Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2003.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to very poor water transparency related to high levels of inorganic turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. High levels of algae at this lake also suggest an impairment by contributing to aesthetically objectionable conditions and nuisance aquatic life. 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. 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 conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) 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 2010 assessment/listing cycle (algal growth and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) for the 2010 cycle.
EXPLANATION: Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Trumbull Lake are “not supported.” Using the median values from these surveys from 2004 through 2008 (approximately 30 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 83, 76, and 81 respectively for Trumbull Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Trumbull Lake in the hypereutrophic category. These values suggest extremely high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column.
The level of inorganic suspended solids is extremely high at Trumbull Lake and suggests that non-algal turbidity contributes to the impairment. The median inorganic suspended solids concentration at Trumbull Lake was 45.8 mg/L, which was the highest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a large population of cyanobacteria exists at Trumbull Lake, which causes an impairment due to nuisance aquatic life at this lake. These data show that cyanobacteria comprised 62% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (35.0 mg/L) was the 30th highest of the 132 lakes sampled. This median is in the worst 25% of the 132 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2004-2008 period. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
The Class B(LW) (aquatic life) uses are assessed as “partially supported” due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. The ISU and UHL lake surveys results, however, show relatively good chemical water quality at Trumbull Lake. During 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 29 samples, and no violations for dissolved oxygen in 30 samples. There were 3 violations of the pH criterion in 30 samples (10%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class B(LW) uses at Trumbull Lake.
Fish consumption uses were assessed (evaluated) 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. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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. Overall the fish contaminant data generated from the 2003 RAFT sampling conducted at Trumbull Lake shows the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
