Assessment Comments
Assessment based on (1) results of IDNR beach monitoring program in 2000-01, (2) ISU lake survey in 2000-01, (3) ISU report on lake plankton, (4) EPA/IDNR fish tissue monitoring in 1997, and (5) reports by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "fully supporting / threatened." The Class B(LW) aquatic life remain assessed (evaluated) as "fully supporting." Fish consumption uses remain "fully supported." The sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2000 and 2001, (2) results of the statewide survey of Iowa lakes conducted in 2000 and 2001 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997. Further monitoring and investigation are needed to better characterize water quality conditions at this lake.
EXPLANATION: Levels of indicator bacteria at Lake Anita beach were monitored once per week during the primary contact recreation seasons (May through September) of 2000 and 2001 as part of the IDNR beach monitoring program. According to U.S. EPA guidelines for determining support of primary contact recreation uses (U.S. EPA 1997b, page 3-35), the geometric mean of fecal coliform bacteria level from at least five samples collected over a 30-day period is compared to the water quality standard of 200 fecal organisms/100ml. If a 30-day geometric mean exceeds 200 orgs/100 ml, the primary contact recreation uses are assessed as "not supported." In addition, the U.S. EPA guidelines state that if more than 10% of the total samples taken during any 30-day period has a bacterial density that exceeds 400 fecal coliform organsims/100 ml, the primary contact recreation uses are assessed as "partially supported." Due to the relatively low numbers of samples collected during any 30-day period (N=5), the use of single-sample maximum values to assess beaches is problematic. With less than 10 samples collected during any 30-day period at Iowa beaches, the occurrence of a single level of bacteria above the single-sample maximum value will result in more than 10% violation of the single-sample maximum value and thus suggest impairment of the primary contact recreation uses. The use of less than 10 samples in an assessment based on a critical value of 10% results in large probabilities (approximately 60%) of incorrectly concluding that an impairment exists. For this reason, the single-sample maximum value is not used to assess support of primary contact recreation uses with data from the IDNR beach monitoring program. At Lake Anita beach, none of the 27 thirty-day periods during summers of 2000 and 2001 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml. The maximum 30-day geometric means were 19 orgs/100ml in 2000 and 6 orgs/100 ml in 2001. None of the 35 weekly samples collected during 2000 and 2001 exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml. The single sample maximum values were extremely low: 82 orgs/100 ml in 2000 and 10 orgs/100 ml in 2001. These are some of the lowest seasonal levels of indicator bacteria reported for the IDNR beach monitoring program. These results suggest (1) full support of primary contact recreation uses at this beach and (2) that levels of bacteria at this beach are extremely low. The Class B(LW) aquatic life uses of this lake are assessed (evaluated) as "fully supported" based on information from the DNR Fisheries Bureau. Despite results of IDNR beach monitoring that suggest full support" of the Class A uses, results from the ISU statewide survey of Iowa lakes suggest that high levels of algal turbidity threatens full support of these uses at Lake Anita. Using the median values from this survey in 2000 and 2001 (approximately six samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 63, 64, and 60, respectively. According to Carlson (1977), the index values for total phosphorus and chlorophyll-a places this lake in the range between eutrophic and hyper-eutrophic lakes; the index value for secchi depth is at the upper boundary of eutrophic lakes. These index values suggest moderately high levels of phosphorus and chlorophyll-a and relatively good (and somewhat better than expected) water transparency. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 21, thus suggesting that phosphorus is the nutrient that limits production of suspended algae at this lake. The levels of inorganic suspended solids at this lake are relatively low and do not suggest the potential for increasing lake turbidity. The median level of inorganic suspended solids in the 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l; the median level at Lake Anita was 3.9 mg/l. The moderately high TSI values for total phosphorus and chlorophyll-a suggest potential impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and through presence of nuisance (=noxious) algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a relatively large portion of the summertime phytoplankton community of Lake Anita, with more than half of the wet mass in bluegreens in mid-summer and greater than 90% of the wet mass in bluegreens in late summer. Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 5% in the late June sampling, to approximately 60% in the mid-July sampling, and up to approximately 90% in the early September sampling.
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported." Although results of ISU lake monitoring in 2000 and 2001 suggest threats to full support of the designated beneficial uses of this lake, the amount of data available for characterizing water quality is not sufficient for developing an accurate assessment of support of these uses. Additional data for this lake are being generated as part of the ongoing ISU lake survey; these data will be used to improve the accuracy of future water quality assessments. While the water quality of this lake remains good, the recreational fishery has declined markedly since the accidental introduction of yellow bass (Morone mississippiensis) in 1995. According the the DNR Fisheries Bureau, the increasingly large population of yellow bass has reduced the bluegill population by 85%, the crappie population by 70%, and the largemouth bass population by 60%. The current (2002) density of yellow bass is estimated at 8,000 fish per acre; the combined panfish density is estimated at less than 300 fish per acre (information from "Iowa Outdoors," February 4, 2003, http://www.iowadnr.com/news/io.html). The DNR Fisheries Bureau plans to chemically renovate the fish population of this lake in late summer 2003. Because the adverse impacts from yellow bass are related to interspecific competition versus degraded water quality (as caused, for example, by common carp), the their adverse impact at Lake Anita is not considered a water quality impact in the context of Section 305(b) reporting or Section 303(d) listing. Fish consumption uses remain assessed as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in August 1997 (see assessment for the 1998 report above).
