Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake plankton communities from 2000-05.
Basis for Assessment
SUMMARY: Based on water quality data and other information generated prior to the chemical renovation of this lake in 2004, the Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting" and the Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting". The Class C (drinking water) uses remain "not assessed" due to lack of monitoring information. Fish consumption uses are “not assessed” due to the lack of recent information upon which to base an assessment. The fish population of this lake was renovated in fall of 2004. Due to this renovation (which removed common carp, a species detrimental to both the lake’s fishery and its water quality), and due to placement of best management practices in the watershed of this lake, water quality conditions at Lake Icaria can be expected to improve in 2005 and in subsequent years. 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, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
Note: A TMDL for siltation at Lake Icaria was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. The Section 303(d) impairments identified for the previous assessment/listing cycles (sitation) are addressed by the TMDL or will be addressed by the lake renovation/watershed project in 2004. For the 2006 assessment/listing cyle, this waterbody remains in IR Category 4a.
EXPLANATION: Although results of the ISU statewide survey of Iowa lakes suggest some reductions in water transparency at this lake, the survey data do not suggest impairment of the Class A uses. 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 63, 57, and 63, respectively. According to Carlson (1977), the index values for total phosphorus and secchi depth place this lake in the range between eutrophic and hyper-eutrophic lakes; the index value for chlorophyll-a is in the upper range of eutrophic lakes. These index values suggest somewhat elevated levels of phosphorus, relatively low levels of chlorophyll-a, and marginally good water transparency. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for this lake is 28. This TN:TP ratio suggests that algal production at this lake is limited by phosphorus availability.
According to Carlson (1991), the occurrence of a high TSI value for phosphorus and Secchi depth relative to that for chlorophyll-a suggests that non-algal turbidity limits algal production. Results of ISU monitoring suggest that moderately high levels of inorganic suspended solids (i.e., non-algal turbidity) as well as populations of zooplankton that graze on algae may also limit algal production at this lake. The levels of inorganic suspended solids at this lake are very high and do suggest the potential for contributing to turbidity such that algal production is limited and water transparency is somewhat reduced. 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. Lake Icaria had the 27th highest median level of inorganic suspended solids (10.9 mg/l), thus suggesting that non-algal turbidity not only limits algal production but also threatens full support of the primary contact recreation and aquatic life uses.
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. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised just over 30% 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 (45 mg/l) was the 27th lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Lake Icaria that would explain the discrepancy between the TSI for total phosphorus (63) and that for chlorophyll-a (57)..
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 (65%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Lake Icaria (9.6 mg/l) was the 51st lowest of the 131 lakes sampled. This levels 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).
The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggested that the Class B(LW) aquatic life uses should be assessed (evaluated) as "partially supported" for the previous (2004) assessment cycle due to excessive nutrient loading to the water column, high levels of non-algal turbidity, and siltation in the lake. In addition, Lake Icaria's fish community had degraded over the last few years due to an over population of yellow bass (Morone mississippiensis) compounded by extremely high common carp numbers that reduced desired game fish species significantly. Thus, a renovation of the lake’s fish population was conducted in fall 2004. Eliminating yellow bass and common carp from the lake, stabilizing the shoreline, and adding fish habitat are expected to improve the lake's fish population. These efforts combined with the extensive soil conservation practices that have taken place in the watershed will further improve the lake's water quality and recreational opportunities.
Results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake during its pre-renovation period. Results of this monitoring show that 3 of the 15 samples collected exceeded the Class B(LW) criteria for dissolved oxygen and that 1 of the 14 samples collected exceeded Iowa’s Class A,B(LW) criteria for pH (maximum = 9.6; minimum = 7.7 pH units). Based on IDNR’s assessment methodology, these results do not suggest violation frequencies are significantly greater than 10% for either parameter and thus do not suggest impairment of either the Class A and Class B(LW) uses of Lake Icaria.
Drinking water (Class C) uses were not assessed due to the lack of water quality information upon which to base an assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-04 show that nitrate levels at this lake (maximum value = 3.0 mg/l; median = 0.8 mg/l) are low relative to the drinking water MCL (10 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are “not assessed” due to the lack of recent information upon which to base an assessment. The most recent fish contaminant monitoring at this lake was conducted in 1993 as part of the U.S. EPA/IDNR fish tissue (RAFT) monitoring program. Although results of the 1993 RAFT monitoring indicated very low levels of contaminants and “full support” of the fish consumption uses, these data are now considered too old (greater than 10 years) to characterize current water quality conditions.
