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 2000-05, and (4) EPA/IDNR fish contaminant monitoring in 2003.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due (1) extremely high levels of algal production (blooms) and (2) extremely poor water transparency that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. An additional impairment to the Class A uses is due to the very high populations of nuisance (noxious) aquatic life (bluegreen algae) at this lake. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. The assessment of the Class B(LW) uses is consistent with the assessment developed for previous Section 305(b) reports. Fish consumption uses are assessed (monitored) as “fully supported” based on results of fish contaminant monitoring in 2003. 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 contaminant monitoring in 2003.
Note: A TMDL for algae and turbidity at Trumbull 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 moved from IR Category 5a from the 2004 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2006 cycle.
EXPLANATION: Results of monitoring conducted by ISU from 2000 through 2004 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are "not supported" due to presence of algal blooms and extremely poor water transparency that violate Iowa’s narrative criterion protecting against aesthetically objectionable conditions. 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 89, 78, and 85, respectively, for Trumbull Lake. According to Carlson (1977), these index values place this lake in the upper range of hyper-eutrophic lakes and suggest extremely high levels phosphorus in the water column , extremely high production of suspended algae, and extremely poor water transparency. These conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable conditions due to blooms of algae and high levels of inorganic suspended solids that reduce water transparency. These TSI values suggest that Trumbull Lake has some of the poorest water quality of any lake in Iowa.
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 (i.e., inorganic suspended solids) do likely limit algal production at Trumbull 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. The median level of inorganic suspended solids at Trumbull Lake (42 mg/l) was the highest of the 131 lakes. Thus, despite the extremely high level of algal production at this lake, non-algal (inorganic) turbidity likely does limit the production of algae as well as contributes to the impairment of beneficial uses through reduced water transparency.
The ISU data also suggest that nitrogen availability and zooplankton grazing may limit algal production at Trumbull Lake. Based on median values of ISU lake sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus (TN/TP) at Trumbull Lake is 10; this TN/TP ratio is low and suggests that algal production may, at times, be limited by the availability of nitrogen. In addition, the presence of extremely large populations of zooplankton at this lake that graze on algae may explain a portion of the discrepancy between the TSI value for total phosphorus (89) and that for chlorophyll-a (78). Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about 40% 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 (571 mg/l) was the second highest of the 131 lakes sampled.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at Trumbull 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 80%. Also, the median per summer sample mass of bluegreen algae at this lake (28.9 mg/l) was the 32nd 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).
Thus, the water quality conditions at Trumbull Lake suggest impairments to the Class A (primary contact) uses primarily due to presence of (1) extremely high levels of algal production (blooms) and (2) extremely poor water transparency that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The extremely poor water transparency is caused by a combination of suspended algae and inorganic suspended solids. Levels of either algae or inorganic suspended solids are sufficiently high to independently cause severe reductions in water transparency at 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. Remarkably—especially considering the extremely poor physical properties of water quality at this lake—the ISU lake survey data show relatively good chemical water quality at Trumbull Lake. Results of this monitoring show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected during summers of 2000 through 2004 and show that only one of 14 samples (7%) exceeded the Class B(LW) criterion for pH (maximum = 9.5; minimum = 8.7 pH units). These results of chemical monitoring do not suggest impairment of either the Class A or Class B(LW) uses.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Trumbull Lake in 2003. The composite samples of fillets from common carp and yellow perch had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp 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 yellow perch fillets were as follows: mercury: 0.021 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 2003 RAFT sampling conducted at Trumbull 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.
