Assessment Comments
Assessment is based on (1) surveys by DNR Fisheries Bureau, (2) results of Syngenta's "Iowa Voluntary Atrazine Monitoring Program" from 2002-04, (3) ISU lake survey from 2000-04, (4) ISU reports on lake plankton communities from 2000-05, and (5) U.S. EPA/IDNR fish contaminant monitoring in 2005..
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting". Despite indications of low levels of dissolved oxygen in 2000, the Class B(LW) aquatic life uses are also assessed (monitored) as "fully supporting”. The Class C (drinking water) uses are assessed (monitored) as “fully supported” based on results of monitoring for atrazine and nitrate. Fish consumption uses are assessed (monitored) as "fully supported/threatened (declining trend/impaired)" based on fish contaminant monitoring in 2005. This is a new impairment for this lake. The 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, (4) results of Syngenta’s voluntary atrazine monitoring program (VMP) from 2002-2004, and (5) results of U.S. EPA / IDNR fish contaminant monitoring in 2005.
EXPLANATION: Using the median values from the ISU survey from 2000 through 2004 (approximately 15 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 62, 58, and 60, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the lower range between eutrophic and hyper-eutrophic lakes; the index values for chlorophyll-a is in the upper range of eutrophic lakes, and the index value for secchi depth is at the upper range of eutrophic lakes. These index values suggest somewhat elevated levels of phosphorus, relatively low production of suspended algae, and marginally good water clarity.
The general agreement between the TSIs for phosphorus, chlorophyll, and Secchi depth suggests that non-phosphorus limitations—which appear to occur at most Iowa lakes—do not occur at Little River Lake. The ISU lake data do suggest, however, that the somewhat elevated levels of inorganic suspended solids (non-algal turbidity) likely limit algal production at Little River Lake as well as contribute to non-algal turbidity that reduces water transparency. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000-04 was 5.2 mg/l; the median level at Little River Lake was equal to this median at 5.3 mg/l.
Neither nitrogen limitation nor zooplankton grazers appear likely to limit algal production at this lake. Based on median values from ISU sampling from 2000-04, the ratio of total nitrogen to total phosphorus for Little River Lake is 23. This ratio suggests that nitrogen limitation does not influence algal production at this lake.
In terms of all Iowa lakes sampled, data from the ISU survey show relatively small populations of zooplankton species at this lake that graze on algae. Although 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 (43 mg/l) was the 24th lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Little River Lake.
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 (nearly 70%) 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 River Lake (9 mg/l) was the 47th lowest of the 131 lakes sampled. This level is in the lower half 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).
These conditions—including moderately good water transparency, relatively low levels of chlorophyll-a, and low levels of bluegreen algae—suggest “full support” of the Class A (primary contact recreation) uses.
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported”. Nutrient loading to the water column, however, remains a concern for support of the Class B(LW) uses at this lake.
The ISU lake survey data also show generally good chemical water quality at this lake. Results of this monitoring show no violations of the Class A,B(LW) criteria for pH in the 13 samples collected during summers of 2000 through 2004 (maximum = 8.8; minimum = 7.8 pH units). Two of 14 samples exceeded the Class B(LW) criterion for dissolved oxygen. Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(LW) uses of Little River Lake.
The assessment of support of the Class C (drinking water) uses (“fully supported”) was based primarily on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from 2002 through 2004. This monitoring showed that the time-weighted mean levels of atrazine in the samples collected in calendar years 2002, 2003, and 2004 were well-below the MCL of 3.0 ug/l. The mean and median atrazine level over this three-year period (N=77) was 1.8 ug/l. The maximum value for this two-year period was 2.7 ug/l. None of the 64 moving annual averages for atrazine for the years 2002, 2003, and 2004 at Little River Lake exceeded the MCL (maximum average = 2.2 ug/l). Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported." In addition, results of the ISU lake survey show that nitrate levels are extremely low at this lake. In the 14 samples collected during the 2002-2004 summer monitoring period, the maximum and median nitrate levels were 3.1 mg/l and 0.2 mg/l, respectively.
Fish consumption uses were assessed (monitored) as “fully supported/threatened (impaired)” with a declining trend based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Little River Lake in 2005. 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 (IDPH), 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 applies to the fish contaminant data generated from the 2005 RAFT sampling conducted in this assessment segment. Although previously assessed as “fully supported”, the levels of contaminants now exceed one or more advisory trigger levels, thus suggesting a potential need to issue a consumption advisory. Iowa DNR’s assessment methodology states that if elevated levels of contaminants suggest the potential for a consumption advisory, the fish consumption uses should be assessed as “fully supported/threatened (impaired)”.
The composite samples of fillets from channel catfish and white crappie had generally low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.92 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of white crappie fillets were as follows: mercury: 0.12 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The level of mercury in the sample of channel catfish fillets, however, far exceed the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory: the level of mercury in this sample was 0.92 ppm. According to the IDNR/IDPH advisory protocol, two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Because, however, the levels of contaminants in the 2005 RAFT sample were more than twice the 1 meal/week trigger level, the fish consumption uses are assessed as “fully supported/threatened” (impaired). Additional monitoring will be conducted in 2006 to determine whether an advisory is needed for this waterbody.
