Lacey Keosauqua Lake IA 04-LDM-1008

Assessment Comments

Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported.”  The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  The Class C (drinking water) uses are “not assessed.”  The fish consumption uses are “not assessed” due to a lack of fish contaminant monitoring at this lake.   Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.  

NOTE:  A dam failure occurred at this lake in mid-May 2002.   The dam was repaired in early summer 2003, and the lake had returned to normal water levels, and was opened for all uses, in mid-July 2003.  

EXPLANATION: Results of IDNR beach monitoring at Lacey Keosauqua Lake from 2006 through 2008 suggest that the Class A1 uses should be assessed (monitored) as “fully supported.”  Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (16 samples), 2007 (15 samples), and 2008 (14 samples) as part of the IDNR 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 Lacey Keosauqua Lake beach, the geometric means of all 29 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   These results suggest generally low levels of indicator bacteria at this lake.   The percentage of samples that exceeded the single-sample maximum criterion (235 E.  coli orgs/100 ml) was 13% in 2006, 0% in 2007 and 7% in 2008.   Based on IDNR’s assessment methodology these results do not suggest an impairment of the Class A1 uses of Lacey Keosauqua Lake.  

Results from the ISU and UHL lake surveys also suggest that the Class A1 uses at Lacey Keosauqua Lake are “fully supported.”  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 49, 52, and 55 respectively for Lacey Keosauqua Lake.   According to Carlson (1977) the Secchi depth value places Lacey Keosauqua Lake in the mesotrophic category while the chlorophyll a and total phosphorus values place Lacey Keosauqua Lake on the lower end of the eutrophic category.   These values suggest low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and low levels of phosphorus in the water column.  

The level of inorganic suspended solids is low at this lake and does not suggest impairment due to high non-algal turbidity.   The median inorganic suspended solids concentration at Lacey Keosauqua Lake was 1.1 mg/L, which was the 8th lowest of the 132 monitored lakes.

Data from the 2004-2008 ISU and UHL surveys suggest a small population of cyanobacteria exists at Lacey Keosauqua Lake, which does not cause an impairment at this lake.   These data show that cyanobacteria comprised only 38% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (2.6 mg/L) was also the 14th lowest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau, and results from the ISU and UHL lake surveys.   The ISU and UHL lake survey results show good chemical water quality at Lacey Keosauqua Lake.   During 2004-2008 there were no violations of the Class B(LW) criterion for ammonia (25 samples), or dissolved oxygen (25 samples).   There were two violations of the Class B(LW) criterion for pH in 25 samples (8%).   Based on IDNR’s assessment methodology these violations were not significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses of Lacey Keosauqua Lake.  

The Class C (drinking water) uses remained "not assessed" due to a lack of water quality information upon which to base an assessment.   The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate.   While the results of the ISU and UHL surveys from 2004-08 show that nitrate levels are low at this lake (maximum value = 1.1 mg/l; median = 0.1 mg/l) relative to the MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.    

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.