Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake phytoplankton communities in 2000.
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. Large populations of bluegreen algae (noxious aquatic plants) suggest an additional impairment of these uses; additional monitoring is needed to confirm this impairment. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened" due to high levels of nutrient loading to the water column and to high levels of non-algal (inorganic) turbidity. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring. 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, and (3) information on plankton 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 non-algal turbidity may adversely affect the Class A and Class B(LW) uses of Lost 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 74, 60, and 71, 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 at the upper boundary of eutrophic lakes. These index values suggest very high levels of phosphorus in the water column, relatively low (and less than expected) levels of chlorophyll-a, and very poor water transparency. According to Carlson (1991), the occurrence of a low chlorophyll-a TSI value relative to those for total phosphorus and secchi depth indicate non-algal particles or color dominate light attenuation. The ISU lake data suggest that non-algal particles do likely limit algal production at Lost Island Lake. 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, 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. Algal production at this lake does not appear limited by either nitrogen availability or zooplankton grazers. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 16.3. This ratio do not suggest a strong possibility for nitrogen limitation. In addition, data from Downing et al. (2002) show relatively small populations of zooplankton species (Cladocerans) at this lake that graze on algae. The average summer mass of these zooplankton grazers (18.5 mg/l) in 2000 was the 63rd lowest of the 131 lakes sampled, thus suggesting only minor influence of algal grazing on algal production. Thus, the high levels of non-algal (inorganic) turbidity at this lake impair the Class A uses due to violation of Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
The presence of nuisance algal species (i.e., bluegreen algae) at this lake suggests an additional impairment to designated uses of this lake. 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. The summer 2000 average mass of bluegreen algae at this lake (37.3 mg/l) was the 27th highest of the 131 lakes sampled and thus suggests a potential impairment due to violations of Iowa’s narrative water quality standard protecting against nuisance aquatic life. The amount of data available for characterizing algal populations at this lake (one season), however, is not sufficient for developing a more accurate assessment of support of these uses. Additional data on plankton have been collected at this lake as part of the ongoing ISU lake survey and will be used to improve the accuracy of future water quality assessments for this lake.
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.
