Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, (3) ISU report on lake phytoplankton communities in 2000, and (4) results of U.S. EPA/IDNR fish tissue monitoring in 1999.
Basis for Assessment
For the 2004 report: SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "not supported" due to aesthetically objectionable algal blooms and due to presence of excessive growth of nuisance aquatic life (bluegreen algae). The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" due to algal blooms and siltation impacts at the lake. Fish consumption uses remain assessed (monitored) as "fully supported." 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, (3) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (4) U.S. EPA/IDNR fish tissue monitoring in 1999.
EXPLANATION: The level of support of the Class A (primary contact recreation) uses are assessed as "not supported" based on results from the ISU statewide survey of Iowa lake. 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 86, 64, and 70, respectively, for Badger Creek Lake. According to Carlson (1977), the index value for total phosphorus places this lake in the upper range of hyper-eutrophic lakes; the index value for chlorophyll-a is in the middle range between eutrophic and hyper-eutrophic lakes, and the index value for secchi depth is in the lower range of hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, moderately high levels of chlorophyll-a (suspended algae), and very poor water transparency. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively lower values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) limits production of algae. The ISU lake data suggest that algal production at Badger Creek Lake is limited by nitrogen availability, zooplankton grazing, and by inorganic turbidity. Based on median values from ISU sampling from 2000-02, the ratio of total nitrogen to total phosphorus for Badger Creek Lake is 6; this ratio strongly suggests that algal production at this lake is limited by nitrogen availability. 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 mass of bluegreen algae in summer 2000 (36 mg/l) ranked 35th highest of the 131 lakes sampled. The levels of inorganic suspended solids at this lake are somewhat high and suggest potential problems with high levels of inorganic turbidity. 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 inorganic suspended solids at Badger Creek Lake was somewhat greater than this median at 6.4 mg/l, thus suggesting a potential contribution to limiting algal production through turbidity and light limitation. These conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae. The presence of nuisance aquatic (algal) species (i.e., bluegreen algae) may also contribute to impairment at this lake. 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. The average mass of bluegreen algae in summer 2000 at this lake (20.4 mg/l) ranked 44th highest of the 131 lakes sampled. The presence of relatively large populations of bluegreen algae suggests a threat to support of the designated uses of this lake due to the potential for violating Iowa’s narrative water quality standard protecting against presence of nuisance aquatic life. Although results of plankton sampling in 2000 suggest a threat to support of designated uses, the amount of data available for characterizing algal populations at this lake is not sufficient for developing a more 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 on plankton have been collected at this lake as part of the ongoing ISU lake survey and will be used to improve the accuracy of future water quality assessments.
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 nuisance blooms of algae and siltation impacts in the lake. Despite these apparent impacts, Badger Creek Lake continues to support a quality recreational fishery. 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).
