Blencoe Lake IA 06-WEM-1724

Assessment Comments

Assessment remains based on (1) information from the IDNR Wildlife Bureau and (2) results of watershed modeling by the IDNR Water Quality Bureau.

Basis for Assessment

SUMMARY:  The Class B(LW) aquatic life uses remain assessed (evaluated) as "not supported" (IR Category 4c) due to hydrological modifications (flow alterations and channel degradation of the Missouri River) that adversely affect this wetland.   This type of impairment is appropriate for Category 4c of Iowa's Integrated Report (i.e., impairment due to a non-pollutant stressor).   This assessment is based on (1) information from the IDNR Wildlife Bureau and (2) results of watershed modeling conducted by the IDNR Water Quality Bureau in 2002.   Fish consumption uses remain "not assessed."  This assessment is the same as that developed for previous assessment/listing cycles.   Note:  this assessment has not been updated following the severe flooding of the Missouri River during summer 2011 and thus does not reflect flood-related changes that may have occurred at this floodplain wetland.

EXPLANATION:  The Class B(LW) aquatic life uses remain assessed as "not supported" due to impacts of hydrological modification of the Missouri River and resultant problems with water level fluctuation in the river's floodplain wetlands (see assessments developed for previous reporting cycles).   Watershed modeling completed on Blencoe Lake in 2002 indicates that sediment delivery to the wetland from the watershed is very low.   In addition, the local DNR biologist indicates that the Missouri River does not breach the original high bank, but occasionally (10 -15 years) flood waters do enter wetlands such as Blencoe Lake that are adjacent to the river.   Based on this information, the previous identification of "siltation" as impairing the aquatic life uses of this wetland was in error.   The impact from hydrologic modification of the Missouri River, and the related problems with maintaining adequate water levels in this riverine wetland, remain.  

The assessment category for this wetland is "evaluated."  In terms of Section 305(b) reporting, "monitored assessments" are based primarily on recent, site-specific ambient monitoring data and thus have relatively high confidence.   IDNR considers waterbodies identified as "impaired" based on "monitored assessments" as candidates for the state's Section 303(d) list.   "Evaluated assessments" are those based on data older than five years or other than site-specific ambient monitoring data (e.g., desktop models or questionnaire surveys of fish and game biologists [=best professional judgment]) and thus have relatively lower confidence.   IDNR does not consider waterbodies identified as "impaired" based on "evaluated assessments" as candidates for the state's Section 303(d) list.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this wetland.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.