A COMPARISON OF SUBMERSED AQUATIC VEGETATION IN MAIN-STEM FLOODPLAIN HABITATS 
AND ISOLATED FLOODPLAIN LAKES OF THE ILLINOIS RIVER; IMPLICATIONS FOR 
RESTORATION. 

Thad R. Cook and Mark A. Pegg.
Illinois Natural History Survey, Illinois River Biological Station, Long Term 
Resource Monitoring Program, 704 North Schrader Ave., Havana, IL 62644.

The importance of aquatic vegetation to the ecological health of aquatic systems 
is widely recognized.  Documentation of species richness, abundance, and their 
importance to the Illinois River and its floodplain lakes began in the late 
1800’s and continues today.  An assessment of submersed (SAV) and rooted 
floating leaf (RFL) vegetation utilizing a stratified random sampling design 
(SRS) began in 1998 to monitor frequency, percent cover and to establish an 
abundance index (AI =relative index of plant density ranking) of these species 
in main-stem, isolated backwater lakes (IBW), contiguous backwater lakes (CBW), 
and isolated floodplain lakes (LK) of La Grange Reach (RM 80-158).  We also 
examined community structure of SAV and RFL species at Spunky Bottoms and 
Emiquon, two isolated floodplain backwater areas of the Illinois River recently 
purchased by The Nature Conservancy.  We compared IBW, CBW and LK strata using 
SRS data from 1998 to 2002.  Data from the Spunky and Emiquon areas were 
collected using different sampling techniques and therefore were used for 
comparison of species presence/absence only.  Stratified random sampling 
collections yielded a total of 13 SAV and RFL species in La Grange Reach.  Of 
the nearly 2,800 sample sites, no SAV was recorded in the IBW and CBW strata.  
Therefore, the LK strata housed all of the SAV species recorded during the SRS.  
Mean frequency (% occurrence in all SRS sites) in the LK strata was 79.2% with 
an AI of 23.4 for all SAV species combined.  Alternatively, RFL were collected 
in all strata demonstrating an ability to withstand a wide range of hydrological 
conditions.  Mean frequencies for RFL in LK, IBW and CBW strata were 32.9%, 2.8% 
and 1.3% respectively.  Mean percent cover (% cover in all SRS sites) estimates 
were .32%, .27% and 15.6% respectively.  Similarly, species diversity was high 
in Spunky bottoms where 12 SAV and RFL species were recorded.  Species 
composition for both the LK strata and Spunky bottoms were similar, but differed 
greatly from that of the IBW and BWC strata.  Emiquon, currently managed for 
agriculture, also had higher diversity than that of the main-stem strata with a 
total of 2 species of SAV recorded.  Monitoring aquatic vegetation within the 
floodplain is needed to understand how environmental factors can influence 
growth and distribution of these important species.  The direction of 
restoration efforts within the Illinois River is moving towards restoring former 
floodplain areas (i.e., drainage and levee districts). Understanding the 
dynamics and benefits of such restoration efforts will prove critical to the 
success of future restoration and management.   

Keywords:  Submersed aquatic vegetation, Rooted floating leafed vegetation, 
restoration, Illinois River