Assessment Comments
Assessment based on (1) surveys by IDNR Fisheries Bureau, (2) results from the IDNR beach monitoring program from 2000 through 2002, and (3) U.S. EPA / IDNR fish tissue monitoring in July 1998.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supporting" due to poor water transparency caused by high levels of inorganic suspended solids; in addition, moderately large populations of bluegreen algae present a threat to full support of these uses. Results of IDNR beach monitoring, however, indicate “full support” of the Class A uses. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to high levels of nutrients, siltation, and turbidity (algal and non-algal). The Class C (drinking water) uses remain "not assessed" due to the lack of data upon which to base an assessment. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 1998. The sources of data for this assessment include (1) results of IDNR beach monitoring from 2000 through 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 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, 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 Three Fires beach, none of the 49 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, 37 orgs/100 ml in 2001, and 52 orgs/100ml in 2002. Three of the 62 weekly samples collected during the 2000-02 period exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml; all three samples (410, 2400, and 720 orgs/100ml) were collected in 2002. The single sample maximum values at this beach were relatively low: 240 orgs/100 ml in 2000, 140 orgs/100 ml in 2001, and 2000 orgs/100ml in 2002. These results suggest (1) full support of primary contact recreation uses at this beach and (2) that levels of bacteria at this beach are generally 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 impair Class A (primary contact recreation) uses of Lake of Three Fires. 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 73, 64, 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 very high levels of phosphorus in the water column, somewhat elevated high levels of chlorophyll-a (suspended algae), and moderately poor to very poor water transparency.
According to Carlson (1991), the occurrence of a high TSI values for total phosphorus and secchi depth, with a relatively low value for chlorophyll-a, suggests that non-algal turbidity limits production of algae. The results of ISU monitoring at this lake are consistent with this pattern. The very high level of inorganic suspended solids at this lake suggests the potential for (1) limitation of algal production and (2) contributions to in-lake turbidity. The median level of inorganic suspended solids (ISS) in the 131 lakes sampled for the ISU lake survey from 2000 through 2002 was 4.8 mg/l. The median ISS value at Lake of Three Fires was 10.3 mg/l; this values is the 24th highest of the 131 lakes sampled. The ISS level at this lake suggests that non-algal turbidity both limits the production of algae and contributes to the turbidity-related impairment of the designated Class A uses.
Other non-phosphorus limitations (e.g., low TN:TP ratio and zooplankton grazers) may also limit algal production at Lake of Three Fires. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Lake of Three Fires is 12. This TN:TP ratio suggest that algal production at this may, at times, be limited by nitrogen availability. 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. The 2000 average summer mass of Cladocerans at this lake (142 mg/l) was the 6th highest of the 131 lakes sampled and thus suggests the likelihood that zooplankton grazers limit algal production at this lake. Thus, both nitrogen limitation and zooplankton grazing may contribute to the lower than expected production of suspended algae at this lake. Thus, these conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable conditions related to high levels of non-algal turbidity (inorganic suspended solids) that reduce water transparency.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may present a threat to full support 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 2000 average summer mass of bluegreen algae at this lake (15.9 mg/l) is relatively high for Iowa lakes and thus suggests at least the potential to threaten full support of the Class A uses. Although results of plankton sampling in 2000 suggest a threat to full support of designated uses, the amount of data available for characterizing algal populations at this lake (one season) is not sufficient for developing a more accurate assessment of support of these uses. Additional data on plankton have been collected at this lake as part of the ongoing ISU lake survey and will be used to improve the accuracy of future water quality assessments.
The water quality conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should remain assessed (evaluated) as "partially supported" due to siltation, excessive nutrient loading to the water column, and moderately high levels of algal and non-algal turbidity. In April 2004, a lake dredging project began that will increase the average depth by approximately four feet and the maximum depth by eight feet. After dredging is complete, the lake will be drained to remove the common carp and gizzard shad that have degraded the quality of the fishery of this lake; the lake will be re-stocked with largemouth bass, channel catfish, and bluegill in fall, 2004. Prior to re-filling of the lake, the shoreline will be stabilized with rock and fish habitat will be placed in the lake bed.
The Class C (drinking water) uses remain "not assessed" due to lack of information upon which to base an assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-02 show that nitrate levels are very low at this lake (maximum value = 1.3 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 remain assessed (monitored) as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 1998 (see assessment for the 2000 report).
