Assessment Comments
Assessment based on (1) surveys by IDNR Fisheries Bureau, (2) results from the IDNR beach monitoring program in 2000 & 2001, and U.S. EPA / IDNR fish tissue monitoring in July 1998. See attached document for details.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting." The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported." The Class C (drinking water) uses remain "not assessed." Fish consumption uses remain assessed as "fully supported." The sources of data for this assessment include (1) results of IDNR beach monitoring in 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 tissue monitoring in 1998. EXPLANATION: Results of IDNR beach monitoring suggest "full support" of the Class A uses. Levels of indicator bacteria at Lake of Three Fires 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 Three Fires beach, none of the 24 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 37 orgs/100 ml in 2001. None of the 34 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 very low: 240 orgs/100 ml in 2000 and 140 orgs/100 ml in 2001. 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.
Despite the 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 and non-algal turbidity may adversely affect the Class A and Class B(LW) uses of Lake of Three Fires. 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 73, 63, and 69, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index values for chlorophyll-a and secchi depth place this lake in the middle and upper range, respectively, between eutrophic and hyper-eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, moderately high levels of chlorophyll-a (suspended algae), and moderately poor water transparency. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation or zooplankton grazing) limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Lake of Three Fires is 15). This TN:TP ratio suggest that algal production at this may be limited by nitrogen. In addition, data from Downing et al. (2002) show a relatively large populations of zooplankton species at this lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 80% of the dry mass of the zooplankton community in the mid-July sample and 85% of the early September sample. Thus, both nitrogen limitation and zooplankton grazing may contribute to the lower than expected production of suspended algae at this lake. The relatively high level of inorganic suspended solids at this lake also suggests the potential for (1) limitation algal production and (2) contributions to in-lake turbidity. The median level of inorganic suspended solids (ISS) in the 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l. The median ISS value at Lake of Three Fires was 14.7 mg/l; this values is the 24th highest of the 130 lakes sampled. The ISS level at this lake suggests that non-algal turbidity limits both the production of algae and contributes to turbidity-related impairments of designated uses for primary contact recreation or aquatic life. The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also contribute to the impairment of the Class A uses of this lake. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of this lake's summertime phytoplankton community, especially in mid and late summer. Sampling in 2000 showed the percent wet mass of bluegreens ranged from approximately 30% in the late June sampling, to 95% in the mid-July sampling, and 70% in the early August sampling. The hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should remain assessed as "partially supported" due to siltation, excessive nutrient loading to the water column, and moderately high levels of algal and non-algal turbidity. Although results of ISU lake monitoring in 2000 and 2001 suggest that nutrient-related impairments may exist, neither the amount of data available for characterizing water quality nor the magnitude of the TSI values are sufficient for identifying impairments with the level of confidence necessary to justify adding this lake to Iowa's Section 303(d) list. Thus, further investigation and monitoring are needed to (1) better characterize current water quality conditions and (2) verify that such impairments exist. 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. The Class C (drinking water) uses remain "not assessed" due to lack of information upon which to base an assessment. Fish consumption remain assessed as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 1998.
