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 phytoplankton 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 (monitored) as "partially supporting" due to presence of non-algal turbidity, aesthetically objectionable blooms of algae, and presence of nuisance algal species (i.e., bluegreen algae). The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened." Fish consumption uses are "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 (RAFT) monitoring in 2001. EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of algal and non-algal turbidity may adversely affect the Class A and Class B(LW) uses of Lake Miami. 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 79, 62, and 72, respectively. According to Carlson (1977), the index values for total phosphorus and secchi depth place this lake in the range of hyper-eutrophic lakes; the index value for secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, moderately low (and less than expected) production of suspended algae, and poor water transparency. 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 Miami had the 23rd highest median level of inorganic suspended solids (15.3 mg/l), thus suggesting that non-algal turbidity limits the production of algae as well as contributes to impairments of both the primary contact recreation and aquatic life uses. These conditions indicate potential impairments to the Class A (primary contact) uses through presence of (1) non-algal turbidity, (2) aesthetically objectionable blooms of algae, and (3) presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) dominate the summertime phytoplankton community of Lake Miami). Sampling in 2000 showed the percent wet mass of bluegreens ranged from approximately 100% in the late June sampling to approximately 85% in the late July and late August samplings. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 10. 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. Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should remain assessed as "fully supported / threatened. Fish consumption uses were assessed as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring at Lake Miami in 2001. Levels of all contaminants in composite samples of fillets from channel catfish and largemouth bass were below one-half of the respective U.S. FDA action levels and IDNR levels of concern.
