Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake plankton communities.
Basis for Assessment
Not assessed for Section 305(b) reports prior to the 2002 reporting cycle.
SUMMARY: The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting / threatened." Fish consumption uses are "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). Further monitoring and investigation are needed to better characterize water quality conditions at this lake. EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that the high nutrient levels and moderately high levels of algal turbidity may adversely affect the Class B(LW) uses of Hooper Area Pond. 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 73, 63, and 61, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index values for chlorophyll-a and secchi depth are in the range between eutrophic and hyper-eutrophic lakes. These index values suggest very high levels of phosphorus in the water column, moderately high (and less than expected) levels of chlorophyll-a, and moderately poor water transparency. 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) other than phosphorus limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Hooper Lake is 13. This TN:TP ratio suggests the possibility that algal production at this lake is limited by nitrogen. Data from Downing et al. (2002), however, 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. Levels of inorganic suspended solids at this lake are relatively low and do not appear to contribute to impairments of the Class B(LW) 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 of ISS at Hooper Area Pond was 5.2 mg/l. The moderately high TSI values for total phosphorus and chlorophyll-a indicate potential threats to the full support of the Class B(LW) aquatic life uses. The presence of nuisance algal species (i.e., bluegreen algae) 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. 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. 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. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
