Assessment Comments
Assessment based on results of (1) IDNR beach monitoring program from 2002-04, (2) EPA/DNR fish tissue (RAFT) monitoring in 2000, (3) ISU lake survey from 2000-04, (4) ISU reports on lake plankton communities from 2000-05, and (5) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to (1) poor water transparency, (2) increasing levels of chlorophyll, and (3) frequent violations of Iowa's pH criteria. Large populations of nuisance aquatic life (bluegreen algae) are also a concern at this lake. The Class B(LW) aquatic life uses are assessed (monitored) as "partially supporting" due to frequent violations of Iowa's pH criteria. The Class C (drinking water) uses are "not assessed" due to the lack of water quality information upon which to base an assessment. Fish consumption uses are assessed (monitored) as "fully supported" based on fish contaminant monitoring in 2000. Sources of information for this assessment include results of (1) IDNR beach monitoring from 2002 through 2004, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2004 by Iowa State University (ISU), (3) information from the 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 2000.
Note: A TMDL for siltation at Lake Keomah was prepared by IDNR and approved by EPA in 2002; thus, this lake was placed into IR Category 4a for the 2004 assessment/listing cycle. Not all of the section 303(d) impairments identified for the current (2006) assessment/listing cycle (algal growth, turbidity, and pH), however, are addressed in the TMDL. Thus, this waterbody was moved from IR Category 4a to Category 5a (impaired; TMDL required) for the 2006 assessment/listing cycle.
EXPLANATION: Results of IDNR beach monitoring at Lake Keomah from 2002 through 2004 suggest that the Class A uses should be assessed (monitored) as “fully supported". Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (31 samples), 2003 (29 samples), and 2004 (16 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 Lake Keomah beach, the geometric means of all 64 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. These results suggest generally low levels of indicator bacteria at this lake. None of the 60 samples collected during recreational seasons of 2002 and 2003 exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. During the 2004 recreational season, 2 of 16 samples exceeded this criterion. Based on IDNR’s assessment methodology, however, the results for the 2004 recreational season do not suggest that significantly more than 10 percent of the samples exceed Iowa’s single-sample maximum criteria, Thus, these results do not suggest an impairment of the Class A uses of Lake Keomah.
Despite results of IDNR beach monitoring that suggest "full support" of the Class A uses, results from the ISU statewide survey of Iowa lakes suggest that these uses are only “partially supported” due to poor water transparency. 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 74, 63, and 66, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index values for chlorophyll-a and Secchi depth place this lake in the middle range between eutrophic lakes and hyper-eutrophic lakes. These index values suggest (1) very high levels of phosphorus, (2) moderately high levels of chlorophyll-a, and (3) relatively 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. Results of ISU monitoring suggest that nitrogen-limitation and possibly inorganic suspended solids combine to limit algal production at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Lake Keomah is 13. This ratio suggest the possibility that production of algae at this lake is, at times, limited by availability of nitrogen.
The levels of inorganic suspended solids at this lake are only slightly elevated relative to other Iowa lakes and suggest only a limited potential for contributing to in-lake turbidities. 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; the median level at Lake Keomah was 3.8 mg/l.
In terms of all Iowa lakes sampled, data from the ISU survey show moderately large populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised almost 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 (82 mg/l) was the 62nd highest of the 131 lakes sampled. These results suggest that algal grazing by these zooplankters may present a non-phosphorus limitation due to zooplankton grazing at Lake Keomah.
The moderately high TSI value for Secchi depth suggests an impairment of the Class A (primary contact) uses due to poor water transparency that violate the state’s narrative water quality standard protecting against aesthetically objectionable conditions. Problems with water transparency at this lake are likely caused by a combination of suspended algae and inorganic turbidity. A comparison of annual TSI values for the 2000-2004 period at Lake Keomah suggests a potential adverse trend in water quality. Annual summer TSI values for Secchi depth have generally been stable over the five-year period but have exceed the impairment threshold of 65 in four of those five years: 2000: 66; 2001: 54; 2002 = 68; 2003 = 67; and 2004 = 68. In addition, annual summer TSI values for chlorophyll-a have generally worsened over the five-year period: 2000 (50 or approximately 7 ug/l chlorophyll-a); 2001 (55), 2002 (69); 2003 (63); 2004 (73 or approximatley 75 ug/l chlorophyll-a). Thus, the TSI values for both Secchi depth and chlorophyll-a likely suggest impairment of the Class A uses.
Data from the ISU survey from 2002-2004 suggest that the presence of nuisance aquatic species (i.e., bluegreen algae) may present an impairment of the Class A uses at this lake. Summer sampling during this period showed the percent wet mass of the total phytoplankton community in bluegreens was approximately 90%. In addition, Lake Keomah had the 14th highest median per summer sample mass of bluegreen algae of the 131 lakes sampled: 59.4 mg/l. This median is in the worst 10 % of the 131 Iowa lakes sampled. The presence of a large population of bluegreen algae at this lake suggests 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 greater than the 90th percentile of this distribution (~59 mg/l) were arbitrarily chosen by IDNR staff to represent the condition of “potential impairment; not supported.” No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the , 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, of necessity, remains "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Based on information from the IDNR Fisheries Bureau, the Class B(LW) uses were assessed as "fully supported". The IDNR fisheries biologist states that algae blooms do, however, occur at Lake Keomah and that summer fish kills have resulted; turbidity at this lake is related primarily to colloidal clays in the watershed that tend to resist settling from the water column in the lake. The ISU lake survey data, however, suggest impairment of the Class B(LW) uses at Lake Keomah, primarily due to frequently high levels of pH. Of the 15 samples collected during the 2000-2004 monitoring period, 7 samples (47%) violated the Class B(LW) criteria for pH of 9.0 pH units (maximum value of 10.0 units). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria. Thus, these results suggest an impairment (partial support/monitored) of the Class A and Class B(LW) uses of this lake. These violations likely reflect the high levels of primary productivity at Lake Keomah and do not reflect the input of pollutants into this lake. While levels of pH in Iowa lakes occasionally exceed the upper Class B(LW) pH criterion of 9.0 units due to expected shifts in the carbonate equilibrium as primary productivity utilizes the available carbon dioxide, the frequency and magnitude of pH violations at this lake suggest special circumstances that cannot be similarly explained given that levels of primary productivity (as suggested by the levels of chlorophyll-a) are only moderately high at Lake Keomah. Four of the seven violations were in the upper 95% of the 1,963 sampled analyzed as part the ISU statewide lake survey from 2000 through 2004: 9.6, 9.9, 9.4, and 9.6 pH units. None of the 15 samples collected at Lake Keomah during the 2000-2004 monitoring period violated the Class B(LW) criteria for dissolved oxygen
Drinking water (Class C) uses were not assessed due to the lack of water quality information upon which to base an 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 at Lake Keomah (maximum value = 1.4 mg/l; median = 0.2 mg/l) are very low relative to the drinking water MCL (10 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 Lake Keomah in 2000. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. 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 2000 RAFT sampling conducted at Lake Keomah: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
