Trumbull Lake IA 06-LSR-1636

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Trumbull Lake are assessed (monitored) as "not supported" due to poor water transparency, aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 18 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 68, 68, and 74 respectively for Trumbull Lake . According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Trumbull Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and very high levels of phosphorus in the water column. The data show 6 violations of the Class A1 criterion for pH in 19 samples (32%).

The level of inorganic suspended solids was moderately high at Trumbull Lake , and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Trumbull Lake (5 mg/L) was ranked 92nd among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a large population of cyanobacteria exists at Trumbull Lake , which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 76% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (62.9 mg/L) was ranked 123rd of the 138 lakes sampled. This median is in the worst 25% of the 138 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 from 2012-2016. 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. 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(monitored) as "not supported" due to violations of the Class B(LW) criterion for pH,excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. This potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation.Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 19 samples(0%), no violations of the criterion for dissolved oxygen in 19 samples(0%), and 6 violations of the criterion for pH in 19 samples(32%). Based on DNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Trumbull Lake .

Note: A TMDL for algae and turbidity at Trumbull Lake was prepared by DNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2014 assessment/listing cycle (algal growth, turbidity, and pH) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) for the 2018 cycle.

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.

Note: The lake was drawn down in 2012 and rough fish were removed throughout the wetland complex and water control structures were installed to help regulate water levels in the wetland complex and at Trumbull Lake. The lake was refilled in 2014. Dramatic water quality improvements were noted.