Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported.” The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to a poor recreational fishery and siltation problems at this lake. Fish consumption uses remain “not assessed” due to a lack of information on which to base an assessment. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
EXPLANATION: For the 2008 assessment/listing cycle, results from the ISU and UHL lake surveys suggest that the Class A1 uses at Manteno Lake are “fully supported.” Using the median values from these surveys from 2002 through 2006 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 57, 58, and 67 respectively for Manteno Lake. According to Carlson (1977) the Secchi depth and chlorophyll a values place Manteno Lake at the upper end of the eutrophic category while the total phosphorus value places Manteno Lake between the eutrophic and hypereutrophic categories. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and high levels of phosphorus in the water column.
The level of inorganic suspended solids is low at this lake and does not suggest impairment due to non-algal turbidity. The median inorganic suspended solids concentration at Manteno Lake was 1.5 mg/L, which was the 9th lowest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a very small population of cyanobacteria exists at Manteno Lake, which does not cause an impairment at this lake. These data show that cyanobacteria comprised only 12% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (0.9 mg/L) was also the 4th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that Manteno Lake has a poor recreational fishery and problems with siltation, therefore the aquatic life uses are assessed (evaluated) as “partially supported.” The ISU and UHL lake survey results show good chemical water quality at Manteno Lake. During 2002-2006 there were no violations of the Class B(LW) criterion for ammonia in 14 samples and no violations of the Class A1,B(LW) criterion for pH in 20 samples. There were two violations of the Class B(LW) criterion for dissolved oxygen in 20 samples (10%). Based on IDNR’s assessment methodology these violations were not significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses of Manteno Lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
