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) U.S. EPA/IDNR fish contaminant monitoring in 2003.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "partially supported" due to (1) poor water transparency caused by a combination of high levels of chlorophyll-a (suspended algae) and high levels of inorganic suspended solids and (2) high levels of pH that frequently exceed the Class A water quality criterion. The Class B(LW) aquatic life uses are assessed (monitored) as "partially supported" primarily due to frequent violations of the Class B(LW) pH criterion and secondarily to algal blooms, sediment re-suspension, and nutrient loading to the water column. Fish consumption are assessed (monitored) as “fully supported” based on 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 turbidity and algae at Little Spirit Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (algal growth, pH, and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
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 only "partially supported." 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 84, 63, and 67, respectively, for Little Spirit Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggest both extremely high levels of phosphorus in the water column, moderately high levels of suspended algae, and relatively poor water transparency. These conditions indicate impairments to the Class A (primary contact) uses through presence of poor water transparency that violates Iowa’s narrative water quality criterion protecting against aesthetically objectionable conditions. Based on the ISU monitoring data, the cause of this poor transparency appears to be a combination of high levels of inorganic suspended solids and high levels of suspended algae.
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, high levels of inorganic suspended solids (turbidity), and the relatively large population of zooplankton grazers all function as non-phosphorus limitations at Little Spirit Lake. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for this lake is 10. This ratio is low and does suggest the potential for nitrogen limitation at this lake.
Data on inorganic suspended solids from the ISU survey suggest that this lake is also subject to occasional episodes of very high levels of non-algal turbidity. 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 Little Spirit Lake (10.0 mg/l) was the 31st highest of the 131 lakes, thus suggesting that non-algal turbidity may limit the production of algae as well as contribute to impairment beneficial uses.
The presence of extremely large populations of zooplankton at this lake that graze on algae, however, may explain the discrepancy between the TSI value for phosphorus (84) and that for chlorophyll-a (63). Sampling from 2000 through 2005 showed that while Cladoceran taxa (e.g., Daphnia) comprised about 60% 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 (225 mg/l) was the 17th highest of the 131 lakes sampled. The large population of zooplankton grazers at Little Spirit Lake suggests the potential for limiting algal production at this lake.
Based on information from the ISU lakes survey and from the IDNR Fisheries Bureau, the turbidity-related impacts to the primary contact and aquatic life uses at this lake will be attributed to both suspended algae (blooms) and re-suspended inorganic material. Despite the generally poor water quality at this lake, a comparison of the TSI values calculated for the 2000-2002 period to the values calculated for the 2002-2004 period does suggest some improvement in water quality at this lake, both in levels of chlorophyll-a (TSI improved from 66 to 63) and in water transparency (Secchi TSI improved from 70 to 67).
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. While data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion (almost 80%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Little Spirit Lake (21 mg/l) was the 41st highest of the 131 lakes sampled. This level is in the lower two-thirds of the 131 Iowa lakes sampled. The presence of a relatively small population of bluegreen algae at this lake does not suggest 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 less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. 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).
According to the IDNR Fisheries Bureau, the impairments to the aquatic life uses of this natural lake are rather hard to quantify but probably affect some spawning activities of nest building species in varying degrees; e.g., bluegill, bullhead, crappie and largemouth bass. Algal blooms do impact water quality through their contribution to sags in dissolved oxygen and the potential fish mortality that can result.
The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 15 samples collected at this lake during summers of 2000 through 2004. Six of 14 samples, however, exceeded the Class B(LW) criterion for pH (maximum = 9.5; minimum = 8.3 pH 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 Little Spirit Lake and do not reflect the input of pollutants into this lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Little Spirit Lake in 2003. The composite samples of fillets from common carp and walleye had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.019 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.04 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 this 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.
