Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, (3) ISU report on lake plankton communities in 2002, 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 (monitored) as "partially supported" due to somewhat elevated levels of algal and non-algal turbidity that contribute to reductions in water transparency. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened" due to high nutrient loading to the water column and slightly elevated levels of algal and non-algal turbidity. Fish consumption are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2001. The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, (3) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (4) results of U.S. EPA / IDNR fish tissue monitoring in 2001. Although not orginally assessed as "impaired" by IDNR for the 2004 Section 305(b) cycle, this lake was added to Iowa's 2004 Section 303(d) list at the recommendation of U.S. EPA Region 7 based on ISU lake monitoring data from 2003 and 2004 that suggest adverse trends in water quality.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that the somewhat elevated levels of turbidity due to algal and inorganic sources may adversely affect the Class A and Class B(LW) uses of Five Island Lake. 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 69, 62, 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 moderately high levels of phosphorus in the water column, somewhat elevated levels of chlorophyll-a, and marginally good (and 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, zooplankton grazing, or some other factor) other than phosphorus limits production of algae. Based on results of the ISU monitoring from 2000-02, the primary non-phosphorus limitation to algal production appears to be inorganic suspended solids. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Five Island Lake is 20. This TN:TP ratio suggests that phosphorus (versus nitrogen) may be the limiting nutrient for algal production at this lake. 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. The summer 2000 average mass of Cladocerans (19 mg/l) was only the 64th highest of the 131 lakes sampled; thus, zooplankton grazers likely have limited influence on limiting algal production. 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 very high and likely contribute to in-lake turbidity and suppression of algal production. 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. Of 131 lakes sampled, Five Island Lake had the 22nd highest median level of inorganic suspended solids (12.4 mg/l), thus suggesting that non-algal turbidity likely limits the production of algae as well as contribute to in-lake turbidity that threatens full support of designated uses at this lake. Thus, the moderately high TSI values for chlorophyll-a and secchi depth suggest potential impairments of the Class A (primary contact) uses through presence of reduced water transparencies caused by algae and by inorganic suspended solids. The influence of the ongoing dredging activities on levels of inorganic suspended solids at this lake is unknown.
Data from Downing et al. (2002) suggest that the levels of bluegreen algae at this lake are low and neither threaten or impair the designated 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. The summer 2000 average wet mass of bluegreen algae at this lake (6.7 mg/l) was the 49th lowest of the 131 lakes and thus does not suggest a significant problem.
In 2000, at the recommendation of the DNR Fisheries Bureau, the Class B(LW) uses were changed from "partially supported" to "fully supported / threatened"; this assessment remains for the 2004 reporting/listing cycle 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. Nonetheless, the IDNR Fisheries Bureau suggests 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. Fish consumption use remain assessed (monitored) as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in September 2001 (see assessment for the 2002 report for more information).
