Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) ISU reports on lake plankton communities from 2000-05, 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 are assessed (monitored) as "fully supporting" based on results of chemical water quality monitoring and based on information of the IDNR Fisheries Bureau. 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 sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (2) surveys by IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
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 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 66, 58, and 59, 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 and Secchi depth are in the upper range of eutrophic lakes. These index values suggest that, despite the relatively high levels of phosphorus, the production of suspended algae is relatively 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 2004, the ratio of total nitrogen to total phosphorus for Kent Park Lake is 15. This ratio suggests that algal production in this lake may, at times, be 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 2004 was 5.2 mg/l; the median level at Kent Park Lake was 3.2 mg/l. This median value is the 34th lowest of the 131 lakes sampled.
The presence of moderately large populations of zooplankton at Kent Park Lake that graze on algae, however, may explain the discrepancy between the TSI value for phosphorus (66) and that for chlorophyll-a (58). In terms of all Iowa lakes sampled, data from the ISU survey show large populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 60% of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (148 mg/l) was the 37th highest of the 131 lakes sampled. This population of zooplankton grazers suggests the potential for this type of non-phosphorus limitation on algal production at Kent Park Lake.
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. While data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion (approximately 60%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Kent Park Lake (9.4 mg/l) was the 49th lowest of the 131 lakes sampled. This levels is in the lower half of the 131 Iowa lakes sampled. The presence of a relatively small population of bluegreen algae at this lake does not suggest a potential violation of Iowa’s narrative water quality standard protecting against occurrence of nuisance aquatic life. This assessment, however, is based strictly on a distribution of the lake-specific median bluegreen algae values for the 2000-2004 monitoring period. Median levels less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the ability to characterize the levels of bluegreen algae at this lake has improved over that of the previous (2004) assessment due to collection of additional data, the assessment category for assessments based on level of bluegreen algae nonetheless remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported". Siltation in the lake, however, remains a concern for support of the Class B(LW) uses.
Results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake. Results of this monitoring show that only 2 of the 15 samples collected exceeded the Class B(LW) criteria for dissolved oxygen and that only 2 of the 15 samples collected exceeded Iowa’s Class A,B(LW) criteria for pH (maximum = 9.2; minimum = 8.2 pH units). Based on IDNR’s assessment methodology, these results do not suggest that violation frequencies for either dissolved oxygen or pH are significantly greater than 10% and thus do not suggest impairment of either the Class A and Class B(LW) uses of Kent Park Lake. The violations of the pH criterion likely reflect the influence of primary productivity at Kent Park Lake and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring at this lake.
