Big Wall Lake IA 02-IOW-656
Wright County S14T90NR24W 8 mi WSW of Dows.
- Cycle
- 2020
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Stable
- Created
- 7/22/2020 2:52:15 PM
- Updated
- 10/13/2020 1:05:52 PM
The Class BLW use is assessed as “not supported” due to violations of the Class BLW criterion for pH. All other designated uses are “not assessed”.
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 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 25 / 5 24 75 44 NO Monitored Full 22990005 6 Inorganic suspended solids 20 / 4 0 11 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. 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 22990005 6 Ammonia 15 / 3 0.058 0.03 0.02 0 / 0 0% / 0% NO Monitored Full 22990005 6 Dissolved oxygen 15 / 3 19.5 8.7 7.93 NA / 1 NA / 7% NO Monitored Full 22990005 6 pH 15 / 3 11.97 9.02 8.85 7 / NA 47% / NA YES Monitored Not 22990005 6 Temperature 15 / 3 29.6 22.6 21.8 0 / 0 0% / 0% 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 25 / 5 0.5 34 2.3 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. NOTE: Information from DNR staff indicate that a control structure was installed in early 2007, thus allowing the ability to manipulate the water level and thus improve water quality conditions at this wetland. Therefore the impairment for flow alteration has been removed at this lake.