ADBNet

Results of IDNR beach monitoring from 2012 through 2014 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 2012 (15 samples), 2013 (15 samples) and 2014 (15 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) 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 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 8 E.  coli orgs/100 ml in 2012, 12 E.  coli orgs/100 ml in 2013 and 16 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 0% in 2012, 7% in 2013 and 7% in 2014.   None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses. However, in the 2014 assessment/listing cycle, the Class A1 uses were listed as "partially supported" due to geometric mean and single sample maximum exceedances.  According to IDNR's methodology, lakes must meet water quality standards for two consecutive assessment/listing cycles to suggest de-listing.  Therefore, the Class A1 uses will remain listed as "partially supported" for the 2016 cycle. 

For the 2016 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 59, and 61 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 relatively low levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was high at Lake Wapello, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Lake Wapello (7 mg/L) was ranked 103rd among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderately large population of cyanobacteria exists at Lake Wapello. These data show that cyanobacteria comprised 95% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (32.3 mg/L) was ranked 99th 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 2010-2014 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 IDNR'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 2010-2014 show that nitrate levels are extremely low at this lake (maximum value = 0.4 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 uses are assessed (monitored) as “partially supported” based on results of IDNR fish contaminant monitoring at Lake Wapello in 2013 and 2014.    The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.    The fish contaminant data generated from the 2013 RAFT sampling conducted at Lake Wapello showed that levels of contaminants in the sample of channel catfish fillets were below advisory thresholds (total PCBs <0.6 ppm; total chlordane <0.2 ppm).  Levels of mercury in largemouth bass, however, were sufficiently high for concern and thus justified follow-up monitoring.    Results from the 2013 sampling showed that the average level of mercury in tissue samples from five largemouth bass exceeded the threshold for a "do not eat" fish consumption advisory of 1.0 ppm.   The average level of mercury was 1.2 ppm (SD = 0.13 ppm; max.  = 1.34 ppm, min = 1.02 ppm).   These levels of mercury were unusually high for an Iowa lake or river.   According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory.    

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".