Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake plankton communities.
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 "partially supporting." The Class C (drinking water) uses remain "not assessed." Fish consumption uses are assessed (evaluated) 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 results of U.S. EPA / IDNR fish tissue monitoring in 1993. 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 Lake Icaria. 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 66, 58, and 64, respectively. According to Carlson (1977), the index values for total phosphorus and secchi depth place this lake in the range between eutrophic and hyper-eutrophic lakes; the index value for chlorophyll-a is in the upper range of eutrophic lakes. These index values suggest relatively high levels of phosphorus, relatively low levels of chlorophyll-a, but relatively poor water transparency. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 26. This TN:TP ratio suggests that algal production at this lake is limited by phosphorus versus nitrogen. 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 suggest the potential for impairing designated uses due to non-algal turbidity. 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, Lake Icaria had the 32nd highest median level of inorganic suspended solids (11.3 mg/l), thus suggesting that non-algal turbidity may threaten full support of the primary contact recreation and aquatic life uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of the summertime phytoplankton community of this lake on a wet mass basis, with from 60 to 70% of the community in bluegreen algae in the early and late summer, respectively. Although bluegreen algae appear to dominate the summertime phytoplankton community, the production of chlorophyll is low at this lake, and the presence of bluegreen algae likely does not present a significant water quality impact. The 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 excessive nutrient loading to the water column, high levels of non-algal turbidity, and siltation in the lake. Fish consumption uses remain assessed as "fully supported" based on results of the U.S. EPA/IDNR fish tissue (RAFT) monitoring in 1993. However, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively low confidence). 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.
