Assessment Comments
Assessment is based on (1) surveys of DNR Fisheries Bureau, (2) results of IDNR beach monitoring program from 2002-04, (3) results of fish tissue (RAFT) monitoring in 1997, (4) ISU lake surveys from 2000-04, and (5) the ISU studies of lake plankton communities from 2000-05.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting " due to high levels of indicator bacteria at Red Haw beach in 2004. The Class B(LW) aquatic life uses are assessed (evaluated) as “fully supporting". Nutrient loading to the water column and siltation impacts, however, remain concerns at this lake. The Class C (drinking water) uses remain "not assessed" due to the lack of information upon which to base an assessment. Fish consumption uses remain assessed (evaluated) as "fully supporting" based on results of fish contaminant monitoring in 1997. 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, (4) information on plankton communities collected from 2000 through 2005 for the ISU lakes survey, and (5) results of U.S. EPA / IDNR fish tissue monitoring in 1997.
EXPLANATION: Results of IDNR beach monitoring at Red Haw Lake from 2002 through 2004 suggest that the Class A uses are "not supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (22 samples), 2003 (19 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. 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 Red Haw Lake beach, the geometric means of one of the 12 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 (18 geometric means) or 2003 (15 geometric means). The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was less than 10% in all three recreation seasons: 2002: 0%; 2003: 0%; 2004: 6%). According to IDNR’s assessment methodology and U.S. EPA guidelines, the occurrence of a geometric mean above Iowa’s Class A water quality criterion suggest impairment (nonsupport) of the Class A (primary contact recreation) uses. Despite this impairment, results of beach monitoring at Red Haw Lake suggest generally very low levels of bacteria and a relatively minor 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 58, 57, and 56, respectively. According to Carlson (1977), the index values for all three parameters place this lake in the middle to upper range of eutrophic lakes. These index values suggest relatively low levels of phosphorus, relatively low levels of chlorophyll-a, and relatively good water transparency.
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 Red Haw Lake. The levels of inorganic suspended solids at this lake are low relative to other Iowa lakes and suggest little potential for contributing to either in-lake turbidity or 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 Red Haw Lake was 3.8 mg/l; this is the 48th lowest median level of the 131 lakes sampled.
Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Red Haw Lake is 24. This TN:TP suggests that algal production at this lake is not limited by nitrogen availability.
Data from the ISU lake survey show the presence of moderately large populations of zooplankton at Red Haw Lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about 60% 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 (118 mg/l) was the 45th highest of the 131 lakes sampled.
A comparison of the TSI values for Secchi depth calculated for the 2000-2002 period to the corresponding values calculated for the 2002-2004 period suggests improvement in water transparency at this lake over the last few years. The TSI values for Secchi depth improved from 62 (0.9 m) to 56 (1.3 m). Based on annual TSI values, lake water transparency appears to have declined somewhat in summers of 2001 and 2002: a Secchi TSI in 2000 of 56 was followed by Secchi TSI values of 63 in 2001 and 64 in 2002. While not suggesting impairment, these TSI values were elevated and appeared trending toward the impairment threshold of 65. TSI values in 2003 (49) and 2004 (53) suggest a return to generally good water transparency at this lake.
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 (about 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 Red Haw Lake (11 mg/l) was the 58th lowest of the 131 lakes sampled. This level 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).
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported". Nutrient loading to the water column and siltation in the lake, however, remain concerns at this lake. Results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake. The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 15 samples collected during summers of 2000 through 2004. Two of 15 samples exceeded the Class A,B(LW) criterion for pH (maximum = 9.6; minimum = 7.9 pH units). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations likely reflect the high levels of primary productivity at Red Haw Lake and do not reflect the input of pollutants into this lake.
The Class C (drinking water) uses remain "not assessed" due to lack of water quality information on 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 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 were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Red Haw Lake in 1997. 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 1997 RAFT sampling conducted at Red Haw Lake: levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
