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 supported" due to high levels of chlorophyll-a (suspended algae) and high levels of inorganic suspended solids that reduce water transparency. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to algal blooms, sediment re-suspension, and nutrient loading to the water column. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake. 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 of monitoring conducted by ISU from 2000 through 2002 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are only "partially supported." 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 84, 66, and 70, respectively, for Little Spirit Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggest both extremely high levels of phosphorus in the water column, moderately high production of suspended algae, and moderately poor water transparency. These conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and high levels of non-algal turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and Secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) other than phosphorus limits production of algae. Results of ISU monitoring suggest that nitrogen limitation, high levels of inorganic suspended solids (turbidity), and the relatively large population of zooplankton grazers all function as non-phosphorus limitations at this Little Spirit Lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 10. This ratio is low and does suggest the potential for nitrogen limitation at this lake. Data on inorganic suspended solids from the ISU survey suggest that this lake is also subject to occasional episodes of high levels of non-algal turbidity. 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. The median level of inorganic suspended solids at Little Spirit Lake (10.3 mg/l) was the seventeenth highest of the 131 lakes, thus suggesting that non-algal turbidity may limit the production of algae as well as contribute to impairment beneficial uses. In addition, data from Downing et al. (2002) show relatively large populations of zooplankton species (Cladocerans) at this lake that graze on algae. The average summer mass of these zooplankton grazers (109.3 mg/l) in 2000 was the 11th highest of the 131 lakes sampled, thus suggesting the potential for these zooplankton grazers to limit algal production. Based on information from the ISU lakes survey and from the IDNR Fisheries Bureau, the turbidity-related impacts to the primary contact and aquatic life uses at this lake will be attributed to both suspended algae (blooms) and re-suspended inorganic material.
The relatively low population of nuisance algal species (i.e., bluegreen algae) at this lake does not appear to either threaten or impair the designated uses at this lake. Although data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta), comprise a significant portion of the summertime phytoplankton community of Little Spirit Lake, especially in late summer, the summer 2000 average mass of bluegreens (6.9 mg/l) was only the 51st highest of the 131 lakes sampled.
According to the IDNR Fisheries Bureau, the impairments to the aquatic life uses of this natural lake are rather hard to quantify but probably affect some spawning activities of nest building species in varying degrees; e.g., bluegill, bullhead, crappie and largemouth bass. Algal blooms do impact water quality through their contribution to sags in dissolved oxygen and the potential fish mortality that can result. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake. This lake was, however, sampled in 2003 as part of the U.S. EPA/IDNR RAFT fish contaminant monitoring program. The results from this sampling, however, are not yet available.
