Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, (3) ISU report on lake phytoplankton communities, and (4) results of U.S. EPA/IDNR fish tissue monitoring in 1999.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (evaluated) as "partially supported." The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported". Fish consumption remain assessed (monitored) as "fully supported." 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, (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (4) U.S. EPA/IDNR fish tissue monitoring in 1999. EXPLANATION: For the 2002 reporting cycle, the level of support of the Class A (primary contact recreation) uses are assessed as "partially supported" based on results from the ISU statewide survey of Iowa 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 83, 67, and 69, respectively, for Badger Creek Lake. 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 upper range between eutrophic and hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, moderately high levels of chorophyll-a (suspended algae), 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) 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 Creek Lake is 7 and thus suggests the possibility of nitrogen limitation at this lake. In addition, data from Downing et al. (2002) show that the zooplankton community of Badger Creek Lake has a relatively large population (approximately 60% dry mass) of species known as algal grazers. The levels of inorganic suspended solids at this lake are relatively low and do not suggest potential problems with high levels of inorganic turbidity. 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 inorganic suspended solids at Badger Creek Lake was slightly greater than this median at 5.5 mg/l, thus suggesting relatively minor contribution either to algal production or to in-lake turbidity. These conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and to the presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of the summertime phytoplankton community of Badger Creek Lake. Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 15% in the late June sampling, to approximately 60% in the late July sampling, and down to approximately 45% in the late August sampling. Although results of ISU lake monitoring in 2000 and 2001 suggest that nutrient-related impairments may exist, neither the amount of data available for characterizing water quality nor the magnitude of the TSI values are sufficient for identifying impairments with the level of confidence necessary to justify adding this lake to Iowa's Section 303(d) list. Thus, further investigation and monitoring are needed to (1) better characterize current water quality conditions and (2) verify that such impairments exist. The hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and siltation impacts in the lake. Fish consumption uses are assessed as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 1999 (see assessment for the 2000 report).
