Lacey Keosauqua Lake IA 04-LDM-1008

Assessment Comments

Assessment based on results of (1) IDNR beach monitoring program in 2000-01, (2) ISU lake survey in 2000-01, (3) ISU report on lake phytoplankton communities in 2000, 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 assessed (evaluated) as "fully supporting / threatened" (minor impacts).   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 2002, 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 IDNR-UHL beach monitoring program in summers of 2000, 2001, and (in part) 2002, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities at Iowa lakes in 2000 from Downing et al.  (2002).   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 from 2000 through 2002 (in part) suggest "full support" of the Class A uses.   Levels of indicator bacteria at Lacey Keosauqua Lake beach were monitored as part of the IDNR beach monitoring program once per week during the primary contact recreation seasons (May through September) of 2000 and 2001; samples were collected in 2002 from mid-April through mid-May when a dam failure occurred at this lake  According to U.S.  EPA guidelines for determining support of primary contact recreation uses (U.S.  EPA 1997b, page 3-35), the geometric mean of fecal coliform bacteria level from at least five samples collected over a thirty-day period is compared to the water quality standard of 200 fecal organisms/100ml.   If a thirty-day geometric mean exceeds 200 orgs/100 ml, the primary contact recreation uses are assessed as "not supported."  In addition, the U.S.  EPA guidelines state that if more than 10% of the total samples taken during any thirty-day period has a bacterial density that exceeds 400 fecal coliform organsims/100 ml, the primary contact recreation uses are assessed as "partially supported."  Due to the relatively low numbers of samples collected during any thirty-day period (N=5), the use of single-sample maximum values to assess beaches is problematic.   With less than 10 samples collected during any thirty-day period at Iowa beaches, the occurrence of a single level of bacteria above the single-sample maximum value will result in more than 10% violation of the single-sample maximum value and thus suggest impairment of the primary contact recreation uses.   The use of less than 10 samples in an assessment based on a critical value of 10% results in large probabilities (approximately 60%) of incorrectly concluding that an impairment exists.   For this reason, the single-sample maximum value is not used to assess support of primary contact recreation uses with data from the IDNR beach monitoring program.   At Lacey Keosauqua Lake beach, none of the 27 thirty-day periods during summers of 2000 and 2001 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml.   The maximum thirty-day geometric means were 14 orgs/100ml in 2000 and 13 orgs/100 ml in 2001.   None of the weekly samples collected during 2000 and 2001 exceeded the U.S.  EPA's recommended single-sample maximum value of 400 orgs/100 ml (maximum sample values were 50 orgs/100 ml in 2000 and 240 orgs/100 ml in 2001).   Based on the total of five samples collected in 2002 before the dam failure, the geometric mean was 38; only the sample collected jus prior to dam failure contained fecal coliforms above the single-sample maximum value of 400 orgs/100ml).   These results suggest (1) full support of primary contact recreation uses at this beach and (2) that levels of bacteria at this beach are very low.  

Results of ISU lake monitoring from 2000-02 also suggest good water quality at this lake.   Using the median values from this survey from 2000 through 2002 (approximately nine samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 66, 43, and 50, respectively.   According to Carlson (1977), the index value for total phosphorus places this lake in the middle range between eutrophic and hyper-eutrophic lakes; the index value for chlorophyll-a is in the middle to lower range of mesotrophic lakes, and the index value for secchi depth is at the boundary between eutrophic and mesotrophic lakes.   Although these index values suggest relatively high levels of phosphorus in the water column, they also suggest extremely low (and much lower than expected) levels of chlorophyll-a, and very good  to 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 2002, the ratio of total nitrogen to total phosphorus for Lacey Keosauqua Park Lake is 10.   This TN:TP ratio does suggest the possibility that nitrogen limitation suppresses the production of suspended algae at this lake.   The relatively high proportion of Daphnia in the zooplankton population of this lake suggest some, but limited, potential for grazing to reduce populations of suspended algae and thus levels of chlorophyll-a.   Sampling by Downing et al.  (2002) in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 45% of the dry mass of the zooplankton community in the late July sample and approximately 90% of the mid-August sample.   The 2000 summer average mass of Cladocerans, however, was only 16.4 mg/l; this level is the 59th lowest of the 131 lakes and does not suggest significant limitations to algal production through zooplankton grazing.   The levels of inorganic suspended solids at this lake are somewhat elevated and suggest the 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 2002 was 4.8 mg/l; the median level at Lacey Keosauqua Park Lake was 3.8 mg/l.  

This lake does not appear to have problems due to presence of nuisance algal species (i.e., bluegreen algae).   Data from Downing et al.  (2002) suggest that bluegreen algae (Cyanophyta) comprise a relatively small portion of the summertime phytoplankton community of this lake.   Sampling in 2000 showed that bluegreen algae comprised approximately 15% of the wet mass of the phytoplankton in the late June and mid August samples but increased to nearly 50% of the mass weight in the late July sample.   The 2000 average summer mass of bluegreen algae at Lacey Keosauqua Lake (1.1 mg/l) was 14th lowest of the 131 lakes sampled, thus suggesting little impact from this nuisance aquatic life.  

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 2000-02 show that nitrate levels are extremely low at this lake (maximum value = 0.4 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 uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.