Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake plankton communities in 2000.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due to extremely large populations of suspended algae and extremely high levels of inorganic turbidity caused by re-suspension of sediment that contribute to aesthetically objectionable conditions at this lake. An additional impairment to the Class A uses is due to the extremely 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 remain "not assessed" due to the lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002).
EXPLANATION: Results of monitoring conducted by ISU from 2000 through 2002 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, extremely high levels of inorganic turbidity, and the related reductions in water transparency. Using the median values from this survey from 2000 through 2002 (approximately nine samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 90, 80, and 87, 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 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 2002 was 4.8 mg/l. The median level of inorganic suspended solids at Trumbull Lake (44 mg/l) was the second 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 2002, 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, data from Downing et al. (2002) show very large populations of zooplankton species at Trumbull Lake that graze on algae. The summer 2000 average mass of Cladocerans (196 mg/l) was the third highest of the 131 lakes sampled. Thus, these data suggest that populations of Cladocerans may tend to suppress expression, although to a limited degree, the production of chlorophyll as suspended algae.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also contribute to impairment at Trumbull Lake. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta), dominate the summertime phytoplankton community of Trumbull Lake. Sampling in 2000 showed that bluegreens comprised approximately over 95% of the wet mass of the phytoplankton during the three summer samplings. The average mass of bluegreen algae in summer 2000 at this lake (62 mg/l) ranked 15th highest of the 131 lakes sampled. The presence of relatively large populations of bluegreen algae suggests an impairment of support of the designated uses of this lake due to the potential for violating Iowa’s narrative water quality standard protecting against presence of nuisance aquatic life. Although results of plankton sampling in 2000 suggest that designated uses are impaired, the amount of data available for characterizing algal populations at this lake (one season) is not sufficient for developing a more accurate assessment of support of these uses. Additional data on plankton have been collected at this lake as part of the ongoing ISU lake survey and will be used to improve the accuracy of future water quality assessments. 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 high levels of inorganic turbidity (and the related reductions in water transparency) that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
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. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake. This lake was, however, sampled in 2003 as part of the U.S. EPA/IDNR RAFT fish contaminant monitoring program. The results from this sampling are not yet available.
