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 plankton communities in 2000.
Basis for Assessment
SUMMARY: This lake is not designated for Class A (primary contact recreation) uses. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting / threatened" due primarily to moderately high levels of algal turbidity and secondarily to moderately high levels on inorganic turbidity. Fish consumption uses are "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 moderately high levels of algal turbidity may threaten full support of the Class B(LW) uses of Hooper Area Pond. 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 66, 66, and 62, respectively. According to Carlson (1977), the index values for all three parameters place this lake in the range between eutrophic and hyper-eutrophic lakes. These index values suggest moderately high levels of phosphorus in the water column, moderately high levels of chlorophyll-a, and marginally good water transparency. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Hooper Lake is 15. This TN:TP ratio suggests the possibility that some nitrogen limitation to algal production exists at this lake. Data from Downing et al. (2002) show very low populations of zooplankton species at this lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) were not present in the late July sample and comprised only 10% of the dry mass of the zooplankton community in the mid-July sample. The summer 2000 average mass of Cladoceran grazers (0.2 mg/l) was the fifth lowest of the 131 lakes sampled. Levels of inorganic suspended solids at this lake are moderately high and appear to contribute significantly to the threats to full support of the Class B(LW) 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 of ISS at Hooper Area Pond was equal to this median (4.8 mg/l). The moderately high TSI value for chlorophyll-a indicates a potential threat to the full support of the Class B(LW) aquatic life uses. The presence of nuisance algal species (i.e., bluegreen algae), however, does not appear to be a significant problem at this lake. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) generally comprise a third or less (on a wet mass basis) of the summertime phytoplankton community of Hooper Area Pond. Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 10% in the late June sampling, to approximately 60% in the late July sampling, and down to approximately 25% in the late August sampling. The summer 2000 average mass of bluegreen algae at this lake (3.5 mg/l) was the 34th lowest of the 131 lakes sampled. This mass is low relative to other Iowa lakes and likely neither threatens nor impairs designated uses at this lake. Thus, the eutrophic conditions at this lake suggest that the Class B(LW) aquatic life uses should be assessed as "fully supported / threatened" due to excessive nutrient loading to the water column and moderately high levels of algal turbidity. Results of ISU monitoring suggest that inorganic suspended solids also contribute to turbidity at this lake. Although the TSI value for chlorophyll-a (66) slightly exceeds the impairment threshold of 65, information from the IDNR Fisheries Bureau suggests that the aquatic life uses of this lake are not impaired by algae. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
