Big Wall Lake IA 02-IOW-656
Wright County S14T90NR24W 8 mi WSW of Dows.
- Cycle
- 2022
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Stable
- Created
- 12/20/2021 2:49:49 PM
- Updated
- 1/27/2022 8:08:20 AM
The Class BLW use was assessed as “not supported” due to violations of the Class BLW criteria for pH and Dissolved Oxygen. All other designated uses were “not assessed.”
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2019 22990005 Big
Wall Lake
Class BLW - 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 22990005 6 Chlorophyll a TSI 20 / 4 24 75 48 NO Monitored FULL 22990005 6 Fixed suspended solids 15 / 3 0 11 0.5 NA NA NA The TSI value for Secchi depth is not used to evaluate the
attainment of the aquatic life use 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 BLW use, but the index value
is limited by the depth of the lake. Thus the combination of total suspended
solids and chlorophyll a was used to determine whether or not the Class
BLW use was impaired in these shallow systems. Class BLW - Conventional 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 22990005 6 Ammonia 15 / 3 0.02 0.19 0.06 NA 0 / 0 4 NO Monitored FULL 22990005 6 Dissolved Oxygen 20 / 4 0.5 19.5 6.4 7 NA / NA 5 YES Monitored NOT 22990005 6 pH 20 / 4 6.75 11.97 8.31 6 NA / NA 5 YES Monitored NOT 22990005 6 Temperature 20 / 4 13.4 28.4 21.4 0 NA / NA 5 NO Monitored FULL 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 22990005 6 Total suspended solids 20 / 4 0.6 34 3 NO Monitored FULL Guidelines for wetland assessment from the Upper Mississippi
River Conservation Committee’s Water Quality Technical Section (2003) state
that a median 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 (SAV) in wetlands and shallow
lakes. High levels of total suspended solids impede the growth of SAV. SAV 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.
Class HH - No Data