Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) ISU report on lake phytoplankton communities, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "fully supporting / threatened." The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened." Fish consumption uses remain "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 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 / threatened." 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 65, 46, and 58, 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 mesotrophic 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 extremely 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. The moderately high levels of total phosphorus, however, suggest a slight threat from such blooms. 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 or zooplankton grazing) limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Kent Park Lake is 15.1. This ratio suggests that algal production in this lake is limited to some degree by the availability of nitrogen. 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 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l; the median level at Kent Park Lake was 2.2 mg/l. This median value is the 16th lowest of the 130 lakes sampled. 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. Although bluegreen algae comprise a significant portion of the summertime phytoplankton community, the production of chlorophyll is extremely low at this lake, and the presence of bluegreen algae likely does not present a water quality impact. 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 presence of relatively large populations of these zooplankton may help explain the extremely low algal production at this lake.
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.
Although results of ISU lake monitoring in 2000 and 2001 suggest threats to full support of the designated beneficial uses of this lake, the amount of data available for characterizing water quality is not sufficient for developing an accurate assessment of support of these uses. 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.
