Pleasant Creek Lake IA 02-CED-459

Assessment Comments

Assessment is based on results of (1) IDNR beach monitoring program from 2002-04, (2) surveys of DNR Fisheries Bureau, (3) ISU lake survey from 2000-04, (4) ISU reports on lake plankton communities from 2000-05, and (5) fish tissue monitoring in 1999.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "fully supporting."  The Class B(LW) aquatic life uses remained assessed (monitored) as “fully supporting."  Fish consumption uses remained assessed (evaluated) as "fully supporting" based on results of fish contaminant monitoring in 1999.   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 on plankton communities collected from 2000 through 2005 for the ISU lakes survey, and (4) results of U.S.  EPA / IDNR fish tissue monitoring in 1999.  

EXPLANATION:  Results of IDNR beach monitoring at Pleasant Creek 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 2002 (31 samples), 2003 (29 samples), and 2004 (16 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.   This assessment approach is based on U.S.  EPA guidelines (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

At Pleasant Creek Lake beach, the geometric means of all 64 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were below the Iowa water quality standard of 126 orgs/100 ml.   Also, none of the 76 samples collected during the three recreation seasons exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines and IDNR’s assessment methodology, these results suggest “full support” of the Class A (primary contact recreation) uses.   These results also suggest that levels of bacteria at this lake are very low.  

Results from the ISU statewide survey of Iowa lakes also suggest "full support" of the Class A uses, as well as the Class B(LW) uses, at Pleasant Creek 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 56, 52, and 52, respectively.   According to Carlson (1977), the index value for total phosphorus places this lake in the middle range of eutrophic lakes; the index values for chlorophyll-a and Secchi depth are in the lower range of eutrophic lakes.   These index values suggest relatively low levels of phosphorus, very low levels of chlorophyll-a, and very good water transparency for an Iowa lake.   These results suggest that this lake does not have threats or impairments due to aesthetically objectionable conditions.  

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 Pleasant Creek Lake.   Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Pleasant Creek Lake is 21.   This ratio suggests that algal production at this lake is limited by phosphorus.  

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 50% 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 (67 mg/l) was the 51st lowest of the 131 lakes sampled.   These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Pleasant Creek Lake.  

The levels of inorganic suspended solids at this lake are very low and do not suggest the potential attenuating light penetration or for threatening or impairing designated uses.   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 Pleasant Creek Lake was 2.4 mg/l.   This median level is the 19th lowest of the 131 lakes sampled.   Thus, the relatively low nutrient levels, combined with very low chlorophyll concentrations and very good water clarity suggests that this lake fully supports its Class A.  

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 (67%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Pleasant Creek Lake (6.6 mg/l) was the 33rd lowest of the 131 lakes sampled.   This level is in the lowest 25% 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).  

Results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake.   Results of this monitoring show that only 1 of the 14 samples collected exceeded the Class B(LW) criteria for dissolved oxygen and that only 2 of the 15 samples collected exceeded Iowa’s Class A,B(LW) criteria for pH (maximum = 9.1; minimum = 8.3 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 Pleasant Creek Lake.  

Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Pleasant Creek Lake in 1999.   Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   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, 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, however, does not apply to the fish contaminant data generated from the 1999 RAFT sampling conducted at Pleasant Creek Lake:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.