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 2000, and (4) EPA/DNR fish tissue (RAFT) monitoring in 1993.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting / threatened" due to the somewhat elevated levels of turbidity related to the moderately high levels of inorganic suspended solids at this lake. Moderately high populations of bluegreen algae at this lake present an additional threat to the full support of these uses. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to excessive nutrient loading to the water column, high levels of non-algal turbidity, and siltation in the lake. The Class C (drinking water) uses remain "not assessed" due to lack of monitoring information. Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of fish contaminant monitoring in 1993. 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 1993.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that moderately high levels of inorganic suspended solids lead to reductions in water transparencies that may threaten full support of the Class A and Class B(LW) uses of Lake Icaria. 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 63, 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 somewhat elevated levels of phosphorus, relatively low levels of chlorophyll-a, and marginally good water transparency. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 28. This TN:TP ratio suggests that algal production at this lake is limited by phosphorus availability. According to Carlson (1991), the occurrence of a high TSI value for phosphorus and Secchi depth relative to that for chlorophyll-a suggests that non-algal turbidity limits algal production. Results of ISU monitoring suggest that moderately high levels of inorganic suspended solids (i.e., non-algal turbidity) as well as populations of zooplankton that graze on algae may also limit algal production at this lake. The levels of inorganic suspended solids at this lake are moderately high and do suggest the potential for contributing to turbidity such that algal production is limited and water transparency is somewhat reduced. 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. Lake Icaria had the 32nd highest median level of inorganic suspended solids (9.9 mg/l), thus suggesting that non-algal turbidity not only limits algal production but also threatens full support of the primary contact recreation and aquatic life uses. In addition, data from Downing et al. (2002) show moderately large populations of zooplankton species at Lake Icaria that graze on algae (Cladocerans). Sampling in 2000 showed that the 2000 average summer mass of Cladoceran grazers at this lake (22.5 mg/l) was the 58th highest of the 131 lakes sampled, thus suggesting at least the potential for these zooplankton grazers to limit algal production.
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. The 2000 summer average mass of bluegreen algae at Lake Icaria (12.8 mg/l) was the 52nd highest of the 131 lakes and suggests that levels of this nuisance aquatic life may threaten full support of designated uses at this lake.
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 (evaluated) as "partially supported" due to excessive nutrient loading to the water column, high levels of non-algal turbidity, and siltation in the lake. In addition, Lake Icaria's fish community has degraded over the last few years due to an over population of yellow bass compounded by extremely high common carp numbers that have reduced desired game fish species significantly. Thus, a renovation of the lake’s fish population is planned for fall 2004. Eliminating yellow bass and common carp from the lake, stabilizing the shoreline, and adding fish habitat will improve the lake's fish population. These efforts combined with the extensive soil conservation practices that have taken place in the watershed will further improve the lake's recreational opportunities and water quality. Drinking water (Class C) uses were not assessed due to the lack of water quality 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 at this lake (maximum value = 3.4 mg/l; median = 1.7 mg/l) are low relative to the drinking water MCL (10 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses. Fish consumption uses remain assessed (evaluated) 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).
