Assessment Comments
Assessment based on (1) special study of low levels of dissolved oxygen conducted by Wisconsin DNR in summer 1997 and 1998 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 / threatened" based on monitoring in 1997 that showed low levels of dissolved oxygen in this river segment. 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.
The Class B(WW) uses remain assessed as "fully supporting / threatened" based on the 1997 study of dissolved oxygen levels by Sullivan and Endris (1998) of the Wisconsin DNR (see assessment for the 1998 report above). The study by Sullivan and Endris (1998) 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. However, because the data from Sullivan and Endris (1998) are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively low confidence).
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.
