Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) ISU report on lake plankton communities in 2000, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting" based on results of the ISU lake survey. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened" due to siltation impacts at this lake. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake. 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 the Class A uses of Kent Park Lake are "fully supported" due to very low levels of chlorophyll and very good water transparency. 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 64, 54, and 57, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the middle range between eutrophic and hyper-eutrophic lakes; the index values for chlorophyll-a is in the middle range of eutrophic lakes, and the secchi depth index value is in the upper range of eutrophic lakes. These index values suggest that, despite the moderately high levels of phosphorus, the production of suspended algae is very low and water transparency is relatively good for Iowa lakes. These results suggest that this lake does not have impairments due to aesthetically objectionable blooms of algae or due to high turbidities. 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. The results of ISU monitoring suggest that, of the parameters measured, the large population of zooplankton that graze on algae most likely is the primary non-phosphorus limitation at this lake, with nitrogen availability potentially limiting some algal production. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Kent Park Lake is 14. This ratio suggests that algal production in this lake is potentially limited by the availability of nitrogen. Similarly The levels of inorganic suspended solids at this lake are relatively low and do not suggest the potential for either limiting algal production or impairing designated uses. 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 at Kent Park Lake was 2.7 mg/l. This median value is the 16th lowest of the 131 lakes sampled. Data from Downing et al. (2002) show relatively large populations of zooplankton species at Kent Park Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 60% of the dry mass of the zooplankton community in the early August sample and 65% of the early September sample. The 2000 summer average mass of Cladocerans at this lake was 95.6 mg/l; this is the 17th highest of the 131 lakes sampled and suggests that the presence of large populations of these zooplankton may contribute to low algal production at this lake.
This lake does not appear to have serious problems due to presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise approximately one-half of the summertime phytoplankton community of this lake. Sampling in 2000 showed that bluegreen algae comprised approximately 70% of the wet mass of the phytoplankton community in the early July and late August samples but comprised only about 30% of the early August sample. The 2000 average summer mass of bluegreen algae at Kent Park Lake (7.6 mg/l) is low relative to levels in other Iowa lakes and does not suggest either a threat or impairment of designated uses.
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should remain assessed as "fully supported / threatened" due to the continuing threat of siltation in the lake. Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring at this lake.
