Assessment Summary
The Class BLW uses are assessed (monitored) as "not supported" due to violations of the Class BLW criterion for Dissolved Oxygen. All other designated uses are “not assessed.”
Assessment Explanation
Sources of
Data:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site Name
|
Site Description
|
|
Iowa DNR
|
6
|
WQ
|
CY 2014-2018
|
22760001
|
Lizard Lake
|
|
Class BLW -
TSI's
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Median Value
|
Median TSI Violation
|
Assessment Type
|
Support Level
|
|
22760001
|
6
|
Chlorophyll a TSI
|
33 / 5
|
24
|
88
|
48
|
NO
|
Monitored
|
Full
|
|
22760001
|
6
|
Total Phosphorus TSI
|
33 / 5
|
53
|
94
|
72
|
NA
|
NA
|
NA
|
|
22760001
|
6
|
Inorganic suspended solids
|
28 / 5
|
0
|
10
|
1
|
NA
|
NA
|
NA
|
- The TSI value
for Secchi depth is not used to evaluate the attainment of aquatic life goals
in shallow lakes. Due to the depth of these shallow lakes, TSI values for
Secchi depth can be misleading. In some instances, the Secchi disk remains
visible at the bottom of the lake and the depth of the lake is recorded as the
Secchi depth. In these instances, water clarity may be sufficient to support
the Class B(LW) uses, but the index value is limited by the depth of the lake.
Thus the combination of total suspended solids and chlorophyll a will be used
to determine whether or not the Class B(LW) uses are impaired in these shallow
systems.
- DNR's
assessment methodology indicates that at least two assessment/listing cycles
with a TSI values less than or equal to 63 are necessary to suggest de-listing
of an impairment. The chlorophyll a TSI value for the 2010
assessment listing cycle was 84, which based on DNR's assessment/listing
methodology indicated an impairment based on the narrative criteria protecting
against aesthetically objectionable conditions. Because the TSI value for the
2018 assessment/listing cycle was less than the trigger of 65 (2018 listing for
chlorophyll a was 58), and because the TSI value for the current listing cycle
is also 48, based on DNR's methodology, these values suggest "full
support" of the Class A1 uses protecting against aesthetically
objectionable conditions and the impairment (5a) for chlorophyll a is suggested
for delisting for the 2020 assessment/listing cycle.
Class BLW -
Conventional Parameters:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Maximum Value
|
Mean Value
|
Median Value
|
# Acute / Chronic Violations
|
% Acute/ Chronic Violations
|
Significantly >10% Violations
|
Assessment Type
|
Support Level
|
|
22760001
|
6
|
Ammonia
|
23 / 4
|
0.24
|
0.06
|
0.02
|
0 / 0
|
0% / 0%
|
NO
|
Monitored
|
Full
|
|
22760001
|
6
|
Dissolved oxygen
|
23 / 4
|
10.83
|
5.22
|
4.45
|
NA / 12
|
NA / 52%
|
YES
|
Monitored
|
Not
|
|
22760001
|
6
|
pH
|
23 / 4
|
10.25
|
7.7
|
7.45
|
2 / NA
|
9% / NA
|
NO
|
Monitored
|
Full
|
|
22760001
|
6
|
Temperature
|
23 / 4
|
30.3
|
21.2
|
21.6
|
0 / 0
|
0% / 0%
|
NO
|
Monitored
|
Full
|
Class BLW -
Lake Planktonic Cyanobacteria:
|
Site ID
|
Data Source ID
|
# Samples
|
Maximum Cyanobacteria Wet Mass
|
Maximum Cyanobacteria % Composition
|
Median Cyanobacteria Wet Mass
|
Median Cyanobacteria % Composition
|
Median Cyanobacteria Wet Mass = 75th
Percentile
|
Assessment Type
|
Support Level
|
|
22760001
|
6
|
8
|
30.002
|
98.6 %
|
0.469
|
26.65 %
|
NO
|
Evaluated
|
NA
|
Class BLW -
Protection of Submerged Aquatic Vegetation:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Median Value
|
Median Value >= SAV
|
Assessment Type
|
Support Level
|
|
22760001
|
6
|
Total suspended solids
|
33 / 5
|
0.5
|
42
|
5.5
|
NO
|
Monitored
|
Full
|
- Guidelines for
wetland assessment from the Upper Mississippi River Conservation Committee’s
Water Quality Technical Section (2003) state that an average total suspended
solids concentration during the growing season of less than 30 mg/L is
necessary to provide sufficient water clarity to support the growth of
submersed aquatic vegetation in wetlands and shallow lakes. High levels of
total suspended solids impede the growth of submersed aquatic vegetation (SAV).
Submersed aquatic vegetation is critical to the health of wetland and shallow
lake ecosystems. The elimination of SAV can degrade habitat quality such that
undesirable aquatic species such as cyanobacteria, common carp and fathead
minnows dominate. As such, the suppression of SAV constitutes a violation of
Iowa’s narrative water quality criteria protecting against undesirable or
nuisance aquatic life.
- DNR's assessment methodology indicates that at least two assessment/listing cycles with a median growing season total suspended solids concentration of 30 mg/L to suggest de-listing of the SAV impairment. The total suspended solids concentration for the 2012 assessment listing cycle was 58, which based on DNR's assessment/listing methodology indicated an impairment. Because the total suspended solids concentration for the 2018 assessment/listing cycle was less than the trigger of 30 (2018 listing for SAV was 5.5), and because the total suspended solids concentration for the current listing cycle is also 5.5, based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (5a) for SAV is suggested for delisting for the 2020 assessment/listing cycle.
Class HH - No
Data
Note: Lizard Lake was drawn down in 2012 and 2013 for restoration work.
