Assessment Comments
Assessment based on results of (1) IDNR beach monitoring program from 2002-04, (2) ISU lake survey from 2000-04, (3) ISU studies of lake plankton communities from 2000-05, and (4) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as “not supporting” due to high levels of indicator bacteria at the lake’s swimming beach; this is a new impairment for this lake. In addition, results of the ISU lakes survey suggest "partial support" of Class A uses due to aesthetically objectionable conditions due to algal blooms. The presence of nuisance algal species (bluegreen algae) presents an additional threat to full support of the Class A uses. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supported". The Class C (drinking water uses) were not assessed due to lack of information upon which to base an assessment. Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring at this lake. The sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2002, 2003, and 2004, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2004 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities collected from 2000 through 2005 for the ISU lakes survey. Note: this lake's fishery was renovated by Iowa DNR in 2006, and watershed improvements were also made (e.g., installation of silt-retention structures. Positive changes in water quality may result from this renovation.
EXPLANATION: Results of IDNR beach monitoring at Viking Lake from 2002 through 2004 suggest that the Class A uses are "not supported" due to exceptionally high levels of indicator bacteria during the 2004 recreation season. Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (29 samples), 2003 (28 samples), and 2004 (23 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A (primary contact recreation) uses: (1) all five-sample, thirty-day geometric means for the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10 % of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A uses should be assessed as “not supported”. Also, if more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A uses should be assessed as “partially supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35of U.S. EPA 1997b).
At Viking Lake beach, the geometric means of 4 of the 19 thirty-day periods during the summer recreation season of 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. None of the geometric means exceeded this standard during the recreational seasons of 2002 (26 geometric means) or 2003 (24 geometric means). Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was greater than 10% in the 2004 recreation season (17%). Less than 10% of the samples exceeded this standard during the recreational seasons of 2002 (3%) and 2004 (4%). According to IDNR’s assessment methodology and U.S. EPA guidelines, the occurrence of geometric means that exceed Iowa’s criterion of 126 orgs/100 ml suggest impairment (nonsupport) of the Class A (primary contact recreation) uses.
Results from the ISU statewide survey of Iowa lakes suggest that high levels of algal turbidity and presence of nuisance algal species may adversely affect the Class A uses of Viking Lake. 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 66, 66, and 62, respectively. According to Carlson (1977), all three index values are in the range between eutrophic and hyper-eutrophic lakes. These index values indicate moderately high levels of phosphorus in the water column, moderately high levels of chlorophyll-a (and suspended algae), and marginally good water transparency. Carlson (1991) suggests that a lake with a relatively high TSI for chlorophyll-a and a relatively low TSI for secchi depth may have large populations of algae such as Aphanizomenon that form flakes in the water column.
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. Of 131 lakes sampled, Viking Lake had a median level of inorganic suspended solids of 4.1 mg/l, thus suggesting that non-algal turbidity is somewhat elevated and may thus limit the production of algae to some degree.
Thus, the occurrence of a moderately high TSI value for chlorophyll-a (66) at Viking Lake indicates impairments to the Class A (primary contact) uses due primarily to blooms of algae that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The IDNR Fisheries Bureau concurs that Viking Lake is impaired by excess algae.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at Viking Lake. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion of this lake’s summertime phytoplankton community. Summer sampling during this period showed the percent wet mass of the total phytoplankton community in bluegreens (cyanobacteria) was approximately 80%. Also, the median per summer sample mass of bluegreen algae at this lake (31.2 mg/l) was the 30th highest of the 131 lakes sampled. This median is in the worst 25% of the 131 Iowa lakes sampled. The presence of a relatively large population of bluegreen algae at this lake suggests the 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 greater than the 75th percentile of this distribution (~29 mg/l) were arbitrarily chosen by IDNR staff to represent the condition of “potential impairment: partially supported.” 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 Class B(LW) aquatic life uses of this lake are assessed (evaluated) as "fully supported" based on information from the DNR Fisheries Bureau. Results of ISU monitoring from 2000 through 2004 suggest moderately good chemical water quality at this lake. Results of this monitoring show that three of the 13 samples collected exceeded the Class B(LW) criteria for dissolved oxygen and that two of the 15 samples collected exceeded Iowa’s Class A,B(LW) criteria for pH (maximum = 9.5; minimum = 7.6 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 Viking Lake.
The Class C (drinking water) uses remain "not assessed" due to lack of water quality information upon which to base such 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 are very low at Viking Lake (maximum value = 0.6 mg/l; median = 0.2 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption are "not assessed" due to the lack of fish contaminant monitoring at this lake.
