Assessment Comments
Assessment based on (1) results of IDNR beach monitoring program from 2000-02, (2) ISU lake survey from 2000-02, (3) ISU report on lake plankton in 2002, (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 (monitored) as "fully supporting / threatened" due to slightly elevated levels of chlorophyll and algal-related turbidity. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting." Fish populations were renovated in Fall 2002 due to an increasingly large population of yellow bass at this lake. Fish consumption uses remain assessed (monitored) as "fully supported" based on fish contaminant monitoring conducted in 1997. The sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2000, 2001, and 2002, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997.
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, 2001, and 2002 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 thirty-day period is compared to the water quality standard of 200 fecal organisms/100ml. If a thirty-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 thirty-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 thirty-day period (N=5), the use of single-sample maximum values to assess beaches is problematic. With less than 10 samples collected during any thirty-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 52 thirty-day periods during summers of 2000, 2001, and 2002 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml. The maximum thirty-day geometric means were 19 orgs/100ml in 2000, 6 orgs/100 ml in 2001, and 13 orgs/100ml in 2002. None of the 64 weekly samples collected during 2000-02 period exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml. The single sample maximum values were very low: 82 orgs/100 ml in 2000; 10 orgs/100 ml in 2001, and 220 orgs/100ml in 2002. These are some of the lower 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 very low.
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 from 2000 through 2002 (approximately nine samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 63, 64, and 62, respectively. According to Carlson (1977), all three index values are in the range between eutrophic and hyper-eutrophic lakes. These index values suggest somewhat elevated levels of phosphorus and chlorophyll-a and marginally good water transparency. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 19, thus suggesting that phosphorus is the nutrient that limits production of suspended algae at this lake. Based on results of plankton sampling by ISU, the 2000 summer average mass of Cladocerans in Lake Anita was 18.8 mg/l; this level is the 66th lowest of the 131 lakes and does not suggest a significant limitation to algal production through zooplankton grazing. The levels of inorganic suspended solids at this lake are relatively low and do not suggest a strong potential for either limiting algal production or for increasing lake turbidity. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2002 was 4.8 mg/l; the median level at Lake Anita was 3.9 mg/l. The somewhat elevated TSI value for chlorophyll-a suggests a threat to full support of the Class A (primary contact) uses through presence of aesthetically objectionable conditions related to blooms of algae.
Results of ISU plankton monitoring in 2000 do not suggest a significant problem due to 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, especially in mid to 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. The 2000 summer average mass of bluegreen algae at Lake Anita (8.6 mg/l), however, was the 59th lowest of the 131 lakes sampled and does not suggest either a threat or impairment of designated uses at this lake.
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported." While the water quality of this lake has remained good, the recreational fishery had declined markedly since the accidental introduction of yellow bass (Morone mississippiensis) in 1995. According the DNR Fisheries Bureau, the increasingly large population of yellow bass reduced the bluegill population by 85%, the crappie population by 70%, and the largemouth bass population by 60%. In 2002, the density of yellow bass was estimated at 8,000 fish per acre; the combined panfish density was 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 Bureua chemically renovated the fish population of this lake in Fall 2003. Because the adverse impacts from yellow bass at this and other lakes are related to inter-specific 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).
