Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, (3) ISU report on lake plankton communities, and (4) results of U.S. EPA/IDNR fish tissue monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "fully supporting / threatened." The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened." Fish consumption are assessed as "fully supported." The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted in 2000 and 2001 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (4) results of U.S. EPA / IDNR fish tissue monitoring in 2001. Further monitoring and investigation are needed to better characterize water quality conditions at this lake. EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of algal turbidity may adversely affect the Class A and Class B(LW) uses of Five Island Lake. 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 69, 60, 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 relatively high levels of phosphorus in the water column, relatively low levels of chlorophyll-a, and moderately poor (but better than expected) 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) other than phosphorus limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Five Island Lake is 22. This TN:TP ratio suggests that nitrogen is not the limiting nutrient for algal production at this lake. In addition, data from Downing et al. (2002) shows a moderately large population of zooplankton species at Five Island Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 15% of the dry mass of the zooplankton community in the mid-July sample and 30% of the early August sample. According to Carlson (1991), the occurrence of a high TSI value for secchi depth relative to that for chlorophyll-a suggests that non-algal turbidity limits algal production. The levels of inorganic suspended solids at this lake are moderately high and may contribute to in-lake turbidity and suppression of algal production. 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. Of 130 lakes sampled, Five Island Lake had the 28th highest median level of inorganic suspended solids (12.0 mg/l), thus suggesting that non-algal turbidity may limit the production of algae as well as contribute to in-lake turbidity. The relatively high TSI values for total phosphorus, chlorophyll-a, and secchi depth suggest potential threats to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae. In addition, data from Downing et al. (2002) suggest that the presence of nuisance algal species (i.e., bluegreen algae) may also threaten full support of the Class A uses. Sampling in 2000 showed the percent wet mass of bluegreens ranged from approximately 45% in the mid-June sampling, to approximately 55% in the late July sampling, and approximately 40% in the late August sampling. In 2000, at the recommendation of the DNR Fisheries Bureau, the Class B(LW) uses were changed from "partially supported" to "fully supported / threatened." The water quality trend for this lake is "improving." According to the DNR Fisheries Bureau, the water quality improvements at Five Island Lake reflect results of the lake dredging project. The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should be assessed as "fully supported / threatened" due to high 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 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 a more 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. Fish consumption use are assessed as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in September 2001. This monitoring showed that levels of all contaminants in the composite samples of fillets from channel catfish and walleye were well-below ½ the respective FDA action levels and IDNR levels of concern. Levels of the primary contaminants of Iowa fish (i.e., chlordane, DDE, dieldrin, mercury, and PCBs) were all below the analytical levels of detection.
