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, and (4) results from the IDNR-county voluntary beach monitoring program from 2006 through 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standard. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses remain “not assessed” due to a lack of fish contaminant monitoring at this lake. 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, and (4) results from the IDNR-county voluntary beach monitoring program from 2006 through 2008.
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 Hickory Grove Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (14 samples), 2007 (15 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 Hickory Grove Lake beach, the geometric means of 3 thirty-day periods during the summer recreation season of 2008 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 21% in 2006, 0% in 2007 and 14% 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 at Hickory Grove Lake.
Results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program, however, show good water quality at Hickory Grove Lake. 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 55, 57, and 57 respectively for Hickory Grove Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Hickory Grove Lake in the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very good water transparency, and relatively low levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were moderately high but do not suggest an impairment due to non-algal turbidity. The median level of inorganic suspended solids in Hickory Grove Lake (3.0 mg/L) was the 48th lowest median of the 132 lakes sampled by the ISU and UHL programs.
Data from the 2004-2008 ISU and UHL surveys suggest a small population of cyanobacteria exists at Hickory Grove Lake, which does not contribute to impairment at this lake. These data show that cyanobacteria comprised 44% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (7.0 mg/L) was the 38th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on results from the ISU and UHL lake surveys. The data from these surveys from 2004-2008 show no violations of the Class B(LW) criteria for ammonia in 25 samples, one violation of the Class B(LW) criterion for dissolved oxygen in 25 samples (4%), and two violations of the Class A1,B(LW) criterion for pH in 25 samples (8%). Based on IDNR’s assessment methodology these results do not suggest impairment of the Class B(LW) uses at Hickory Grove Lake.
Information from the IDNR Fisheries Bureau suggests that high levels of nutrients enter the lake during rain events and that a restoration project is beginning.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.