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 phytoplankton communities in 2000.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "not supported" due to algal blooms and high levels of inorganic turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The occurrence of blooms of bluegreen algae present an additional potential impairment to designated uses at this lake. The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" due to high levels of nutrients, algal blooms, and high levels of inorganic suspended sediment. Fish consumption remain "not assessed" due to a lack of fish contaminant monitoring at this lake. 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 of monitoring conducted by ISU from 2000 through 2002 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are "not supported." 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 87, 77, and 83, respectively, for Crystal Lake. According to Carlson (1977), these index values place this lake in the upper range of hyper-eutrophic lakes and suggest extremely high levels of phosphorus, extremely high levels of suspended algae, and (3) extremely poor water transparency. According to Carlson (1991), the occurrence of a low chlorophyll-a TSI value relative to those for total phosphorus and secchi depth indicate non-algal particles or color dominate light attenuation. The ISU lake data suggest that, while non-algal particles do likely limit algal production at Crystal Lake, nitrogen limitation and zooplankton grazing may also limit algal production. 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. Of 131 lakes sampled, Crystal Lake had the 11th highest median level of inorganic suspended solids (20.4 mg/l), thus suggesting that non-algal turbidity limits the production of algae and is primary cause of the extremely poor water transparency at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 8. This ratio suggests a strong possibility that algal production at this lake is limited by nitrogen availability. Despite the high level of inorganic suspended solids at Crystal Lake, the level of chlorophyll-a is extremely high (fourth highest of the 131 lakes sampled) and is alone sufficient to cause transparency-related impairments at this lakes. Data from Downing et al. (2002) show moderately large zooplankton populations at Crystal Lake, including a relatively large population of species known as algal grazers; the median summer mass of zooplankton grazers at this lake in 2000 (25.6 mg/l) was the 50th highest of the 131 lakes sampled. The extremely high levels of phosphorus and the extremely high levels of primary productivity at this lake likely overwhelm any limitations by zooplankton grazers on algal production. These conditions indicate impairments to the Class A (primary contact) uses through presence of blooms of algae and poor water transparency due to algal and inorganic turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The IDNR Fisheries Bureau concurs that turbidity-related impairments due to algae and suspended solids exist at this lake.
Data from Downing et al. (2002) also suggest that bluegreen algae (Cyanophyta), can, at times (especially late summer), dominate the summertime phytoplankton community of Crystal Lake). Sampling at Crystal Lake in summer 2000 showed that bluegreen algae comprised approximately 50% of the phytoplankton community in the early July sample, less than 5% in the late July sample, and approximately 90% in the early September sample. The 2000 summer average mass of bluegreen algae at Crystal Lake (53.4 mg/l) was the 17th highest of the 131 lakes sampled and suggests a potential impairment due to violation of Iowa’s narrative standard protecting against presence of 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. 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 for this lake.
The hyper-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 (evaluated) as "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. Fish consumption remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.
