Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake plankton communities from 2000-05.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supporting" due to very poor water transparency due primarily to high levels of non-algal turbidity. Large populations of bluegreen algae (noxious aquatic plants) suggest an additional impairment of these uses. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting". High levels of nutrient loading to the water column and high levels of non-algal (inorganic) turbidity remain concerns regarding full support of the Class B(LW) uses. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring. The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (2) surveys by IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of non-algal turbidity may adversely affect the Class A and Class B(LW) uses of Lost Island Lake. Using the median values from this survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 68, 62, and 72, respectively. According to Carlson (1977), the index values for total phosphorus and chlorophyll-a are in the range between eutrophic and hyper-eutrophic lakes. The index value for Secchi depth is in the lower range of hyper-eutrophic lakes. These index values suggest relatively high levels of phosphorus in the water column, relatively low (and less than expected) levels of chlorophyll-a, and very 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 non-algal particles do likely limit algal production at Lost Island Lake. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2004 was 5.2 mg/l. Of 131 lakes sampled, Lost Island Lake had the 18th highest median level of inorganic suspended solids (14.3 mg/l), thus suggesting that non-algal turbidity limits the production of algae as well as contributes to impairments of both the primary contact recreation and aquatic life uses.
Algal production at this lake does not appear limited by either nitrogen availability or zooplankton grazers. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for this lake is 22. This ratio do not suggest a strong possibility for nitrogen limitation.
The presence of typically large populations of zooplankton at Lost Island Lake that graze on algae, however, may explain the discrepancy between the TSI value for phosphorus (68) and that for chlorophyll-a (62). Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about half of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (112 mg/l) was the 49th highest of the 131 lakes sampled. This level of zooplankton grazers may influence algal production at this lake.
These conditions indicate impairments to the Class A uses through presence of poor water transparency that violates Iowa’s narrative water quality criterion protecting against aesthetically objectionable conditions. Based on the ISU monitoring data, the cause of this poor transparency is primarily high levels of inorganic suspended solids; moderately high levels of suspended algae also likely contribute to this problem.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at Lost Island Lake. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion of this lake’s summertime phytoplankton community. Summer sampling during this period showed the percent wet mass of the total phytoplankton community in bluegreens (cyanobacteria) was approximately 75%. Also, the median per summer sample mass of bluegreen algae at this lake (42 mg/l) was the 21st highest of the 131 lakes sampled. This median is in the worst 25% of the 131 Iowa lakes sampled. The presence of a large population of bluegreen algae at this lake suggests the potential violation of Iowa’s narrative water quality standard protecting against occurrence of nuisance aquatic life. This assessment, however, is based strictly on a distribution of the lake-specific median bluegreen algae values for the 2000-2004 monitoring period. Median levels greater than the 75th percentile of this distribution (~29 mg/l) were arbitrarily chosen by IDNR staff to represent the condition of “potential impairment: partially supported.” No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the ability to characterize the levels of bluegreen algae at this lake has improved over that of the previous (2004) assessment due to collection of additional data, the assessment category for assessments based on level of bluegreen algae nonetheless remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported". Excessive nutrient loading to the water column and high levels of non-algal turbidity, however, remain concerns for the Class B(LW) uses of this lake. Additional data for this lake are being generated as part of the ongoing ISU lake survey; these data will be used to improve the accuracy of future water quality assessments. The ISU lake survey data from 2000 through 2004 suggest good chemical water quality at Lost Island Lake: no violations of the Class B(LW) criteria for dissolved oxygen occurred in the 14 samples collected, and no violations of pH criteria occurred in the 15 samples collected.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
