Lacey Keosauqua Lake IA 04-LDM-1008

Assessment Comments

Assessment based on results of (1) IDNR beach monitoring program from 2002 through 2004, (2) the ISU lake survey from 2000-04, (3) ISU reports on lake plankton communities from 2000-05, and (4) surveys by IDNR Fisheries Bureau. Dam failure occurred in mid-May 2002; the dam was repaired and the lake returned to normal water levels in July 2003.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting”.   The Class B(LW) aquatic life are also assessed (monitored) as "fully supporting".   The Class C (drinking water) uses, and the fish consumption uses, both remain "not assessed" due to lack of recent monitoring.   Previous Section 305(b) assessments for Lacey-Keosauqua Lake contain conflicting information suggesting that the lake has problems with non-algal turbidity and that the fishery is relatively poor.   Data from the ISU lake survey from 2000 through 2004, however, suggest that the water quality at this lake--in terms of nutrient levels and water transparency--is well above average for Iowa lakes.   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) IDNR/UHL beach monitoring in 2003 and 2004, (3) surveys by IDNR Fisheries Bureau, and (4) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.   NOTE:  A dam failure occurred at this lake in mid-May 2002.   The dam was repaired in early summer 2003, and the lake had returned to normal water levels, and was opened for all uses, in mid-July 2003.

EXPLANATION:  Results of IDNR beach monitoring at Lacey-Keosauqua Lake from 2002 through 2004 suggest that the Class A uses are "fully supported."  Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2003 (16 samples) and 2004 (16 samples) as part of the IDNR beach monitoring program.   (A dam failure occurred at this lake in May 2002; thus, too few samples (6) were collected during the 2002 recreational season to be of use for developing an assessment.)  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.   This assessment approach is based on U.S.  EPA guidelines (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

At Lacey-Keosauqua Beach beach, the geometric means of all 24 thirty-day periods during the summer recreation seasons of 2003 and 2004 were below the Iowa water quality standard of 126 orgs/100 ml.   Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion did not exceed 10% in either of the two recreation seasons (2003:  6%; 2004:  0%).    According to U.S.  EPA guidelines and IDNR’s assessment methodology, these results suggest “full support” of the Class A (primary contact recreation) uses.  

Results of ISU lake monitoring from 2000-04 also suggest good water quality at this lake.   Using the median values from this survey from 2000 through 2004 (approximately nine samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 58, 47, and 48, respectively.   According to Carlson (1977), the index value for total phosphorus places this lake in the upper range of eutrophic lakes; the index values for chlorophyll-a and Secchi depth are in the middle to upper range of mesotrophic lakes.   These index values suggest relatively low levels of phosphorus in the water column, extremely low (and much lower than expected) levels of chlorophyll-a, and exceptional water transparency for Iowa lakes.   These results suggest that this lake does not have either threats or impairments due to aesthetically objectionable blooms of algae or to high levels of inorganic turbidity.  

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.   The results of ISU monitoring suggest that nitrogen-limitation and the somewhat elevated levels of inorganic suspended solids likely combine to limit algal production.   Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Lacey Keosauqua Park Lake is 18.   This TN:TP ratio does suggest a slight possibility that nitrogen limitation suppresses the production of suspended algae 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 two-thirds 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 (44 mg/l) was the 25th lowest of the 131 lakes sampled.   These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Lacey-Keosauqua Lake.  

The levels of inorganic suspended solids at this lake are extremely low and suggest little potential for limiting algal production.   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 at Lacey Keosauqua Park Lake was 2.3 mg/l.  

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 (approximately 50%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Lacey Keosauqua Lake (1.9 mg/l) was the 10th lowest of the 131 lakes sampled.   This level is in the lowest 10% 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 ISU lake survey data also show 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 10 samples collected during summers of 2000 through 2004 (maximum = 8.5; minimum = 7.1 pH units).   One of 9 samples violated the Class B(LW) criterion for dissolved oxygen.   Based on IDNR’s assessment methodology, however, this single violation does not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus does not suggest an impairment of the Class B(LW) uses of Lacey Keosauqua Park Lake.  

The Class C (drinking water) uses remained "not assessed" due to a 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 are extremely low at this lake (maximum value = 0.4 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.