Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) ISU report on lake plankton 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 the somewhat elevated levels of chlorophyll-a (suspended algae) and the moderately high levels of inorganic turbidity / sediment re-suspension that indicate the potential for aesthetically objectionable conditions to occur. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting / threatened" due to excessive nutrient loading to the water column and siltation in the lake. Fish consumption uses remain "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 suggest that the somewhat elevated levels of chlorophyll-a, as well as the moderately high levels of inorganic suspended solids, may threaten full support of the Class A uses of Upper Pine 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 69, 63, and 59, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the upper range between eutrophic and hyper-eutrophic lakes; the index value for chlorophyll-a is in the lower range between eutrophic and hyper-eutrophic lakes, and the index value for Secchi depth is in the upper range of eutrophic lakes. These index values suggest moderately high to very high levels of phosphorus, somewhat elevated levels of chlorophyll-a, and relatively 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 results of ISU monitoring suggest that zooplankton grazing and moderately high levels of inorganic suspended solids likely limit algal production at this lake; algal production at this lake does not appear to be limited by nitrogen availability. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Upper Pine Lake is 70. This ratio is relatively high and suggests that the production of algae at this lake is limited by the availability of phosphorus and that this lake has an excess of nitrogen (the 2000-02 median level of total nitrogen at this lake (6.5 mg/l) was the 10th highest of the 131 lakes sampled). The presence of relatively large populations of zooplankton at Upper Pine Lake that graze on algae may explain, in part, the discrepancy between the TSI value for phosphorus and those for chlorophyll-a and secchi depth. Downing et al. (2002) show that Cladoceran taxa (e.g., Daphnia) comprised approximately 50% of the dry mass of the zooplankton community in the late July sample and 65% of the late August sample. The summer 2000 average mass of Cladocerans at this lake (144 mg/l) was the 5th highest of the 131 lakes sampled, thus strongly suggesting the potential for zooplankton grazers to limit algal production. The levels of inorganic suspended solids at this lake are moderately high and suggest the potential for limiting algal production as well as contributing to the slight reduction in water transparency at this lake.. 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 Upper Pine Lake was 4.3 mg/l. Despite the indications of good water quality, the high TSI value for total phosphorus suggests a threat to the full support of the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae as well as due to moderately high levels of inorganic turbidity.
Levels of nuisance algal species (i.e., bluegreen algae) at this lake appear to be low and neither threaten nor impair designated uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) tend to dominate the summertime phytoplankton community of this lake. Sampling in 2000 showed the percent wet mass of bluegreens ranged from nearly 90% in the late early July sampling, to approximately 60% in the late July sampling, and up to approximately 70% in the late August sampling. The summer 2000 average mass of bluegreens (9.3 mg/l), however, is only somewhat elevated relative to other Iowa lakes and thus does not suggest a significant water quality impact.
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 "fully supported / threatened" due to excessive nutrient loading to the water column and siltation in the lake. Fish consumption uses remain "not assessed due to the lack of recent fish contaminant monitoring at this lake."
