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 algal turbidity and algal blooms that create aesthetically objectionable conditions. Large populations of nuisance aquatic life (bluegreen algae) suggest an additional impairment of the Class A uses at this lake. Levels of inorganic suspended solids are sufficiently high to indicate at a threat to full support of these uses from inorganic turbidity. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to nutrient, nuisance algal blooms, and occasional fish kills (organic enrichment) that sometimes follow algal die-off. 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: The Class A (primary contact recreation) uses are assessed (evaluated) as "partially supported" based on results from the ISU statewide survey of Iowa 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 78, 71, and 68, respectively, for Indian Lake. According to Carlson (1977), the index values for total phosphorus and chlorophyll-a place this lake in the range of hyper-eutrophic lakes; and the index value for secchi depth is in the upper range between eutrophic and hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, very high levels of chlorophyll-a (suspended algae), and moderately poor water transparency. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively lower 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 availability and zooplankton grazing may serve as non-phosphorus limitations to algal production at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Indian Lake is 11. This TN:TP ratio suggests a good possibility that the production of algae at this lake is limited by the availability of nitrogen. During the 2000-02 ISU surveys, however, the level of inorganic suspended solids at Indian Lake (4.8 mg/l) was equal to the overall median level for the 131 lakes sampled. This median level suggests that contributions of inorganic suspended solids to in-lake turbidity are likely secondary to algae but may serve to limit algal production to some degree. These water quality conditions suggest impairments to the Class A (primary contact) uses primarily through presence of algal turbidity and blooms that create aesthetically objectionable conditions that violate Iowa’s narrative water quality standards. The IDNR Fisheries Bureau concurs with this assessment.
The presence of nuisance aquatic (algal) life at this lake may indicate an additional impairment to the lake’s designated uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) dominate the summertime phytoplankton community of Indian Lake. Sampling in 2000 showed the percent wet mass of bluegreens comprised from 95% to 100% of the phytoplankton community in the three summer samples from this lake. The average summer mass of bluegreen algae at this lake (38 mg/l) was the 27th highest of the 131 lakes sampled. This level of bluegreen algae suggests potential impairment of the Class A and Class B(LW) uses of this lake due to violations of Iowa’s narrative water quality standard protecting against nuisance aquatic life. Although results of plankton sampling in 2000 suggest impairment of designated uses, the amount of data available for characterizing algal populations at this lake (one season) 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. The hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and impacts from organic enrichment (i.e., fish kills following algal die-off) in the lake. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
