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 (monitored) as "partially supporting” due to high levels of pH that frequently exceed Iowa water quality criteria. 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 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 moderately high levels of algal turbidity may threaten full support of the Class B(LW) uses of Hooper Area Pond. Despite this potential threat, water transparency remains relatively good at this lake, and IDNR Fisheries feels that the Class B(LW) uses remain “fully supported”.
Using the median values from the ISU statewide lake survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 65, 65, and 59, respectively. According to Carlson (1977), the index values for all total phosphorus and chlorophyll-a in the middle range between eutrophic and hyper-eutrophic lakes; the index value for Secchi depth is in the upper range of eutrophic lakes. These index values suggest moderately high levels of phosphorus in the water column, moderately high levels of chlorophyll-a, and relatively good water transparency.
Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Hooper Area Pond is 15. This TN:TP ratio suggests the possibility that some nitrogen limitation to algal production exists at this lake.
In terms of all Iowa lakes sampled, data from the ISU survey show relatively small populations of zooplankton species at this lake that graze on algae. Although sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised over 50% 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 (48 mg/l) was the 29th lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Hooper Area Pond.
The levels of inorganic suspended solids at this lake are in the range from “low” to typical” for Iowa lakes and thus do not suggest a strong potential for 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 of ISS at Hooper Area Pond was 4.4 mg/l.
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 (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 Hooper Area Pond (4.1 mg/l) was the 18th lowest of the 131 lakes sampled. This level is in the lowest 25% 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.
Information from the IDNR Fisheries Bureau suggests that the aquatic life uses of this lake are not impaired by algae or other factors. Thus, the Class B(LW) aquatic life uses are assessed as "fully supported". Nutrient loading to the water column and moderately high levels of algal turbidity, however, remain concerns at this lake. In addition, the trophic state index value for Secchi depth (59) is well below the impairment threshold of 65, thus suggesting relatively good water transparency at this lake.
The ISU lake survey data suggest an impairment due to high levels of pH at this lake. Only one violation of the Class B(LW) criteria for dissolved oxygen occurred in the 13 samples collected during summers of 2000 through 2004. Based on IDNR’s assessment methodology, the occurrence of this violation does not suggest an impairment of aquatic life uses at this lake. Four of 14 samples, however, violated the Class B(LW) criterion for pH (maximum = 9.3; minimum = 7.8 pH units). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10% of the samples exceed Iowa’s pH criteria and thus suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations, however, likely reflect high levels of primary productivity at Hooper Area Pond and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
