Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-02, (2) ISU report on lake phytoplankton communities in 2000, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting / threatened" due to slightly poor Secchi depth (=water transparency). The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to siltation and water quality impacts of common carp. Fish consumption uses remain “not assessed.” The 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, 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 inorganic turbidity may threaten full support of the Class A uses of Badger 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 73, 50, 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 value for chlorophyll-a, however, is much lower and is at the boundary between mesotrophic and eutrophic lakes. The index value for Secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) very high levels of phosphorus in the water column, (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, zooplankton grazing, or some other factor) limits production of algae. The ISU lake data suggest that algal production at Badger Lake is limited by zooplankton grazing and possibly by inorganic turbidity. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Badger Lake is 122, thus indicating excess nitrogen in the water column (note: Badger Lake had the highest median summer total nitrogen over the 2000-02 period (14.3 mg/l) of any of the 131 lakes sampled for the ISU survey). The levels of inorganic suspended solids at this lake are moderately high and do suggest the potential for reducing water transparency due to high turbidities. 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 at Badger Lake was 7.5 mg/l; this median level was the 38th highest of the 131 lakes sampled. 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 average summer mass of Cladoceran taxa in 2000 (78 mg/l) was the 21st highest of the 131 lakes sampled.
Thus, the somewhat elevated TSI value for Secchi depth suggests a threat to the full support of the Class A (primary contact) uses; based on the ISU lake survey data, the moderately high levels of inorganic suspended solids appears to be the likely cause of the reduced water transparency. The presence of nuisance aquatic 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 average summer mass of bluegreen algae in 2000 at this lake (4 mg/l) was the 38th lowest of the 131 lakes sampled. Thus, presence of bluegreen algae at this lake does not appear to either threaten or impair designated uses.
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.
