Assessment Comments
Assessment is based on results of (1) ISU lake surveys from 2000-04, (2) ISU reports on lake plankton communities from 2000-05, (3) results of the IDNR beach monitoring program from 2002-04, (4) the ISU 2001 diagnostic/feasbility study, (5) surveys of the DNR Fisheries Bureau, and (6) EPA/DNR fish contaminant monitoring in 2002.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as “not supporting” due to high levels of indicator bacteria at one of the lake’s two public swimming beaches. In addition, results of the ISU lakes survey suggest "partial support" of Class A uses due to aesthetically objectionable conditions (poor water transparency) related primarily to high levels of inorganic turbidity and secondarily to blooms of algae. The presence of nuisance (=noxious) aquatic life (bluegreen algae) also present a potential impairment of the Class A uses. The Class B(LW) aquatic life uses remained assessed (evaluated) as “fully supporting.” Drinking water uses remain “not assessed” due to lack of water quality information. Fish consumption uses remain assessed (monitored) as “fully supported” based on results of fish contaminant monitoring in 2002. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2002-2004, (2) results of the statewide survey of Iowa lakes sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (3) surveys by IDNR Fisheries Bureau, (4) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 2002 and (6) the ISU diagnostic/feasibility study in 2001.
Note: A TMDL for nutrients and algae at Clear Lake was prepared by IDNR and approved by EPA in 2005; thus, suggesting that this lake should be placed into IR Category 4a (TMDL approved) for the 2006 assessment/listing cycle. Because, however, the 2006 Section 303(d) impairments due to indicator bacteria was not addressed in the TMDL, this waterbody will remain in Category 5a (impaired; TMDL required) for the 2006 assessment/listing cycle.
EXPLANATION: Results of IDNR beach monitoring from 2002 through 2004 suggest that the Class A (primary contact recreation) uses are “not supported” at Clear Lake Beach but are "fully supported" at McIntosh Woods Beach. Results of IDNR beach monitoring at Clear Lake Beach from 2002 through 2004 suggest that the Class A uses are "not supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (29 samples), 2003 (29 samples), and 2004 (23 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A (primary contact recreation) uses: (1) all thirty-day geometric means for the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10 % of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A uses should be assessed as “not supported”. Also, if more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A uses should be assessed as “partially supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35of U.S. EPA 1997b).
At Clear Lake Beach, the geometric means of 13 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 1 of 25 geometric means violated in 2002 and 12 of 19 geometric means violated in 2004. None of the geometric means exceeded this standard during the recreational season of 2003 (25 geometric means). Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was significantly greater than 10% in the following recreation seasons: 2002 (6 of 29 samples) and 2004 (10 of 23 samples). Significantly less than 10% of the samples exceeded this standard during the recreational season of 2003 (2 of 29 samples). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A (primary contact recreation) uses due to geometric mean values that exceed state water quality criteria.
At McIntosh Woods Beach, the geometric means of all 62 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were below the Iowa water quality standard of 126 orgs/100 ml. Also, none of the 74 samples collected exceeded Iowa’s single-sample maximum criterion. According to U.S. EPA guidelines and IDNR’s assessment methodology, these results suggest “full support” of the Class A (primary contact recreation) uses. These results also suggest extremely low levels of bacteria at this beach.
Results from the ISU statewide survey of Iowa lakes suggest that high levels inorganic turbidity that reduce water clarity, in addition to moderately high levels of algal turbidity, may adversely affect the Class A uses of Clear 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 66, 63, and 68, respectively. According to Carlson (1977), the index values for all three parameters (total phosphorus, chlorophyll-a, and Secchi depth) are in the range between eutrophic and hyper-eutrophic lakes. These TSI values suggest high levels of phosphorus in the water column, relatively low levels of chlorophyll-a, and 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 Clear 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, Clear Lake had the 32nd highest median level of inorganic suspended solids (9.6 mg/l), thus suggesting that these very high levels of non-algal turbidity may limit the production of algae as well as contribute to poor water transparency.
In addition to inorganic sources of turbidity, the somewhat elevated levels of chlorophyll-a at Clear Lake suggest that suspended algae also contribute to poor water transparency. The overall 2000-02 median chlorophyll-a level at Clear Lake (28 ug/l) is the 41st highest of the 131 lakes sampled. Neither nitrogen limitation nor zooplankton grazing appear to limit algal production at Clear Lake. Based on median values from ISU sampling from 2000-04, the ratio of total nitrogen to total phosphorus for this lake is 23; this ratio suggests that algal production at this lake is limited by availability of phosphorus as opposed to nitrogen.
The results of ISU plankton monitoring from 2000 through 2005 show a relatively small population of zooplankton grazers at Clear Lake. This lake had the 37th lowest per summer sample mass of zooplankton (Cladoceran) grazers of the 131 lakes sampled. This low level of zooplankton grazers would likely be unable to suppress algal production.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at this 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. Sampling from 2000 through 2004 showed that the percent wet mass of bluegreen algae in the phytoplankton community of Clear Lake in summers of the 2000-2004 period was approximately 80%. Also, the median per summer sample mass of bluegreen algae at this lake (29.0 mg/l) was the 31st highest of the 131 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.” The 2000-04 median for Clear Lake is equal to this 75th percentile value; thus, the Class A uses are considered (evaluated) as “partially supported” due to presence of this nuisance aquatic life. Please note, however, that no criteria exist upon which to base a more accurate identification of lake impairments due to bluegreen algae. 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).
The Class B(LW) aquatic life uses are assessed as "fully supporting" based on information from the DNR Fisheries Bureau. The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected during summers of 2000 through 2004. Three of 15 samples exceeded the Class B(LW) criterion for pH of 9.0 pH units (maximum value = 9.1; minimum value = 8.3 pH units). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations likely reflect the high levels of primary productivity at Clear Lake and do not reflect the input of pollutants into this lake.
Drinking water (Class C) uses remain “not assessed” due to the lack of water quality information needed for this assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-04 show that nitrate levels are very low at this lake (maximum value = 0.43 mg/l; median = 0.21 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Clear Lake in 2002. The composite samples of fillets from channel catfish and walleye had low levels of contaminants. 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: mercury: 0.045 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 2002 RAFT sampling conducted at Clear 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.
