ADBNet

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Lake Wapello Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (15 samples), 2015 (17 samples) and 2016 (17 samples), as part of the DNR beach monitoring program. According to DNR’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) the geometric mean of the samples from each recreation season of 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 sampling season geometric mean exceeds the state criterion of 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 from 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 16 E. coli orgs/100 ml in 2014, 42 E. coli orgs/100 ml in 2015 and 79 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2014, 6% in 2015 and 24% in 2016. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2016. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Wapello are assessed (monitored) as "partially supported" due to poor water transparency based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 60, 62, and 56 respectively for Lake Wapello. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Wapello in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and relatively low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.Although the index value for Secchi is below the impairment trigger of 65 for this assessment cycle, Lake Wapello was listed as partially supporting its Class A1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Secchi must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Lake Wapello will remain listed as "partially supported" for the 2018 assessment/listing cycle.

Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Lake Wapello. These data show that cyanobacteria comprised 91% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (22 mg/L) was ranked 95th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Lake Wapello.

The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU surveys from 2012-2016 show that nitrate levels are extremely low at this lake (maximum value = 0.4 mg/l; median = 0 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.

Thus, follow-up monitoring was conducted in August 2014 as part of an Iowa DNR study on levels of mercury in Iowa fish.Tissue samples from 13 largemouth bass from Lake Wapello were analyzed for mercury. The length of the fish ranged from 8.8 to 19.9 inches. The average level of mercury in the 13 samples was 0.5 ppm (SD=0.28 ppm) with a maximum concentration of 0.82 ppm. Nine of the 13 samples contained levels of mercury above Iowa's 1 meal/week advisory threshold of 0.3 ppm, but none of the samples contained mercury above "do not eat" advisory threshold of 1.0 ppm. Based on the results monitoring in 2013 and the results of this follow-up monitoring in 2014, a 1 meal/week advisory was issued for this lake. The existence of this advisory suggests that the fish consumption uses at Lake Wapello should be assessed as "partially supporting".