Assessment Summary
Shrickers Slough is part of a backwater complex in Clinton County in Pool 14 of the Upper Mississippi River between river miles 508 and 510. Shrickers Slough receives year-round flow directly from Rock Creek. The designated uses for Shrickers Slough are those given to the adjoining Mississippi River (i.e., Class A1, BWW1). Because Shrickers Slough is a backwater and functions similar to a wetland, no attempt was made to assess this wetland for support of Class A1 (primary contact recreation) use. The Class BWW1 use was assessed as "not 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 were “not assessed.” This assessment of the Class BWW1 use was consistent with previous Section 305(b) assessments of this type.
Assessment Explanation
Data Sources:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site
Name
|
Site
Description
|
|
LTRMP
|
17
|
WQ
|
CY 2018-2022
|
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/Backwater 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
|
66 / 5
|
41
|
76
|
64
|
NO
|
Mon
|
Full
|
|
99990001
|
17
|
Total Phosphorus TSI
|
67 / 5
|
58
|
91
|
77
|
NA
|
NA
|
NA
|
- Although the index value for
Chlorophyll a is below the impairment trigger of 65 for this assessment cycle,
the Class BWW1 use of Shrickers Slough was assessed as "not
supported" due to aesthetically objectionable conditions. Based on DNR's
methodology, the median TSI value for Chlorophyll a must be 63 or less before a
lake can be removed from the state's Section 303(d) list (IR Category 5).
Therefore, Shrickers Slough will remain listed as "not supported" for
the 2024 assessment/listing cycle.
Class BWW1 - Binomial Parameters:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Minimum Value
|
Maximum Value
|
Mean Value
|
# Violations
|
# Acute / Chronic Violations
|
Violations needed for impairment
|
Violates Significantly >10% Rule?
|
Assessment Type
|
Support Level
|
|
99990001
|
17
|
Dissolved Oxygen
|
68 / 5
|
3.6
|
19.6
|
10.8
|
5
|
NA / NA
|
11
|
NO
|
Mon
|
Full
|
|
99990001
|
17
|
pH
|
68 / 5
|
6.5
|
9
|
8
|
0
|
NA / NA
|
11
|
NO
|
Mon
|
Full
|
|
99990001
|
17
|
Temperature
|
68 / 5
|
0.5
|
29.6
|
17.1
|
0
|
NA / NA
|
11
|
NO
|
Mon
|
Full
|
Class BWW1 - Toxic Parameters:
|
Site ID
|
Data Source ID
|
Parameter Name
|
# Samples / # Years
|
Maximum Value
|
Mean Value
|
Median Value
|
# Acute / Chronic Violations
|
>1 Acute / Chronic Violation
|
Assessment Type
|
Support Level
|
|
99990001
|
17
|
Ammonia
|
67 / 5
|
0.017
|
0.01
|
0
|
0 / 0
|
NO
|
Mon
|
Full
|
Class BWW1 - 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
|
|
99990001
|
17
|
Total suspended solids
|
34 / 5
|
10.03
|
172.03
|
19.49
|
NO
|
Mon
|
Full
|
|
99990001
|
17
|
Turbidity
|
34 / 5
|
7
|
50
|
17
|
NO
|
Mon
|
Full
|
|
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
|
34 / 5
|
0.15
|
0.58
|
0.32
|
YES
|
Mon
|
Not
|
Class HH - No Data
