ADBNet

Assessment Comments

Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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.”  Fish consumption uses are “not assessed.”  Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.

EXPLANATION: Results of IDNR beach monitoring at Lake Wapello from 2004 through 2006 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 2004 (22 samples), 2005 (23 samples), and 2006 (28 samples) as part of the IDNR 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 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 Lake Wapello beach, the geometric means of all 61 thirty-day periods during the summer recreation seasons of 2004, 2005, and 2006 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.   Also, the number of samples exceeding the one-time maximum criteria of 235 orgs/100 ml was below 10% for all years (2004: 5%, 2005: 0%, 2006: 0%).   Thus, these results do not suggest an impairment of the Class A1 uses of Lake Wapello.  

For the 2008 assessment/listing cycle, results from the ISU and UHL lake surveys also indicate that the Class A1 (primary contact recreation) uses of Lake Wapello are assessed (monitored) as “fully supported.”  Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 48, 53, and 53 respectively for Lake Wapello.   According to Carlson (1977) the Secchi depth score places Lake Wapello at the upper end of the mesotrophic category, while the chlorophyll a and total phosphorus values place Lake Wapello in 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.  

Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was also extremely low at this lake and does not suggest impairment due to high non-algal turbidity.   The median inorganic suspended solids concentration at Lake Wapello was 1.0 mg/L, which was the 2nd lowest of the 132 monitored lakes.

Data from the 2002-2006 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Lake Wapello.   These data show that cyanobacteria comprised 98% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (13.2 mg/L) was the 51st lowest of the 132 lakes sampled.   These results suggest full support of the Class A1 uses at Lake Wapello.  

The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on data from the ISU and UHL lake surveys and information from IDNR’s Fisheries Bureau.   Results of the ISU and UHL lake surveys from 2002 through 2006 show no violations of the Class B(LW) criterion for ammonia in 17 samples or for dissolved oxygen in 23 samples.   Data for pH show 2 violations of the Class A1,B(LW) criterion for pH in 21 samples (10%).   Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses of Lake Wapello.

The Class C (drinking water) uses remain "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 2002-06 show that nitrate levels are extremely low at this lake (maximum value = 0.2 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.    

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