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: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to algal blooms and large populations of bluegreen algae. The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" due to nutrient loading to the water column, moderately high levels of algal turbidity, and siltation impacts. 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 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 and information from the DNR Fisheries Bureau suggest that high levels of algal turbidity impair the Class A and Class B(LW) uses of Meadow Lake. Using the median values from the Iowa State University statewide surveys of Iowa lakes from 2000 through 2002 (approximately nine samples), Carlson's trophic state indices for total phosphorus and chlorophyll-a at Meadow Lake are 77, 64 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 is in the middle range between eutrophic and hyper-eutrophic lakes, and the index value for secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, somewhat elevated (but less than expected) levels of chlorophyll-a (suspended algae), and marginally good 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) other than phosphorus limits production of algae. The ISU lake data suggest that a combination of three factors (non-algal (inorganic) particles, nitrogen limitation, and zooplankton grazing) limit algal production at Meadow Lake. The levels of inorganic suspended solids at this lake are moderately high and suggest at least the potential for contributing to in-lake turbidity and limiting production of suspended algae. 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 Meadow Lake was equal to this median (4.8 mg/l); this was the 58th highest level of the 131 lakes sampled. Nitrogen availability may also limit algal production at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Meadow Lake is 11. This TN:TP ratio is low and suggests that nitrogen availability may limit algal production at this lake. In addition, data from Downing et al. (2002) suggest relatively large populations of zooplankton species at Meadow Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 70% of the dry mass of the zooplankton community in the mid-July sample; this percentage, however, decreased to less than 5% in the early August sample. The 2000 average summer mass of Cladoceran grazers (80.6 mg/l) was the 20th highest of the 131 sampled, thus suggesting the likelihood that zooplankton grazing limits algal production. The water quality conditions at Meadow Lake suggest that the moderately high TSI value for chlorophyll-a indicates the potential for impairing the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae. The IDNR Fisheries Bureau also notes that Meadow Lake is impaired by algae and that anglers complain about algae at this lake.
The level of nuisance algal species (i.e., bluegreen algae) at Meadow Lake is one of the highest in Iowa and thus suggests an impairment of designated uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) entirely dominate the summertime phytoplankton community of Meadow Lake. Sampling in 2000 showed the percent wet mass of bluegreens ranged from approximately 95 to 100% in three summer samples. The 2000 summer average mass of bluegreen algae at Meadow Lake (102.8 mg/l) is the eighth highest of the 131 lakes sampled for the ISU survey, thus strongly suggesting a violation of Iowa’s narrative water quality standard protecting against nuisance aquatic life. The amount of data available for characterizing algal populations at this lake (one season), however, is not sufficient for developing a more accurate assessment of support of these uses. 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 for 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 be assessed as "fully supported / threatened" due to excessive nutrient loading to the water column, moderately high levels of algal turbidity, and siltation in the lake. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
