Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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 “partially supported” due to violations of the Class A1 criterion for pH. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH. Fish consumption uses are “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program.
EXPLANATION: Results of IDNR county beach monitoring from 2006 suggest that the Class A1 uses are assessed (evaluated) as "fully supported." Levels of indicator bacteria at Little Sioux Lake beach were monitored approximately once per week during the primary contact recreation season (May through August) of 2006 (16 samples) as part of the IDNR county beach monitoring program. Because only one year of data was collected for indicator bacteria the assessment is considered evaluated (lower confidence) rather than monitored (higher confidence). 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 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 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 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).
At Little Sioux Lake beach, the geometric means of all 12 thirty-day periods during the summer recreation season of 2006 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 also less than 10% in 2006 (6%). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
For the 2008 assessment/listing cycle, results from the ISU and UHL lake surveys indicate that the Class A1 (primary contact recreation) uses of Little Sioux Park Lake are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH. Additional data from the ISU and UHL lake surveys, shows exceptional water quality at Little Sioux Park Lake. Using the median values from these surveys from 2002 through 2006 (approximately 21 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 42, 44, and 48 respectively for Little Sioux Park Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus scores all place Little Sioux Park Lake in the mesotrophic category. These values suggest extremely levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and extremely low levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was extremely low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Little Sioux Park Lake was 1.0 mg/L, which was the 3rd lowest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a very small population of cyanobacteria exists at Little Sioux Park Lake. These data show that cyanobacteria comprised only 34% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (1.8 mg/L) was the 8th lowest of the 132 lakes sampled. These results suggest full support of the Class A1 uses at Little Sioux Park Lake.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH. Results of the ISU and UHL lake surveys from 2002 through 2006 show no violations of the Class B(LW) criterion for ammonia in 15 samples, or dissolved oxygen in 21 samples. The pH data, however, show 9 violations of the Class A1,B(LW) criterion for pH in 21 samples (43%). Based on IDNR’s assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (partial support/monitored) of the Class B(LW) uses of Little Sioux Park Lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
