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Summary

Longitudinal distribution

• Vegetation stratified random sampling was conducted in Pools 4, 5, 7, 8, 12, 13, 26, and Alton and La Grange Pools in 2002.

• The estimated percent frequencies of submersed aquatic vegetation in the shallow water areas in Pools 4, 8, 13, 26, and La Grange Pool were 35%, 53.4%, 43.0%, 2.3%, and 0%, respectively (Tables 2, 5, 7, 8, and 9). The longitudinal pattern of submersed aquatic vegetation is the same as revealed in the previous 4 years from 1998 to 2001. Pools 5 (28.5%), 7 (39.3%), and 12 (12.8%) and Alton Pool (0%) also showed the same general pattern (Tables 3, 4, and 6).

• This pattern is also consistent with the longitudinal pattern displayed in the aerial photos of 1989 that submersed aquatic vegetation was abundant in the Upper Mississippi River reaches upstream of Lock and Dam 13, but rare or negligible elsewhere in the Upper Mississippi River System (UMRS; Rogers and Theiling 1999). A deviation from this longitudinal pattern was observed after the 1987–89 drought and in 1993 after an unusually high flood disturbance, when little submersed aquatic vegetation occurred in the entire UMRS. We did not sample the entire UMRS in 2002, but we have no reason to suspect a deviation from the normal pattern occurred in 2002.

• The estimated percent frequencies of rooted floating-leaf vegetation in Pools 4, 5, 7, 8, 12, 13, and 26 and Alton, and La Grange Pools were 10.0%, 9.8%, 12.2%, 18.4%, 10.4%, 23.5%, 3.5%, 0%, and 0.3%, respectively (Tables).

• Rooted floating-leaf species shifted in dominance from white water lily (Pools 4, 5, 7, and 8) to American lotus (Pools 12, 13, and 26). This same longitudinal pattern has occurred since 1998.

Within-pool Distribution

• The within-pool distribution patterns of submersed aquatic vegetation were highly heterogeneous between pools but remained little changed since 1998.

• Submersed aquatic vegetation was sparse and species-poor in upper Pool 4 above Lake Pepin compared with the lower Pool 4 below Lake Pepin (Figure 2). Rooted floating-leaf vegetation followed the same general pattern. The most common submersed species included coontail, wildcelery, water stargrass, and Canadian waterweed.

• Submersed aquatic vegetation was widely distributed throughout Pools 5 and 7 (Figures 4 and 6). Rooted floating leaf vegetation was somewhat more limited in distribution in the lower ends of each pool. The most common submersed species in Pool 5 included sago pondweed, water stargrass, Canadian waterweed, and coontail. The most common submersed species in Pool 7 included coontail and Canadian waterweed.

• Submersed aquatic and rooted floating-leaf vegetation was distributed widely throughout Pool 8 except in the lower end where water depth generally exceeded 1 m (Figure 8). The most common submersed species included Canadian waterweed, coontail, and water stargrass.

• In Pool 12, submersed and rooted floating-leaf vegetation was restricted mostly to the lower half of the pool (Figure 10). The most common submersed species included coontail and sago pondweed.

• A considerable amount of submersed aquatic vegetation was recorded in Pool 13, most of which occurred in the contiguous backwaters and impounded areas at the lower half of the pool (Figure 12). Most of the rooted floating-leaf vegetation was found in contiguous backwaters and along the shoreline in impounded areas in the lower half of the pool. The most common submersed species included coontail and sago pondweed.

• An insignificant amount of submersed aquatic and rooted floating-leaf vegetation was found in Pool 26, in the isolated backwater areas of the Illinois River (Figure 14).

• No submersed or rooted floating-leaf species were found in the connected channels and backwaters of Alton Pool.

• In La Grange Pool, submersed aquatic vegetation was found to exist in the lakes on the Illinois River floodplain and was absent in the river's backwater areas (Figure 17). Most rooted floating-leaf vegetation was found within lakes. Eurasian watermilfoil was the most common submersed species recorded.

• The distribution of submersed aquatic vegetation appears to be correlated with the physical parameters of water depth, current velocity, and fetch.

Status and Trend

• The spatial extents of submersed aquatic vegetation in the five key pools have remained stable since 1998 based on the frequencies of the sites sampled that supported submersed aquatic vegetation.
  
  
• In Pool 8, the amount of submersed vegetation per site, based on the abundance index, displayed a steady decrease from 1999 to 2001, but rebounded in 2002.  Pool 13 increased steadily from 1999 to 2002.

• Pool 13 has shown a slight increase in the frequency of rooted floating-leaf vegetation from 1998 to 2002 while the other pools have remained stable.
  
  
• Two exotic submersed species have been recorded, Eurasian watermilfoil and curly pondweed.  Both species have been recorded in Pools 4, 5, 7, 8, 11, 12, 13, and isolated lakes of the La Grange Pool.  Curly pondweed has also been recorded in Alton Pool.  Other than Eurasian watermilfoil in the isolated lakes of the La Grange Pool, neither species has been dominant, occuring in 15% or less of the sites in all pools and years.
  

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