Mississippi River IA 01-NEM-77

Assessment Comments

Assessment based on (1) a 1998 study of low levels of dissolved oxygen conducted by Wisconsin DNR and (2) a 1999 USGS publication on the ecological health of the Upper Mississippi River system.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW) aquatic life uses remain assessed (evaluated) as "fully supporting" based on an assessment of the ecological health of the Upper Mississippi River published in 1999.   Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river reach.   The sources of data used for this assessment are (1) Sullivan and Endris (1998) and (2) a report on ecological status and trends of the UMR by USGS (1999).

EXPLANATION:  The Class A uses were not assessed due to lack of information on levels of indicator bacteria in this reach of river.  

A study of dissolved oxygen levels in 1997 (Sullivan and Endris 1998; see assessment for the 1998 report), however, does suggest a concern with levels of dissolved oxygen in the main channel of the UMR.   This study showed low levels of dissolved oxygen in the main channel of the Mississippi River during late June/early July 1997 during a period of high water temperatures and low river flow from Pool 9 downriver to Pool 12.   Follow-up investigation suggested that these low levels of dissolved oxygen were due to high densities of zebra mussels in this river reach.   These results suggest a concern regarding levels of dissolved oxygen in this reach of the Upper Mississippi River.

Chapter 16 of the USGS (1999) report ("Assessments and forecasts of the ecological health of the Upper Mississippi River System floodplain reaches"), identifies Pools 1-13 as a "moderately impacted" ecosystem with declining structural diversity and threats to native mussels from zebra mussels.   They note, however, that the ability of this river reach to recover from disturbances has been demonstrated by improving populations of aquatic macroinvertebrates and aquatic vegetation.   These authors suggests that the recovery of these aquatic communities is, at least in part, related to improved water quality over the last 25 years due to national clean water programs.  

Fish consumption uses remain "not assessed" due to lack of recent fish tissue monitoring in this river reach.