Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, (3) ISU reports on lake plankton communities from 2002-05, and (4) results of U.S. EPA/IDNR fish tissue monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to somewhat elevated levels of algal and non-algal turbidity that contribute to reductions in water transparency. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting". Nutrient loading to the water column and slightly elevated levels of algal and non-algal turbidity, however, remain concerns at this lake. Fish consumption are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2001. 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, (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey, and (4) results of U.S. EPA / IDNR fish tissue monitoring in 2001. Although not originally assessed as "impaired" by IDNR for the 2004 Section 305(b) cycle, this lake was added to Iowa's 2004 Section 303(d) list at the recommendation of U.S. EPA Region 7 based on ISU lake monitoring data from 2003 and 2004 that suggested adverse trends in water quality.
Note: A TMDL for algae and turbidity at Five Island Lake was prepared by IDNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (algal growth and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that the somewhat elevated levels of turbidity due to algal and inorganic sources may adversely affect the Class A and Class B(LW) uses of Five 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 69, 64, and 66, respectively. According to Carlson (1977), all three index values are in the range between eutrophic and hyper-eutrophic lakes. These index values suggest moderately high levels of phosphorus in the water column, moderately high levels of chlorophyll-a, and moderately poor 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. Based on results of the ISU monitoring from 2000-04, the primary non-phosphorus limitation to algal production appears to be inorganic suspended solids. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Five Island Lake is 25. This TN:TP ratio suggests that phosphorus (versus nitrogen) may be the limiting nutrient for algal production at this lake.
In terms of all Iowa lakes sampled, data from the ISU survey show relatively small populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about one-quarter 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 (58 mg/l) was the 40th lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Five Island Lake.
The levels of inorganic suspended solids at this lake are very high and likely contribute to in-lake turbidity and potential suppression of algal production. 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, Five Island Lake had the 22nd highest median level of inorganic suspended solids (12.4 mg/l), thus suggesting that non-algal turbidity likely limits the production of algae as well as contribute to in-lake turbidity that threatens full support of designated uses at this lake. Thus, the moderately high TSI values for chlorophyll-a and secchi depth suggest potential impairments of the Class A (primary contact) uses through presence of reduced water transparencies caused by algae and by inorganic suspended solids. The influence of the ongoing dredging activities on levels of inorganic suspended solids at this lake is unknown.
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. While data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion (60%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Five Island Lake (10 mg/l) was the 55th lowest of the 131 lakes sampled. This level is in the lower half of the 131 Iowa lakes sampled. The presence of a relatively small population of bluegreen algae at this lake does not suggest a 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 less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. 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).
In 2000, at the recommendation of the DNR Fisheries Bureau, the Class B(LW) uses were changed from "partially supported" to "fully supported"; this assessment remains for the 2006 reporting/listing cycle. The water quality trend for this lake is "improving." According to the DNR Fisheries Bureau, the water quality improvements at Five Island Lake reflect results of the lake dredging project. Nonetheless, the IDNR Fisheries Bureau suggests that the high nutrient loading to the water column and moderately high levels of algal and non-algal turbidity remain concerns at this lake. The ISU lake survey data show good chemical water quality at this lake. These data show no violations of the Class B(LW) criteria for dissolved oxygen in the 15 samples collected, or for pH in the 14 samples collected, at Five Island Lake during summers of 2000 through 2004.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Five Island Lake in 2001. The composite samples of fillets from channel catfish and walleye had low levels of contaminants; levels of the primary contaminants were all below levels of detection. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows<0.0181 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses. This scenario, however, does not apply to the fish contaminant data generated from the 2001 RAFT sampling conducted at Five Island Lake: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
