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 phytoplankton communities.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supporting" primarily due to high levels of non-algal turbidity The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened." Fish consumption uses are "not assessed." 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, and (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002). 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 Lost 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 75, 59, and 70, 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 chlorophyll-a is in the upper range of eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, relatively low (and less than expected) levels of chlorophyll-a, 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, Lost Island Lake had the 22nd highest median level of inorganic suspended solids (16.0 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. In addition to impacts from non-algal turbidity, the high levels of total phosphorus in the water column suggest potential impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and 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 Lost Island Lake).
Sampling in 2000 showed the percent wet mass of bluegreens ranged from just above 80% in the mid-June sampling to approximately 100% in the mid-July and early August samples. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 15. Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should remain assessed as "fully supported / threatened," with threats from excessive nutrient loading to the water column and due to high levels of non-algal turbidity in the lake. 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 uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
