Assessment Summary
The Class BWW1 use was assessed as "partially supported" (IR 5a) due to poor water transparency as expressed by (1) the trophic state index (TSI) values for chlorophyll-a and Secchi depth and (2) the UMRCC protocol assessing water transparency to allow growth of submersed aquatic vegetation (SAV). All other designated uses are “not assessed”. This assessment of the aquatic life uses is consistent with previous Section 305(b) assessments.
Assessment Explanation
Sources of
Data:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site Name
|
Site Description
|
|
LTRMP
|
17
|
WQ
|
CY 2014-2018
|
99990001
|
Shrickers Slough
|
LTRMP station M508.1F
|
In 2003, the Upper Mississippi River Conservation Committee’s Water Quality Technical Section proposed water quality benchmarks necessary to sustain submersed aquatic vegetation in the Upper Mississippi River (“Proposed water quality criteria necessary to sustain submersed aquatic vegetation in the Upper Mississippi River, Upper Mississippi River Conservation Committee Water Quality Technical Section, October 2003). Submersed aquatic vegetation is an important component of the aquatic habitat in the Upper Mississippi River (UMR) navigation pools. Leaves, seeds and vegetative propagules are a source of food for waterfowl. The submerged plants provide a substrate for invertebrate and periphyton colonization, habitat for larval and adult fish, and help stabilize fine sediments from boat waves and wind-induced sediment resuspension. Submersed aquatic plants have been used to assess water quality and to provide a measure of ecosystem health. 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. The SAV benchmarks are designed to ensure that that the annual 1% light penetration depth will be between 1 to 1.5 m. The benchmarks are as follows: Secchi depth: 0.5 meters; total suspended solids: 25 mg/l (updated to 30 mg/l by Wisconsin DNR); and turbidity: 20 NTU. The benchmarks are to be applied as a growing season average (May 15 -September 15). These benchmarks reflect the minimum light criteria necessary to sustain and enhance SAV on the river. LTRMP data were used to calculate overall median growing season (May to September) levels of Secchi depth, total suspended solids, and turbidity for the assessment period.
Class BWW1 - Wetland TSI's:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Median Value
|
Median TSI Violation
|
Assessment Type
|
Support Level
|
|
99990001
|
17
|
Chlorophyll a TSI
|
69 / 5
|
38
|
76
|
62
|
NO
|
Monitored
|
Full
|
|
99990001
|
17
|
Total Phosphorus TSI
|
69 / 5
|
52
|
100
|
76
|
NA
|
NA
|
NA
|
|
99990001
|
17
|
Inorganic suspended solids
|
69 / 5
|
0
|
156.2
|
7.7
|
NA
|
NA
|
NA
|
Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Shrickers Slough was listed as partially supporting its Class BWW1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Shrickers Slough will remain listed as "partially supported" for the 2020 assessment/listing cycle.
Class BWW1 -
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
|
|
99990001
|
17
|
Dissolved oxygen
|
69 / 5
|
26.8
|
10.5
|
9.6
|
NA / 3
|
NA / 4%
|
NO
|
Monitored
|
Full
|
|
99990001
|
17
|
pH
|
69 / 5
|
9.3
|
8.1
|
8
|
2 / NA
|
3% / NA
|
NO
|
Monitored
|
Full
|
|
99990001
|
17
|
Temperature
|
69 / 5
|
28.6
|
17.1
|
17.5
|
0 / 0
|
0% / 0%
|
NO
|
Monitored
|
Full
|
Class BWW1 -
Protection of Submerged Aquatic Vegitation:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Median Value
|
Median Value>=SAV
|
Assessment Type
|
Support Level
|
|
99990001
|
17
|
Total suspended solids
|
69 / 5
|
2.88
|
172.03
|
16.44
|
NO
|
Monitored
|
Full
|
|
99990001
|
17
|
Turbidity
|
69 / 5
|
2
|
84
|
13
|
NO
|
Monitored
|
Full
|
|
WQ Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Median Value
|
Median Value<=SAV
|
Assessment Type
|
Support Level
|
|
99990001
|
17
|
Secchi
|
69 / 5
|
0.1
|
1.54
|
0.4
|
YES
|
Monitored
|
Not
|
Class HH -
Toxic Parameters: No Data. Fish tissue assessment was switch from "full support" to 3a "Not assessed" based on the age on the data.
