10 samples), 2005 (6 samples), and 2006 (6 samples) as part of the IDNR county beach monitoring program. Because limited data was collected in 2005 and 2006 30-day geometric means were not able to be calculated this assessment is considered evaluated (lower confidence) as opposed to monitored (higher confidence). Also, no data were collected in 2007, 2008, 2009, or 2010. 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 Littlefield Lake beach, the geometric means of all 4 thirty-day periods during the summer recreation season of 2004 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. There were not enough samples collected in 2005 and 2006 to calculate 30-day geometric means, therefore the assessment is considered “evaluated.” The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 10% in 2004 and 0% in 2005 and 2006. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support/evaluated of the Class A1 (primary contact recreation) uses.
For the 2012 assessment/listing cycle, results from the ISU and UHL lake surveys indicate that the Class A1 (primary contact recreation) uses of Littlefield Lake are assessed as “not supported” due to aesthetically objectionable conditions caused by poor water transparency and nuisance algae blooms. Data from the ISU and UHL lake surveys, show poor water quality at Littlefield Lake. Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 64, and 77 respectively for Littlefield Lake. According to Carlson (1977) the Secchi depth, and total phosphorus scores place Littlefield Lake in the hypereutrophic category, while the chlorophyll a value places Littlefield Lake in between the eutrophic and the hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was very high at this lake and suggests that non-algal turbidity contributes to the impairment at this lake. The median inorganic suspended solids concentration at Littlefield Lake was 12.5 mg/L, which was the 10th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Littlefield Lake, which also contributes to the aethetically objectionable conditions at this lake. These data show that cyanobacteria comprised 46% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (70.7 mg/L) was also the 11th 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 from 2006-2010. 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” although nutrient loading and the impacts of sedimentation remain concerns at this lake. Results of the ISU and UHL lake surveys from 2006 through 2010 show no violations of the Class B(LW) criterion for ammonia in 22 samples, or for dissolved oxygen in 22 samples. The pH data show 4 violations of the Class A1,B(LW) criterion for pH in 22 samples (18%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 or B(LW) uses of Littlefield Lake. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose de-listing based on pH violations. For both the 2010 and 2012 assessment/listing cycles, less than 10% of the pH samples violated the criteria, therefore the pH impairment is suggested for de-listing for the 2012 Integrated Report.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
