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
For the 2002 report: 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 "partially supporting." 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 high levels of total phosphorus may threaten full support of the Class A uses of Badger Lake. 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, 49, and 60, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index value for chlorophyll-a is in the upper range of mesotrophic lakes, and the index value for secchi depth is in the upper range of eutrophic lakes. These index values suggest (1) very high levels of phosphorus, (2) extremely low, and much less than expected, production of suspended algae, and (3) relatively good, and better than expected, 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) limits production of algae Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Badger Lake is 125, thus indicating excess nitrogen in the water column. The levels of inorganic suspended solids at this lake are relatively low and do not suggest a strong potential for impairing designated uses due to high turbidities. 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 Badger Lake was 6.8 mg/l. The suppression of algal production through zooplankton grazing, however, appears possible. Data from Downing et al. (2002) show relatively large populations of zooplankton species at Badger Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 30% of the dry mass of the zooplankton community of the mid-July sample and 35% of the early August sample. The high TSI value for total phosphorus suggest threats to the full support of the Class A (primary contact) uses through potential presence of aesthetically objectionable blooms of algae. 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) comprise a relatively small portion (less than 20% wet mass) of the summertime phytoplankton community of this lake.
The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should remain assessed as "partially supported." Water quality conditions at this lake are stable but not improving. The lake continues to receive some silt from the watershed. Common carp are a major problem in keeping the water turbid in the upper arm of the lake. Fish growth, especially crappie, however, has greatly improved. The fish consumption use remain "not assessed" due to lack of fish tissue 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. Thus, the assessment category is considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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.
